EPS 2018 Programme

2 Jul 2018, 08:00 → 6 Jul 2018, 18:15 Europe/Prague

Žofín Palace

This page only displays the programme of the 45th European Physical Society Conference on Plasma Physics.

For more information go to https://eps2018.eli-beams.eu/

Monday, 2 July

09:00 → 09:40 CONFERENCE OPENING CEREMONY

Chair: R. Dendy (live stream to Žofín Small Hall)

Convener: R. Dendy

09:40 → 10:20 HANNES ALFVÉN PRIZE LECTURE

Chair: R. Dendy (live stream to Žofín Small Hall)

Convener: R. Dendy

09:40 I1.001 Energetic particles in astrophysics and the laboratory

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.001.pdf Energetic particles in astrophysics and the laboratory Tony Bell1,2 1 University of Oxford, UK 2 Rutherford Appleton Laboratory, UK Particle acceleration is prevalent on all scales in the Universe, from the solar system to clusters of galaxies. Energetic particles arrive at the Earth as cosmic rays (CR) with energies ranging from GeV to EeV. Observations show that acceleration to 100s of TeV takes place at the outer shocks of supernova remnants (SNR). Diffusive shock acceleration (DSA) robustly produces cosmic rays at the observed energies, with the observed energy spectrum, and with the required high efficiency. Cosmic ray streaming excites plasma instabilities that drive MHD turbulence, scatter the CR, confine the CR near the shock and mediate the acceleration process. The instabilities also amplify the magnetic fields as observed in SNR. The origin of ultra-high energy cosmic rays (UHECR) at energies up to 100 EeV is much less certain, although DSA on kpc scales in outflows from active galaxies is a likely explanation. Energetic particles are also a feature of laser-produced plasmas. Although the scales differ by very many orders of magnitude, the underlying concepts are surprisingly similar. Dedicated laboratory experiments have the potential to validate and further clarify the plasma physics of astrophysical particle acceleration.

Speaker: T. Bell

10:20 → 10:45 COFFEE

10:45 → 12:30 PLENARY SESSION

Chair: S. Coda (live stream to Žofín Small Hall)

Convener: S. Coda

10:45 I1.002 Runaway Electron experiments at COMPASS in support of the EUROfusion ITER physics research

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.002.pdf Runaway Electron experiments at COMPASS in support of the EUROfusion ITER physics research J. Mlynar1 , O. Ficker1,2 , E. Macusova1 , V. Plyusnin3 , J. Urban1 , M. Vlainic4 , V. Weinzettl1 , the COMPASS team1 & the EUROfusion MST1 Team* A more detailed list of co-authors shall be provided in the contribution. 1 Institute of Plasma Physics of the CAS, 18200 Prague, Czech Republic 2 FNSPE, Czech Technical University in Prague, 11519 Prague, Czech Republic 3 IST - IPFN, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal 4 Institute of Physics, University of Belgrade, P.O. Box 68, 11080 Belgrade, Serbia * See the author list of H. Meyer et al., Nuclear Fusion 57 (2017) 102014 Research into generation, confinement and mitigation of Runaway Electrons (REs) in tokamaks presents one of the key tasks of the fusion energy development due to the risk of damage of the ITER plasma facing components by post-disruption RE beams. Two major groups of experi- ments aimed at improved understanding and control of REs were carried out on the COMPASS tokamak. In the first group, the effects of Massive Gas Injection (MGI, Ar or Ne, ∼ 1020 par- ticles) and impurity seeding (∼ 1019 particles) were studied systematically. The observed phe- nomena include generation of the post-disruption RE beam, current conversion from plasma to REs, and formation and decay of RE filaments. Studies of the penetration of impurity gas puff into RE dominated discharges complement this work. Differences between Ar and Ne penetration into the RE beam were mainly attributed to their ionisation potentials and atomic masses in accordance with spectral measurements. A distinctive drop of the background plasma temperature and electron density was observed following an additional deuterium injection into the RE beam. This change slowed down the RE current dissipation significantly. The second group of experiments was focused on the role of the magnetic field in the physics of REs. In particular, the RE currents formation and decay were studied depending on the plasma elon- gation, magnetic field strength, feedback on plasma current and, most importantly, on multiple sources of the magnetic field perturbations. Special attention was given to the effects of the Resonant Magnetic Perturbation (RMP) on the RE current formation and decay. The benefit of the RE experiments on COMPASS was reinforced by diagnostic enhancements (fast cameras, Cherenkov detector, vertical ECE etc.), the loop voltage control and the modelling efforts (for example, the CODE and the MARS-F codes). The current status of the art in the RE studies on COMPASS will be given in the framework of results achieved in the coordinated EUROfusion RE research programme. Major challenges linked to the planned RE research shall be outlined.

Speaker: Jan Mlynar

11:20 I1.003 Progress in inertial confinement fusion via lasers: how close to ignition and burn?

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.003.pdf Progress in inertial confinement fusion via lasers: how close to ignition and burn? Riccardo Betti Laboratory for Laser Energetics, University of Rochester, Rochester, NY, USA Recent progress in both direct- and indirect-drive ICF (inertial confinement fusion) has considerably improved the prospects for achieving thermonuclear ignition with megajoule-class lasers. Fusion yields from recent indirect-drive HDC (high-density carbon) implosions have exceeded 50 kJ, bringing the fusion core close to burning-plasma conditions. The improvements come from enhanced control of the hohlraum energetics, use of more-efficient HDC ablators, and reduced impact of engineering features. When scaled to NIF laser energies, recent direct-drive implosions on OMEGA are expected to produce close to 300 kJ of fusion yield. Those implosions have benefited from a significant increase in implosion velocity obtained through larger-diameter targets and thinner ice layers. A new statistical approach used in designing OMEGA targets has demonstrated a considerable predictive capability, thereby enabling the design of targets with improved performance. In addition, more advanced fusion schemes like shock ignition are rapidly developing thanks to dedicated experiments designed to validate the physics basis of such new schemes. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, the University of Rochester, the New York State Energy Research and Development Authority, and LLNL under Contract DE-AC52-07NA27344. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.

Speaker: Riccardo Betti

11:55 I1.004 The accretion-ejection connection in young solar-type stars

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.004.pdf The accretion-ejection connection in Young Solar type stars C. Dougados1 , J. Bouvier1 , S. Cabrit 2 , S. Alencar3 1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France 2 LERMA, Observatoire de Paris, Paris, France 3 Departamento de Física, ICEx, UFMG„ Belo Horizonte, Brazil One of the crucial open question in star formation is to understand the link between the accretion of matter onto the young star and the launching of large scale supersonic jets/outflows. In both cases, the magnetic field is thought to play a crucial role. In young convective solar type stars, the strong stellar magnetic field directs the flow of matter from the inner accretion disk onto the star. This magnetospheric accretion scenario best explains the photometric and spectral variability observed in these young stars. I will first review most recent advances brought on this topic by coordinated synoptic observations performed in particular with the COROT and K2 spatial telescopes. On the other hand, magnetic ejection models also currently best explain the strong correlation between accretion and ejection processes observed in forming stars. However, the role played by the jets and outflows in the extraction of mass and angular momentum from the protoplanetary disk and in its evolution are still critical open issues. I will review in this talk most recent observations of the launching regions of jets and outflows, from the X-ray to the millimetric domain, and discuss their implications for both launching models and disk evolution. I will particularly insist on the remaining puzzles and discuss the potential of new instruments, like ALMA, to progress on these issues.

Speaker: Catherine Dougados

12:30 → 14:00 LUNCH

14:00 → 16:00 POSTER SESSION

Mánes Exhibition Hall: MCF P1.1x, BSAP P1.4x
Mánes Multifunctional Hall: BPIF P1.2x, LTDP P1.3x

14:00 P1.1001 Alpha - particle and NBI - ion deposition in a compact spherical torus due to slowing down

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1001.pdf α - Particle and NBI - Ion Deposition in a Compact Spherical Torus due to Slowing Down A. Nicolai1, M. Gryaznevich1,2,3 1 Tokamak Energy Ltd., Culham Science Centre, Abingdon, Oxon, OX14 3DB,UK 2 Imperial College, London, SW7 2AZ, UK 3 DTU Fysik, Technical University of Denmark, DK The power, torque and current deposition of NBI (Neutral Beam Injection) ions (Pb=1MW, Eb=40-70keV) and the generated thermonuclear α - particles in a high field spherical tokamak (R/a=40/25, Bt=3T) is determined by slowing down processes and the orbit losses. Therefore we investigate the particle orbits by Monte Carlo simulation (NFREYA) accounting for the Fokker - Planck equation. For the tracking of the orbits until completion of slowing down the guiding center equations are used. Both, the full gyro and the guiding center description allow to estimate the first orbit losses of the α - particles, the generation of which depends on the profiles of the plasma parameters which are characterized by a peaking parameter p defined by n=(f(r))p. A parabolic profile is assumed for f(r). We find that the α-particle first (gyro) orbit containment is due to the large toroidal field around 0.4 for flat profiles (p ≈ 0.125) and somewhat larger (20%) for peaked temperature and density profiles (2 < p < 4). Repetitive pellet injection with a repetition time of 100 ms was assumed to increase the the peaking parameter of the density profile. With an effective pellet radius of 0.38 mm and a pellet speed of 3.2 km/sec an almost triangular (p ≈ 2) density profile can be achieved. Taking into account the slowing down processes due to the Fokker – Planck equation the power containment computed by guiding center tracking of the α particles is ≈ 0.3. Here each collision event effects new orbit parameters in particular at small pitch angles. At large pitch angles the counter - and co – orbits are rather stable. The NBI deposition profiles of the current, torque and power show the expected energy dependence. The total driven current and the torque increase with increasing beam tangency radius Rb. By means of the finite difference solution of the Fokker - Planck equation (obtained by the code NFIFPC) the distribution function of the fast ions and related quantities are computed. These calculations e.g. yield a characteristic peak of the distribution function fmax=5 10-8 msec3/cm6 in the co – region of velocity space and a driven current (73 kA for 1 MW α- power) which is comparable to the Monte - Carlo result.

Speaker: Albert Nicolai

14:00 P1.1002 Banana kinetic equation and plasma transport in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1002.pdf Banana kinetic equation and plasma transport in tokamaks K. C. Shaing1, M. S. Chu1, S. A. Sabbagh2, and J. Seol3 1 National Cheng Kung University. Tainan City 701, Taiwan 2 Columbia University, New York, NY 10027, USA 3 National Fusion Research Institute, Daejeon 305-333, Korea In a high temperature fusion relevant tokamak plasma, effects of finite banana width are important to plasma dynamics. A banana kinetic equation that includes effects of finite banana width is derived for both electrostatic and electromagnetic waves with frequencies lower than the gyro-frequency, and the bounce frequency of the trapped particles [1,2]. The radial wavelengths are assumed to be either comparable to or shorter than the banana width but much wider than the gyro-radius. One of the consequences of the banana kinetics is that the parallel component of the vector potential is not annihilated by the orbit averaging process, and appears in the banana kinetic equation. The equation is solved to calculate neoclassical quasilinear transport fluxes in the superbanana plateau, and other collisionality regimes caused by both electrostatic and electromagnetic waves. The transport fluxes can be used to model wave and chaotic magnetic field induced thermal particle or energetic alpha particle losses in tokamaks. It is found that electrostatic turbulence induced transport losses are reduced as a result of the banana kinetics. On the other hand, the parallel component of the vector potential enhances losses when it is the sole transport mechanism. Especially, the drift resonance can cause significant transport losses in the chaotic magnetic field in the hitherto unknown low collisionality regimes. In general, it is the interference between the electrostatic, and vector potentials, that ultimately determines whether the banana kinetics enhances or improves the electromagnetic wave induced transport losses. The banana kinetics also provides an isotope scaling. The implications on energetic alpha particle confinement in ITER will be addressed. Acknowledgement This work was supported by Taiwan Ministry of Science and Technology under Grant No. 100-2112-M-006- 004-MY3. References [1] K C. Shaing, Phys. Plasmas 24, 122504 (2017) [2] K. C. Shaing, M. S. Chu, S. A. Sabbagh, and J. Seol, accepted to appear in Phys. Plasmas 25 (2018)

Speaker: Kerchung Shaing

14:00 P1.1003 Modeling of sawtooth-induced fast particle redistribution in NSTX-U

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1003.pdf Modeling of sawtooth-induced fast particle redistribution in NSTX-U D. Kim , D. Liu , M. Podestà and F.M. Poli , 1 2 1 1 Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA 1 2 Department of Physics and A stronomy, University of California, Irvine, CA 92617, USA The effects of sawtooth on fast ion transport have been studied in L-mode sawtoothing discharges during the 2016 experimental campaign on National Spherical Torus Experiment Upgrade (NSTX-U) [1]. Experimental observations show that passing particles are strongly redistributed from the plasma core to the edge, while trapped particles are weakly affected by sawteeth [2]. TRANSP [3] simulations using the implemented standard sawtooth models can reproduce the experimental neutron rate drops with a proper parameter set. However, since the different effect of sawtooth crash on fast ions with different orbit type and energy is not taken into account in the sawtooth model, detailed simulation results do not agree with the experimental measurement. Therefore a more comprehensive and improved model for quantitative simulations needs to be developed including the characteristics of fast ion so that more reliable interpretation of sawtoothing discharges can be possible. As a first step of the development of the improved sawtooth model, simulations using the ORBIT code [4] have been carried out [5]. The simulation results confirm the experimental observation that fast ions are redistributed by sawtooth crash based on their orbit type and energy. In real space, due to a sawtooth crash passing particles in the core region are expelled and move outside the q=1 surface while a sawtooth crash does not have significant effects on trapped particles. The initial TRANSP simulation using the kick model [6] based on the ORBIT modeling result shows improvement of fast ion redistribution before and after a sawtooth crash but more simulations are required as the neutron rate still has discrepancy compared to the experimental measurement. This work is supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under contract number DE-AC02-09CH11466. References: [1] Battaglia D.J. et al., accepted to Nucl. Fusion (2018) [2] Liu D. et al., submitted to Nucl. Fusion (2017) [3] Hawryluk R. An empirical approach to tokamak transport Physics Close to Thermonuclear Conditions vol 1 ed B. Coppi et al. (Brussels: Commission of the European Communities) p 19. (1980) [4] White R.B. and Chance, M.S. Phys. Fluids 27 (1984) 2455 [5] Kim D., Podestà M., Liu D. and Poli F.M., submitted to Nucl. Fusion (2018) [6] Podestà M., Gorelenkova M. and White R.B., Plasma Phys. Control. Fusion, 56 (2014) 055003

Speaker: Doohyun Kim

14:00 P1.1004 New type of charge-exchange particle analyzer

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1004.pdf NEW TYPE OF CHARGE-EXCHANGE PARTICLE ANALYZER Yu.V. Gott1, A.A. Kadyrgulov1,2 1 NRC «Kurchatov Institute», Moscow, Russia 2 Research Institute «Moscow Power Engineering Institute», Moscow, Russia The application of effective methods of charge-exchange neutral particle diagnostics for determination of the plasma ion temperature on modern plasma installations is of great practical interest. In this paper, a new type of analyzer is proposed, in which ionization of charge- exchange particles occurs when they are reflected from a metallic surface. As an ionizer used a set of parallel installed plates of tantalum - an ionizer such as "jalousie" Experimental results of using the analyzer on the T-10 facility are presented and an estimate of the ion plasma temperature in ohmic plasma heating is performed. It is shown that the sensitivity of the proposed analyzer increased by almost 10 times in comparison with the analyzer, in which ionization of the charge-exchange particles was carried out on carbon foil 50 Å thick. The replacement in the device of the detector - the secondary electron multiplier on the microchannel plates by the channeltron multiplier allowed to significantly reduce the noise from hard X-rays.

Speaker: Yuri Vladimirovich Gott

14:00 P1.1005 High Resolution EUV Spectroscopy on FTU with Tin Liquid Limiter

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1005.pdf High Resolution EUV Spectroscopy on FTU with Tin Liquid Limiter F. Bombarda1, M.L. Apicella1, G. Apruzzese1, L. Carraro2, L. Gabellieri1, E. Giovannozzi1, M. Iafrati1, G. Mazzitelli1, M.E. Puiatti2, A. Romano1, B. Tilia1, M. Valisa2, B. Zaniol2, and the FTU team* 1 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy 2 Consorzio RFX, Corso Stati Uniti 4, 35127, Padova, Italy *See G. Pucella et al., Nucl. Fusion 57 102004 (2017) FTU is an all-metal limiter machine characterized by an extremely low level of impurities of any kind, therefore it is particularly well suited for investigating the performances of liquid metal limiters under high thermal loads (up to 18 MW/m2). During recent experimental campaigns the plasma behaviour has been studied with a Tin Liquid Limiter (TLL), while previous tests were carried out with a Lithium Liquid Limiter [1]. In the last campaign, a 2m grazing incidence Schwob-Fraenkel XUV spectrometer [2], observing the plasma emission in the range from 20 to 340 Å, was installed on FTU. Experimental data of Tin spectra from high temperature plasmas are scanty; for this reason, our first goal was the identification of the main spectral lines, to support further studies of the possible influence of Tin in the plasma core, and to complement previous observation regarding vaporization and plasma contamination. The high spectral resolution of the Schwob instrument when equipped with a 600 g/mm or 1200 g/mm grating allowed the identification of spectral lines of Sn ionization stages up to SnXXIV. The tin lines have been isolated against the metal-dominated background spectrum typical of FTU plasmas in a limited range of plasma parameters (BT=5.3 T, Ip=0.5/0.7 MA, Te ≤ 1.5 keV, ne ≤ 1020 m-3). The vertical position of the TLL was varied on a shot by shot basis in a range of 4 cm up to the last closed magnetic surface. The unresolved transition array at about 135 Å [3] that was recorded previously with a survey, low resolution SPRED instrument, has now been resolved. The combination of these observations with those of other instruments in the visible spectral range have led to estimated values of Sn relative concentration of the order of 5×10-4 in the plasma core [1]. [1] G. Mazzitelli, et al., “Comparison between Liquid Lithium and Liquid Tin Limiters in FTU”, EPS 2017. [2] J.L.Schwob et al., Rev. Sci. Instrum. 58 (1981)1601. [3] G. Apruzzese, et al, “First Spectroscopic Results with Tin Limiter on FTU Plasma”, ISLA 2017.

Speaker: Francesca Bombarda

14:00 P1.1006 Measurement of slowing down time at neutral beam heated KSTAR deuterium plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1006.pdf Measurement of the beam slowing-down time at neutral beam heated KSTAR deuterium plasma Jong-Gu Kwak1, Y.S. Lee1 1 National Fusion Research Institute, Daejeon, Korea Fusion product alpha particle whose energy is about 3.5 MeV is used to sustain the fusion reaction after the ignition, so behaviour of the fast ion confinement is one of key issues at the burning fusion plasma. As the KSTAR plasma performance is improved with neutral heating power(~5 MW) and operational boundary of the H-mode discharge is extended over MHD no-wall limit(βN~4) with higher stored energy region, the confinement of fast ions with injected energy of 100 keV neutral beam is also important as well as increasing thermal ion confinement with the plasma current. Recent KSTAR experimental campaign also showed the fully non-inductive discharge with high betap(βp ~3), which is one of promising candidate scenarios of steady state operation at KSTAR. It is explained by the enhancement of fast ion confinement with reducing TAE(Toroidal Alfen Eigenmode) activity. In addition, because there is a lot of production of fast neutrons coming from via D(d,n)3He reaction in neutral beam heated plasma, the neutron flux could be used for characterizing the confinement time of energetic particle at deuterium plasma by applying blip beam or measuring the absolute flux value, but in this study, the blank beam with 10 msec which is routinely used for other plasma diagnostic is used for estimating the confinement time of energetic particle. In this presentation, we also report on the estimating beam slowing down time at various KSTAR discharges including ITB(Internal Transport Barrier) and high betap using blank beam method as well as its feasibility test of blank beam method.

Speaker: Jong-Gu Kwak

14:00 P1.1007 Overview of Magnetic Flux Surface Measurements at W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1007.pdf Overview of Magnetic Flux Surface Measurements at W7-X M. Otte1, S. Bozhenkov1, V. Bykov1, T. Andreeva1, M. Endler1, S. A. Lazerson2 and the W7-X team 1 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 2 Princeton Plasma Physics Laboratory, Princeton, USA The existence of closed and nested magnetic flux surfaces is mandatory in magnetic confinement plasma machines and is one of the optimization criteria at the Wendelstein 7-X (W7-X) stellarator. The existence and quality of vacuum magnetic flux surfaces was already confirmed during the initial operation phase OP1.1, and the error field was found in the expected range as well [1, 2]. However, a comparison with field line tracing simulations taking into account the ideal but also the as-built geometry of the coils revealed small but measurable deviations in the radial profile of the rotational transform  /2. A systematic decrease of iota of / ~ 1-2% with respect to the ideal coil geometry could be derived from the measurements. The effect, also observed at the predecessor experiment W7-AS [3], is related to the deformation of the non-planar coils of up to ~ 10-15 mm under electromagnetic loads, which are generating the rotational transform. In the first divertor campaign OP1.2a, performed in the second half of 2017, the accessible magnetic configuration space was extended. Additional flux surface measurements were performed for new magnetic configurations. The experimental results are compared with different field coil models. Furthermore, measurements addressing the potential error field have been conducted again. The dominating n, m = 1 Fourier harmonic was characterised in amplitude and phase for different magnetic configurations. Utilizing the flux surface diagnostic, it could be shown that this error field component can be compensated with the trim coil set installed outside the plasma vessel, which results in a symmetrisation of the heat loads on the divertors during plasma operation [4]. References [1] M. Otte et al., Plasma Phys. Control. Fusion 58 (2016) [2] T.S. Pedersen et al., Nature Comm. 7 (2016) [3] M. Otte et al., Stellarator News 100 (2005) [4] S.A. Lazerson et al., this conference

Speaker: Matthias Otte

14:00 P1.1008 Application of the microwave beam steering from poloidal correlation reflectometry for investigation of the L- and I-mode turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1008.pdf Application of the microwave beam steering from poloidal correlation reflectometry for investigation of the L- and I-mode turbulence D.Prisiazhniuk1 , G.D.Conway1 , T.Happel1 , S.Freethy1 , P.Manz1 , A.Krämer-Flecken3 , U.Stroth1,2 and the ASDEX Upgrade Team 1 Max Planck Institute for Plasma Physics, 85748 Garching, Germany 2 Physik-Department E28, Technische Universität München, 85748 Garching, Germany 3 Institut für Energieforschung - Plasmaphysik, Forschungszentrum Jülich, 52425, Germany Poloidal correlation reflectometry (PCR) is a powerful tool to study correlation properties of turbulent density fluctuations [1, 2]. In the typical application of PCR several poloidally and toroidally separated receiving antennas simultaneously measure the reflected beam from the cut-off layer in the plasma. The correlation of the receiving antenna signals allows to determine the velocity, the correlation length and life time of turbulent density fluctuations [3]. In this contribution an alternative application of the PCR diagnostic is proposed. All receiving antenna signals are combined in post-processing software with different phases to create a total receiving beam in a specific direction using the phased antenna array concept. The principle of this method is similar to the synthetic aperture microwave imaging (SAMI) system [4, 5], but with only 4 receiving horn antennas. The method is robust and can be applied to every discharge. Using the PCR antenna cluster at ASDEX Upgrade the total receiving beam can be steered in the poloidal direction (θ ' ±10◦ ) and in the toroidal direction (φ ' ±4◦ ) with characteristic 3 dB half-width beams of order ∆θ ≈1.5◦ and ∆φ ≈2.7◦ - thus operating as a steerable Doppler reflectometer with corresponding backscaterring wavenumbers k⊥ ' ±3 cm−1 and ∆k⊥ ' 0.6 cm−1 The application of the method to L- and I-mode plasmas is presented. The measured velocity from the Doppler shift is compared with classical PCR time delay analyses [2] and with other diagnostics. Influence of the magnetic field line pitch angle is also shown. Quasi coherent modes with k⊥ ≈ 1 cm−1 can be decoupled from background turbulence and enhanced. Observations of the intermittent events reported in [6] are discussed. References [1] A.Krämer-Flecken et al., Nucl. Fusion 57, 066023 (2017) [2] D.Prisiazhniuk et al., Plasma Phys. Control. Fusion 59, 025013 (2017) [3] D.Prisiazhniuk et al., "Density fluctuation correlation measurements in ASDEX Upgrade using poloidal correlation reflectometry", sumbitted to PPCF (2018) [4] D.A. Thomas et al., Nucl. Fusion 56, 066023 (2016) [5] S.J. Freethy et al., Nucl. Fusion 55, 124010 (2013) [6] T.Happel et al., Nucl. Fusion 56, 064004 (2016)

Speaker: Dmitrii Prisiazhniuk

14:00 P1.1009 Nonlinear Doppler reflectometry power response.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1009.pdf Nonlinear Doppler reflectometry power response. O. L. Krutkin1,2, E. Z. Gusakov1, S Heuraux2, C Lechte3 1 Ioffe Institute, St Petersburg, Russia 2 Institut Jean Lamour UMR 7198 CNRS, Université de Lorraine, 54000 Nancy, France 3 Institute of Interfacial Process Eng. and Plasma Technology, 70569 Stuttgart, Germany Understanding and control of plasma turbulence is one of the major goals of fusion research, since the turbulent transport plays a key role in plasma confinement. One of the tools used for turbulence characterization is Doppler reflectometry, which utilizes a microwave beam to probe the plasma at oblique incidence with respect to the magnetic surface. The backscattered signal can provide turbulence "poloidal" wavenumber spectrum and its Doppler shift, which is connected to poloidal velocity of plasma. However, interpretation of experimental measurements is not always straightforward. In case of small turbulence level, when Born approximation over the turbulence amplitude is applicable, the diagnostic response was extensively studied both analytically [1] and numerically [2]. In the case of strong turbulence, when multiple forward scattering is dominant, analytical predictions have been made [3] and nonlinear effects were observed in full-wave simulations [4, 5]. Recently, intermediate regime with power of scattering signal enhanced due to high order nonlinear scattering effects was observed numerically in full-wave computations utilizing IPF-FD3D code [4] and interpreted using physical optics model [6]. While simple and effective, this model possesses a limited domain of validity because it only takes into account plasma-wave interaction in the very vicinity of the cutoff. To overcome this limitation, transition from linear regime to regime with enhanced power is studied in the present paper analytically using the first (Born) and the second order of approximation over the turbulence amplitude. Transition criteria are derived and their discrepancies from the physical optics model predictions are discussed. To confirm analytical results, full-wave numerical modeling with IPF-FD3D code [4] is performed. The research was supported by RSF grant 17-12-01110, Verdansly scholarship for PhD students and by the Ioffe institute. [1] E Z Gusakov and A V Surkov Plasma Phys. Control. Fusion 46 (2004)1143 [2] Hirsch M, Holzhauer E, Baldzuhn J, Kurzan B and Scott B Plasma Phys. Control. Fusion 43 (2001)1641 [3] E Z Gusakov, A.V. Surkov, and A Yu Popov Plasma Phys. Control. Fusion 47 (2005) 959 [4] C Lechte et al Plasma Phys. Control. Fusion 59 (2017) 075006 [5] O. L. Krutkin, A.B. Altukhov, A.D. Gurchenko, et al. Proc. 44th EPS Conf. on Contr. Fusion and Plasma Physics (Belfast) ECA vol. 41F (2017) P2.108 [6] J R Pinzón et al Plasma Phys. Control. Fusion 59 (2017) 035005

Speaker: Oleg Krutkin

14:00 P1.1010 Runaway electron diagnostics for the COMPASS tokamak using EC emission

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1010.pdf Runaway electron diagnostics for the COMPASS tokamak using EC emission M. Farnik1,2 , J. Urban1 , J. Zajac1 , O. Bogar1,3 , O. Ficker1,2 , E. Macusova1 , J. Mlynar1,2 , J. Cerovsky1,2 , M. Varavin1 , V. Weinzettl1 , M. Hron1 and the COMPASS team1 1 Institute of Plasma Physics of the CAS, Prague, Czech Rep. 2 FNSPE, Czech Technical University, Prague, Czech Rep. 3 FMPI, Comenius University in Bratislava, Bratislava, Slovakia Electron cyclotron emission measured vertically along the line of a constant magnetic field can yield information about the electron velocity distribution function and its evolution during a discharge [1]. A vertical ECE (V-ECE) diagnostic is available on COMPASS, a compact-sized tokamak operated at IPP Prague. We report on results from this diagnostic during runaway electron (RE) experiments. The V-ECE diagnostic on COMPASS consists of a 16-channel radiometer E-band horn an- tenna with a 76.5 - 88.3 GHz frequency range front-end. Simulations using the SPECE ray- tracing code [2] have aided the final diagnostic design and are employed for experimental data interpretation. Realised measurements of extraordinary and ordinary mode (X/O mode) in low- density (ne < 3 · 1019 m−3 ) RE experiments will be presented. The detected signal can be at- tributed to the 3rd harmonic emission from 50 - 140 keV electrons. However, the optical depth is rather low, which complicates the measured data interpretation. V-ECE measurements in low-density flattop discharges and in discharges with massive gas injections (MGI) of high-Z elements show correlations with other RE diagnostics, such as hard X-rays (HXR), photoneutron detectors and high-speed visible light cameras. Our results seem to be in an agreement with the principles of the primary runaway generation mechanisms. References [1] K. Kato, I. H. Hutchinson, Phys. Rev. Lett. 56(4) 340-343 (1986) [2] D. Farina, et al., AIP Conf. Proceedings 988 128-131 (2010)

Speaker: Michal Farník

14:00 P1.1011 Development of a pop-up Langmuir probe array for the W7-X high-heat-flux divertor

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1011.pdf Development of a pop-up Langmuir probe array for the W7-X high-heat-flux divertor K. C. Hammond1 , J. Biermann1 , M. Endler1 , J. Fellinger1 , S. Freundt1 , F. Gottong1 , S. Klose1 , M. Krause1 , J. Kügler1 , L. Rudischhauser1 , J. Wendorf1 , and the W7-X team 1 Max Planck Institute for Plasma Physics, Greifswald, Germany Divertor target-mounted Langmuir probes are foreseen as a crucial diagnostic during Oper- ational Phase 2 (OP 2) of the W7-X experiment to aid our understanding of detachment, edge fueling, strike patterns, and other scrape-off layer phenomena. The high-heat-flux divertor [1], to be used during this period, will be water-cooled to withstand the sustained power flux from continuous discharges lasting up to 30 minutes. Since it is not forseen to actively cool the probes, however, they must periodically withdraw from the plasma to avoid damage from overheating. Finite-element modeling indicates that, in the worst case, the graphite-tipped probes must stay retracted for 10 s after 200 ms of plasma exposure. The system currently under design will consist of poloidal arrays of probes in two of the ten island divertors. The arrays will span up to 400 mm of their respective horizontal target elements with 25 to 50 mm of separation between each probe. Both the probes and the mechanisms driving the reciprocation will be integrated into the targets. The driving mechanism consists of a rigid, current-carrying loop which moves in response to the Lorentz force from the W7- X magnetic field. Although most of the instrumentation will be mounted on the back sides of divertor target modules and therefore not accessible during the operational phase, the interface between the probes and the drive units will permit the probes to be periodically removed and replaced from the plasma-facing side. The in-vessel cabling system is designed for compatibility with high-speed measurements using the “Mirror Langmuir probe” technique [2]. Here we present the current status of the project. Topics to be addressed include the techni- cal challenges which had to be overcome to realize the system, solutions developed for those challenges, and the results of simulations and prototype testing to predict and qualify the per- formance of the probes. References [1] A. Peacock et al., 25th IEEE Symposium on Fusion Engineering (SOFE), San Francisco, CA, USA, 2013, pp. 1-8 [2] B. LaBombard and L. Lyons, Rev. Sci. Instrum. 78, 7 (2007)

Speaker: Kenneth Hammond

14:00 P1.1012 Use spectrum simulation code to test D-alpha spectrum of fast ion design work on HL-2A

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1012.pdf Use spectrum simulation code to test D-alpha spectrum of fast ion design work on HL-2A P. Chen1, J. Wu1, L. M. Yao1, Y.J. Chen1, H. Wen1, M. T. Zou1, W. Zhang1, J. T. Shen1, H. Y. Zhou2 1 School of Physics, University of Electronic Science and Technology of China, Chengdu, China 2 Southwestern Institute of Physics, Chengdu, China Abstract—In magnetic confined fusion devices, the fast ion is the main source for the self-sustained burning phases, so it is very important to understand the behavior of fast ion. On HL-2A Tokamak device, the fast ions were also generated by neutral beam heating, microwave heating and fusion. This paper was focus on the fast deuterium ion simulation and experimental design work. When the fast ions collide with the neutral beam, some fast ions neutralize, then radiate electromagnetic wave, some of which is in the visible spectrum, but the intensity of this light is usually below the continuum radiation level and is about two orders of magnitude lower than the thermal charge-exchange spectrum (CXS), beam emission spectrum (BES). To investigate the fast ion behavior, this paper dedicated to evaluate the fast ion spectrum on HL-2A, one is using the simulation of spectra (SOS) program to simulate the spectra, and the second is to extract the fast ion spectrum by fitting the experimental data of BES spectrum.

Speaker: Peng Chen

14:00 P1.1013 Density fluctuations measurement from fixed and sweeping microwave reflectometer during L-H transition on the COMPASS tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1013.pdf Density fluctuations measurement from fixed and sweeping microwave reflectometer during L-H transition on the COMPASS tokamak O. Bogar1,2 , J. Zajac1 , M. Varavin1 1 Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic 2 Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia Microwave reflectometry is a versatile diagnostics that allows to perform both density profile and density fluctuation measurement. Fast sweeping reflectometry uses the O-mode polarization in frequency range 18-54 GHz. The sweeping time 6 µs followed by 1.5 µs of recovery time allows the density profile reconstruction from the frequency spectra with high temporal and spa- tial resolution. Fixed frequency measurement records the time evolution of the phase fluctuation at the plasma density layer given by probing frequency. IQ detection separates measurements of phase and amplitude of the reflected signal. IQ signal as well as IF signal is recorded at 200 Msamples/s. New dynamic calibration based on frequency marker and delay line tech- nigue was performed in order to suppress the frequency non-linearity at high sweeping rates. We investigate both the density fluctuation spectra and the fast density profile dynamics dur- ing the L-H transitions with varying discharge parameters. This contribution presents radial dependence of frequency spectra and radial profile of density fluctuation level from these two technigues.

Speaker: Ondrej Bogar

14:00 P1.1014 New methods of neutron emissivity tomographic reconstruction for fusion plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1014.pdf New methods of neutron emissivity tomographic reconstruction for fusion plasma J. Bielecki 1 1 Institute of Nuclear Physics Polish Academy of Sciences (IFJ PAN), PL-31-342 Krakow, Poland Reconstruction of the neutron emissivity distribution in fusion devices is a useful tool for retrieving information on spatially resolved fusion rates. The reconstruction is performed from a limited number of line-integrated quantities measured by a set of neutron detectors. Usually the coverage of a plasma cross-section is very sparse. Thus, the problem of tomographic reconstruction is very challenging due to its ill-posed character. Several approaches to the reconstruction of neutron emissivity in magnetic-confinement fusion devices have been developed. In this work two recently developed methods are presented: (i) the method based on genetic algorithms (GA) and (ii) the method based on Metropolis–Hastings Monte Carlo (MC) algorithm. GA are inherently parallel and the search is performed from a population of points. Therefore, the method has the ability to avoid being trapped in a local optimal solution. The developed MC method is based on a biased random walk. The algorithm generates pseudo-random samples within the domain that contains the solution. The properly chosen objective function ensures the convergence to the desired solution. The applied Metropolis– Hastings algorithm can overcome the problem of trapping of the random walk in local minima, because it offers a possible method for jumping out of them by accepting, with some finite probability, changes in the direction opposite to indicated by the objective function. Both methods have been tested using a set of synthetic models. The methods have been validated in terms of accuracy, speed and resilience against the noise present in the line- integrated input data. The obtained results show that both methods provide accurate reconstruction results, comparable with those obtained by the standard methods routinely used for tokamak plasma (e.g. Tikhonov Regularization, Minimum Fisher Information, etc.) Acknowledgement: The author gratefully acknowledges the financial support of the Polish National Science Centre (NCN), (grant no. DEC-2017/01/X/ST2/00126.) which financially supported this research.

Speaker: Jakub Bielecki

14:00 P1.1015 Pulse Reflectometer and Doppler back-scattering diagnostics in the TCV Tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1015.pdf Pulse Reflectometer and Doppler back-scattering diagnostics in the TCV Tokamak P. Molina Cabrera, S. Coda, L. Porte, N. Offeddu, and the TCV team[1] Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland. Both profile pulse reflectometer and Doppler back-scattering (DBS) diagnostics have been developed for the TCV Tokamak[1] using a steerable quasi-optical launcher and universal polarizers. A pulse reflectometer is being developed to complement Thomson Scattering measurements of electron density, greatly increasing temporal resolution and also effectively enabling fluctuation measurements. Pulse reflectometry consists of sending short pulses (<1ns) of varying frequency and measuring the roundtrip group-delay with precise chronometers. To improve resolution and flexibility, a fast arbitrary waveform generator (AWG - 65GSa/s, analog BW up to 20GHz) is used as a microwave pulse source to commercial frequency multipliers that bring 8-12GHz pulses up to the V-band (50- 75GHz). Two different timing techniques have been tested: direct digital sampling and traditional analog detection featuring constant-fraction-discriminators (CFD) and time-to- analog converters (TAC). AWG-driven pulse reflectometry has the potential to remain competitive when compared to other profile reflectometry techniques and may provide a new perspective in the study of density fluctuations. The design and progress in construction will be presented along with preliminary data from plasma discharges. The characterization of profiles and fluctuations in the pedestal region would be the focus of these first experiments. A variable configuration V-band heterodyne Doppler back-scattering diagnostic has been recently made operational in TCV. The diagnostic uses a fast AWG as the main oscillator and a commercial vector network analyzer extension module as the main mm-wave hardware. It allows sweepable single or multi-frequency operation, leveraging on the flexibility of the AWG source and fast digital sampling in the receiver. A flexible launcher antenna inherited from TCV's electron cyclotron heating launchers allows 3D toroidal (+/- 180°) and poloidal (10-58°). Sweeping of the poloidal angle may be done inside the shot. A pair of fast HE11 miter-bend polarizers allow flexible coupling to either O or X mode and programmable polarization changes during the shot. These have been used to measure the magnetic-field pitch angle in the edge of the plasma by monitoring the backscattered signal power. Ray-tracing simulations reveal an available k perp range between 3-16 cm-1 with a resolution of 2-4 cm-1. Perpendicular rotation velocity estimates compare well against ExB plasma poloidal rotation estimates from charge exchange recombination spectroscopy. [1] See author list of S. Coda et al 2017 Nucl. Fusion 57 102011

Speaker: Pedro Andres Molina Cabrera

14:00 P1.1016 Development and installation of a scintillator based detector for fast-ion losses in the MAST-U tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1016.pdf Development and installation of a scintillator based detector for fast-ion losses in the MAST-U tokamak J.F. Rivero-Rodriguez1,2, M. Garcia-Munoz2,3, L. Sanchis2,3, R. Martin4, K.G. McClements4, R.J. Akers4, A. Snicker5, J. Ayllon-Guerola1,2, J. Buchanan4, P. Cano-Megias2,3, J. Galdon-Quiroga2,3, D. Garcia-Vallejo1, J. Gonzalez-Martin1,2 and the MAST Upgrade and MST1 Team* 1 Department of Mechanical Engineering and Manufacturing, University of Seville, Spain. 2 Centro Nacional de Aceleradores (CNA) (Universidad de Sevilla, CSIC, Junta de Andalucía). 3 Department of Atomic, Molecular and Nuclear Physics, University of Seville, Spain. 4 CCFE, Culham Science Centre, Abingdon, Oxon, OX13 3DB, UK. 5 Aalto University, Department of Applied Physics, P.O. Box 14199, FI-00076 A scintillator-based detector for fast-ion losses due to MHD instabilities and externally-applied 3D fields has been developed and installed in the MAST-U tokamak [1]. The detector has a pitch-angle resolution of 2-3º and sufficient energy resolution to separate all three NBI injection energy components. The detector head is mounted on a rotatory drive to change the aperture orientation on a shot-to-shot basis, adapting the detector velocity-space coverage to the equilibrium q95, an especially important feature for a spherical tokamak. A synthetic diagnostic that includes detector head geometry, scintillator efficiency and optical transmission has been constructed. Full orbit simulations have been carried out using the ASCOT [2] and LOCUST [3] codes to estimate the predicted signals in MHD quiescent plasmas heated by on- and off-axis NBI and with and without externally applied 3D fields. The impact that externally applied 3D fields with different toroidal and poloidal spectra have on the NBI distribution has been estimated and will be discussed in the presentation. [1] J.F. Rivero-Rodriguez et al, 22nd Topical Conference on High Temperature Plasma Diagnostic (accepted). [2] E. Hirvijoki et al, Comput. Phys. Commun. 185 (2014), 1310-1321. [3] R. Akers et al., 39th EPS Conference & Int. Congress on Plasma Physics, P5.088 (2012) * See author list of “H. Meyer et al 2017 Nucl. Fusion 57 102014”

Speaker: Juan Francisco Rivero-Rodriguez

14:00 P1.1017 ITER steady state magnetic diagnostic

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1017.pdf ITER steady state magnetic diagnostic I. Ďuran1, S. Entler1, M. Kočan2, G. Vayakis2, P. Agostinetti3, M. Brombin3, J. M. Carmona4, G. Gambetta3, N. Marconato3, P. Moreau5, J. Šebek6, M. Kohout6, M. Walsh2 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 ITER Organization, St. Paul Lez Durance Cedex, France 3 Consorzio RFX, Padova, Italy 4 AVS, Elgoibar, Spain 5 CEA, Saint-Paul-Lez-Durance, France 6 Institute of Physics of the CAS, Prague, Czech Republic Magnetic measurements at long pulse magnetic confinement fusion devices require implementation of the true steady state magnetic field sensors in order to achieve required precision of plasma position measurement. Inductive sensors can suffer from a range of temperature gradient and radiation induced offsets which together with the intrinsic offsets of analogue integrators can lead to unwanted artificial drifts of their output signals. Steady state magnetic diagnostic set on ITER is based on sixty Hall effect sensor units welded onto the outer vacuum vessel skin within three toroidally separated full poloidal arrays. Each sensor unit contains two Hall sensors with bismuth sensitive layer measuring horizontal and vertical magnetic field and the thermocouple monitoring Hall sensors temperature. Temperature monitoring of each sensor unit features the in-situ auto calibration feature provided by embedded indium capsule. Advanced electronic Hall sensor controller form essential part of this diagnostic system. It provides high noise immunity employing synchronous detection and automated offset and planar Hall voltage elimination by periodic switching of Hall sensor input and output terminals. Proposed poster presentation will provide overview of present status of development, qualification, and manufacturing of the steady state magnetic sensors for ITER tokamak. Key results of the R&D programme spanning over several years and comprising neutron irradiation testing, measurement of Hall coefficient at high magnetic fields up to 12 T and high temperatures up to 220 C, long term temperature cycling etc. will be presented. It will be shown that resulting steady state magnetic diagnostic will comply with ITER requirements in terms of performance as well as compatibility with operation in ITER environment.

Speaker: Slavomir Entler

14:00 P1.1018 Nuclear reaction ion discrimination in plasma-laser interactions by coupling contiguous TOF-SiC devices

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1018.pdf Nuclear reaction ion discrimination in plasma-laser interactions by coupling contiguous TOF-SiC devices S. Cavallaro1, M. Mazzillo2,L. Calcagno1, and A. Sciuto3 1 Dept.of Physics and Astronomy, University of Catania, Catania, Italy 2 ST-Microelectronics, Str.le Primosole,50 Catania, Italy 3 CNR-IMM, VIII strada n.5, 95121 Catania, Italy Nuclear reactions produced in high intensity laser-target interaction involve, depending on atomic composition of the target, the simultaneous presence of different ion species, as proton, deuteron, 3 He, 4He, etc. Typically, nuclear reactions, as d+ d, d+3He, p+7Li, d+6Li, d+7Li, p+11B, produce output-ion energies of several MeV whose contributions can be mixed its self or to that of impurity protons. Ion discrimination is basically performed by means of analysis of pits observed on tracks detector, which is critically dependent on calibration, or qualitatively evidenced by fast TOF devices based on SiC and diamond detectors. By using these TOF devices , if two ion species are present in the same spectrum, the discrimination of their contribution is not directly attainable. Recently, a new method which allows to discriminate the contribution of two ion species in the wide energy range of the involved nuclear reactions, has been published [1]. It is based on charge response of two TOF-SiC contiguous detectors to the two ion species. The response of the detectors of suitable active thicknesses, associated to different energy losses, can determine the ion specific contribution in each TOF interval. In this contribution an extension of the method to more complexes cases of ion discrimination, with various detector characteristics, is presented and discussed. . [1] S. Cavallaro “Plasma-laser ion discrimination by TOF technique applied to coupled SiC detectors.” EPJ Web of Conferences 167, 04003 (2018).https://doi.org/10.1051/epjconf/ 201816704003 PPLA 2017

Speaker: Salvatore Cavallaro

14:00 P1.1019 Coupled Fokker-Planck and transport simulations of runaway electrons in COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1019.pdf Coupled Fokker-Planck and transport simulations of runaway electrons in COMPASS E. Macusova1 , J. Urban1 , O. Ficker1,2 , J. Mlynar1 , J. Decker3 , Y. Peysson4 , J. Cerovsky1,2 , M. Farnik1,2 , M. Hron 1 , R. Panek 1 , V. Weinzettl1 , M. Vlainic5 , the COMPASS team1 & the EUROfusion MST1 team ∗ 1 Institute of Plasma Physics of the CAS, CZ-18200 Prague 8, Czech Republic 2 FNSPE, Czech Technical University in Prague, CZ-11519 Prague 1, Czech Republic 3 Swiss Plasma Centre, EPFL, CH-1015 Lausanne, Switzerland 4 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 5 Institute of Physics, University of Belgrade, Belgrade, Serbia ∗ See the author list H. Meyer et al 2017 Nucl. Fusion 57 102014 An extensive study of discharges with the runaway electrons (RE) generation [J. Mlynar et al. invited, EPS 2018] was performed within several dedicated campaigns at the COMPASS tokamak [Panek et al. PPCF 2016]. The formation of the RE population and its dynamics are strongly sensitive to the background plasma parameters (density, magnetic field, electric field, impurity content etc.). Signals from RE related diagnostics at COMPASS such as HXR or neu- tron detectors correspond to high energy RE losses. The low energy part of the RE population and its losses are given by the ECE radiometer and the Cherenkov detector respectively. The lack of direct measurement of the RE momentum distribution function motivates us to use sophis- ticated numerical models as a complementary tool to obtain more comprehensive information and insight. Presented RE simulations are based on coupling of the fast transport code METIS [Artaud et al. NF 2010] and the 1D + 2V relativistic bounce-averaged kinetic Fokker-Planck solver LUKE [Decker and Peysson, EUR-CEA-FC 2004]. The LUKE code includes avalanche source of RE, radiation losses, fast particles radial transport with phase-space dependence and trapping effect. The METIS-LUKE coupling allows us to calculate time and space resolved electron distribution function and an improved evolution of plasma profiles. Plasma parameters vary slowly in COMPASS quiescent and flat-top RE discharges. This makes them good candi- dates for METIS-LUKE simulations which can give a better understanding of the RE related physics. We demonstrate how METIS-LUKE simulations can reconstruct RE formation based on available, indirect diagnostics, such as plasma current, loop voltage or electron temperature.

Speaker: Eva Macusova

14:00 P1.1020 Measurements of the radial ion flow velocity profile using the multi-channel Mach probe in the boundary plasma of the W7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1020.pdf Measurements of the radial ion flow velocity profile using the multi- channel Mach probe in the boundary plasma of the W7-X stellarator J. Cai1,3, Y. Liang1, S. Liu1,3, P. Drews1, C. Killer2, A. Knieps1, Y. Li1,3, M. Henkel1, D. Nicolai1, G. Satheeswaran1, Daniel Höschen1, A. Hiller1 and the W7-X Team 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung– Plasmaphysik , 52425 Jülich, 2 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany Germany 3 Institute of Plasma Physics, Chinese Academy of Sciences, PO Box 1126, Hefei 230031, People's Republic of China Ion flow velocity measurement in the edge and scraper-off layer (SOL) is important to understand the edge physics in fusion devices for the aims of impurity control and advanced confinement. During the Wendelstein 7-X (W7-X) experimental campaign OP1.2a [1, 2], the multi-channel (MC) Mach probe mounted on the multi-purpose manipulator (MPM) [3] has been used to measure the radial profiles of ion flow velocity as well as the electron density and temperature profile. This MC-Mach probe consists of two polar and two radial arrays of directional Langmuir pins (28 pins in total) serving for different aims, of which the polar arrays could obtain a polar distribution of ion saturation current while the radial arrays are used to study the dynamic process of radially propagated event. Besides, a sweeping voltage from -200V to 200V is applied to one of the Mach probe pins, by which the electron density and temperature profile could be obtained. In this paper, the first measurement of radial ion flow velocity profile using the MC-Mach probe in the boundary plasma of W7-X with island divertor will be presented. The impacts of magnetic topology on the edge ion flow will be discussed. Reference [1] Y Liang, O Neubauer, et al., Nuclear Fusion 57 (6), 066049, (2017) [2] RC Wolf, A Ali, A Alonso, et al., Nuclear Fusion 57 (10), 102020, (2017) [3] D Nicolai, V Borsuk, P Drews, Y Liang, et al., Fusion Engineering and Design 123, 960-964, (2017)

Speaker: Jianqing Cai

14:00 P1.1022 Dynamics of levels population of sputtered particles in plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1022.pdf Dynamics of levels population of sputtered particles in plasma E. Marenkov1 , C. A. Johnson2 , A.A. Eksaeva1,3 , A. Kreter3 1 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russian Federation 2 Auburn University, Auburn, Alabama 36849, USA 3 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung-Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), Jülich, Germany Measurements of the intensity of radiation from sputtered atoms is one of the methods for definition of sputtering parameters, such as velocity distribution of sputtered species or their distribution over excited states. Corresponding experiments conducted on linear plasma devices, e.g. PSI-2 or PISCES allow to get insight on physics of impurities transport in plasma with parameters close to those of tokamak edge. Spatial variation of radiation of sputtered atoms depends both on atomic processes respon- sible for excitation and photon emission and various geometry factors such as distribution of plasma temperature and density or distribution of sputtered particles over velocities and directi- ons. In this work we apply a radiative-collision model giving full description of population of excited levels of sputtered atoms and their radiation to experimental results on molybdenum (Mo) sputtering in helium (He) plasma at the PSI-2 installation. Recently obtained data set on the crossections of electron impact excitation, deexcitation, ionization and spontanious emis- sion including 800 excited levels of Mo is used [1]. Our calculations reproduce reasonably well the experimental results. One of the main features of the excited levels dynamics is a large number of levels having long, up to 10−4 s time scales. This eventually leads to a maximum in dependence of intensity on the distance from the target, located at approximately 1 cm for some lines, observed in the experiments. The model presented in this work is a further improvement of a ”two-levels” model employed in earlier ERO code calculations [2]. The latter supposes that all the excited levels very quickly come to the equilibrium values except of two levels responsible for radiation of a specific line. Shortcomings of this approximation comparing to the presented one are discussed. References [1] R.T. Smyth, C.A. Johnson, D.A. Ennis et al., Phys. Rev. A, 96, 4 (2017) [2] A. Eksaeva, D. Borodin, A. Kreter et al., Physica Scripta, T170 (2017)

Speaker: Evgeny Marenkov

14:00 P1.1023 Studying ELM filaments with Doppler reflectometry in ASDEX upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1023.pdf Studying ELM filaments with Doppler reflectometry in ASDEX upgrade E. Trier1,2 , P. Hennequin2 , M. Hoelzl1 , C. Lechte3 , M.Cavedon1 , G. Conway1 , T. Happel1 , B. Kurzan1 , F. Mink1,4 , F. Orain1,5 , J. Pinzon1,4 , B. Vanovac6 , E. Wolfrum1 , the ASDEX Upgrade Team and the EUROfusion MST1 Team∗ 1 Max Planck Institute for Plasma Physics, D-85748 Garching, Germany 2 LPP, Ecole Polytechnique, CNRS, F-91128 Palaiseau Cedex, France 3 Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie IGVP, Universität Stuttgart, 70569 Stuttgart, Germany 4 Physik-Department E28, Technische Universität München, 85747 Garching, Germany 5 CPHT, Ecole Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France 6 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands During edge localized modes (ELMs), filament structures are expelled from the edge of H- mode plasmas [1]. In the non-linear development of the underlying instabilities leading to the formation and expulsion of filaments, shear flows have been shown to be an important ingredi- ent, and are now included in the modeling tools. It is therefore essential to investigate experi- mentally the dynamics of the filaments during an ELM crash, and to compare them to simula- tions. In this respect, the Doppler reflectometers installed in ASDEX Upgrade probe the density fluctuations in the pedestal region and can detect filaments and their movement during an ELM. In this contribution, we report observations of an acceleration, followed by a reversal of the filaments velocity during type-I ELMs. Assuming it is due to a poloidal motion, this would cor- respond to an initial velocity increase in the electron diamagnetic direction, before a reversal in the ion direction; but a possible influence coming from radially propagating structures is a priori not excluded and needs to be considered. By changing the probing beam angle, and hence the direction of the probed wavevector, it is possible to distinguish whether these velocity changes are due to radial or poloidal motions. Possible changes in the measurement localization due to filament-induced modifications of the density profile are also discussed. These measurements are compared with the modelling of an ELM done with the non-linear MHD code JOREK [2, 3], using full wave simulations [4] to simulate the Doppler reflectometry diagnostic. References [1] A. Kirk et al., Phys. Rev. Lett. 96, 185001 (2006) [2] F. Orain et al., Phys. Plasmas 20, 102510 (2013) [3] F. Mink et al., Nucl. Fusion 58, 026011 (2018) [4] C. Lechte et al., Plasma Phys. Control. Fusion 59, 075006 (2017) ∗ See author list of "H. Meyer et al 2017 Nucl. Fusion 57 102014"

Speaker: Elisee Trier

14:00 P1.1024 First results from the thermal Helium beam diagnostic at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1024.pdf First results from the thermal Helium beam diagnostic at ASDEX Upgrade E. Wolfrum1, M. Griener1, M. Cavedon1, J.M. Muñoz Burgos2, O. Schmitz3, U. Stroth1 and the ASDEX Upgrade Team 1 Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany 2 Astro Fusion Spectre, astrofusionspectre@gmail.com 3 Engineering Physics Department, University of Wisconsin-Madison, Madison, USA Line ratio spectroscopy on thermal Helium is a diagnostic method allowing the determination of electron density and electron temperature simultaneously [1,2,3,4]. The line ratio of two singlet transitions is mainly dependent on density, while the ratio of a singlet and a triplet transition is dominantly dependent on electron temperature. Evaluable signal of He I line radiation can only be collected in plasmas restricted to certain combinations of density and temperature. At the low end of both quantities the signal is too weak due to the low excitation rate and towards higher electron densities and temperatures the neutral Helium density is strongly attenuated. Such a diagnostic has recently been implemented at the tokamak ASDEX Upgrade. It is very well suited to investigate the plasma edge, with the measurable radial region from the far scrape-off layer (SOL) to the near SOL and in low density cases even across the separatrix into the confined region. A piezo valve [5], mounted at the vessel optical head for line ratio spectroscopy wall very close to the plasma is used to 2 lenses inject neutral helium into the plasma. As shown in the figure, the lines of sight, 53 lines of sight (LOS) optimised for radial resolution (~ 4 mm), dip tube for 2D GPI cover a radial range of 8 cm in the plasma edge region, with additional ones for poloidally resolved measurements. The line resolved emission intensities of four He I lines are measured simultaneously with a newly developed 32 channel piezo valve [5] polychromator system, based on dichroic mirrors, small band interference filters and linear array photomultiplier tubes. With a data acquisition rate of 900 kHz this helium cloud, measured with GPI diagnostic provides not only a good spatial but also an excellent temporal resolution. The capabilities of the diagnostic are demonstrated in selected examples. The characteristics of electron density and temperature profiles in the near and far SOL are measured across regime transitions, such as I-phase to H-mode or L-mode to I-mode. The effect of a regime transition can be seen across the whole SOL from the separatrix to the wall. Because of the high spatial and temporal resolution not only changes in profiles can be determined but also the propagation velocity of fast transient events such as bursts and blobs can be measured. 1 B. Schweer et al, J. Nucl. Mater. 198 (1992) 174 2 O. Schmitz et al, Plasma Phys. Control. Fusion 50 (2008) 115004 3 U. Kruezi et al, Rev. Sci.Instrum. 83, 065107 (2012). 4 M. Griener et al, Plasma Phys. Control. Fusion 60 (2018) 025008 5 M. Griener et al, Rev. Sci.Instrum. 88 (2017) 033509

Speaker: Elisabeth Wolfrum

14:00 P1.1025 SOL-KiT – a new fully implicit code for kinetic modelling of electron transport in the Scrape-Off Layer

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1025.pdf SOL-KiT – a new fully implicit code for kinetic modelling of electron transport in the Scrape-Off Layer S. Mijin1, R. J. Kingham1, F. Militello2 1 Imperial College London, London, UK 2 CCFE, Culham, UK The problem of electron transport along the open field lines in the Scrape-Off Layer(SOL) of the tokamak has been of interest in predicting heat flow onto plasma-facing components of the reactor, namely the divertor. Currently, fluid codes used to treat the SOL mainly use some form of the Braginskii transport equations, assuming either local Spitzer-Härm heat flow, or using a flux limiter[1]. This assumption cannot capture non-local effects due to steep temperature gradients in the upstream region of the SOL (e.g. during ELMs), which can significantly change the heat flow, and has been identified as a possible deficiency of the fluid approach to SOL modelling[2]. Previous approaches to kinetic modelling of the SOL have mostly been focused on solving the full Vlasov-Fokker-Planck equation, sometimes coupled with neutral physics[3,4]. We take a slightly different approach, using a spherical harmonic decomposition of the electron distribution function – a method widely used in laser plasmas[5,6] (with some success in SOL modelling[7]). This allows for an integrated treatment of both the almost collisionless upstream region, as well as the highly collisional divertor region of the SOL. We couple this approach for the plasma with a Boltzmann collision approach for inelastic electron collisions with atomic hydrogen and follow the atomic state distribution of hydrogen with a simple collisional-radiative model. To solve the Vlasov-Fokker-Planck-Boltzmann system, we use the newly developed fully implicit code SOL-KiT, and will present the model behind the code, as well as both individual and integrated benchmarking of various model features. 1 Fundamenski W. Plasma Phys. Control. Fusion 47 (2005) R163-R208 2 Chankin A. V. et al. J. Nucl. Mat. 390-391 (2009) 319-324 3 Batishchev O. et al. J. Plasma Phys. 61 2 (1999) 347-364 4 Chankin A. V. et al. Contrib. Plasma Phys. 52 5-6 (2012) 500-504 5 Kingham R.J. et al. J. Comp. Phys. 194 (2004) 1 6 Tzoufras M. et al., J. Comp. Phys. 230 (2011) 6475 7 Allais F. et al. J. Nucl. Mat. 337-339 (2005) 246-250

Speaker: Stefan Mijin

14:00 P1.1026 SOLPS modeling of impurity seeded plasmas in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1026.pdf SOLPS modeling of impurity seeded plasmas in ASDEX Upgrade F. Hitzler1,2 , M. Wischmeier1 , F. Reimold3 , M. Bernert1 , X. Bonnin4 , A. Kallenbach1 , the ASDEX Upgrade Team5 and the EUROfusion MST1 Team6 1 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 2 Physik-Department E28, Technische Universität München, 85747 Garching, Germany 3 Forschungszentrum Jülich, 52425 Jülich, Germany 4 ITER Organization, 13067 St. Paul-lez-Durance, France 5 See author list "A. Kallenbach et al., 2017 Nucl. Fusion 57 102015" 6 See author list "H. Meyer et al., 2017 Nucl. Fusion 57 102014" Power exhaust is a critical issue for future fusion devices. The unmitigated power loads at the divertor targets can easily exceed the foreseen material limit of 10 MWm−2 . A reduction of these power loads can be achieved by controlled impurity seeding. The resulting high densities and low temperatures in the divertor lead to the so-called detachment state, which is characterized by strongly mitigated target particle and power fluxes. In order to optimize the impurity seeding recipe and to identify the potential of mixing impurities to maximize the impurity radiation while minimizing the impact on the pedestal validated numerical simulations are crucial. In this contribution impurity seeding of nitrogen and argon is investigated using the SOLPS code package for interpretative simulations, comparing the modeling results to experimental data from ASDEX Upgrade. Impurity seeding scans were performed with constant perpendic- ular diffusive transport coefficients, neglecting drifts and neo-classical transport effects. The modeling results show a change of the impurity distribution with increasing seeding rate. With the onset of detachment in the inner divertor the impurity radiation and density on the low field side suddenly drop, while they increase on the high field side and in the confined plasma region. This leads to a temperature drop in the confined region in the order of 12 % for argon, and 2 % for the nitrogen seeding cases at comparable divertor conditions. The mechanisms causing this redistribution are examined in this work. The stronger effect of argon can partly be explained by its radiation efficiency. Expectations from atomic databases yield argon radiation efficiencies in coronal equilibrium which are much higher than those for nitrogen. Comparing the calculated radiation efficiencies to the modeling results, it can also be observed that impurity transport in the simulation leads to a deviation from the coronal equilibrium which results in so-called non-coronal enhancement, i.e. enhanced radiation efficiencies. Focusing on the comparison of radiation patterns using synthetic diagnostics and spectro- scopic data, the code results will be validated with selected ASDEX Upgrade H-mode discharges.

Speaker: Ferdinand Hitzler

14:00 P1.1027 Scaling of the scrape-off layer width in MAST L-mode plasmas as measured by infrared thermography

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1027.pdf Scaling of the scrape-off layer width in MAST L-mode plasmas as measured by infrared thermography S. Elmore1, A. J. Thornton1, R. Scannell1, A. Kirk1 and the MAST Team1 1 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK Understanding the plasma parameters that affect the scrape off layer (SOL) width is a key issue for future tokamaks as the power entering the SOL (of order 100 MW [1] in ITER) and the SOL width (of order millimetres [2]) determine the heat flux to the divertor surfaces. The Eich scaling [2] can be used to characterise the divertor heat flux profile as an exponential decay for the SOL width and a Gaussian spreading factor due to diffusion around the last closed flux surface (LCFS). In this work, attached, double null, L-mode infrared (IR) profiles measured at the upper outer divertor on MAST are characterised by the fall off length, λq, and the spreading factor, S as returned from profile fits to the data using the Eich parameterisation for plasmas spanning an operational space of 400 kA ≤ IP ≤ 900kA, 0MW ≤ PNBI ≤ 3.1MW, 0.87 × 1019 𝑚−3 ≤ ̅̅̅ 𝑛𝑒 ≤ 4.6 × 1019 𝑚−3; where IP is plasma current, PNBI is neutral beam heating power and ̅̅̅ 𝑛𝑒 is line-averaged density. Regression of the data has shown that the strongest dependence of λq is on IP to the power of -1.04, which is consistent with multimachine scalings of H-mode plasmas [3]. Regressions including other variables for example, the parallel connection length (L||), will be performed to assess how they affect λq. The parallel connection length is particularly relevant to MAST-U where it can vary by a factor three. Midplane Thomson scattering (TS) measurements of the electron temperature and density fall off lengths allow approximation of the heat flux width at the midplane using either sheath or conduction limited models of the SOL. Surprisingly, the results suggest that the sheath limited approximation gives the best agreement between the IR and TS heat flux widths, independent of the regime; a full study will be performed in this work to investigate this result. The best regression for the spreading parameter, S, showed a strong negative dependence on the poloidal magnetic field, as has been seen in ASDEX Upgrade [4]. A comparison of double and single null plasmas will be presented to investigate the dependence of S on magnetic configuration. [1] A. Loarte et al., Nucl Fusion 47 (2007) S203-63 [2] T. Eich et al., Phys. Rev. Lett 107 (2011) 215001 [3] T. Eich et al., Nucl. Fusion 53 (2013) 093031 [4] B. Sieglin et al., Plasma Phys Control Fusion 58 (2016) 055015

Speaker: Sarah Elmore

14:00 P1.1028 Computer simulation of dust dynamics for various materials of the edge fusion plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1028.pdf Computer simulation of dust dynamics for various materials of the edge fusion plasma A.K. Issanova1), N.Kh. Bastykova1), S.K. Kodanova1), T.S. Ramazanov1) 1 Institute of Experimental and Theoretical Physics, Al-Farabi Kazakh National University, Al-Farabi 71, Almaty, 050040, Kazakhstan The influences of dust formation from candidate materials and their lifetime are the most important characteristics of the dust dynamics of the edge fusion plasma [1-4]. Descriptions of the evolution of dust formation from candidate materials and their lifetime can play a significant role in the formation of edge dusty plasma. Therefore these results can be useful for estimating the penetration length of dust particles made from different materials moving in fusion devices. In this work we consider the dynamics and lifetime of an individual dust particle formed on the wall surface of fusion reactor. To describe the dynamics of the dust particle the equations of motion, the equations of mass and energy balance, and the equations for charging the dust particle are solved. Calculations are made for dust particles consisting of different materials of Be, Ni, Mo and W, which depend on the differences in material properties and thermochemical properties. Dust particle charge and energy fluxes have been obtained depending on the dust temperature. And also the temperature and radius of the dust particle are obtained, as a function of time. On the basis of these calculations, estimates of the dust lifetime have been obtained. [1]. L. Vignitchouk, P. Tolias and S. Ratynskaia // Plasma Phys. Control. Fusion, 56, 095005 (2014) [2]. Tanaka Y., Pigarov A.Yu., Smirnov R.D., Krasheninnikov S.I., Ohno N., Uesugi Y. Modeling of dust- particle behavior for different materials in plasmas // Phys. Plasmas, 14, 052504 (2007) [3]. S. K. Kodanova, N. Kh. Bastykova, T. S. Ramazanov, and S. A. Maiorov // IEEE Transactions on Plasma Science, 4, 525-527 (2016) [4]. S. K. Kodanova , N. Kh. Bastykova , T. S. Ramazanov, G. N. Nigmetova, and S. A. Maiorov // IEEE Transactions on Plasma Science, 10.1109/TPS.2017.2763965 (2018)

Speaker: Ainur Issanova

14:00 P1.1029 3D tokamak Wall description within ITER Integrated Modelling and Analysis (IMAS) framework

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1029.pdf 3D tokamak Wall description within ITER Integrated Modelling and Analysis (IMAS) framework D. Penko1 , L. Kos1 , S. Mastrostefano2 , D. Yadykin3 , F. Villone4 and EUROfusion-IM Team∗ 1 Faculty of Mechanical Engineering, University of Ljubljana, Slovenia 2 Magnetic Fusion Energy and Electrical Sciences,University of Tuscia, Italy 3 Department of Earth and Space Sciences, Chalmers University of Technology, Sweden 4 Ass. EURATOM/ENEA/CREATE, DAEIMI, Università di Cassino, Italy An utility has been developed for storing and accessing ITER fusion device 3D wall grid geometry within the Integrated Modelling Analysis Suite (IMAS) [1], that is being developed and used at the ITER Organization and more widely in the EUROfusion community. The 3D grid geometry data is being stored in IMAS In- terface data structures (IDS) [2] which provide standard- ised data archival and retrieval together with easier data sharing and distribution. The data can then be accessed and further processed in many post-process simulations and calculations. The main objective of the “IMAS 3D wall” is to facilitate the access and usage of ITER 3D wall together with ITER grid geometry model by numerical codes, for modelling applications that can span Resistive Wall Mode (RWM) models [3] e.g. the CarMa code [4] or halo-currents modelling codes, or else for other fusion devices. References [1] S. Pinches, 44th EPS Conference on Plasma Physics P4.155, Europhysics Conference Abstracts Vol. 41F ISBN: 979-10-96389-07 [2] F. Imbeaux, et al, Nuclear Fusion 55 (12), 123006, (2015) [3] F. Villone , Y.Q. Liu, Effects of three-dimensional conducting structures on Resistive Wall Models, Theory of fusion plasmas, Varenna, August 2008 [4] F. Villone, Y. Liu, A. Pironti, G. Rubinacci, S. Ventre, ITER passive and active RWM analysis with the CarMa code, 38th EPS Conference on Plasma Physics (2011) ∗ See http://www.euro-fusionscipub.org/eu-im

Speaker: Dejan Penko

14:00 P1.1030 Numerical modelling of detached plasma experiments with differential pumping in Magnum-PSI

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1030.pdf Numerical modelling of detached plasma experiments with differential pumping in Magnum-PSI R. Chandra1 , G. R. A. Akkermans1 , I. G. J. Classen1 , R. Perillo1 , H. J. de Blank1 , P. Diomede1 , E. Westerhof1 1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands Sufficient decrease of plasma pressure, ion and heat flux along the scrape-off layer of a toka- mak fusion reactor are imperative to ensure the survival of the divertor tiles. This specific con- dition, defined as detachment, occurs within low temperature, high density, highly recycling plasma that can also be realized in linear plasma devices such as Magnum-PSI [1]. In Magnum- PSI, high recycling is achieved by utilizing differential pumping across three vacuum chambers. Experiments have been conducted to mimic detachment in the Magnum-PSI linear device by varying the neutral background pressure at the chamber of the recycling target via H2 gas puff- ing [2], while the hydrogen plasma source parameters are kept constant across the experiments. Numerical modelling is carried out to help gain further insights regarding the physics behind detachment. The experiments are benchmarked with a coupled fluid-kinetic approach using the B2.5- EU- NOMIA code package [3]. EUNOMIA is a Monte Carlo neutral simulation optimized for linear geometry. Thomson scattering measurements without gas puffing are used as a plasma bound- ary condition at the source in the simulation, and the gas pressure in the target chamber will be varied. The resulting electron density and temperature simulated profiles near the target are compared with profiles measured in experiments. This paper presents the result of the bench- mark tests, and identifies the collisional processes and other physical effects relevant to the detached plasma state. References [1] H. J. N. van Eck et al., Plasma Sources Science and Technology 20, 4 (2011) [2] I. Classen et al., Abstract, 59th Annual Meeting of the APS Division of Plasma Physics, http://meetings.aps.org/link/BAPS.2017.DPP.PP11.77 (2017) [3] R. C. Wieggers et al., Contributions to Plasma Physics, 52(5-6):440-444 (2012)

Speaker: Ray Chandra

14:00 P1.1031 Conceptual design of the COMPASS-U tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1031.pdf Conceptual design of the COMPASS-U tokamak R. Panek, J. Havlicek, M. Hron, R. Dejarnac, M. Komm, J. Urban, V. Weinzettl and the COMPASS team Insitute of Plasma Physics of the CAS, Za Slovankou 3, Prague, Czech Republic The Institute of Plasma Physics of the CAS in Prague has recently started construction of new COMPASS-U tokamak. It will be a compact, medium-size (R = 0,85 m, a = 0,3 m), high-magnetic-field (5 T) device. COMPASS-U will be equipped by a flexible set of poloidal field coils and capable to operate with plasma current up to 2 MA and, therefore, high plasma density (~ 1020 m-3). The device is designed to generate and test various DEMO relevant magnetic configurations, such as conventional single null, double null, single and double snow-flake. The plasma will be heated using 4 MW Neutral Beam Injection (NBI) heating system with future extension by at least 4 MW Electron Cyclotron Resonant Heating (ECRH|) system. The COMPASS-U tokamak will consist of a new vacuum vessel, new toroidal and poloidal field coils and support structure in a vacuum cryostat. The power supply system will be upgraded with two new flywheel generators in order to satisfy energy demands of the high-magnetic field device (approx. 200 MW, 400 MJ). The magnetic coils will be manufactured of copper and cooled in a cryostat to liquid-nitrogen temperature in order to decrease their resistivity and lower the ohmic losses associated with the high coil currents (up to 200 kA) at acceptable levels. COMPASS-U will be equipped with lower and upper closed, high neutral density divertors. Due to high PB/R ratio COMPASS-U will represent a device which will be able to perform ITER and DEMO relevant studies in important areas, such as the plasma exhaust or development of new confinement regimes. The divertors will use conventional materials in the first stage, however, in the later stage, the liquid metal technology, which represents a promising solution for the power exhaust in DEMO, will be installed into the lower COMPASS-U divertor. The metallic first wall will be operated at high temperature (approx. 300 °C) during plasma discharge, which will enable to explore the edge plasma regimes relevant to ITER and DEMO operation. The first plasma of the COMPASS-U tokamak is planned for 2022. In this contribution, we will present the concept of the COMPASS-U tokamak and design of the main tokamak components.

Speaker: Radomir Panek

14:00 P1.1032 Three-dimensional simulations of edge plasma transport with LHW-induced magnetic perturbations on EAST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1032.pdf Three-dimensional simulations of edge plasma transport with LHW-induced magnetic perturbations on EAST S. Xu1,2 , M. Rack1 , Y. Liang1,2 , J. Huang1 , M. Jia1,2 , Y. Feng3 , J. Cosfeld1 , H. Zhang2 , S. Liu2 , Y. Gao1 , K. Gan2 , W. Feng2 , L. Wang2 , W. Zholobenko1 , D. Reiter1 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung-Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China 3 Max-Planck-Institute für Plasmaphysik, 17491 Greifswald / 85748 Garching, Germany Recent experiments from the Experimental Advanced Superconducting Tokamak (EAST) show that lower hybrid waves (LHWs) can profoundly change the magnetic topology by induc- ing helical current filaments flowing along magnetic field lines in the scrape-off layer [1, 2]. The spectrum of LHW-induced perturbation fields automatically adjusts to the edge-safety- factor, because the helicity of current filaments closely fits the pitch of the edge field line. It has been proved in the experiments that such flexible magnetic perturbations have powerful abilities in controlling heat load on divertor targets, controlling impurities, as well as mitigating Edge- Localized Modes (ELMs). However, the underlying physical mechanisms are still unclear. To better understand the physics behind, here it is investigated how these magnetic perturbations caused by LHWs affect the edge plasma transport utilizing the 3D Monte Carlo code EMC3- EIRENE. The 3D magnetic topology structure is reflected in the plasma properties, due to much stronger parallel field transport compared with cross field diffusion. Good quantitative agree- ments between simulations and experiments demonstrate that the EMC3-EIRENE code now is capable of taking into account the LHW-induced magnetic perturbation fields with both phys- ical and geometrical effects being considered. The larger current of filaments caused by the increased LHWs input power can further deepen the penetration depth of the additional trans- port channel by extending the stochastic edge layer, and influence the ratio of heat (or particle) flux between split striated and original strike line on divertor targets. The 3D simulation results also indicate that the additional plasma transport channel induced by LHWs can significantly cause the redistribution of heat load between inner and outer divertor targets, which could not be found by the field line tracing method in previous works [3, 4]. References [2] Y. Liang et al., Phys. Rev. Lett. 110 235002 (2013) [3] M. Rack et al., Nucl. Fusion 54 064016 (2014) [1] J. Li et al., Nat. Phys. 9 817-821 (2013) [4] W. Feng et al., Nucl. Fusion 57 126054 (2017)

Speaker: Shuai Xu

14:00 P1.1033 Investigation of negative ions in detached fusion plasmas in the York Linear Plasma device

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1033.pdf Investigation of negative ions in detached fusion plasmas in the York Linear Plasma device J.Branson, T. Gans, K. Gibson, E. Wagenaars York Plasma institute, Department of Physics, University of York, Heslington, York, United Kingdom Studies on tokamak divertors and operating scenarios almost unanimously conclude that plasma detachment is necessary for stable and continuous operation of large, power plant scale tokamak devices. That is to say cooling of the plasma exhaust from the hot core is essential to preserve plasma facing components. This is usually achieved via the puffing of neutral gas into the target area encouraging recombination and redistribution of energy. At lower temper- atures relevant to a detached tokamak divertor, around 1eV, the main process of neutralization of species is molecular activated recombination (MAR) [1]. This process is subdivided into two mechanisms whose relative contributions to detachment are not fully understood. Both mech- anisms involve the interaction between exited molecules with ions. One involves interaction with an electron yielding a H− which goes on to interact with H+ becoming H + H. The second involves interaction with H+ , creating a H2 + which goes on to collide with an electron and divide into H + H. The York Linear Device is a magnetised plasma device capable of producing plasma conditions relevant to tokamak divertors. The diagnostic accessibility of this device is far better than a standard tokamak, making it an ideal device for the study of the fundamentals of detachment. In this experiment we use laser photo-detachment to measure the density of negative ions us- ing a custom Langmuir probe and YAG laser [2, 3]. The probe geometry is different to standard straight-wire probes by including a right angled bend, bringing the axis of the wire along that of the YAG beam. This diagnostic technique assesses the population of Hydride (H− ) ions which are involved in one of the two MAR chains. The linear device is also equipped with Thomson scattering and Raman scattering diagnostics to analyze the same plasma. The electron temper- atures and molecular rotational temperatures may thus be studied in the same plasma under the same conditions as those used in the photodetachment experiments. This gives a full overview of the physics behind detachment which may be extrapolated to larger machines. References [1] S. I. Krasheninnikov, A. Yu. Pigarov and D. J. Sigmar, Physics letters A 214, 5-6 (1996) [2] M. Bacal, Review of Scientific Instruments 71, 3981 (2000) [3] S. Kajita, S. Kado, T. Shikama, B. Xiao, S. Tanaka, Contrib. Plasma Physics 44, 7-8 (2004)

Speaker: Joseph Francis Branson

14:00 P1.1034 Tokamak GOLEM for fusion education - chapter 9

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1034.pdf Tokamak GOLEM for fusion education - chapter 9 V. Istokskaia1 , M. Shkut1 , J. Cerovsky1 , M. Farnik1 , B. Leitl1 , L. Hudec1 , P. Macha1 , V. Svoboda1 , J. Stockel1,2 , J. Adamek2 1 Faculty of Nuclear Sciences and Physical Engineering CTU in Prague, Prague, Czech Rep. 2 Institute of Plasma Physics AS CR, Prague, Czech rep. The GOLEM tokamak (R = 0.4 m, a = 0.085 m, Btor < 0.5 T, Ipl < 8 kA) is the oldest tokamak in the world still operational. Its main mission is education of future fusion specialists in the Czech Republic. Furthermore, the GOLEM tokamak serves also as a training facility of students throughout the world, because of its unique fully remote control system [1]. This contribution is devoted to description of several students0 projects, related mainly to diagnostics development, investigation of selected issues of tokamak physics and plasma performance on GOLEM: • Design of new amplifiers for two linear AXUV arrays of 20 photodiodes. This detection sys- tem will be implemented to a pinhole camera and integrated to the GOLEM diagnostics sys- tem. By using tomography methods, the temporal evolution of the plasma radiation and the plasma position in the poloidal cross section will be determined. • A research on runaway electrons (RE) physics is focused on generation mechanisms of RE, detection of HXR radiation and investigation of RE losses. Furthermore, some selected fea- tures of runaway discharges are investigated. In particular, the combined probe head composed of the Ball Pen and Langmuir probe [2] is exploited to measure the radial profiles of plasma potential and the electron temperature during the Anomalous Doppler Instability. • Investigation of plasma radiation by using spectroscopy methods and applying the coronal- radiative model. Ratio of helium and hydrogen spectral lines are used to determine the electron temperature. Results are compared with other methods of Te measurements on GOLEM. • Improvement of plasma performance. A table-top experiment modelling power supplies cir- cuits of the GOLEM tokamak is designed to test the plasma current control without interfering tokamak operation. It is shown that by adding precisely selected resistors to the primary cir- cuit, a flat-top phase of plasma current can be achieved. Furthermore, a guideline for discharge scenarios for different values of electron density is now being created. References [1] V. Svoboda, et al., Fus. Eng. and Des. 68, 1310-1314 (2011) [2] J. Adamek, et al., Rev. Sci. Instr. 87, 043510 (2016)

Speaker: Valeriia Istokskaia

14:00 P1.1035 Work progress on GOL-NB multiple-mirror trap

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1035.pdf Work Progress on GOL-NB Multiple-Mirror Trap V.V. Postupaev1,2, V.I. Batkin1,2, A.D. Beklemishev1,2, A.V. Burdakov1,3, V.S. Burmasov1,2, I. A. Ivanov1,2, K. N. Kuklin1, K. I. Mekler1, A. F. Rovenskikh1, and E. N. Sidorov1 1 Budker Institute of Nuclear Physics, 630090 Novosibirsk, Russia 2 Novosibirsk State University, 630090 Novosibirsk, Russia 3 Novosibirsk State Technical University, 630092 Novosibirsk, Russia The GOL-NB project is a next-step experiment on multiple-mirror plasma confinement in the Budker Institute of Nuclear Physics [1]. Currently, it enters the assembly state with the first plasma in a start configuration scheduled for the first half of 2018. The final configuration of the device will include a 2.5-m-long central gasdynamic trap with two attached multiple-mirror sections of 3 m each, and two end magnetic flux expanders that house a start plasma creation system, plasma receiver endplates and a system of biased electrodes for plasma stabilization. Plasma will be heated by two 0.75 MW, 25 keV neutral beams. The device is the deep reconstruction of the previous GOL-3 multiple-mirror trap; it reuses some part of the magnetic system and infrastructure from the latter. In the final configuration, GOL-NB will be a scaled-down physical model of a future fusion-grade reactor system. The GOL-NB assembly schedule uses one of the engineering advantages of linear confinement systems. Fast start of commissioning of different subsystems and the first plasma can be achieved before readiness of the each component of magnetic and vacuum systems. Currently, the start configuration includes both expander tanks, a cold start plasma source, a multiple-mirror solenoid with 34 coils (instead of 2×28 coils in the final system), and a short temporary section for the on-site commissioning of NBIs. Before start of the assembly, experiments with a prototype plasma source in the existing section of magnetic system were done. We demonstrated that a plasma stream from an arc source was successfully compressed by the converging magnetic field and transported through a 3-m-long vacuum system thus imitating the process of start plasma creation in GOL-NB. No significant differences of plasma transport in regimes with the multiple- mirror field from ones in a uniform magnetic field were found. [1] V.V. Postupaev, et al., Nuclear Fusion, 57, 036012 (2017).

Speaker: Vladimir V. Postupaev

14:00 P1.1036 Beta induced alfvén eigenmode driven by energetic ions on HL-2A

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1036.pdf Beta induced Alfvén Eigenmode Driven by Energetic Ions on HL-2A P.W. Shi1, W. Chen1, Z. B Shi1, X.R. Duan1 1 Southwestern Institute of Physics, Chengdu, China Beta induced Alfvén eigenmode (BAE) has become a major concern since the first observation on DIII-D [1]. Those weak damping modes often enhance transports and cause substantial reductions of EPs [2]. To better understand the instabilities, more experimental evidences should be needed. In the present paper, the energetic ions induced BAEs (i-BAEs) on HL-2A will be given. The i-BAEs are driven by the passing particles with energy of 15-45keV and the mode frequencies are about 60-90kHz. A typical example is shown as Fig.1(a). The radial mode structure can be measured by the microwave reflectometer with working frequency of 34-48GHz and it is localized in the region of ρ = 0.1 − 0.25. The i-BAE has been finally confirmed by the Alfvén mode code (AMC) [3]: the eigenfrequency of 90kHz is in accordance with the experimental observation and the mode structure agrees well with that measured by the microwave reflectometer. The i-BAEs can be excited more easily in low electron density discharges because ion Landau damping is relatively weak in those cases. Both stationary and non-stationary i-BAEs can be observed during NBI heating. The ion temperature and neutron count decline obviously when the non-stationary i-BAEs appear, which suggests a badly deterioration of the plasma confinement. Finally, the mode frequency is found to be modulated by electron cyclotron resonance heating (ECRH), which indicates the ECRH may be an effective candidate for the suppression of i-BAEs. Fig.1 (a) Stationary i-BAE and (b) the corresponding mode structure detected by microwave reflectometer. (c)The q profile and Alfvén continuum for stationary i-BAE with n=2. (d) The radial mode structure given by the AMC. Reference [1] W. W. Heidbrink et al. Phys. Rev. Lett.71, 855 (1993) [2] L. Chen and F. zonca, Rev. Mod. Phys. 88, 015008 (2016). [3] H. S. Xie et al Phys. Plasmas 22, 022518 (2015)

Speaker: Peiwan Shi

14:00 P1.1037 Reverse of tokamak plasma rotation under tearing-mode locking by external resonant magnetic perturbation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1037.pdf Reverse of Tokamak Plasma Rotation under Tearing-Mode Locking by External Resonant Magnetic Perturbation N.V. Ivanov, A.M. Kakurin National Research Centre «Kurchatov Institute», Moscow, Russia Rotation of tokamak plasma attracts considerable attention in the fusion research because this rotation, particularly under shear of rotation velocity, affects plasma stability and confinement. The plasma rotation velocity in the vicinity of a rational magnetic surface can be influenced by the development of the tearing mode. According to experiments and numerical modelling, the tearing-mode locking by externally applied static Resonant Magnetic Perturbation (RMP) can be followed by a rotation reverse of the Resonant Plasma Layer (RPL) occupied by magnetic island structure (see [1, 2]). This reverse extends due to plasma viscosity to some area surrounding the RPL. Results of calculations and analysis of the plasma rotation reverse subject to the tearing mode locking are presented in this paper. The main attention is paid to conditions necessary for the rotation reversals separately in toroidal and poloidal directions, as well as for the concurrent changes of both rotation directions. The dynamics of the plasma toroidal and poloidal rotation-profile variations are also presented. The TEAR code [3, 4] used for the calculations is based on the visco-resistive MHD approximation that gives coupled diffusion-type equations for the magnetic flux perturbation and for the plasma rotation velocities in toroidal and poloidal directions. In the case of sufficiently large magnetic islands [5] the mode locking occurs due to the effect of the RMP-produced electromagnetic torque applied to the RPL. The toroidal and poloidal electromagnetic torque components are balanced by corresponding components of the viscous torque depending on the RPL rotation velocities with respect to plasma velocities outside RPL. At the mode locking, the superposition of the RPL toroidal and poloidal velocity projections on the direction of the mode phase velocity (the [r×B] direction) is inhibited till the full stop of the mode rotation. Therefore, if the initial directions of these velocity projections coincide, one of the toroidal or poloidal velocities can change its sign. These alternative possibilities depend on the interrelation between plasma toroidal and poloidal viscosity coefficients. The concurrent reversals of the RPL toroidal and poloidal rotation velocities at the mode locking can occur under the account of the electron diamagnetic drift in the mode rotation [6, 7]. [1] Hender T.C., et al. Nucl. Fusion 32 (1992) 2091 [2] Ivanov N.V., Kakurin A.M. Nucl. Fusion 57 (2017) 016021 [3] Ivanov N.V., Kakurin A.M., Konovalov S.V. 24th IAEA FEC (2012) TH/P3-22, PAS&T/TF 36, v. 2, p. 55 (2013), see http://vant.iterru.ru/vant_2013_2/6.pdf [4] Ivanov N., Kakurin A.M. Physics of Plasmas 21 (2014) 102502 [5] Eliseev L.G., et al. Physics of Plasmas 22 (2015) 052504 [6] Hosea J.C., et al. Phys. Rev. Lett. 30 (1973) 839 [7] Fitzpatrick R. Nucl. Fusion 33 (1993) 1049

Speaker: Nikolay Ivanov

14:00 P1.1038 Neoclassical tearing mode induced by error field penetration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1038.pdf Neoclassical tearing mode induced by error field penetration S. Nishimura1 , R. Numata2 1 Faculty of Science and Engineering, Hosei University, Koganei, Japan 2 Graduate School of Simulation Studies, University of Hyogo, Kobe, Japan In tokamaks, magnetic islands are generated by both the neoclassical tearing mode and the forced magnetic reconnection due to intrinsic or externally applied error fields. In addition, interaction between the neoclassical tearing mode and error fields is of great importance in tokamaks. It is known that the rotating neoclassical tearing mode is decelerated and locked by error fields, once error field amplitude exceeds a critical value. Even when the neoclassical tear- ing mode is stable, penetration of error fields directly produces non-rotating magnetic islands that continue growing due to plasma responses, which are so-called born-locked modes. Those locked modes are often observed in precursor phases of tokamak disruptions[1]. Much work has been done to understand interaction between the unstable neoclassical tear- ing mode and the error fields. For example, in our previous work, a low dimensional model of rotating magnetic islands is introduced to understand simulation results based on reduced magnetohydrodynamic (MHD) equations[2]. While, a relation between the stable neoclassical tearing mode and the error fields has not been fully discussed so far. In this study, a simulation code solving reduced MHD equations in two-dimensional slab geometry is developed to study the effects of error fields on the stable neoclassical tearing mode. The reduced MHD equations are composed of a vorticity equation, a generalized Ohm’s law and a pressure evolution equation. Perturbed bootstrap currents are phenomenologically introduced in the generalized Ohm’s law. The error fields are introduced through edge boundary conditions of magnetic flux perturbations. Nonlinear simulations are conducted in parameter regimes, where the neoclassical tearing mode is stable for any initial magnetic island width. In simulations, the error field penetration is observed, when plasma flow velocity and diamag- netic drift velocity almost cancel out. Once the error field penetration occurs, magnetic islands grow to sizes much larger than those expected from given error field amplitude. This indicates that the error field penetration destabilizes the stable neoclassical tearing mode. Our results are suggestive to a mechanism of spontaneous growth of the born-locked modes. References [1] R. J. La Haye, R. Fitzpatrick, T. C. Hender, A. W. Morris, J. T. Scoville, and T. N. Todd, Phys. Fluids B 4, 2098 (1992). [2] S. Nishimura, M. Yagi, K. Itoh, S.-I. Itoh, and S. Benkadda, Nucl. Fusion 50, 054007 (2010).

Speaker: Seiya Nishimura

14:00 P1.1039 Configuration Characteristics of Tokamak-like Stellarator, Chinese First Quasi-axisymmetric Stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1039.pdf Configuration Characteristics of Tokamak-like Stellarator, Chinese First Quasi-axisymmetric Stellarator Haifeng Liu1,4, Akihiro Shimizu2, Mitsutaka Isobe2,3, Shoichi Okamura2, Shin Nishimura2, and Chihiro Suzuki2 Yuhong Xu1, Changjian Tang1,4, Hai Liu1, Xin Zhang1, Bing Liu1, Jie Huang1, Huarong Du1, Xianqu Wang1, Dapeng Yin5, Yi Wan5and CFQS team1,2 1 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China 2 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan 3 SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan 4 Physics Department, Sichuan University, Chengdu 610041, China 5 Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd, Hefei, 230000, China As an internationally collaborative project, the Chinese First Quasi-axisymmetric Stellarator (CFQS) will be fabricated and operated by Southwest Jiaotong University in China and National Institute for Fusion Science in Japan. The CFQS is a tokamak-like stellarator with low-aspect ratio. Via scan of the magnetic configurations with various aspect ratios, major radius and numbers of modular coils, the plasma boundary and modular-coil system for CFQS have been designed and optimized. The candidate parameters of CFQS are as follows: the major radius is 1.0 m, the toroidal magnetic field strength is 1.0 T, the toroidal periodic number is 2 and the aspect ratio is 4.0. The 16 modular coil system has been optimized and designed via minimizing the normal component of magnetic field on the target plasma boundary surface generated from the modular coils, as well as adjusting the main Fourier components of magnetic field strength produced by the modular-coil system to the original ones derived from the target configuration. With these optimized modular coils, VMEC free boundary calculation is conducted to check the beta limit of MHD equilibrium. Mercier stability, ballooning stability and neoclassical transport are calculated to evaluate the property of CFQS configuration. The MHD equilibrium of configuration is almost stable up to beta = 1%. The neoclassical transport in the CFQS is less than that in the W7-X in 1/n regime.

Speaker: Haifeng Liu

14:00 P1.1040 Toroidal Alfven Eigenmode study on the Globus-M Spherical Tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1040.pdf Toroidal Alfven Eigenmode study on the Globus-M Spherical Tokamak Yu.V. Petrov1, N.N. Bakharev1, V.V. Bulanin2, V.K. Gusev1, G.S. Kurskiev1,A.A. Martynov,3 S.Yu Medvedev3, V.B. Minaev1, M.I. Patrov1, A.V. Petrov2, N.V. Sakharov1, P.B. Shchegolev1, A.Yu. Telnova, S.Yu. Tolstyakov1, A.Yu. Yashin2. 1 Ioffe Institute, St. Petersburg, Russia 2 Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia 3 Keldysh Institute of Applied Mathematics, Moscow, Russia. In this report we describe the latest results of investigation of the toroidal Alfvén eigenmodes (TAE), which were identified earlier in experiments with NBI heating on the spherical tokamak Globus-M [1]. The experiments were continued at increased magnetic field from 0.4 to 0.5 T and plasma current from 200 to 250 kA. The mode character has changed with the increase of the field. While the TAE bursts became more frequent, the fast particle losses induced by them became weaker. The dependence of fast particle losses and redistribution induced by TAE on the values of magnetic field and plasma current are presented. During the last experimental campaign, the multichannel Doppler backscattering reflectometry (DBS) was applied for the first time to study TAE localization [2]. Multichannel probing at frequencies of 20, 29, 39 and 48 GHz was applied. It allowed us to observe the TAE fluctuations at four locations on major radius simultaneously. The measurements have shown that the TAE fluctuations registered by means of DBS are localized on the periphery of the plasma column, in the region of normalized minor radii of ρ=0.5-0.75. Modeling of the Alfven continuum and TAE mode structure for Globus-M conditions were made by means of a software package base on the modified KINX and CAXE codes [3]. Comparison of the experimental data and calculated spectra, as well as the analysis of the structure of the global modes, showed that the oscillation frequencies observed in the experiment are closer to the frequencies of the TAE modes localized near the plasma boundary in the region of magnetic surfaces with safety factor values q = 2.5, 3.5 . [1] Petrov Yu. V. et al. 2015 J. PLASMA PHYS. 81 515810601 [2] Bulanin V.V. et al. 2017 TECH. PHYS. LETT. 43 1067-1070 [3] Gusev V.K. et al. 2018 TECH. PHYS. LETT. 44 65 in Russian

Speaker: Yury Petrov

14:00 P1.1041 A reduced drift magnetic island theory of neoclassical tearing modes for low collisionality tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1041.pdf A reduced drift magnetic island theory of neoclassical tearing modes for low collisionality tokamak plasmas A.V. Dudkovskaia1, J.W. Connor2, D. Dickinson1, P. Hill1, K. Imada1, H.R. Wilson1,2 1 York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, UK 2 CCFE, Culham Science Centre, Abington Oxon OX14 3DB, UK Successful operation of next generation fusion devices, such as ITER, directly depends on understanding the physics of the NTM onset and its control techniques. This, in turn, requires a more quantitative theory of the NTM threshold physics. In our new theoretical approach, we solve the drift kinetic equation for both the ion and the electron plasma components, employing an expansion in the small ratio of island width to tokamak minor radius to obtain orbit-averaged equations. From these we derive the streamlines, S, along which the distribution function is constant, if collisions are neglected. This S function describes drift islands of the same geometry as the real magnetic islands but shifted radially by a value comparable to the poloidal Larmor radius in the absence of the electrostatic potential. The radial shift of the islands is in opposite directions for the two streams and . Adding a low level of collisions provides the S dependence of the distribution function, showing it is flattened inside the S islands (not the magnetic islands, Fig. 1) due to a competition between the ion parallel flow and plasma drifts. Hence, the density and temperature profile flattening becomes incomplete for magnetic islands comparable to the ion banana orbit width, reducing the bootstrap current drive and hence suppressing the drive for NTMs with widths . These results provide a new understanding of how finite ion orbit width effects influence the NTM threshold. Fig. 1. The distribution function flattening across the O-points of the drift islands (the magnetic island is centred at ): (a) and (b) for the two streams and . (c) The sum over the two streams, representative of density, showing almost complete flattening across the magnetic island at for , but a substantial gradient for .

Speaker: Aleksandra V. Dudkovskaia

14:00 P1.1042 A simplified approach to the physics of runaway electron beam dissipation in tokamak disruptions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1042.pdf A SIMPLIFIED APPROACH TO THE PHYSICS OF RUNAWAY ELECTRON BEAM DISSIPATION IN TOKAMAK DISRUPTIONS∗ J. R. Martin-Solis 1 , E.M. Hollmann 2 , M. Lehnen 3 and A. Loarte 3 1 Universidad Carlos III de Madrid, Avda.Universidad 30, Leganes, 28911-Madrid, Spain. 2 University of California-San Diego, La Jolla, California 92093-0417, USA. 3 ITER Organization, Route Vinon sur Verdon, CS90046 13067 St. Paul-lez-Durance, France. ABSTRACT The injection of large amounts of high-Z impurities by Massive Gas Injection (MGI) or Shattered Pellet Injection (SPI) constitutes the most promising candidate for the mitigation of runaway electrons during disruptions in large devices like ITER [1,2]. In this paper, the dissipation and decay of the runaway current by injection of high-Z impurities during tokamak disruptions is analyzed using a simplified approach, based on the kinetic treatment of Ref. [3], which includes the effect of the collisions with the plasma particles and the impurity ions, the synchrotron radiation losses associated with the pitch angle scattering of the runaway electrons when colliding with the impurity atoms as well as the bremsstrahlung radiation. The model allows to get simple estimates of the runaway current duration, the runaway distribution function and energy during the dissipation phase. A comparison of the effects associated with the different runaway loss mechanisms (collisions, synchrotron and bremsstrahlung radiation losses) will be presented . Extrapolations to ITER indicate that injection of a few kPa · m3 of Ar could be a promising scenario for runaway electron dissipation during disruptions if the impurities can be efficiently delivered into the plasma. Effects associated with the runaway scraping-off due to the VDE of the runaway beam during the decay of the current will be also considered. [1] E.M. Hollmann et al., Phys.Plasmas 22, 021802 (2015). [2] M. Lehnen et al., J. Nucl. Mater. 3948, 463 (2015). [3] P. Aleynikov and B.N. Breizman, Phys.Rev.Lett. 114, 155001 (2015). ∗ This work was carried out with financial support from Dirección General de Investigación, Cientı́fica y Técnica, Project No. ENE2015-66444-R (MINECO/FEDER, UE). ITER is the Nuclear Facility INB no. 174. This paper explores physics processes during the plasma operation of the tokamak when disruptions take place; nevertheless the nuclear operator is not constrained by the results of this paper. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

Speaker: Jose Ramon Martin-Solis

14:00 P1.1043 Plasmoid reconnection in transient coaxial helicity injection on HIST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1043.pdf Plasmoid reconnection in transient coaxial helicity injection on HIST M. Nagata, A. Fujita, Y. Ibaraki, Y. Kikuchi and N. Fukumoto Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280, Japan The Spherical Torus (ST) is a promising candidate for an advanced fusion reactor due to the compactness. Elimination of the central solenoid coil to allow an approach to lower aspect ratio configurations requires for the non-inductive plasma start-up and the transient coaxial helicity injection (T-CHI) is a leading candidate for its method. One of the most important issues in T-CHI is whether it can establish a current sufficient in closed flux surfaces for succeeding current drive and heating. Understanding the flux closure during the start-up process is the primary purpose of the T-CHI experiment on the Helicity Injected Spherical Torus (HIST: R=0.30 m, a=0.24 m, A=1.25) [1]. Also, the CHI provides a good platform for pursuing MHD relaxation and magnetic reconnection physics. Magnetic reconnection is an essential element in understanding of self-organization phenomena such as sawtooth oscillations and Taylor relaxation in fusion plasmas and also eruptive mass ejection of solar flares in astrophysical plasmas. To prove the flux closure issue in the CHI start-up, we have investigated the fast magnetic reconnection driven by multiple plasmoids [2]. Here, we report that in the formation process of T-CHI start-up plasma with the plasmoid reconnection, (i) two or three small-size plasmoids are generated in elongated toroidal current sheet with the full width δ ~0.05 m, a long length L=0.6-1 m and a high density ne= 0.3-2x1020 m-3, (ii) one of plasmoids becomes a large-scale closed flux surface during the decay phase, and (iii) in the He discharge, the reconnection rate on the mid-plane is slower than that in the H2 discharge and the self-generated toroidal magnetic energy (poloidal current) increases rapidly, leading to the formation of a doublet-type magnetic configuration. The observation of the regular oscillations of the reconnecting magnetic field Bz, ne and the axial out flow Vz in the current sheet provides a strong evidence of the plasmoid reconnection. These findings could verify that the plasmoid reconnection in the elongated current layer in the presence of the strong toroidal field allows the fast flux closure in the T-CHI. References [1] M. Nagata, et al., Phys. Plasmas 10, 2932 (2003). [2] F. Ebrahimi and R. Raman, Phys. Rev. Lett. 114, 205003 (2015).

Speaker: Masayoshi Nagata

14:00 P1.1044 Progress in the modelling of 3-D effects on MHD stability with the PB3D numerical code and implications for ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1044.pdf Progress in the modelling of 3-D effects on MHD stability with the PB3D numerical code and implications for ITER T. Weyens1, A. Loarte1, G.T.A. Huijsmans2,3 1ITER Organization, Route de Vinon sur Verdon, 13067 Saint Paul Lez Durance, France 2 Eindhoven University of Technology, Eindhoven, The Netherlands 3 CEA, IRFM, F-13108, Saint-Paul-lez-Durance, France The magnetohydrodynamic (MHD) stability of tokamaks is often investigated with the assumption of axisymmetric equilibria, which is in many cases justifiable. There are important cases, however, when 3-D aspects of the equilibria have significant consequences for the stability of these configurations. Examples thereof include the noticeable lowering of attainable pedestal heights in H- mode plasmas, as seen for example in the JET TF ripple experiments [Saibene 2007] and in the mitigation of ELMs due to the 3-D effects on the plasma configuration by ELM control coils [Evans 2008]. The PB3D (Peeling Ballooning in 3-D) code has been developed to allow the study of such 3- D ideal MH stability effects for peeling ballooning modes [Weyens 2017] and is under constant improvement. In this paper we present recent advances in its simulation capabilities, such as the development of a new interface with general 3-D VMEC equilibria that do not need to have any kind of symmetry, both from free and fixed-boundary simulations, and the implementations for the calculation of vacuum potential energy due to plasma boundary perturbations which are essential to model peeling mode stability. The paper will also describe simulations performed to assess the 3-D edge MHD stability of H-mode plasmas in the reference ITER scenarios from pre-fusion plasma operation to high Q DT operation. These simulations focus foremost on the ballooning stability of these configurations taking into account the effects of toroidal field (TF) ripple as well as the influence of other types of 3-D effects such as those applied for ELM control. Both effects can be rather complex in ITER because, for instance, the ripple map varies in both magnitude and shape when the toroidal field is varied, as the ferromagnetic inserts are optimized for 5.3T operation and over-compensate the TF ripple corrections for lower TF values. In these ballooning stability studies, MHD equilibria are created with VMEC starting from ITER reference 2-D plasma equilibria by varying pedestal pressure magnitude and considering various TF ripple levels and maps (e.g. with/without ferromagnetic inserts) and with a range of toroidal current waveforms (current magnitudes, toroidal harmonic and phases) in the ELM control coils. The ballooning stability of these 3-D equilibria is being assessed with PB3D and the results will be presented in this paper. [Saibene 2017] Saibene, G., et al., EFDA-JET CP(07)03/62 report (2007). [Weyens 2017] Weyens, T., et al., In: J. Comput. Phys. 330 (2017) 997. [Evans 2008] Evans, T., et al., Nuclear Fusion 48 (2008) 024002.

Speaker: Toon Weyens

14:00 P1.1045 Onset conditions of helical cores in tokamaks for extrapolation to ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1045.pdf Onset conditions of helical cores in tokamaks for extrapolation to ITER A. Wingen1 , R.S. Wilcox1 , L.F. Delgado-Aparicio2 , M.R Cianciosa1 , S.P. Hirshman1 , S.K. Seal1 1 Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA 2 Princeton Plasma Physics Laboratory, Princeton, NJ, USA Large, spontaneous m/n = 1/1 helical cores are predicted in tokamaks such as ITER with ex- tended regions of low- or reversed- magnetic shear profiles and q near 1 in the core. Their impact on ITER has not yet been fully quantified. Beneficial effects can include flux pumping and pre- venting sawteeth. On the other hand fast ion confinement is predicted to degrade significantly and the ensuing rotation breaking could be detrimental to tearing mode and microturbulence suppression. The threshold for the spontaneous symmetry breaking is determined using VMEC scans, beginning with reconstructed 3D equilibria from DIII-D and Alcator C-Mod based on observed internal 3-D deformations. The helical core is a saturated internal kink mode; its onset threshold, shown by the black line in Fig. 1, is proportional to (d p/dρ)/Bt2 around q = 1. Below the threshold, applied 3-D fields can drive a helical core to finite size, as in DIII-D. The helical core size ζ thereby depends on the magnitude of the applied perturbation. Above it, a small, random 3-D kick causes a bifur- cation from axisymmetry and excites a spontaneous helical core, which is in- dependent of the kick size. The on- set threshold is very sensitive to the Figure 1: Onset of helical cores for an ITER mock-up dis- q-shear in the core. Helical cores oc- charge (15 MA, H-mode), compared to 3-D reconstructed cur frequently in Alcator C-Mod dur- DIII-D and C-Mod discharges. The y-axis is normalized ing ramp-up when slow current penetra- so that the thresholds for all machines coincide, with: 6 tion results in a reversed shear q-profile, ζDIII−D = 2.545, ζIT ER = 0.5 and ζC−Mod = 0.145 10 Pa. which is favorable for helical core formation. A comparison of the helical core onset threshold for discharges from DIII-D, C-Mod and ITER, shown by the markers in Fig. 1, confirms that while DIII-D is marginally stable, C-Mod and especially ITER are highly susceptible to heli- cal core formation without externally applied 3-D magnetic fields. This work is supported by the US Department of Energy under DE-AC05-00OR22725, DE-AC02-09CH11466 and DE- FC02-04ER54698 and used resources of the Oak Ridge Leadership Computing Facility.

Speaker: Andreas Wingen

14:00 P1.1046 Causality Study of MHD Events in LHD Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1046.pdf Causality Study of MHD Events in LHD Plasmas K. Ichiguchi1,2 , B.A. Carreras3 , S. Sakakibara1,2 1 National Insititute for Fusion Science, Toki, 509-5292, Japan 2 SOKENDAI, The Graduate University of Advanced Studies, Toki, 509-5292, Japan 3 Universidad Carlos III 28911, Madrid, Spain In high beta experiments in the Large Helical Device (LHD), partial collapse phenomena caused by the interchange mode can be observed[1]. These phenomena occurs in two types of discharge condition. One is the inward shift of the vacuum magnetic axis. This condition enhances the magnetic hill, where the driving force is enhanced.. The other is ramp-up of the net toroidal current that increases the rotational transform. This condition reduces the magnetic shear, where the stabilizing effect is reduced. In both cases, the growth of the interchange modes leads to the partial collapse of the electron temperature profile. In some of the collapses, clear correlation between the decay of the mode frequency and the growth of the mode is seen. That is, the disappearance of the mode frequency and the beginning of the mode growth look to syn- chronize. The mode frequency is mainly due to the ExB rotation and the diamagnetic rotation of the plasma, and the former is usually dominant [2] Therefore, these results suggest that the plasma rotation play a significant role in the collapse phenomena. In the nonlinear simulation for the interaction of the interchange mode and the ExB shear flow, we obtained that the flow has a stabilizing contribution against the mode growth [3]. However, the causality of the events is not still clear, whether the plasma rotation stopping causes the mode growth or the mode growth stops the rotation.. van Milligan et al., [4] show that the transfer entropy [5] is a powerful tool to investigate such causality. They examine the transfer entropy for the causality studies in the fluctuations observed in the TJ-II experiments. Thus, we apply this method to the time evolution of the magnetic fluctuations and the mode frequency. Utilizing the results, we also discuss the similarity and the difference in the collapse property between the cases of the hill enhancement and the shear reduction in the aspect of the causality. References [1] S. Sakakibara, et al., Nucl. Fusion, 55, 083020 (2015). [2] Y. Takemura, et al., 2013, Plasma and Fusion Res. 8, 1402123. [3] K. Ichiguchi et al., Proc. IAEA FEC 2016 Kyoto, TH/P1-4. [4] B. Ph. van Milligan, et al,. Nucl. Fusion 54, 023011 (2014). [5] T. Shreiber, Phys, Rev. Letters, 85, 461 (2000).

Speaker: Katsuji Ichiguchi

14:00 P1.1047 Perturbative 3D Ideal MHD Stability of Tokamak Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1047.pdf Perturbative 3D Ideal MHD Stability of Tokamak Plasmas M.S. Anastopoulos-Tzanis 1,2 , B.D. Dusdson 1 , C.J. Ham 2 , C.C. Hegna 3 , P.B. Snyder 4 , H.R. Wilson 1,2 1) York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, UK 2) Culham Science Centre, Abingdon, Oxon OX14 3DB, UK 3) Departments of Engineering Physics and Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA 4) General Atomics, San Diego, California 92186-5608, USA Control of edge localised modes (ELMs) is required for ITER to prevent damage to the di- vertor. One method of control is the application of non-axisymmetric resonant magnetic per- turbations (RMPs). Experimentaly either ELM mitigation (increase of frequency) or complete suppression (removal) is seen. However, the physics mechanism responsible for the occurrence of those states is still an open question. In this work, the non-axisymmetric part of the equilib- rium is postulated to have the key impact on MHD instabilities, potentially modifying stability boundaries. Linear perturbation theory is employed to study the 3D ideal MHD stability follow- ing the formalism of [C.C. Hegna, Physics of Plasmas 21, 2014]. The symmetry breaking due to the non-axisymmetric equilibrium geometry induces toroidal mode coupling. A numerical framework for the calculation of coupling is developed, based on the ideal MHD stability code ELITE [H.R. Wilson et al., Physics of Plasmas 9, 2002] that provides axisymmetric toroidal modes and fixed boundary non-axisymmetric equilibria. To validate result, the nonlinear MHD code BOUT++ [B.D. Dudson et al., Computer Physics Communications 180, 2009] is employed to simulate mode coupling and qualitative agreement is observed. The external 3D field has a strong impact on stability above a certain threshold and decrease of MHD growth rates was observed due to stronger coupling with higher toroidal modes. Such a result could provide vital insight for understanding the exact mechanism responsible for ELM suppression and optimal RMP coil design. The author wishes to thank all collaborators for fruitful discussions and advice. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053 and from the RCUK Energy Programme [grant number EP/P012450/1], as well as the Fusion CDT programme through the EPSRC grant [EP/L01663X/1]. To obtain further information on the data and models under- lying this paper please contact PublicationsManager@ukaea.ac.uk.

Speaker: Michail Anastopoulos-Tzanis

14:00 P1.1048 Certain developments on the equilibrium of magnetized plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1048.pdf 45 EPS Conference on Plasma Physics 12914 Certain developments on the equilibrium of magnetized plasmas G. N. Throumoulopoulos1*, A. Evangelias1, D. A. Kaltsas1, A. Kuiroukidis2, 3 P. J. Morrison , G. Poulipoulis1 1 Physics Department, University of Ioannina, GR 451 10 Ioannina, Greece 2 Technological Education Institute of Serres, GR 62124 Serres, Greece 3 Department of Physics and Institute for Fusion Studies, University of Texas, Austin, Texas 78712, USA *e-mail: gthroum@cc.uoi.gr Recent results will be presented on steady states of magnetically confined plasmas obtained by conventional and Hamiltonian methods. The presentation consists of three parts. The first one concerns the derivation of a generalized Grad-Shafranov equation describing helically symmetric equilibria with pressure anisotropy and incompressible plasma flow of arbitrary direction with application to straight-stellarator configurations [1]. The impact of pressure anisotropy and flow on the equilibrium characteristics is also examined. In the second part the axisymmetric equilibrium code HELENA is extended for pressure anisotropy and flow parallel to the magnetic field and ITER-pertinent equilibria are constructed. In the third part the Hamiltonian formulation of helically symmetric plasmas is established within the framework of extended MHD, a simplified two-fluid model including Hall-ion and electron-inertia contributions [2,3]. Four families of Casimir invariants are obtained and they are used to construct Energy-Casimir variational principles for deriving generalized extended MHD equilibrium equations with arbitrary flow. The system is then cast into the form of Grad-Shafranov-Bernoulli equations. In addition, an example of an incompressible double-Beltrami equilibrium will be presented in connection with a straight-stellarator configuration. References: 1. A Evangelias, A Kuiroukidis and G N Throumoulopoulos, Plasma Phys. Control. Fusion 60 025005, 12pp (2018). 2. D. A. Kaltsas, G. N. Throumoulopoulos and P. J. Morrison, Physics of Plasmas 24, 092504, 14pp (2017). 3. D. A. Kaltsas, G. N. Throumoulopoulos and P. J. Morrison, Helically symmetric extended MHD: Hamiltonian formulation and equilibrium variational principles, https://arxiv.org/abs/1801.10138, 16pp; submitted to J. Plasma Physics.

Speaker: George N. Throumoulopoulos

14:00 P1.1049 Coupled nonlinear MHD-particle simulations for ITER with the JOREK+particle-tracking code

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1049.pdf Coupled nonlinear MHD-particle simulations for ITER with the JOREK+particle-tracking code D.C. van Vugt1,2 , G.T.A. Huijsmans1,3 , M.Hoelzl4 , N.J. Lopes Cardozo1 , A. Loarte2 1 Eindhoven University of Technology, Eindhoven, The Netherlands 2 ITER Organization, 13067 St. Paul Lez Durance Cedex, France 3 CEA Cadarache, IRFM, 13108 St. Paul Lez Durance Cedex, France 4 IPP Garching, Boltzmannstraße 2, 85748 Garching bei München, Germany There are many effects in tokamak physics which cannot be described with solely a magne- tohydrodynamic (MHD) code or with particle tracking methods. These include heavy impurity transport, behaviour of fast ions and neutral particles, radiation modelling, and impurity pro- duction by sputtering, especially in a non-stationary background plasma and with feedback to this plasma. Their consistent modelling is very important to reproduce plasma behaviour, par- ticularly for future tokamaks such as ITER. For instance the behaviour of W (production by sputtering, transport, ion/recombination balance, radiation emission, etc.) can be modelled in a stationary or time-varying MHD plasma background by coupling to a particle tracer model. In this paper we present the extension of the non-linear MHD code JOREK [1] with a particle tracking code. This code follows particles with a kinetic 6D full-orbit or 5D guiding-center ap- proximation in the JOREK mesh. Additionally the code contains modules to calculate the ioni- sation and recombination probabilities of atoms/ions in the plasma, as well as the corresponding radiated power emitted, with the rates for the atomic processes from ADAS data. Particle colli- sions (e.g. between W and background DT ions) are modelled with the binary collision model (BCM) [2], which has been found to reproduce key impurity transport mechanisms such as the thermal force and the corresponding temperature screening effects. Sputtering sources are im- plemented using the Eckstein formulation. The particle density and radiation is finally projected onto the JOREK finite element representation. The JOREK+particle-tracking code can be used either one-way (evaluation of the conse- quence of the JOREK plasma behavior on particles) or through a coupled run, where the pro- jected quantities from the particle distributions are used as source terms in the MHD equations in JOREK. Such simulations are required, for example, when the modelled W radiation levels are high and can decrease the plasma temperature, when fast particles affect MHD stability, etc. Examples of both one-way and coupled simulations will be shown in the paper. References [1] G.T.A. Huysmans and O. Czarny. In: Nuclear Fusion 47.7 (2007). DOI: 10.1088/0029-5515/47/7/016. [2] Y. Homma and A. Hatayama. In: Journal of Computational Physics 231.8 (2012). DOI: 10.1016/j.jcp. 2011.12.037.

Speaker: Daniel Cornelis van Vugt

14:00 P1.1050 Analysis of MHD activity in Wendelstein 7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1050.pdf Analysis of MHD activity in Wendelstein 7-X stellarator H. Thomsen, C. Brandt, K. Rahbarnia, T. Andreeva, S. Bozhenkov, H. Laqua, T. Klinger, A. Koenies, N. Lauf, U. Neuner, J. Schilling, T. Stange, M. Zanini and the W7-X Team Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany The Wendelstein 7-X stellarator (W7-X) in Greifswald has started its second experimental phase in October 2017. The installation of the uncooled divertor modules allowed for a higher energy limit as compared to the first experimental phase conducted in limiter configuration. The magneto-hydrodynamic (MHD) diagnostic systems had been extended prior to the start of this second experimental phase and the Mirnov diagnostic and the X-ray tomography system have been put into operation. Performance-wise, long discharge lengths of up to 30 s have been achieved and a peak diamagnetic energy of 1 MJ has been measured. In this specific high-performance experimental program, the density has been increased by means of pellet fueling during the first phase. In the second phase without pellet fueling, the temperature increased (input heating was kept constant) while the line-averaged density signal decreased; the measured diamagnetic energy was constant. The second phase was ended by MHD mode activity leading to an abrupt decrease in the stored energy by approx. 150 kJ. Mirnov and X-ray diagnostics show an oscillatory pre-trigger prior to the crash. These signatures resemble the observations obtained during ECCD current drive experiments, where the driven currents lead to similarly fast crashes. In this contribution we present the analysis of the crashes in these experiment programs.

Speaker: Henning Thomsen

14:00 P1.1051 Locked-Tearing Mode Control by 3D Magnetic Field Entrainment in the presence of Static Error Fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1051.pdf Locked-Tearing Mode Control by 3D Magnetic Field Entrainment in the presence of Static Error Fields 1 M. Okabayashi, 2S. Inoue, 3E. Strait, 3N.Z. Taylor, 1N. Ferraro, 3J. de Grassie, 4J. Hanson, 3R. La Haye, 1S. Jardin and 1N. Logan 1 Princeton Plasma Physics Laboratory, PO Box 451, Princeton, NJ 08543-0451, USA 2 National Institutes for Quantum and Radiological Science and Technology, 801-1 Mukoyama, Naka, Ibaraki 311-0193, Japan 3 General Atomics, PO Box 85608, San Diego, CA 92186-5608, USA 4 Columbia University, 2960 Broadway, New York, NY 10027-6900, USA DIII-D experiments on control of locked tearing modes using applied 3D fields are in good qualitative agreement with predictions of a non-linear reduced MHD code (AEOLUS- IT) [1]. The plasma condition was the ITER base line scenario target with low safety factor discharges. The simulation is nonlinear, but highlights fundamental processes by simplifying the physics to isolate a single helicity with m/n=2/1, using only the vorticity equation and Ohm’s law without any additional transport properties. In the experiment, internal mode structures were monitored by the perturbed rotation and ion temperature profiles measured by Charge Exchange Recombination (CER) in this very low mode frequency (zero-100 Hz) regime. Experiments have illuminated several critical physical processes that are qualitatively consistent with non-linear reduced MHD simulations. One example is the consistency of external kink- and tearing- mode structure in the partial / full applied 3D field penetration. This shows that the possible non-linear process of kink-tearing mode coupling during tearing mode locking can be well represented by a relatively simplified model. Another example is the qualitative agreement of the formation of second-harmonic-type rotational structure very near q=2 surface with very little fundamental component. On the other hand, the magnetic structure remains fundamental. This implies a possible second harmonic effect for non-linear self-stabilization. Predictive understanding of mode time-evolution is crucial to designing a feedback scheme that will help to avoid disruptions in present and future devices. This work was supported in part by the US Department of Energy under DE-AC02-09CH11466, DE-FC02- 04ER54698, DE-FG02-04ER54761 (1) S. Inoue et al., NF 2017 57, 116020-10, S. Inoue et al., PPCF 2018 online

Speaker: Michio Okabayashi

14:00 P1.1052 Effect of the pressure gradient in the connection region on the PBM stability

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1052.pdf Effect of the pressure gradient in the connection region on the PBM stability S.K. Kim1, S. Saarelma2, Y.S. Na1 and O.J. Kwon3* 1 Department of Nuclear Engineering, Seoul National University, Seoul, Korea 2 Culham Centre of Fusion Energy, Culham, U.K 3 Department of Physics, Daegu University, Daegu, Korea *Email address: ojkwon@daegu.ac.kr Abstract The width of the plasma edge pedestal, formed by the transport barrier and the pressure at the top of the pedestal strongly affect performance of tokamak fusion plasmas. To achieve the plasma of performance target in future devices such as ITER, optimization of the edge pedestal is required. However, achieving the improvement of the pedestal pressure and width still has many difficulties and understanding of pedestal physics remains as a challenge. We have investigated the dependence of pedestal properties such as the pedestal height and the pedestal width on the pressure gradient just inside the pedestal top (𝜓𝜓N =0.9), 𝛼𝛼𝑖𝑖 , numerically using the parameters of the JET-like plasma (𝐼𝐼𝑝𝑝 =1.4MA, 𝐵𝐵𝑡𝑡 =1.7T, 𝛿𝛿=0.37, 𝛽𝛽N =2.25) as the basis of the analysis. We used MISHKA [1], an ideal MHD stability code and EPED1 [2], a predictive model of the edge pedestal to analyse the edge stability and predict its structure. As a result, improvement of pedestal properties can be achieved by reducing 𝛼𝛼𝑖𝑖 , which is consistent with experimental findings [3, 4]. Larger Shafranov shift, 𝛥𝛥𝑠𝑠ℎ , also improves the pedestal width and height [5, 6]. Positive correlation between poloidal beta and pedestal height [7, 8] is found to be due to stabilization of peeling-ballooning mode (PBM) with 𝛥𝛥𝑠𝑠ℎ . From this result, we suggest the possible correlation between pedestal structure and core pressure profile including the effect of 𝛥𝛥sh and 𝛼𝛼𝑖𝑖 . References: [1] A. B. Mikihailovskii et al., 1997 Plasma. Phys. Reports 23(10) 844 [2] P. B. Snyder et al., 2009 Phys. Plasmas 16 056118 [3] N. Aiba et al., 2008 Journal of Physics: Conference Series 123 012008 [4] N. Hayashi et al., 2011 Nucl. Fusion 51 073015 [5] J. W. Connor et al., 2016 Plasma Phys. Controlled Fusion 58 085002 [6] P. B. Snyder et al., 2011 Nucl. Fusion 51 103016 [7] A. W. Leonard et al., 2008 Phys. Plasmas 15 056114 [8] I. T. Chapman et al., 2015 Nucl. Fusion 55 013004

Speaker: Ohjin Kwon

14:00 P1.1053 Design study of the magnetic field coils and configuration for the Chinese First Quasi-axisymmetric Stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1053.pdf Design study of the magnetic field coils and configuration for the Chinese First Quasi-axisymmetric Stellarator A. Shimizu1, H. Liu2, M. Isobe1,3, S. Okamura1, Y. Xu2, X. Zhang2, B. Liu2, J. Huang2, X. Wang2, H. Liu2, C. Tang2,4, D. Ying5, Y. Wang5 and CFQS team1,2 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu, 509-5292, Japan 2 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China 3 SOKENDAI (The Graduate University for Advanced Studies), Toki, Gifu 509-5292, Japan 4 School of Physical Science and Technology, Sichuan University, Chengdu 610041, China 5 Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd, Hefei 230000, China The Chinese First Quasi-axisymmetric Stellarator (CFQS) is a future quasi-axisymetric (QA) stellarator device, which will be constructed in Southwest Jiaotong University (SWJTU) in China. This is the international joint project of National Institute of Fusion Science in Japan and SWJTU, and its design work has been continued jointly. A QA stellarator has mainly axisymmetric magnetic field components in the special magnetic coordinates (Boozer coordinates), which determine the guiding centre orbit, therefore, the neoclassical properties of the QA stellarator are similar to tokamak although inductive current is not required. About ten years ago, CHS-qa, has been designed as a post CHS device, which is a low aspect ratio (~3.2) QA stellarator. Based on this design, new configuration for the CFQS is obtained. The present parameters of magnetic field strength, the major radius, the aspect ratio and the toroidal periodic number are 1.0 T, 1.0 m, 4.0, and 2 respectively. The 16 modular coil system is optimized by the NESCOIL code for this configuration. By using this coil system, the free boundary equilibrium calculation by the VMEC is conducted, and the Shafranov shift and bootstrap current are estimated. The bootstrap current reaches 30 kA at ~1.5 %, and the good QA properties are maintained up to this . For the flexibility of the magnetic field configuration, 3 pairs of poloidal field coils are considered. The Shafranov shift is suppressed by the vertical field produced by those coils.

Speaker: Akihiro Shimizu

14:00 P1.1054 Numerical studies of plasmoids during the nonlinear evolution of double tearing modes in slab and cylindrical geometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1054.pdf Numerical studies of plasmoids during the nonlinear evolution of double tearing modes in slab and cylindrical geometry W. Guo1, J. Ma1, Z. Yu1 ,Q. Yu2 1 Institute of Plasma Physics, Chinese Academy of Science, Hefei, Anhui , China 2Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany Email:wfguo@ipp.ac.cn Double tearing mode (DTM) is an important kind of magnetohydrodynamics (MHD) instability that often occurs with reversed central magnetic shear configuration in tokamak discharges. A nonlinear MHD code based on a conservative perturbed MHD model by splitting primary variables in original MHD equations into equilibrium part and perturbed part has been developed. The nonlinear evolution of double tearing mode in slab and cylindrical geometry is numerically investigated in high Lundquist number regime. The onset of the secondary and tertiary islands (plasmoids) due to the tearing unstable current sheets formed during the fast reconnection phase and a new nonlinear evolution process characterized by two fast reconnection phase are investigated and discovered. More effects, including the flow, guiding field, viscosity etc. are under way. In cylindrical geometry plasmoid generations different from slab geometry during the nonlinear DTM evolution are observed. The details will be presented. (a) (b) Plasmoids during the nonlinear evolution of DTM in high Lundquist number regime:(a) Multiple (five) secondary islands formation in nonlinear evolution of double tearing mode with equilibrium current sheets distance y0=0.2,(b)A typical picture of a new quasi-stationary characterized as two pairs of coexisting islands with well preserved symmetry. *This work is supported National Key R&D Program of China under Grant No. 2017YFE0300402 and the National Natural Science Foundation of China under Grant Nos. 11475219,11775268.

Speaker: W. Guo

14:00 P1.1055 Low-frequency fishbone driven by passing fast ions in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1055.pdf Low-frequency fishbone driven by passing fast ions in Tokamak plasmas Limin Yu1 , Feng Wang2 , G. Y. Fu3 1 Department of Physics, East China University of Science and Technology, Shanghai, China 2 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian, China 3 Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China The internal kink modes with dominant poloidal and toroidal wave number m = 1 and n = 1 can be strongly destabilized by both the perpendicular and tangential neutral-beam injec- tion [1, 2]. With perpendicular injection, the driven modes can be considered as either an energetic particle mode (EPM) with mode frequency comparable to the toroidal precession frequency of the trapped energetic ion [3] or a "gap" mode with mode frequency close to the thermal ion diamagnetic frequency [4]. With tangential injection, both the high-frequency mode and the low-frequency mode have been observed [2]. For the high-frequency branch, the mode was considered as an EPM with frequency determined by energetic particle toroidal circulation frequency [5, 6]. For the low-frequency branch, the mode was modeled as a "gap" mode with the thermal ion diamagnetic frequency [7]. In this work, within the framework of the theory of EPM, the low-frequency mode driven by a resonant interaction between the passing beam ions and the wave with ω = ωφ − ωθ is studied, where ωφ and ωθ are respectively the circulation frequency in toroidal and poloidal direction of passing fast ions. With the effect of finite orbit width (FOW) of fast ions, the instability can be excited by passing fast ions. It is found that magnetic shear at the q=1 radius plays an important role in the instability whereas the effect of the background plasma beta is weak. In particular, there exists a critical magnetic shear below which the beam ion beta threshold for EPM excitation is very small. For moderate or higher magnetic shear the beam ion beta threshold is about a few percent. These results are consistent with experimental observation of the low-frequency fishbone in the HL-2A tokamak [8]. References [1] K. McGuire, et al., Phys. Rev. Lett. 50, 891 (1983) [2] W. W. Heidbrink, et al., Phys. Rev. Lett. 57, 835 (1986) [3] Liu Chen, et al., Phys. Rev. Lett. 52, 1122 (1984) [4] B. Coppi, F. Porcelli, Phys. Rev. Lett. 57, 2272 (1986) [5] Shaojie Wang, Phys. Rev. Lett. 86, 5286 (2001) [6] Feng Wang, et al., Nucl. Fusion 57, 056013 (2017) [7] R. Betti, J. P. Freidberg, Phy. Rev. Lett. 70, 3428 (1993) [8] Liming Yu, et al, J. Phys. Soc. Jpn. 86, 024501 (2017)

Speaker: Limin Yu

14:00 P1.1056 Statistical analysis of disruptions at COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1056.pdf Statistical analysis of disruptions at COMPASS E. Matveeva1,2, J. Havlicek1, A. Havránek1, O. Hronova1, V. Weinzettl1, R. Pánek1 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic Understanding of disruptions plays an important role for design of the future fusion devices as they induce large thermal and mechanical loads on a vacuum vessel. Statistical analysis of the set of discharges during the period of August – December 2017 was performed in order to improve our knowledge of disruptions on COMPASS. About 25 % of COMPASS discharges are disruptive which provides a good opportunity of disruption studies. Disruption rate dependence on the operational limits (Greenwald limit, plasma current limit), auxiliary power and plasma current is investigated. Asymmetrical disruptions are of particular concern because they induce additional currents and, therefore, forces in the vacuum vessel. In addition to this they might lead to a resonant amplification of the forces. The COMPASS tokamak is equipped with magnetic diagnostics, which allow measurements of the plasma current at five toroidal locations. This enables detailed investigation of asymmetrical disruptions (almost 80 % of disruptive discharges on COMPASS). It is observed that a plasma current asymmetry is detected for upward, downward and inward disruptions. However, rotation of asymmetry is never found during the upward disruptions. Asymmetrical disruptions parameters such as magnitude, frequency, number of rotations and duration of asymmetry are analysed within the contribution.

Speaker: Ekaterina Matveeva

14:00 P1.1057 Effects of electron cyclotron resonance heating on toroidal Alfvén eigenmodes in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1057.pdf Effects of electron cyclotron resonance heating on toroidal Alfvén eigenmodes in tokamak plasmas J. Ferreira1, F. Nabais1, P. Rodrigues1, R. Coelho1, A. Figueiredo1, M. Garcia-Munoz2, T. Johnson3, P. Lauber4, S. E. Sharapov5, P. Vallejos3, M. A. Van Zeeland6, V. Bobkov4, I.G.J. Classen7, M. Fitzgerald5, B. Geiger4, J. Galdon-Quiroga2, J. Gonzalez-Martin2, L. Guimarãis1, M. Mantsinen8,9, V. Nikolaeva1, M. Rodriguez-Ramos2, L. Sanchís2, P. A. Schneider4, A. Snicker10, and the AUG Team and the EUROfusion MST1 Teama 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal 2 Department of Atomic, Molecular and Nuclear Physics, Faculty of Physics, University of Seville, 41012 Seville, Spain 3 VR/Royal Institute of Technology KTH, Sweden 4 Max Planck Institute fur Plasmaphysik, Garching, Germany 5 CCFE, Culham Science Centre, Abingdon, Oxfordshire, United Kingdom 6 General Atomics, PO Box 85608, San Diego, United States of America 7 FOM-Institute DIFFER, Nieuwegein, The Netherlands 8 Barcelona Supercomputing Center (BSC), Barcelona, Spain 9 ICREA, Barcelona, Spain 10 Aalto University, Aalto, Finland A set of dedicated ASDEX-Upgrade experiments was recently carried out in order to study the effects of localized electron cyclotron resonance heating (ECRH) on energetic-ion- driven toroidal Alfvén eigenmodes (TAE). It was found that for discharges with a monotonic profile of the safety factor, off-axis ECRH can make TAEs more unstable on timescales of a few milliseconds while the effect of on-axis ICRH is much weaker [1]. To understand the mechanisms responsible for this effect, detailed calculations were performed using the ideal MHD code MISHKA[2], and the recently upgraded hybrid MHD-drift-kinetic code CASTOR-K [3, 4]. The distributions of the energetic ion populations accelerated by ion cyclotron resonance heating (ICRH) were computed with the SELFO code [5]. A competition between the mechanics that drive and damp the TAEs modes will be shown to be sufficient to explain the observations. To assess the stability of Alfvén eigenmodes different computer codes developed by different groups have to be integrated. One problem that arises is how to exchange the full particle distributions between them without appreciable loss of information. A new standard format to exchange energetic particle distributions has been recently proposed[6], based on generalised distribution functions in terms of the gyrocentre's constants of motion (energy, magnetic moment, and toroidal canonical momentum), and has recently been adapted by a set of codes such as ASCOT [7], CASTOR-K [3,4], HAGIS [8], and SELFO [5]. These recent upgrades not only improve the quality and robustness of the code interfaces, but more importantly they also increase the accuracy of the results. [1] S.E. Sharapov et al., Plasma Phys. Control. Fusion 60 (2018) 014026 [2] A.B. Mikhailovskii et al., Plasma Phys. Rep. 23 (1997) 844 [3] D. Borba and W. Kener, J. Comput. Phys. 153 (1999) 101 [4] F. Nabais et al., Plasma Sci. Technol. 17 (2015) 89 [5] J. Hedin et al., Nuclear Fusion 42 (2002) 527 [6] M. Fitzgerald, P. Rodrigues, et al., to be published [7] E. Hirvijoki, et al., Comp. Phys. Comm. 185 (1998)1310 [8] Pinches, S. D. et al., Comp. Phys. Comm. 111 (1998) 133 a See the author list of H. Meyer et al., Nuclear Fusion 57 (2017) 102014.

Speaker: Jorge Ferreira

14:00 P1.1058 Asymmetric scrape-off layer currents during MHD and disruptions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1058.pdf Asymmetric scrape-off layer currents during MHD and disruptions* J.P. Levesque1, J. Bialek1, J.W. Brooks1, S. DeSanto1, C.J. Hansen2, M.E. Mauel1, G.A. Navratil1, and I.G. Stewart1 1 Columbia University, New York, New York, USA 2 University of Washington, Seattle, Washington, USA During disruptions, large asymmetric currents arise in the first wall and vacuum vessel that have the potential to damage tokamaks, and understanding this behaviour is important for mitigating disruption loads. In this presentation, we report asymmetric scrape-off-layer (SOL) and vessel currents measured during MHD activity and disruptions in the HBT-EP tokamak. Low-field-side diagnostic tiles measure currents to the vessel with poloidal resolution in three toroidal locations. Tiles and the associated wall segments can be moved radially between shots to investigate radial SOL current structure and dependence on wall geometry. Additionally, a biased electrode in the SOL influences MHD dynamics measured by magnetic sensors and the SOL tiles (see Figure). Measurements reveal poloidal and toroidal structure of currents to the wall that correlate with rotating MHD activity during the main discharge and disruption. Tile currents exceed the ion saturation current during transient events. Electrically-isolated regions of the vacuum vessel detect toroidal vessel currents oscillating between co- and counter-Ip directions when the sections are connected via diagnosed jumpers. Asymmetric vessel currents correlate with rotating kink modes, and reach ~5% of the pre-disruption plasma current during the current quench [1]. Relative increases in local plasma current measured by segmented Ip Rogowski coils coincide with nearby counter-Ip vessel currents. Measurements are interpreted in the context of Wall Touching Kink Mode (WTKM) [2] and Asymmetric Toroidal Eddy Current (ATEC) [3] models, which give contrary predictions for the sign of asymmetric toroidal vessel current during disruptions. Both models are needed to explain HBT-EP disruption data. Magnetic sensors and SOL current tiles pictured *Supported by U.S. Department of Energy, Office of in (a) measure MHD activity with poloidal and Fusion Energy Science, Grant DE-FG02-86ER53222. toroidal resolution. Sensor layout and SOL flux [1] J.P. Levesque et al., Nucl. Fusion 57 086035 (2017) surfaces for a discharge with SOL biasing are shown in (b). Tile current (c) and magnetic (d) [2] L.E. Zakharov et al., Phys. Plasmas 19 055703 (2012) fluctuations versus poloidal angle show rotating [3] R. Roccella et al., Nucl. Fusion 56 106010 (2016) MHD responding to applied SOL current (e).

Speaker: Jeffrey Levesque

14:00 P1.1059 Estimations of disruption forces in the COMPASS Upgrade tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1059.pdf Estimations of disruption forces in the COMPASS Upgrade tokamak V. Yanovskiy1, J. Havlicek1, M. Hron1, M. Komm1, E. Matveeva1,2, R. Panek1, J. Urban1 and the COMPASS team 1 Institute of plasma physics of the CAS, Prague, Czech Republic 2 Fac. Math & Phys., Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic This paper presents the analysis of disruptions in COMPASS Upgrade tokamak [1], which is a medium-size high-magnetic-field device currently in the conceptual design phase. Due to the high plasma current (up to 2 MA) and the strong magnetic field (up to 5 T), large electromagnetic forces on conducting structures surrounding plasma are expected during disruptions. To address this issue, electromagnetic loads on the vacuum vessel during disruptions are estimated analytically using a novel approach to the problem [2]. These analytical results will serve as a baseline for more detailed numerical calculations considering a volumetric 3D description of conducing structures. The uncertainties in the extrapolation of the available experimental data on disruptions to new tokamaks point at a potential threat to their structural integrity [3]. Therefore, the development of adequate protective means becomes a necessity. For that reason, the possibility of implementation of a disruption force damper (DFD) [4] within the present design constraints is considered. The study reveals optimal choice of the vacuum vessel parameters which guarantee safe operation of the COMPASS Upgrade tokamak. [1] Panek R et al 2017 Fusion Eng. Des. 2017 123 11 [2] Pustovitov V D and Kiramov D I 2018 Plasma Phys. Control. Fusion in press https://doi.org/10.1088/1361- 6587/aab056 [3] Hender T C et al 2007 Nucl. Fusion 47 S128–202 [4] Pustovitov V D, Rubinacci G and Villone F 2017 Nucl. Fusion 57 126038

Speaker: Vadim Yanovskiy

14:00 P1.1060 Nonlinear modeling of the effect of multi-locked modes on heat transport

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1060.pdf 45 EPS Conference on Plasma Physics 13474 Nonlinear modeling of the effect of multi-locked modes on heat transport Q.M. Hu1, X.D. Du2, Q. Yu3, E. Kolemen4, N. Logan1, R. Nazikian1 1 Princeton Plasma Physics Laboratory, Princeton NJ 08543-0451, USA 2 University of California Irvine, Irvine CA 92697, USA 3 Max-Plank-Institut für Plasmaphysik, 85748 Garching, Germany 4 Mechanical and Aerospace Engineering, Princeton University, Princeton NJ, USA Experimental evidence of the formation of multiple helicity island chains during the locked [1] mode phase preceding plasma disruption is observed on DIII-D . To understand the experimental results, nonlinear numerical modeling of multi-components (m/n = 2/1, 3/1, 4/1 etc) resonant magnetic perturbations (RMPs) penetration has been studied based on reduced MHD equations. It is found that after field penetration, the non-rotating magnetic islands, having helicity of 2/1, 3/1 and 4/1, flatten the temperature at the corresponding rational surfaces, and the co-existence these islands significantly enhances the plasma heat transport from q = 2 rational surface to plasma edge. As a result, the core temperature is decreased by more than 50% in a time scale of 100 ms. In addition, the temperature profile from 2/1 to 4/1 rational surface can be nearly flattened even if there is no island overlap, and the temperature inside the islands are determined by outboard separatrix of the island. The mild increase of RMP amplitude leads to an island overlap between 3/1 and 4/1, and further induces the rapid cooling the temperature inside 2/1 rational surface. The results indicate that by the presence of error field of application of RMPs, the plasma is susceptible to multi-helicity locked modes. These island chains further deteriorate plasma thermal confinement, which may be responsible for the fast thermal quench proceeding plasma in major disruption. Fig. Time evolution of Te profile and 2D profile of Te together with magnetic flux surface. Acknowledgement: The experimental target plasma described here were performed on the DIII-D National User Facility operated by General Atomics in San Diego, CA for the U.S. Department of Energy under contract number DE-AC02-09CH11466, early career research program DE-FOA-0001386, and award number DE-SC0015878 and DE-FC02-04ER54698. [1] Du X.D., et al, A Key Role of Multiple, High-order, Small Locked Island Chains in Triggering Plasma Major Disruption in DIII-D tokamak, to be submitted.

Speaker: Qiming Hu

14:00 P1.1061 MHD equilibria with magnetic islands in TJ-II using SIESTA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1061.pdf MHD equilibria with magnetic islands in TJ-II using SIESTA B. Centurión1 , J. J. Martinell1 , A. López-Fraguas2 , J.M. Reynolds3 and D. López-Bruna2 1 Instituto de Ciencias Nucleares, UNAM, A. Postal 70-543, México D.F., Mexico 2 Laboratorio Nacional de Fusión, As.EURATOM-CIEMAT, 28040 Madrid, Spain 3 Universidad Carlos III, Leganes 28021, Spain Experiments in the TJ-II heliac show a correlation between the position of magnetic rational surfaces and a modification of the electron temperature profile [1], measured using Electron Cyclotron Emission (ECE) in low density Electron Cyclotron Resonance heated discharges. On plasma discharges heated using Neutral Beam Injection, ECE cannot be used due to the high density; however, using the heliac’s flexibility, different rational surfaces can be swept along the minor radius by varying the helical current and it was found that the transport was reduced at the position of the rational surfaces. Bolometry studies have also shown a correlation between transport barriers appearing on rational surfaces and MHD activity [2]. This may also lead to transitions of the L-H type. These observations suggest that the plasma confinement can be im- proved by strategically placing rational surfaces, which in in turn give rise to a transport barrier. Since magnetic islands are likely to form at rational surfaces because the magnetic perturbations are resonant there, investigation of the presence of magnetic islands is quite interesting in the context of confinement improvement. Using SIESTA code we calculated MHD equilibria with magnetic islands in TJ-II to deter- mine the properties of the islands. The starting equilibrium state is the one obtained by the VMEC code with nested magnetic surfaces. Standard computations use the heliac’s toroidal periodicity of 4 periods to reduce the code runtime, but this, when used in SIESTA, limits the toroidal periodicity of the islands to multiples of 4. To solve this limitation we tailored the input parameters to run VMEC without 4-period symmetry. In this way, running SIESTA with those equilibria, magnetic islands of any periodicity are obtained, including those resonant at ι = 3/2 whose magnetic islands were previously absent from the simulations. The results also show 2D pressure profiles that match the location of the magnetic islands observed in the Poincaré plots of the field lines. References [1] D. López-Bruna et al., Plasma Phys. Control. Fusion 53, 124022 (2011) [2] D. López-Bruna et al., Nuclear Fusion 53, 073051 (2013)

Speaker: B. Centurión

14:00 P1.1062 Analysis of MGI disruptions and runaway electron beams at COMPASS using tomography and fast camera data

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1062.pdf Analysis of MGI disruptions and runaway electron beams at COMPASS using tomography and fast camera data O. Ficker1,2 , M. Imrisek 1,3 J. Mlynar1 , E. Macusova1 , J. Svoboda2 , V. Weinzettl1 , J. Urban1 J. Cerovsky1,2 , M. Farnik1,2 , V. Plyusnin5 , R. Panek1 , M. Hron1 , M. Vlainic4 the COMPASS team1 & the EUROfusion MST1 Team* 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 FNSPE, Czech Technical University in Prague, Prague, Czech Republic 3 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 4 Institute of Physics, University of Belgrade, Belgrade, Serbia 5 IST - IPFN, Lisbon, Portugal * See the author list "H. Meyer et al 2017 Nucl. Fusion 57 102014" The tomographic inversion of signals from SXR and AXUV detector arrays is a valuable tool in various operational scenarios on COMPASS. However, runaway electron (RE) beam genera- tion and mitigation experiments conducted at COMPASS [1] present a challenge to this method as this scenario creates a very noisy environment and conditions far from the optimal design parameters of the detectors. The massive gas injection, subsequent disruption and RE beam generation and decay phases are a source of quickly changing intensities of radiation in a broad range of wavelengths (bremsstrahlung and line radiation of the gas atoms and ions). In particu- lar, the semiconductor-based detectors are also strongly affected by the HXR radiation produced due to the interaction of relativistic electrons with the wall. On the other hand, the tomographic inversion in this scenario might be a valuable source of information about the gas penetration speed, beam position, total radiated power and profile of the beam-gas interaction which might be related to the beam current profile or electron energy. Values of some of these quantities, in particular the ones related to the gas transport, can be also derived from high-speed camera im- ages that are usually only weakly affected by the HXR radiation. This contribution summarizes the difficulties of using tomography in this scenario and the different effect of various mitigation gases (Ar, Ne, D) on the radiation signals, including the high-speed camera data. References [1] Mlynar J. et al, invited, this conference [2] Panek R. et al. 2016 Plas. Phys. Contr. Fusion 58 014015 [3] Vlainic M. et al. 2015 J. Plasma Phys. 81 475810506

Speaker: Ondrej Ficker

14:00 P1.1063 Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1063.pdf Observation of suprathermal ions with Neutral Particle Analyzers during electron cyclotron heating in the TJ-II stellarator. J.M. Fontdecaba1 , J. Hernández-Sánchez1 , N. Panadero1 , K.J. McCarthy1 , A. Cappa1 and TJ-II Team 1 Laboratorio Nacional de Fusión Ciemat, 28040 Madrid, Spain The plasmas in the TJ-II stellarator are created and maintained using two gyrotrons tuned to the second harmonic of the electron gyrofrequency. Additional heating can be applied using neutral beam injection or the plasma can be maintained with microwave power to produce a pure ECRH discharge. In the case of pure ECRH plasmas the majority ions are not directly heated by external sources rather by collisions with the hot electrons, hence their population distribution function is considered Maxwellian. The bulk ion temperature is clearly detached from the electron temperature, the usual value for the ion temperature is around 80 eV whereas the electron temperature is about 1 keV. Under such conditions the count rates in the high energy channels (> 1 keV) of the TJ-II neutral particle analyzers (NPA) are at the background level, indicating the abscence of ions in the high energy tail. However, suprathermal ions have been found in TJ-II ECRH plasmas using spectroscopic methods [1]. Thus it is necessary to confirm their presence with the NPA diagnostics. In a recent experiment, we modulated the full power of one of the two gyrotrons to produce two clearly separate phases of the ECRH plasmas, one with full power, the other with half power. Also the radial position, where the microwaves heat the plasma, was varied during the experiment. During the experiments the NPA was tuned to scan high energy ions. As a result, in some configurations, signal levels above the normal backgroud levels were detected in the high energy channels when full power was applied. This can be an indication of the presence of suprathermal ions in the plasma. One possible explanation for the generation of suprathermal ions is a parametric decay insta- bility of the heating wave in a local maximum of the density [2]. We have designed an experi- ment to inject pellets in the ECRH plasma to modify the density profile while scanning the high energy ion tail with the NPA diagnostics in different positions to investigate the influence of the density profile on the suprathermal ion population. References [1] D. Rapisarda, B. Zurro, V. Tribaldos, A. Baciero and TJ-II Team, Plasma Physics and Controlled Fusion 10, 309 (2007). [2] E.Z. Gusakov and A.Yu. Popov, Plasma Physics and Controlled Fusion 60, 025001 (2018).

Speaker: Josep Maria Fontdecaba

14:00 P1.1064 Non-monochromatic RF power injection to control lower hybrid parametric instabilities in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1064.pdf Non-monochromatic RF power injection to control lower hybrid parametric instabilities in tokamak plasmas F. Napoli1, C. Castaldo1, A. Cardinali1, S. Ceccuzzi1, R. Cesario1, G. Ravera1, A. Tuccillo1, B. J. Ding2, M.H.Li2 1 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy 2 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, PR China In present day LHCD experiments, parametric instabilities must be controlled for the accessibility of the driver pump to the inner layers of a tokamak plasma [1]. Previous works already studied, theoretically [2] and experimentally [3], the parametric interaction of a non-monochromatic pump driver with plasmas in the lower hybrid range of frequencies. The purpose of such studies was to find experimental conditions useful to mitigate, or better suppress, the parametric instabilities. However, if we consider the technical feasibility of the pump modulation, no practical conclusions could be drawn since stabilization effects on parametric instabilities can be achieved only if the frequency bandwidth of the modulated driver pump is larger than the resonance width of the parametric instability. Unfortunately, this condition is seriously limited by the frequency bandwidth of available power sources. This work presents a new nonlinear parametric dispersion relation for an amplitude modulated pump driver. This equation is based on an accurate nonlinear kinetic model of lower hybrid wave propagation, useful to analyse the instabilities emerging in the outer layers of a tokamak plasma [4,5]. We first validate numerical solutions of the new parametric dispersion relation reproducing the experimental observations of lower hybrid amplitude modulated pump experiments [3]. Furthermore, by changing the driver pump coherence, we study how undesirable parametric effects can be significantly reduced in the SOL plasma for EAST and FTU tokamaks. As a breakthrough of this study, we find a new amplitude modulation scheme exploitable within the frequency bandwidth of microwave power sources available for lower hybrid experiments. [1] R. Cesario, et al., Nature Comms, 1 55 (2010) [2] V. Stefan, Phys. Fluids, 26 1789 (1983) [3] K. Matsumoto, et al., Plasma Phys., 25 1441 (1983) [4] F. Napoli, et al., Plasma Phys. Contr. Fusion, 55 095004 (2013) [5] F. Napoli, C. Castaldo, 44th EPS Conf. on Plasma Phys. (2017)

Speaker: Francesco Napoli

14:00 P1.1065 Design considerations and research and development of a comb-line traveling wave antenna for helicon current drive in DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1065.pdf Design Considerations and Research and Development of a Comb-line Traveling Wave Antenna for Helicon Current Drive in DIII-D* R.I. Pinsker1, C.P. Moeller1, J.S. deGrassie1, M.W. Brookman1, A. Nagy2, H. Torreblanca1, R.C. O'Neill1 and M. Porkolab3 1 General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, USA 2 Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451, USA 3 Massachusetts Institute of Technology, Cambridge, MA 02139, USA A project to demonstrate high-efficiency off-axis current drive intends to couple 1 MW of power at 476 MHz to DIII-D plasmas in the fast wave polarization, also known as the whistler or helicon wave, to enable a proof-of-principle experiment on helicon current drive [1]. A traveling wave antenna of the comb-line type is in the final stages of design for installation in the DIII-D tokamak in late 2018. The antenna consists of a toroidal array of 30 modules, each 5 cm wide, so that the array is 1.5 m wide. Power is fed from one end of the array to generate a wave traveling in one toroidal direction at a value of n|| = 3 to drive current non-inductively. A 12-element prototype comb-line was operated at low power (< 0.5 kW) in DIII-D in 2016, where it was demonstrated that the plasma-antenna coupling was adequate to transfer at least 75% of the power to propagating helicon waves in the plasma, rather than being resistively dissipated in the structure or coupled out of the antenna at the 'downstream' end [2]. The scaling of the measured coupling efficiency for the low-power prototype to the high-power antenna depends crucially on two factors: the resistive losses in each element and the strength of the mutual reactance between adjacent elements. In this contribution we quantify the importance of these parameters in determining the optimum number of modules for a wave- launching structure of this kind. To assess the significance of multipactor discharge in the antenna and feed structures and to qualify the module design for operation at high electric fields, a test stand has been constructed with up to 0.1 T dc magnetic field available and with more than 10 kW of rf power in the operating band of the antenna (~0.5 GHz). Initial testing of one quarter of one module at high 'Q' has already demonstrated conditioning out of multipactor in the module, and investigation of the effect of the magnetic field on multipactor and on high-voltage standoff has begun. In the near future, we will use the test stand to qualify the vacuum transmission line that will convey 1 MW of power from the feedthroughs to the input end of the comb-line antenna and to investigate the effect of anti-multipactor coating techniques. [1] R. Prater, C.P. Moeller, R.I. Pinsker, et al., Nucl. Fusion 54, 083024 (2014) [2] R.I. Pinsker, et al., IAEA Conference EX/P3-22 (2016) __________________________________   *Work supported in part by the US Department of Energy under DE-FC02-04ER54698 and DE-AC02- 09CH11466.

Speaker: Robert I. Pinsker

14:00 P1.1066 Alpha channeling by inverse nonlinear damping of ion Bernstein waves

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1066.pdf Alpha channeling by inverse nonlinear damping of ion Bernstein waves C. Castaldo1, A. Cardinali1 1 ENEA, C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, Italy Second harmonic cyclotron damping of mode-converted ion Bernstein waves on minority Tritium ions in D-H(T) tokamak plasma has been proposed as an efficient method to improve the fusion yield expected in thermal equilibrium [1]. Despite the dilution due to the presence of the Hydrogen, which is necessary to allow the mode conversion of the fast magnetosonic waves, the acceleration of T ions in the energy range of 50-100 keV, i.e. near the peak of DT fusion cross section, produces higher reactivity than the ideal isotopic blend DT at thermal equilibrium for the same kinetic profiles. In this scenario, IBW nonlinear inverse Landau damping on the fusion alpha particles might be observed at Doppler-shifted half-integer resonant layer 𝜔 = (3/2)Ω! + 𝑘∥ v∥ (Fig. 1). The nonlinear RF-induced diffusion tensors in velocity and physical space are here derived in the frame of single-particle dynamics. We then discuss numerical solutions of the relevant Fokker-Planck equation, taking into account the collisions of the alpha particles with the plasma background as well as the source and sink terms. During the time evolution of the alpha particle distribution function towards the steady state, inverse nonlinear Landau damping might channel a fraction of the alpha power into the ion Bernstein wave power. This will provide a method for implementing the concept of alpha channeling [2]. 1 IBW region ω = 3/2Ω α 0,9 -1 k = 2.0 m 0,8 || DH hybrid DH cut-off resonance 0,7 o /v 0,6 ||res FW region v 0,5 -1 k = 3.3 m || 0,4 0,3 ω=2Ω Τ 0,9 0,95 1 1,05 1,1 R/R o Fig. 1. Scheme of alpha power channeling in tokamak plasma with isotopic composition such that 𝑛! 𝑛! = 0.9 and 𝑛 ! 𝑛! = 0.05 and magnetic field on axis is 𝐵! = 2.8  𝑇. The FW are coupled from the low field side, at the operating frequency 𝑓! = 32  𝑀𝐻𝑧. The resonant parallel velocities v∥,!"# , normalized to the velocity vo at the peak (3.5 MeV) of the a source energy spectrum, are shown for parallel wavenumber 𝑘∥ = 3.3  𝑚 !! (red, dashed line) and 𝑘∥ = 2.0  𝑚 !! (blue, continuous line). Here R is the major radius coordinate and Ro is the position of the magnetic axis. [1] C. Castaldo, A. Cardinali, Phys. Plasmas 17 072513 (2010) [2] N. J. Fish and M. H. Hermann, Nucl. Fusion 35, 1753 (1995)

Speaker: Carmine Castaldo

14:00 P1.1067 Neutral beam ion shine-through calculations for the reduced field and current plasmas in ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1067.pdf Neutral beam ion shine-through calculations for the reduced field and current plasmas in ITER A. Snicker1 , K. Särkimäki1 , J. Varje1 , M. Schneider2 , A. Polevoi2 1 Aalto University Department of Engineering Physics, Otakaari 1, 02015, Espoo, Finland 2 ITER organization, Route de Vinon-sur-Verdon, CS90046, 13067 St Paul-lez-Durance, France ITER research plan includes Pre-fusion Power operation (PFPO) phases that plan an operation with reduced fields and currents. The aim of the reduced field and current operation is to have an H-mode access in H and He plasmas. This is important since the predictions of the threshold power by extrapolating empirical scaling laws are uncertain and because only limited amount of heating power will be available. In the second phase of the PFPO, a neutral beam ion (NBI) operation is expected. The access to H-mode favors operation in low electron density, on the other hand the NBI shine-through poses a lower limit to electron density. Fortunately, the NBI system can be operated with lower voltage (=lower injection energy). The aim of this contribution is to assess the limits of the NBI system in the PFPO in terms of the shine-through. This is done by carrying out beamlet- based NBI simulations and calculating the shine-through heat power load at the wall structures, especially to the so called shielding block that locates under the first-wall panels and will get significant heat load from gaps between the blanket modules and thus will be the first structure exceeding engineering limits in terms of heat power load. The injection energy of the NBI system cannot be changed arbitrarily due to beam perveancy 2.5 , where E considerations. Namely, the power needs to be scaled according to PNBI ∝ Einj inj is the injection energy and PNBI the NBI power. In the simulations with the hydrogen beams into helium plasmas it was observed, however, that the shine-through power depends much stronger 3.9 , where P is the on the injection energy than beam perveancy condition, namely PST ∝ Einj ST shine-through power (or the power load at the critical shielding block element). This study will be utilized to guide the operational window and maximum NBI pulse duration in the ITER PFPO phase. The results will be compared against earlier studies such as [1]. References [1] M.J. Singh et al., New J. Phys. 19, 055004 (2017)

Speaker: Antti Timo Olavi Snicker

14:00 P1.1068 Optimization of ECRH operation at high densities in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1068.pdf Optimization of ECRH operation at high densities in Wendelstein 7-X S. Marsen1 , K. J. Brunner1 , H.P. Laqua1 , D. Moseev1 , T. Stange1 , W7-X Team 1 Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstraße 1, 17491 Greifswald, Germany One of the major goals of Wendelstein 7-X is to achieve steady state operation (up to 30 min.) at plasma parameters relevant for a future fusion reactor. This includes operation at plasma pressures requiring a density above 1020 m−3 . The only steady state capable heating currently available is ECRH using high power gyrotrons. Wendelstein 7-X is equipped with 10 gyrotrons providing up to 7.5MW to the plasma vessel. The power is transmitted to the machine using a quasi optical transmission line where the polarization and launching angle can be remotely controlled by the central W7-X control system. Using X-mode polarization break down can easily be achieved and the launched power is nearly perfectly absorbed (>99%) over a wide range of plasma parameters. Here, the achievable density is limited by the X-mode cut-off density of n = 1.2 · 1020 m−3 at the used frequency of 140GHz. In order to reach higher densities O-mode polarization is necessary where the single pass absorption depends more sensitively on the plasma parameters and is typically in the order of 50...80%. Plasma start-up in O-mode is not possible because a target plasma with Te > 1keV is necessary to deposit enough energy to sustain a hot plasma. During the first experimental campaigns of W7-X a scenario to achieve ECR heated plasmas at densities above the X-mode cut-off was developed. The target plasma was created using two or three gyrotrons in X-mode. After creating a low density target plasma with ne ≈ 2 · 1019 m−3 the remaining gyrotrons were switched on in O-mode and the density was ramped up to ne ≈ 6 · 1019 m−3 . While ramping up the denstiy the polarization of the start-up gyrotrons was changed to O-mode. Thus, a purely O-mode heated plasma was created. Using pellet injection the density could then be further increased. Line averaged densities of ne = 1.4 · 1020 m−3 as measured by a single channel interferometer were achieved. The exceeding of the X-mode cut-off was confirmed by ECE measurements where the signal was lost eventually. In order to maximize the heating efficiency a three pass heating scheme was established reflecting the beams through the plasma axis once at the high-field side of the vessel and once at the low field. Thus, a total absorption of >90% could be reached as determined by stray radiation measurements. Reducing the amount of non-absorbed microwave power in the vessel is not only necessary to maximize the plasma performance but also in terms of safe machine operation since in vessel components can suffer from heating up due to stray radiation. The stray radiation levels measured around the machine were comparable to or even lower than expected levels.

Speaker: Stefan Marsen

14:00 P1.1069 OLGA – efficient full wave code for the coupling of LH grills

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1069.pdf OLGA – an efficient full wave code for coupling of lower hybrid grills J. Preinhaelter1, J. Hillairet2, J. Urban1 1 Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic 2 CEA, IRFM, F-13108 Saint Paul-lez-Durance, France Lower hybrid (LH) waves are very important for heating and current drive in tokamaks. Phased arrays of rectangular waveguides, generally called grills, are typically used as launchers. We have developed a full wave code OLGA [1] which solves, in the 3D geometry of the grill structure, the problem of the coupling efficiency, namely the power density spectrum of the emitted waves, the power reflection coefficient, the power lost by the waves launched in the inaccessible region and the directivity of the waves transmitted to the accessible region. An efficient adaptive full wave solver is used to determine the wave propagation in 1D plasma slab geometry. We adopted an iterative evaluation of the integrands in the inaccessible region to handle their near to singular behaviour and the spectral power density caused by eigenmodes. We have implemented the scattering matrix formalism for determining the coupling of multi- row, multi-junction, active-passive structures (such as the C3 and C4 launchers on TORE SUPRA) [2]. The extended code is still computationally fast by the use of 2D splines of the plasma surface admittance in the accessibility region of the k  space, by the use of high order Gaussian quadrature rules for the integration of the coupling elements and by the application of the symmetry rules of the coupling elements for the multi-periodic structures. We successfully benchmark the coupling of the C3 and C4 launchers as determined OLGA with the ALOHA-1D, ALOHA-2D and TOPLHA results for a TORE SUPRA discharge. We calculate the 3D electric field in front of the grill and estimate the effects of the plasma slab eigenmodes. References [1] J. Preinhaelter et al. Nucl. Fusion 52 (2012) 083005 [2] J. Preinhaelter et al. Nucl. Fusion 57 (2017) 116060

Speaker: Josef Preinhaelter

14:00 P1.1070 Synergies between H-NBI fast-ions and ICRF heating in the non-activated operational phase of ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1070.pdf Synergies between H-NBI fast-ions and ICRF heating in the non-activated operational phase of ITER R. Bilato1 , A.R. Polevoi2 , M. Schneider2 , M. Brambilla1 , E. Fable1 , M. Weiland1 , Ye.O. Kazakov3 , E. Lerche3 , A. Loarte2 , J. Ongena3 , S.D. Pinches2 , D. Van Eester3 1 Max-Planck Institut für Plasmaphysik - Germany, EURATOM Ass. 2 ITER Organization, Route de Vinon sur Verdon, CS 90 046, 13067 St Paul-lez-Durance Cedex, France 3 LPP-ERM/KMS, Association Eurofusion-Belgian State, TEC partner, Brussels, Belgium To access the type-I ELMy H-mode scenarios in ITER during the Pre-fusion Power Operation 2 (PFPO-2) with hydrogen and helium plasmas, it is necessary to operate at reduced confining magnetic field to exceed the power threshold for the L-H transition [1]. During this operation phase it is planned the commissioning of the baseline auxiliary power heating, made up of 33 MW of NBI (hydrogen at a maximum injection energy of 870 keV), 20 MW of ECRH and 20 MW of ICRF (f=40-55 MHz) [2]. Depending on the ICRF frequency and the confining magnetic field, hydrogen can resonate at its harmonic cyclotron frequency (1st at half field and 2nd at one-third field) with the launched ICRF waves [2]. In particular, the NBI-ICRF synergies when the NBI species resonates at its 1st harmonic using three-ion scenarios have been recently observed in JET [3]. Therefore, synergies between fast-protons of NBI heating and ICRF waves can have an impact on ICRF-heating performances. To investigate these synergies, here, we use the 2-dimensional full-wave TORIC solver for the wave propagation and absorption of ICRF waves, and SSFPQL solver for the kinetic equation of the heated species in the simultaneous presence of NBI sources and ICRF heating. TORIC and SSFPQL are interfaced in such a way that the coefficients of TORIC wave equation are built directly from the numerical solutions of SSFPQL [4]. The kinetic equation is solved for all the ion species that can resonate with ICRF waves. The target plasma is generated with ASTRA transport code with appropriate pedestal [5], boundary conditions [6], and transport model [7]. As main scan parameters we consider ICRF frequency and H concentration. As common feature, we find that NBI heating increases the fraction of ICRF power directly absorbed by hydrogen and substantially broadens the profile of ICRF power absorbed by hydrogen. [1] Y. Martin, et al., J. of Physics: Conf. Series 123 (2008) 012033. [2] M. Schneider, et al., Proc. 44th EPS Conf. on Plasma Physics, (2017) P5.153. [3] J. Ongena et al., EPJ Web Conf. 157 (2017) 02006. [4] R. Bilato, et al., Nucl. Fusion, 51 (2011) 103034. [5] A.R. Polevoi, et al, Nucl. Fusion, 57 (2017) 022014. [6] A.S. Kukushkin, Nucl. Fusion, 53 (2013) 123025. [7] A.R. Polevoi, et al., Proc. 39th EPS Conf. on Plasma Physics, (2012) P4.032.

Speaker: Roberto Bilato

14:00 P1.1071 Synchrotron spectra, images, and polarization measurements from runaway electrons in the Alcator C-Mod tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1071.pdf Status of high-electron-temperature experiments at GDT mirror trap A. G. Shalashov1,2, P. A. Bagryansky1, E. D. Gospodchikov1,2, L. V. Lubyako1,2, V. V. Maximov1, V. V. Prikhodko1, V. Ya. Savkin1, E. I. Soldatkina1, A. L. Solomakhin1, and D. V. Yakovlev1 1 Budker Institute of Nuclear Physics SB RAS, Novosibirsk, Russia 2 Institute of Applied Physics RAS, Nizhny Novgorod, Russia The paper summarizes results of experiments on electron cyclotron resonance plasma heating (ECRH) and related issues at the axially symmetric large-scale gas-dynamic magnetic mirror trap GDT in the Budker Institute (Novosibirsk, Russia). Previously we reported on plasma discharges with extremely high temperature of bulk electrons in this machine – the on-axis electron temperature 600–700 eV at the plasma density about 0.7×1019 m-3 was achieved and values of Te > 900 eV were observed in select individual shots – more than a threefold increase with respect to previous experiments both at GDT and at other comparable devices [1]. The breakthrough is made possible by application of 0.7 MW / 54.5 GHz ECRH in addition to standard 5 MW heating by neutral beams. Through its significant impact on plasma parameters, ECRH poses a threat to the subtle magnetohydrodynamic equilibrium of plasma confined in a magnetic mirror machine. In particular, when the microwave power was focused in a narrow near-axial plasma region thereby leading to a highly peaked radial profile of the electron temperature, the duration of effective heating was always limited to about 0.6 ms; later on, the flute instability developed preventing further absorption of microwaves. Recently, we introduce a new technique which counters such detrimental effects of microwave heating and enables to maintain high electron temperature for the whole duration of plasma discharge. We show that a value of on-axis electron temperature up to 450 eV at plasma density 1.2×1019 m-3 can be supported steadily for more than 1 ms limited only by available heating and magnetic confinement systems. Stable high-temperature discharge regime offered a unique opportunity to validate experimentally the gas-dynamics confinement mechanism in a new realm of parameters. [1] P. A. Bagryansky, A. G. Shalashov et al., Phys. Rev. Lett. 114 205001 (2015).

Speaker: Roy Alexander Tinguely

14:00 P1.1072 Modelling of ICRF heating in ASDEX Upgrade discharges with pure wave heating relevant to the ITER baseline scenario

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1072.pdf Modelling of ICRF heating in ASDEX Upgrade discharges with pure wave heating relevant to the ITER baseline scenario M.J. Mantsinen1,2, V. Bobkov3, D. Gallart1, T. Pütterich3, O. Sauter4, the EUROfusion MST1 Team* and the ASDEX Upgrade Team 1 Barcelona Supercomputing Center, Barcelona, Spain 2 ICREA, Barcelona, Spain 3 Max-Planck-Institut fur Plasmaphysik, Garching, Germany 4 Swiss Plasma Center, EPFL-SPC, Switzerland *See the author list of H. Meyer et al. 2017 Nuclear Fusion 57 102014. The baseline or reference scenario is one of the basic operational scenarios foreseen for ITER. It is envisaged to deliver fusion power of 500 MW and fusion gain Q10 using ELMy H-mode discharges at Ip =15 MA, BT = 5.3 T, normalized plasma pressure N = 1.8 and normalized confinement H98y2 = 1 with a safety factor q95 = 3. Experiments on present-day devices provide important insights in preparing ITER operation. This paper focuses on modelling of ICRF heating in ASDEX Upgrade (AUG) plasmas with pure wave heating, i.e. ICRF and ECRF heating. These discharges are of interest because they approach the conditions of burning ITER baseline plasmas with predominant electron heating by fusion-born alpha particles and small externally applied torque. The discharges were carried out at Ip = 0.9-1.15 MA, BT = 1.8-1.85 T with q95 = 3 and 3.6. Up to 3.9 MW of ICRF power was applied with a frequency of 30 MHz tuned to a H minority ion resonance at r/a  0.2-0.3 on the high-field side. Up to 3.4 MW of ECRF power was applied using 140 GHz in X3 mode. Stable discharges with N = 1.2-1.7 and H98y2 = 0.75-1.1 were obtained. We have modelled the discharges using the ICRF modelling code PION. Considering nH/(nH+nD) = 5% which is typical in AUG plasmas and the full ICRF toroidal mode number spectrum, we find that H minority heating dominates, absorbing 55-70 % of PICRF, while direct electron damping and 2nd harmonic D damping are about 25-40 % and 5-10 %, respectively. Due to the off-axis ICRF resonance, the average energy of ICRF-accelerated ions is relatively low, and they heat prominently bulk ions in collisions. The total ICRF electron heating is limited to about 40% of PICRF. We find that the electron heating fraction by ICRF could be improved (1) by operating at 1.95T which moves the ICRF resonance to the plasma center or (2) using 55 MHz which places the 2nd harmonic H resonance in the plasma center. The latter provides an energetic H minority tail that favours strong electron heating (up 70% of of PICRF) with a central power deposition and a similar single-pass damping as H minority heating.

Speaker: Mervi Mantsinen

14:00 P1.1073 Simulation studies of neon pellet ablation clouds for plasma disruption mitigation in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1073.pdf Simulation studies of neon pellet ablation clouds for plasma disruption mitigation in tokamaks. N. Bosviel1 , R. Samulyak1 , P. B. Parks3 1 Stony Brook University, Stony Brook, USA 2 General Atomics, San Diego, USA A leading candidate for the ITER plasma disruption mitigation system is the Shattered Pellet Injection (SPI) [1] that performs fragmentation of a large, frozen, neon-deuterium pellet before its injection into a tokamak, and forms a stream of small fragments into plasma, causing a ther- mal quench. In this work, we report numerical studies of properties of ablation clouds formed by the injection of a single neon pellet into a tokamak. Simulations of a large number of pellet fragments are in progress. Simulations use the numerical pellet ablation model [2] based on the FronTier code. The main features of the model include an explicit tracking of the solid pellet - ablated gas inter- face, kinetic models for the energy deposition of hot electrons into the ablation cloud, a pellet surface ablation model, atomic processes in the cloud, radiation losses, an improved electrical conductivity model, and MHD in the electrostatic approximation. Verification studies have been performed by comparing spherically-symmetric simulations with a semi-analytic model that improves the Neutral Gas Shielding model [3]. Good agreement of pellet ablation rates and properties of the ablation flow at the sonic radius have been achieved. Simulations are also in agreement with theory on the scaling laws for the pellet ablation rate G, 5/3 4/3 1/3 namely G ∼ Te r p ne , where r p is the pellet radius, and Te and ne are the temperature and density of the background tokamak plasma. In the presence of MHD forces and atomic processes, the dense, cold ablated material gradu- ally ionizes and streams along magnetic lines, forming a narrow ablation channel. Simulations study the dependence of ablation channel properties and the pellet ablation rate on the magnetic field strength, and parameters of the background plasma, including the pedestal. References [1] L.R. Baylor, et al, Disruption mitigation system developments and design for ITER, Fusion Sci. Technol. 68, 211 (2015) [2] R. Samulyak, T. Lu, P. Parks, A magnetohydrodynamic simulation of pellet ablation in the electrostatic approximation, Nucl. Fusion 47, 103 (2007) [3] P. B. Parks, R. J. Turnbull, Effect of transonic flow in the ablation cloud on the lifetime of a solid hydrogen pellet in a plasma, Phys. Fluids 21, 1735 (1978)

Speaker: Roman Samulyak

14:00 P1.1074 Validation of modelling of JT-60SA tokamak scenarios with METIS code

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1074.pdf Validation of modelling of JT-60SA tokamak scenarios with METIS code J-F Artaud1, J. Garcia1, G. Giruzzi1, F. Imbeaux1 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. The integrated modeling code METIS [1] is a faster than real-time scenario simulation suite which can be applied to a significant variety of plasma modelling activities due to its comprehensive list of physical models. It allows analyses of current diffusion and heat and particle transport and sources including W. Recently, in the framework of the construction of JT-60SA, it has been adapted for JT-60SA scenario preparation and development. We have used METIS to optimize the scenario development of JT-60SA [2] especially during the ramp-up phase, with the aim of saving flux consumption, which is a key point to achieve longer duration discharges (the available poloidal flux is limited due to the maximum current allowed in central solenoid coils) [3,4]. We present here the activity of validation and some studies of scenario optimization developed for JT-60SA. The activity of validation has consisted, firstly, in a benchmark of METIS results against CRONOS simulations of JT-60SA scenario based on models tuned on JET and JT-60U experiments [5]. For this benchmark, METIS parametrisation has been kept as close as possible to that used for JT-60SA scenario development. Results display a good agreement between METIS and CRONOS (the much more sophisticated modelling suite), although some discrepancies appear for high beta scenarios. The second part of the validation has consisted of studies of the capability of METIS to simulate ramp-up of selected JET experiments. This study allowed highlighting the capacity of METIS to simulate the ramp-up of a device with similar size to JT-60SA. Comparisons between METIS predictions and experiments show good agreement, even if some limitations appear. Differences appear, in particular, in kinetic profile predictions. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the EURATOM research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The authors gratefully acknowledge members of the JT-60SA Integrated Project Team for data exchange and fruitful discussions. [1] METIS: A FAST INTEGRATED TOKAMAK MODELLING TOOL FOR SCENARIO DESIGN, J-F Artaud et al, submitted to Nuclear Fusion [2] JT-60SA Research Plan, Research Objectives and Strategy, Version 3.3, 2016, March: JT-60SA Research Unit (http://www.jt60sa.org/pdfs/JT-60SA_Res_Plan.pdf) [3] H. Urano et al, Fusion Engineering and Design 100 (2015) 345–356 [4] T Wakatsuki et al, Plasma Phys. Control. Fusion 57 (2015) 065005 (12pp) [5] J. Garcia et al, Nucl. Fusion 54 (2014) 093010

Speaker: Jean-François Artaud

14:00 P1.1075 Progress in simulation of ITER First Plasma operation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1075.pdf Progress in simulation of ITER First Plasma operation Y.Gribov1, A.A.Kavin2, V.E.Lukash3, K.M.Lobanov2, A.B.Mineev2,4, M.L.Dubrov3, R.R.Khayrutdinov3, J. A. Snipes1, P.C. de Vries1 1 ITER Organization, CS 90 046, 13067 St. Paul-lez-Durance, France 2 Joint Stock Company “NIIEFA” Saint Petersburg, Russia 3 NRC Kurchatov Institute, Moscow, Russia 4 Saint Petersburg State University, Saint Petersburg, Russia This paper presents a progress in simulation of ITER First Plasma operation since it was reported in [1]. New 0D plasma transport study was performed assuming hydrogen gas and Fe as a single impurity (stainless steel limiter), taking into account the Dreicer mechanism of runaway electron generation and their avalanche multiplication. The Fe influx to the plasma was described by physical sputtering of the limiter due to the wall bombardment by hydrogen and Fe ions. It was shown that the gas pressure lower limit, ≈ 0.3 mPa, is defined by the generation of runaway electrons. The gas pressure upper limit, ≈ 0.7 mPa (obtained using rather optimistic assumption - the plasma minor radius ≈ 1.6 m), is defined by insufficient ionization of the Fe impurity (“uncompleted burnthrough”). With the increase of the prefill gas pressure to values higher than this upper limit (e.g. to 0.75 mPa), the maximum value of the plasma current reduces very fast to less than 0.05 MA. The pressure upper limit reduces with reduction of the plasma minor radius. A set of the First Plasma scenarios were designed using the TRANSMAK code and simulated with the DINA code (free boundary plasma equilibrium, 0D plasma transport with steel limiters). Two scenarios were designed with the goal of formation at the gas breakdown a large area with the magnetic field null. Such “wide null” magnetic configuration is preferable for the Ohmic gas breakdown. In one scenario the center of the breakdown region was located at R = 5.7 m, Z = 0. In another scenario, the center of the breakdown region was shifted vertically by 1.5 m (R = 5.7 m, Z = 1.5 m). Another two scenarios of PF system operation were designed to get at the gas breakdown in the breakdown region vertical magnetic field Bz ≈ 1.5 mT and 2.5 mT corresponding to the “Shafranov” field of plasmas with the currents 0.03 MA and 0.05 MA, respectively. Such magnetic configurations may be preferable for plasma initiation with ECRF assist. The simulations take into account the vertical magnetic field produced by magnetized steel rebar of the Tokamak Complex producing at First plasma operation about 10 mT of vertical magnetic field opposite to the direction of “Shafranov” field. [1] A.B.Mineev, et al., Study of ITER First Plasma initiation using a 3D electromagnetic model, 25th IAEA Fusion Energy Conference, St. Petersburg, Russia, 2014, PPC/P3-20.

Speaker: Yury Gribov

14:00 P1.1076 Initial results of a Machine Learning-based real-time disruption predictor on DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1076.pdf The Development of First Plasma Operations on ITER J. A. Snipes1, H. Anand1, K. Blackler1, P.C. de Vries1, J. L. Fernandez-Hernando1, Y. Gribov1, T. C. Luce1, I. Nunes2, I. Prieto-Diaz1, L. Zabeo1 1 ITER Organization, CS 90 046, 13067 St. Paul-lez-Durance, France 2 Instituto Superior Técnico, Lisbon, Portugal ITER construction is well underway and first plasma operations on ITER are planned at the end of 2025. Individual plant system commissioning will begin with the Steady State Electrical Network in late 2018 and proceed as each of the initial plant systems becomes available up to the closure of the cryostat in late 2024. That defines the start of integrated commissioning and final preparations for plasma operation. Operational plant system commissioning must include commissioning with the Central Interlock System (CIS) and the Plasma Control System (PCS) to ensure investment protection and coordinated central control functions can be carried out. An additional Plasma Investment Protection System (PIPS) will also need to be commissioned initially for superconducting magnet protection of the poloidal field (PF) and central solenoid (CS) coils to avoid approaching force and field limits. Control and investment protection diagnostic commissioning will also be carried out as each diagnostic comes on line. The development, testing, and pre-pulse validation of control algorithms will be carried out using the Plasma Control System Simulation Platform (PCSSP) and similar simulation platforms for PIPS and CIS investment protection functions. First plasma scenarios will begin in hydrogen at a toroidal field of 2.65 T with attempts to achieve Ohmic breakdown within a limited neutral pressure range calculated to be around 0.3 mPa < p < 0.5 mPa. At higher neutral pressures, plasmas are not expected to reach the first plasma requirements of Ip ≥ 100 kA for at least 100 ms. If Ohmic breakdown is unsuccessful, electron cyclotron heating will be progressively added in 0.83 MW increments for short pulses (< 300 ms), possibly up to a total of 6.7 MW injected power. Plasma control scenarios must be designed to ensure that the maximum plasma current does not exceed 1 MA to stay within j x B structural limits of the vacuum vessel supports to the temporary poloidal stainless steel limiters. A backup option to improve breakdown conditions may also be to operate at full toroidal field up to 5.3 T after full magnet commissioning. The development of first plasma operations, initial PCS and investment protection commissioning, initial control and investment protection algorithm development and testing, and first plasma operation scenarios will be described.

Speaker: Cristina Rea

14:00 P1.1077 Assessment of the ITER baseline operation scenario using CORSICA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1077.pdf Assessment of the ITER baseline operation scenario using CORSICA S.H. Kim1, T.A. Casper2, J.A. Snipes1 and A. Loarte1 1 ITER Organization, Route de Vinon sur Verdon - CS 90046,13067 St Paul-Lez-Durance Cedex, France 2 Woodruff Scientific, Inc. 4000 Aurora Ave N. Ste. 6 Seattle, WA 98103 USA The ITER baseline operation aims at demonstrating controlled burn of D-T plasmas in the type-I ELMy H-mode regime and with a high fusion gain (Q~10). Improved physics understanding and updated specifications of the ITER components are being continuously integrated to develop more reliable candidate ITER baseline operation scenarios [1-4]. An integrated modelling of the ITER baseline operation including entry to burn, flat-top burning plasma, and exit from burn was previously performed using CORSICA [5-6] within relatively narrow ranges of plasma parameters and operational conditions. In this work, the previously proposed candidate ITER baseline operation scenarios have been further improved with updated modelling features including the density evolution during the L-H transition, density profile peaking, updated EC system configuration, improved edge pedestal evolution and ramp-down shape optimization. Then, the feasibility of these scenarios has been investigated across a range of plasma parameters and operational conditions to take into account the modelling uncertainties. A set of comparative studies performed by varying assumptions of the H-mode threshold power and triggering conditions has shown that reliable access to H- mode would be possible across a wide range of density evolution time-scales during the L-H transition, if the W concentration is kept below 1.0×10-5 and the isotopic mass dependence is included in the Martin H-mode threshold power scaling [7]. Another set of studies on the flat- top burning plasma performance conducted by varying the flat-top density, density profile peaking factor, edge pedestal estimates and combination of the ITER HCD systems has shown that Q~10 operation would be achievable with a moderate total auxiliary heating power (~50MW). An optimization of the current ramp-up and ramp-down studied by applying various HCD power waveforms has shown that early entry to burn puts the stress on the PF6 coil whereas late one reduces the poloidal flux available for the flat-top phase. The shape optimization was important for the ramp-down phase to avoid exceeding the force limits on the coils. The improved ITER baseline operation scenarios and analysis results presented in this paper will be a good basis for further development as the understanding on the burning plasma physics improves. [1] Parail V et al 2013 Nucl. Fusion 53 113002 [2] Casper T A et al 2014 Nucl. Fusion 54 013005 [3] Kessel C E et al 2015 Nucl. Fusion 55 063038 [4] Koechel F et al 2017 Nucl. Fusion 57 086023 [5] Crotinger J A et al 1997 LLNL Report UCRL-ID-126284; NTIS #PB2005-102154. [6] Kim S H et al, 42nd EPS conference on Plasma Phys. Control. Fusion, Lisbon, Portugal, 2015, ECA Vol.39, P4-170 [7] Martin Y R et al 2008 Journal of Physics; Conference Series 123, 012033

Speaker: Sun Hee Kim

14:00 P1.1079 A generalized plasma shape and position controller for the TCV tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1079.pdf A generalized plasma shape and position controller for the TCV tokamak F. Pesamosca1, S. Coda1, F. Felici1, H. Anand2 1 EPFL-SPC, 1015 Lausanne, Switzerland. 2 ITER Organisation, 13067 St.-Paul-lez-Durance Cedex, France. Improved performance of a tokamak plasma for controlled thermonuclear fusion is obtained via shaping the plasma to achieve an elongated cross section. The challenge of this approach lies in the fact that elongated plasmas are vertically unstable, and need to be feedback controlled. In the TCV tokamak, an advanced shape control algorithm was recently implemented, integrated within the digital control system, and tested for accessing advanced configurations, in particular negative triangularity and snowflake plasmas. In the present architecture, shape control and position stabilization are coupled problems as they share the same set of actuators, the poloidal field coils, and rely on the same information coming from a real time equilibrium reconstruction code, introducing a computational delay in the feedback loop. This feature limits the routine use of the advanced shape controller since the delay reduces the operational window for vertical stabilization and requires fine online tuning of the controller over many shots. A new proposed approach [1] is able to tackle this issue by a frequency separation of the shape and position control problems. Fast estimations of the plasma position obtained directly from magnetic measurements are used to stabilize the vertical dynamics at high frequency, while the shape and position control act on slower time scales on a stable system. This decoupling controller is designed using loop shaping techniques from control theory on TCV plasma models with progressively increasing levels of complexity. This scheme, similar to what will be used on the ITER tokamak, is being implemented in TCV and is expected to provide reliable access to advanced configurations avoiding undesired vertical displacement events. It will be in fact possible to leverage on former operational experience on plasma stabilization with the analog control system for a large variety of plasma shapes. Experimental tests of the generalized shape and position controller in TCV plasma discharges will be presented. Improved performance will be quantified through a comparison of dedicated figures of merit for identical shots, which will be performed featuring respectively the new digital and the former analog architecture. The final goal is to commission a unified control system for TCV magnetic control to be used in routine operation. [1] De Tommasi et al. “On plasma vertical stabilization at EAST tokamak". In: 2017 IEEE Conference on Control Technology

Speaker: Federico Pesamosca

14:00 P1.1080 Shape reconstruction and eddy currents estimation via Kalman Filter at the EAST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1080.pdf Shape reconstruction and eddy currents estimation via Kalman Filter at the EAST tokamak G. De Tommasi1,2, A. Mele1,2, A. Pironti1,2, B.J. Xiao3 1 Dipartimento di Ingegneria Elettrica e Tecnologie dell’Informazione, Università degli Studi di Napoli Federico II, via Claudio 21, 80125, Napoli, Italy 2 Consorzio CREATE, via Claudio 21, 80125, Napoli, Italy 3 Institute of Plasma Physics, Chinese Academy of Sciences, 350 Shushanhu Rd., 230031, Hefei, Anhui, P.R. China Plasma shape control is a core issue for thermonuclear fusion reactors. In order to achieve high control performances, the magnetic control system of a tokamak device must rely on a fast and accurate shape reconstruction algorithm, which is capable of precisely estimating the poloidal flux map that best fits the available experimental measurements at every control cycle. In this work, a possible solution to this problem is discussed, based on the well known Kalman filtering theory. The CREATE equilibrium codes [1], [2] have been used to generate linearized models of the plasma response, which can be embedded in an optimal state observer in order to achieve a fast and accurate reconstruction of the plasma shape, plus an estimate of the eddy currents 1. Comparison between the flux map of the EAST tokamak reconstructed using Kalman induced in the passive structures. This reconstruction is filtering (in gray) and the one computed by EFIT (in red). also suitable for a real-time implementation, as it entails only matrix multiplications and a single matrix inversion. As a testbed, the proposed solution has been applied to experimental data coming from the EAST tokamak. [1] R. Albanese e F. Villone, «The linearized CREATE-L plasma response model for the control of current, position and shape in Tokamaks,» Nuclear Fusion, vol. 38, 1998. [2] R. Albanese, G. Calabrò, M. Mattei e F. Villone, «Plasma response model for current, shape and position control at JET,» Fusion Engineering Design, vol. 66, pp. 725-728, 2003.

Speaker: Adriano Mele

14:00 P1.1081 Fast-ion transport in advanced tokamak scenarios with qmin close to two at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1081.pdf Fast-ion transport in advanced tokamak scenarios with qmin close to two at ASDEX Upgrade B. Geiger1 , R. Akers2 , A. Bock1 , M. Dunne1 , L. Giannone1, J. Hobirk1 , A.S. Jacobsen1 , P. Lauber1 , P. Zs. Pölöskei1 , M. Salewski3, P. A. Schneider1 , A. Snicker4 , A.J. van Vuuren1 , M. Willensdorfer1 and the ASDEX Upgrade Team 1 MPI für Plasmaphysik, D-85748 Garching, Germany 2 CCFE, Culham Science Centre, Abingdon, Oxon, United Kindom 3 PPFE, Department of Physics, DTU, DK-2800 Kgs. Lyngby, Denmark 4 Department of Applied Physics, Aalto University, FI-00076 AALTO, Finland Steady state operation of tokamaks is demanding since the toroidal plasma current needs to be sustained by non-inductive means [1]. Although external current drive sources are available, their extensive use would yield an unacceptably high recirculated power fraction in future fu- sion power plants. Thus, advanced tokamak scenarios are needed that feature high fractions of the intrinsic bootstrap current. The latter can be maximized in discharges with off-axis cur- rent distributions (low central poloidal fields) and internal transport barriers (strong gradients). Such discharge conditions are, however, difficult to maintain since they are prone to impurity accumulation [2] and ideal modes [3]. Recently, a stable advanced scenario with a current hole [4] in the plasma center and inter- nal transport barriers in the electron and ion temperature channels was maintained for several confinement times in ASDEX Upgrade. The discharges are almost non-inductive even though counter electron cyclotron current drive (ECCD) was used for current-profile tailoring in the plasma center. However, the high plasma pressure and the exotic safety factor profile (qmin close to two) yield a variety of magneto-hydrodynamic modes that might reduce the confine- ment of suprathermal particles. The corresponding fast-particle transport will be discussed to- gether with the analysis of the stability and performance of the new discharge scenario. This involves detailed diagnostic measurements and their interpretation, as well as modelling results of the thermal and fast-ion transport. References [1] WENNINGER, R. et al., Nuclear Fusion 57 (2017) 016011. [2] DUX, R. et al., Nuclear Fusion 44 (2004) 260. [3] WESSON, J. et al., Nuclear Fusion 25 (1985) 85. [4] FUJITA, T. et al., Nuclear Fusion 43 (2003) 1527.

Speaker: Benedikt Geiger

14:00 P1.1082 Inward transport induced by the Long Lived Mode in HL-2A H-mode plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1082.pdf Inward Transport Induced by the Long Lived Mode in HL-2A H- mode plasma J. Wu1, T. Lan1, J. R.Wu1, M. Xu2, L. Nie2, W. Chen2, L. M. Yu2, J. Cheng2, L. W. Yan2, X. R. Duan2, Y. Liu2, T. J. Deng1, H. Q. Xu1, S. Zhang1, Y. Yu1, X. Sun1, A. D. Liu1, J. L. Xie1, H. Li1, G. Zhuang1, W. D. Liu1 1 KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, P.R. China 2 Southwestern Institute of Physics, Chengdu 610041, P.R. China In the past two decades, the fluctuation induced inward flux was mainly studied in stellarators[1, 2] and less in tokamak[3, 4]. From the frequency resolved expression of fluctuation induced flux, the cross phase between electric field fluctuation E and pressure fluctuation ne is the main term that changes the direction of turbulence transport flux[5] which is different from the zonal flow to suppress turbulence by reducing the amplitude of fluctuation level[6]. In HL-2A tokamak plasmas, the inward flux induced by the Long Lived Mode (LLM) has been firstly observed in spontaneous L-H transition by using Langmuir probe array. The LLM is a kind of energetic particle modes (EPMs) excited by the resonance between internal kink mode and precessional motion of energetic trapped ions [7] or excited by energetic electron[8] in core region of HL-2A. In the edge region with strong E  B shear, the radial flux induced by LLM is reversed to inward because the cross phase term cos E n becomes e negative. By using the long-range correlation in radial direction between Langmuir probe and core soft X-ray signal, we find the poloidal electric field fluctuation E phase reversal is the main cause that leading to the inward transport. The other probe settled in the poloidal distance of 80 mm also observers the same inward flux phenomenon, which indicates the inward flux has a global characteristic. Furthermore, the inward flux may help to build the transport barrier and improve the confinement of turbulence transport. References [1] M. Shats. et al Phys. Rev. Let. 79 (1997) 2690. [2] K. Toi. et al Plasma Phys. Control. Fusion 44 (2002) A237. [3] J. Boedo. et al Nucl. Fusion 40 (2000) 1397. Y.Xu. et al Phys. Rev. Lett. 97 (2006) 165003. [4] D. Kong. et al Nuclear Fusion 58 (2018) 034003. [5] P.W. Terry. et al Phys. Rev. Let. 87 (2001). [6] H.G. Shen. et al Phys. Plasmas 23 (2016) 042305. [7] R.B. Zhang. et al Plasma. Phys. Control. Fusion. 56 (2014) 095007. [8] L.M. Yu. et al Nucl. Fusion 57 (2017).

Speaker: Jie Wu

14:00 P1.1083 Cross-machine validation of TGLF and GENE on Alcator C-Mod and ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1083.pdf Conferenceonon Plasma Plasma Physics, Physics 2018, Prague, Czech Republic P1.1083 Cross-Machine Validation of TGLF and GENE on Alcator C-Mod and ASDEX Upgrade A.J. Creely1, N. Cao1, G.D. Conway2, S.J. Freethy1,2, T. Görler2, R.M. McDermott2, P. Rodriguez-Fernandez1, G. Tardini2, A.E. White1, and the ASDEX Upgrade Team 1 Massachusetts Institute of Technology, Plasma Science and Fusion Center, Cambridge, USA 2 Max Planck Institute for Plasma Physics, Garching, Germany A cross machine validation study of the turbulent transport code TGLF [1] is performed with experimental data from Alcator C-Mod and ASDEX Upgrade. As validation of gyrokinetic and gyro-fluid codes becomes more widespread, the importance of validating these codes across machines becomes increasingly evident, with the ultimate goal of building confidence in predictions for future machines. In particular, cases for which ion-scale models robustly under-predict electron heat transport have been identified on Alcator C-Mod, requiring multi- scale effects to achieve agreement [2], but previously had not been identified on ASDEX Upgrade. Recent work has also shown that rigorous validation requires comparison of many experimental parameters to simulations, not only heat fluxes [3, 4]. This study therefore compares experimental electron and ion heat fluxes, electron temperature fluctuations (measured with CECE), and perturbative thermal diffusivity (measured with partial sawtooth heat pulses [5]) from more than 10 L-mode discharges on Alcator C-Mod and ASDEX Upgrade to the outputs of both ion-scale and multi-scale TGLF simulations, run within the VITALS framework [6]. A few cases are also compared with the gyrokinetic code GENE [7]. Results to date show good agreement between experiment and multi-scale TGLF on most discharges from both devices, but disagreement with ion-scale TGLF in some cases on both devices, though the disagreement is more prevalent on Alcator C-Mod. The dominant turbulent mode at low wavenumber may, in part, differentiate these cases. [1] G.M. Staebler et al., Phys. Plasmas 23, 062518 (2016). [2] N.T. Howard et al., Phys. Plasmas 23, 056109 (2016). [3] N.T. Howard et al., Plasma Phys. Controlled Fusion 60, 014034 (2018). [4] C. Holland, Phys. Plasmas 23, 060901 (2016). [5] A.J. Creely et al., Nucl. Fusion 56, 036003 (2016). [6] P. Rodriguez-Fernandez et al., Fusion Sci. Technol., Accepted (2017). [7] F. Jenko et al., Phys. Plasmas 7, 1904 (2000). This work is supported by the US DOE under grant DE-SC0006419 and by the US DOD under the NDSEG Fellowship.

Speaker: Alexander James Creely

14:00 P1.1084 Characterization of isotope effect on confinement of NBI-heated plasmas on LHD

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1084.pdf Characterization of Isotope Effect on Confinement of NBI-Heated Plasmas on LHD H. Yamada1,2, K.Tanaka1,3, T.Tokuzawa1, R.Seki1,4, C.Suzuki1, M.Yokoyama1,4, K.Ida1,4, M.Yoshinuma1, K.Fujii5, S.Murakami5 and LHD Experiment Group 1 National Institute for Fusion Science/NINS, Toki, Japan 2 The Univ. Tokyo, Kashiwa, Japan, 3 Kyushu Univ., Kasuga, Japan, 4 SOKENDAI, Toki, Japan, 5Kyoto Univ., Kyoto, Japan Energy confinement and thermal transport has been widely regarded as gyro-Bohm in tokamak as well as stellarator-heliotron for a single kind of ion. However, this gyro-Bohm model predicts confinement degradation in deuterium (D) plasmas because of larger normalized gyro radius * than in hydrogen (H) plasmas, which conflicts with major experimental observations. This study aims to quantify a peculiarity in dependence on * in H and D plasmas in order to address this unresolved issue. The first deuterium plasma campaign in LHD reveals characteristics of isotope effect from elaborated experiments on NBI-heated plasmas. Thermal energy confinement time gives the regression expression scaling with the isotope mass (A) as A0.15, which shows moderate improvement in D plasmas. This positive isotope dependence contradicts with gyro-Bohm and is similar to the recent result from L-mode plasmas in JET-ILW. Operational flexibility of magnetic field, density, and heating power enables adjustment of three major non-dimensional parameters, those being *, collisionality * and  , and dimensionally similar plasmas of H and D in all these three parameters can be obtained. Then TASK3D-a / FIT3D is used for analysis of heating power deposition, power balance and local thermal transport. If gyro-Bohm nature predominates in these plasmas, thermal diffusivity normalized by Bohm diffusion should be the same in a pair of dimensionally similar plasmas of H and D. Different characteristics from this conjecture have been found in electron and ion loss channels. Electron heat diffusivity normalized by Bohm diffusion in H is lower than that in D and even lower by more than a factor of 1/2 which means net improvement. This trend is robust and insensitive to parameters such as *, *,  and Ln. In contrast, ion thermal diffusivity shows same characteristics in low collsionality regime while that in D compared with the case with H degrades with the increase of collsionality. These results have shown definitively that the gyro-Bohm nature is violated in the comparison of H and D plasmas in LHD.

Speaker: Hiroshi Yamada

14:00 P1.1085 Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1085.pdf Experimental constraint on the radial mode number of the Geodesic Acoustic Mode in MAST Ohmic plasma B. Hnat1, S. Gadgil1, A. Kirk1, F. Militello2, N. Walkden2, and the MAST team2 1 CFSA, Department of Physics, University of Warwick, Coventry, UK 2 EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK Reciprocating Mach probe data is used to estimate the radial wave number of oscillatory zonal flows in Ohmic MAST plasma. An intermittent ~10 kHz mode, previously identified as a Geodesic Acoustic Mode (GAM), is detected in the wavelet decomposition and windowed spectra of plasma potential fluctuations of the MAST tokamak edge plasma. Two-points phase differencing technique is then applied to probe pins with radial and poloidal separations giving an estimate of the radial wave number at the desired range of frequencies. The phase velocity of propagation and an estimate of the shearing rate of the GAM is obtained. We measure the radial mode number range kr ~ 0.3-1.0 1/cm and a radial propagation speed of up to ~1 km/s. The GAM shearing rate is an order of magnitude smaller than the growth rate of drift-like turbulence. These results are consistent with the estimates obtained previously from multi-fluid numerical simulations of GAM in MAST.

Speaker: Bogdan Hnat

14:00 P1.1086 Suppression of runaway generation during disruptions by magnetic perturbation on J-TEXT tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1086.pdf Suppression of runaway generation during disruptions by magnetic perturbation on J-TEXT tokamak Z. Y. Chen1 , Z. F. Lin1, D. W. Huang1, R. H. Tong1, W. Yan1, Y. H. Ding1, Y. Liang1 and J-TEXT Team 1. International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China Corresponding author: Z Y Chen E-mail: zychen@mail.hust.edu.cn High-energy runaway electrons generated during the plasma disruption could result serious damage to plasma-facing components. The next generation fusion machines, like ITER and DEMO, will need a reliable method for controlling or suppressing runaway electrons. Previous experimental results show that the massive gas injection can’t provide enough impurities to achieve robust runaway suppression due to low gas mixture efficiency and extreme high Rosenbluth density for runaway avoidance.The transport of runaway electrons is affected by the magnetic perturbation. Robust runaway suppression has been reached on J-TEXT with mode penetration or mode locking by the application of resonant magnetic perturbation (RMP) with m/n=2/1 before the thermal quench. The strong stochastics in the whole plasma cross section expel out the runaway seed and results in runaway free disruptions on J-TEXT. This provides alternative runaway suppression during disruptions for large scale tokamak. It is found that hydrogen supersonic molecular beam injection has the capacity to eliminate RE current by provoking magnetic perturbations which increase RE losses rapidly. 1

Speaker: Zhong Yong Chen

14:00 P1.1087 Residual zonal flows in tokamaks in the presence of energetic ions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1087.pdf Residual Zonal Flows in Tokamaks in the Presence of Energetic Ions T.S. Hahm1,∗ and Y.W. Cho1 1 Department of Nuclear Engineering, Seoul National University, Seoul, Republic of Korea ∗ tshahm@snu.ac.kr Zonal flow, an axisymmetric potential fluctuation driven by turbulent Reynolds stress, plays a key role in turbulence regulation with its flow shear. It gets reduced by collisionless process in toroidal geometry, but to a non-zero value called the residual zonal flow level [1]. In this study, we investigate the residual zonal flow in the presence of energetic ions using modern gyro- kinetic approach[2]. We find that the residual zonal flow can be enhanced for the intermediate radial wavelength range on the order of thermal ion banana width, due to the presence of slowing down energetic ions. References [1] M.N.Rosenbluth and F.L. Hinton Phys. Rev. Lett. 80, 724 (1998) [2] T.S. Hahm, Physics of Fluids 31, 2670 (1988)

Speaker: Taik Soo Hahm

14:00 P1.1088 Experimental observations of ITG and TEM instabilities on J-TEXT tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1088.pdf Experimental observations of ITG and TEM instabilities on J-TEXT tokamak P. Shi1, G. Zhuang1,2*, J. Chen3, Y.N. Zhou1 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, Huazhong University of Science and Technology, Wuhan 430074, China 2 School of Physical Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China 3 Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, California 90095, USA Recently, two different quasi-coherent (QC) density fluctuations have been measured by the newly developed far-forward collective scattering measurements on J-TEXT tokamak Ohmic plasmas. The two QC instabilities have characteristic frequencies in the range of 30 − 100𝑘𝐻 (low-frequency) and 150 − 250𝑘𝐻𝑧 (high-frequency) respectively. And the corresponding characteristic normalized wavenumber is estimated to be in the range of 𝑘𝜃 𝜌𝑠 < 0.1 and 0.15 < 𝑘𝜃 𝜌𝑠 < 0.3 respectively. Furthermore, the propagation directions in plasma frame for the low-frequency (LF) and high-frequency (HF) QC instabilities are identified to be ion and electron diamagnetic direction respectively. Considering the features of the two QC modes and the discharge conditions on J-TEXT, the LF and HF QC modes are predicted to be the ion-temperature-gradient (ITG) driven instability and the trapped electron mode (TEM) respectively. In addition, the variations of ITG and TEM modes during density ramp-up have been investigated. More details will be showed in the poster.

Speaker: Peng Shi

14:00 P1.1089 Prediction of kinetic profiles using a new transport solver based on global optimization techniques

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1089.pdf Prediction of kinetic profiles using a new transport solver based on global optimization techniques M. Honda, S. Ide, E. Narita and N. Hayashi National Institutes for Quantum and Radiological Science and Technology, Naka, Ibaraki 311-0193, Japan To validate transport models driven by turbulence, which generally predominates transport in tokamaks, and/or predict kinetic profiles using them, coupling of a transport solver and transport models is indispensable. Many turbulent transport models show strongly nonlinear dependence on the gradient of kinetic profiles and such stiff behavior makes it difficult to robustly obtain smooth kinetic profiles without wiggles in less computation time. In [1], we have proposed the basic concept of an intrinsically oscillation-free transport solver based on global optimization techniques, even though stiff transport models are employed. The code, dubbed GOTRESS, benefiting from both a genetic algorithm [2] and Nelder-Mead method [3], solves the steady-state transport equations. GOTRESS does not require any derivatives in the course of calculation because the governing equations are not spatially discretized. Instead, the integral equations are successively solved at each grid to fit the conducted heat fluxes to the target fluxes that are obtained by integrating heat source and sink over the volume. Multi- species, collisional equipartition, actual shaped equilibria are all taken into account. GOTRESS is parallelized by MPI to reduce computation time. Even in a strong reversed shear plasma such as a current hole plasma, it just takes tens of seconds until GOTRESS satisfies a convergence criterion with CDBM or IFS/PPPL model, the latter of which is a very stiff model. Owing to MPMD, GOTRESS can be executed in a straightforward manner together with a parallelized transport model like TGLF and/or a neural-network-based transport model even if it is written in Python. GOTRESS can be exploited as a kernel of an integrated transport modeling, which makes it possible to robustly predict steady state profiles in future devices such as JT-60SA and also to check the validity of prescribed profiles that have been used. References [1] M. Honda, The 25th International Conference on Numerical Simulation of Plasmas, Leu- ven, Belgium, 2017; submitted to Comput. Phys. Commun. [2] P. Charbonneau, Astrophys. J. Suppl. Ser. 101 (1995) 309. [3] J. A. Nelder and R. Mead, Computer J. 7 (1965) 308.

Speaker: Mitsuru Honda

14:00 P1.1090 Observation of nonlocal transport on J-TEXT

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1090.pdf Observation of nonlocal transport on J-TEXT Zhoujun Yang1, Xiaoming Pan1, Hao Zhou1, Yuejiang Shi2, Aike Wang3, Lizhi Zhu1, Xiaolong Zhang1, Peng Shi1 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China 2 Department of Nuclear Engineering, Seoul National University, Seoul, Republic of Korea 3 Southwestern Institute of Physics, Chengdu,610000, China Corresponding author: Zhoujun Yang E­mail: yangzj@hust.edu.cn Nonlocal transport (NLT) induced by supersonic molecular beam injection (SMBI) has been observed on J­TEXT. Besides the anomalous phenomenon on electron temperature profile, acceleration of the core toroidal rotation is also observed during the non­local transport process. The threshold of plasma density above which NLT disappears is also found related with LOC­SOC as other tokamaks. To understand the physic of NLT, some more signals are focused, including the radiation, magnetic fluctuation, temperature fluctuation. They are compared for the discharges with or without NLT, even for LOC and SOC. Some interesting phenomenon have been discovered, especially for the magnetic fluctuation. They may show the potential effect for NLT.

Speaker: Zhoujun Yang

14:00 P1.1091 Impurity transport and trapped particle modes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1091.pdf Impurity transport and trapped particle modes M. Idouakass1, E. Gravier1, M. Lesur1, J. Médina1, T. Réveillé1, X. Garbet2, Y. Sarazin2, T. Drouot1 1 Institut Jean Lamour - UMR 7198 CNRS-Université de Lorraine, Nancy, France 2 CEA, IRFM, 13115, Saint-Paul-Lèz-Durance, France Impurities can have negative effects on the plasma confinement. First they will contribute to plasma dilution, reducing the fuel present for a given pressure. Second, these impurities are ionized multiple times, and will radiate a significant part of the plasma energy from the core. In addition, other species can be introduced in the plasma edge to decrease the heat and particle fluxes on the walls, and these particles can then propagate into the plasma core. We investigate the influence of the impurity profile on trapped particle modes, and the transport of these impurities. This is done using the gyrokinetic code TERESA-4D, which simultaneously describes trapped-ion (TIM) and trapped-electron (TEM) driven modes and treats the passing particles adiabatically [1, 2]. Its most interesting property is that it enables the full-f treatment of multiple populations of trapped ions, electrons, and impurities at low numerical cost. However, this code is collisionless, therefore it allows to study turbulent transport, but not neoclassical transport and its interplay with anomalous transport. In this work, a self consistent treatment of a population of impurities [3, 4] uncovers a strong influence on the dynamics of the turbulence in the plasma. We show that the sign of the impurity gradient can modify the nature of the instability [5], and that the impurity flux depends non-monotonously on the ratio impurity over ion density gradients. Furthermore, we show that the nature of the turbulence can have a strong influence on the zonal flow/drift mode energy ratio. References [1] G. Depret, X. Garbet, P. Bertrand, A. Ghizzo, Plasma Phys. Controlled Fusion 42, 949 (2000) [2] T. Drouot, E. Gravier, T. Reveille, A. Ghizzo, P. Bertrand, X. Garbet, Y. Sarazin, T. Cartier-Michaud, Eur. Phys. J. D 68, 280 (2014) [3] H. Du et al., Phys. Plasmas 23, 072106 (2016) [4] N. Bonanomi et al., Nuclear Fusion 58, 036009 (2018) [5] M. Idouakass, E. Gravier, M. Lesur, J. Médina, T. Réveillé, T. Drouot, X. Garbet, Y. Sarazin (submitted)

Speaker: Thierry Reveille

14:00 P1.1092 Neoclassical transport in the High density H-mode in Wendelstein 7-AS - revisited with new tools

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1092.pdf Neoclassical transport in the High density H-mode in Wendelstein 7-AS – revisited with new tools H. M. Smith, A. Mollén, C. D. Beidler Max Planck Institute for Plasma Physics, Greifswald, Germany In view of the aim for long-pulse operation of Wendelstein 7-X, it is important to understand under which circumstances one can expect to avoid impurity accumulation. Unless the impu- rity sources at the edge were kept small in Wendelstein 7-AS (W7-AS) normal confinement (NC) plasmas, impurities often accumulated in the centre which resulted in a radiation collapse that terminated the discharge [1]. However, this was avoided in so-called high-density H-mode (HDH) plasmas, which were NBI heated and characterised by a density exceeding a certain heating-power-dependent threshold (1.5 − 2.1 · 1020 m−3 ). The transport in the HDH regime was analysed in Ref. [2], but the experimentally observed efficient flush-out of impurities could not be explained by neoclassical transport, and there was no definite experimental evidence for turbulent mode activity at the plasma edge. Recently, analytical work [3, 4] has shown that when the impurities are in the highly collisional Pfirsch-Schlüter regime and the main ions in the long mean free path regime, neoclassical “temperature screening” (outward flux of impurities driven by the temperature gradient) can prevent accumulation in stellarators, even when the radial electric field points inwards. To include this effect in a numerical analysis of the neoclassical impurity transport in the W7-AS HDH mode, one needs a more detailed physics model than was used in previous investigations. In this work, we therefore use the SFINCS code [5, 6], which enables us to include the full linearised Fokker-Planck collision operator as well as the variation of the electrostatic potential on the flux surface. The SFINCS results are compared with results from the DKES code [7], which employs a pitch-angle scattering collision operator. References [1] R. Burhenn, Y. Feng, K. Ida, H. Maassberg et al., Nucl. Fusion 49, 065005 (2009). [2] R. Burhenn, J. Baldzuhn, R. Brakel, H. Ehmler et al., Fusion Science and Technology 46, 115 (2004). [3] P. Helander, S. L. Newton, A. Mollén and H. M. Smith, PRL 118, 155002 (2017). [4] S. L. Newton, P. Helander, A. Mollén and H. M. Smith, J. Plasma Phys. 83 905830505 (2017). [5] M. Landreman, H. M. Smith, A. Mollén and P. Helander, Phys. Plasmas 21 042503 (2014). [6] A. Mollén, M. Landreman, H. M. Smith, S. Braun and P. Helander, Phys. Plasmas 22 112508 (2015). [7] S. P. Hirshman, K. C. Shaing, W. I. van Rij, C. O. Beasley, Jr., and E. C. Crume, Jr., Phys. Fluids 29, 2951 (1986).

Speaker: Håkan Smith

14:00 P1.1093 Investigation of zonal flow stability using spatial averaging

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1093.pdf Investigation of zonal flow stability using spatial averaging S. Gadgil1, B. Hnat1, G. Rowlands1 1 University of Warwick, United Kingdom Zonal flows are of great interest inside magnetically-confined plasmas as their interaction with turbulence may in principle be used to control plasma confinement via processes such as shearing of turbulent eddies due to the alternating nature of the velocities of the zonal flows. Zonal flows are structures with a poloidal wavenumber of zero and a larger radial wavenumber but with plasma flow in the poloidal direction. The growth of zonal flows from drift modes has been extensively studied and non- linear processes are found to be the driving forces, chiefly 4-wave interactions. The linear decay of zonal flows can be attributed to energy transfer to compressible poloidal oscillations(GAMs) via Landau damping and the non-linear decay can be attributed to a tertiary Kelvin-Helmholtz instability. However, building upon previous work, the linear stability of zonal flows was re-examined using a spatial averaging technique. In particular the spatial averaging was applied to the dispersion relation obtained from the linearised Extended Hasegawa-Wakatani equations. The spatially independent dispersion relation was solved to yield linear growth rates for a small drift wave perturbation against a zonal flow background. The growth rates come from resonance terms which suggests Landau-damping of zonal flows and transfer of energy to drift waves. The growth rates and energy predictions were compared to measurements from a simulation and found to match reasonably well under a certain range of parameters. 1

Speaker: Sanket Gadgil

14:00 P1.1094 Calculations of impurity transport in Wendelstein 7-X plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1094.pdf Calculations of impurity transport in Wendelstein 7-X plasmas A. Mollén1,†, M. Landreman2 , H. M. Smith1 , J. A. Alcusón1 , P. Xanthopoulos1 , J. M. García-Regaña3 , A. Iantchenko4 , S. Buller4 , A. Langenberg1 , P. Helander1 1 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 2 Institute for Research in Electronics and Applied Physics, University of Maryland, USA 3 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain 4 Department of Physics, Chalmers University of Technology, Göteborg, Sweden Collisional transport theory has traditionally predicted impurity accumulation in stellarators driven by the inward pointing radial electric field, and impurities are a major concern for the capability of stellarators as a fusion energy source. However, recent advances in analytical [1, 2] and numerical [3, 4, 5] studies suggest that the standard neoclassical theory lack several effects that can be crucial when analyzing the impurity transport, and perhaps the situation is less severe than previously thought. Moreover, initial calculations of impurity transport in the first experimental campaign of the Wendelstein 7-X stellarator indicate that neoclassical theory alone is not capable of explaining the experimentally inferred results and particularly towards the plasma edge turbulent transport can play an important role. In the present work we perform a kinetic transport analysis of impurities in experimental Wendelstein 7-X plasmas. To calculate the neoclassical transport we employ the SFINCS (Stel- larator Fokker-Planck Iterative Neoclassical Conservative Solver) code [4, 6], which solves the time-independent radially local linearized 4D drift-kinetic equation for the perturbed distri- bution function and calculates fluxes. The code can account for flux-surface variations of the electrostatic potential, the full linearized Fokker-Planck-Landau collision operator, tangential magnetic drifts, an arbitrary number of kinetic species (including non-trace impurities), and it can be run iteratively to find the ambipolar radial electric field. Neoclassical calculations are supplemented by predictions of the turbulent impurity transport using the GENE code [7]. References [1] P. Helander, et al., Phys. Rev. Lett. 118 (2017) 155002. [2] I. Calvo, et al., Plasma Phys. Control. Fusion 59 (2017) 055014. [3] J. M. García-Regaña, et al., Nucl. Fusion 57 (2017) 056004. [4] A. Mollén, et al., submitted to Plasma Phys. Control. Fusion (2017). [5] J. L. Velasco, et al., arXiv:1712.03872 (2017). [6] M. Landreman, et al., Phys. Plasmas 21 (2014) 042503. [7] F. Jenko, et al., Phys. Plasmas 7 (2000) 1904. † albert.mollen@ipp.mpg.de

Speaker: Albert Viktor Mollén

14:00 P1.1095 Spatio-temporal dynamics of turbulence coupling with zonal flows

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1095.pdf Spatio-temporal dynamics of turbulence coupling with zonal flows M. Sasaki1,2 , T. Kobayashi3 , K. Itoh2,3,4 , N. Kasuya1,2 , Y. Kosuga1,2 , A. Fujisawa1,2 , S. Inagaki1,2 , S.-I. Itoh1,2,5 1 Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816-8580, Japan 2 Research Center for Plasma Turbulence, Kyushu University, Kasuga, 816-8580 Japan 3 National Institute for Fusion Science, Toki, 509-5292, Japan 4 Institute of Science and Technology Research, Chubu University, Aichi, 487-8501, Japan 5 Department of Innovative Energy Science and Engineering, Graduate School of Engineering, Chubu University, Aichi, 487-8501, Japan Formation mechanism of spatial profile of turbulence is one of important subjects in fusion plasma research. There are mechanisms to determine the spatial profile of the turbulence; one is the propagation, such as the avalanche and turbulence spreading [1], and the other is the in- teraction with the sheared flows, where the effects of flow shear [2] and of flow curvature [3] have been theoretically predicted. Experimental observations on the spatial profiles of turbu- lence within the scale of flow shears have been reported [4]. Therefore, a unified model that can predict the spatial structure of turbulence, including the mechanisms of the propagation and the interaction with the sheared flows, is required. In this study, we investigate the phase-space dynamics of turbulence coupling with the zonal flows, based on the wave-kinetic framework. We focus on the oscillatory branch of zonal flows, which is called geodesic acoustic modes (GAMs), on which there are many experimental obser- vations. Spatio-temporal structures of the turbulence and GAMs are obtained numerically. Due to the turbulence trapping by the GAM [5], the turbulence is accumulated at regions where the curvature of the GAM (spatial-second-derivative of the flow) is negative, and the turbulence is suppressed at the positive curvature region. The roles of the flow shear and curvature on the tur- bulence spatial profile are illustrated. The phase relation is sustained with the propagation of the GAM [6]. Hence, there appear a new global characteristic velocity for turbulence propagation, in addition to the local group velocity and that of the turbulence spreading. References [1] O. D. Gurcan, P. H. Diamond, T. S. Hahm, Z. Lin, Phys. Plasmas, 12, 032303 (2005). [2] H. Biglari, P. H. Diamond, P. W. Terry, Phys. Plasmas, 2, 1 (1990). [3] K. Itoh, et. al., Plasma Phys. Control. Fusion, 57, 075008 (2015). [4] T. Tokuzawa, Nucl. Fusion, 57, 025001 (2017). [5] M. Sasaki, et. al., Sci. Rep. 7, 16767 (2017). [6] M. Sasaki, et. al., Phys. Plasmas, 25, 012316 (2018).

Speaker: Makoto Sasaki

14:00 P1.1096 Search for zonal structures on the radial electric field and Reynolds stress profiles on COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1096.pdf Search for zonal structures on the radial electric field and Reynolds stress profiles on COMPASS O. Grover1,2 , J. Seidl1 , J. Adamek1 , P. Vondracek1,3 , M. Tomes1,3 , J. Havlicek1 , P. Junek1 , V. Weinzettl1 , M. Hron1 , R. Panek1 and the COMPASS team1 1 Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic 2 FNSPE, Czech Technical University in Prague, Czech Republic 3 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic The recent observation of stationary zonal-flow-like structures on JET with Doppler back- scattering [1] has motivated the search for similar structures in the radial electric field Er well on COMPASS [5]. The diagnostic used on COMPASS is a complex probe head mounted on a horizontal reciprocating manipulator on the outer midplane which enables a direct measurement of Er as well as the radial-poloidal component of the Reynolds stress tensor Rrp . The Reynolds stress has been identified in recent models and experiments [2] as a likely driver of poloidal zonal flows which are expected to play a key role in the L-H transition and the associated limit cycle oscillations (LCO) [3]. The probe head features both Langmuir and ball-pen probes [4] which enables a correction for the effect of the electron temperature on measurements of Er . It was demonstrated that the probe diagnostic can measure radial profiles of Er which cover the full extent of the Er well and remain stationary during both the inward and outward recip- rocations. The search for stationary structures on the Er profile was complicated by saw-teeth crashes which modulate Er . For this reason, dedicated scenarios were developed. No stationary zonal-flow-like structures have been observed when the Er well is so narrow that its radial scale is comparable to the expected radial scale of the structures. The probe diagnostic was also used to measure fluctuations of the density δ ne and the electric field Er during LCO with a frequency of 2-5 kHz. The δ ne , Er evolution is found to be consistent with type-J LCO [3] where the Er is mostly driven by the pressure gradient and not by the Reynolds stress. The magnetic signature of the LCO is toroidally symmetric and propagates from the LFS to the HFS, i.e. left-right asymmetric (as opposed to top-down on other devices). References [1] J. C. Hillesheim, E. Delabie, H. Meyer, et al., Physics Review Letters 116, 065002 (2016) [2] G. R. Tynan, I. Cziegler, P. H. Diamond, et al., Plasma Physics and Controlled Fusion 58, 044003 (2016) [3] J. Cheng, J. Dong, K. Itoh, et al., Nuclear Fusion 54 114004 (2014) [4] J. Adamek, H. W. Müller, C. Silva, et al., Review of Scientific Instruments 87, 043510 (2016) [5] R. Pánek, J. Adámek, M. Aftanas, et al., Plasma Physics and Controlled Fusion 58, 014015 (2016)

Speaker: Ondrej Grover

14:00 P1.1097 Experimental investigation of the mean turbulence structure tilt angle and its comparison with gyrokinetic simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1097.pdf Experimental investigation of the mean turbulence structure tilt angle and its comparison with gyrokinetic simulations J.R. Pinzón1,2 , T. Happel1 , C. Angioni1 , P. Hennequin3 , E. Blanco4 , T. Estrada4 , U. Stroth1,2 and the ASDEX Upgrade Team1 1 Max-Planck Institut für Plasmaphysik,Garching, Germany 2 Physics-Department E28, TUM, Garching Germany 3 Laboratoire de Physique de Plasmas, Ecole Polytechnique, Palaiseau, France 4 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain The experimental characterization of the turbulence and its comparison with theory and sim- ulations is fundamental for the understanding of the turbulence dynamics in fusion plasmas. Detailed fluctuation measurements are required in order to investigate specific phenomena. In particular, the tilt angle of the turbulence structures in the radial-perpendicular plane, is a quan- tity predicted by theories and gyrokinetic simulations, which can provide information on the tur- bulence interaction with sheared flows and the type of the dominant micro-instabilities [1], e.g. ion-temperature gradient (ITG) and trapped-electron mode (TEM) instabilities. Nevertheless, tilt angle measurements are challenging, especially in the confined region of fusion plasmas. Radial correlation Doppler reflectometry is an experimental technique that provides infor- mation on the radial structure of the density turbulence. It is based on the correlation analysis of two Doppler reflectometry channels measuring at different radial positions. A new analysis technique of the time delays of the correlation has been developed. It provides a measurement of the tilt angle and can be applied in the confined region of fusion plasmas where Doppler reflectometry measurements are usually performed. The tilt angle measurement method is applied at the ASDEX Upgrade tokamak. A low density L-mode discharge is investigated. Two phases with either dominant ion or dominant electron heating are considered. The tilt angle is measured in the confined region ρpol = 0.70 − 0.84 for the first time in the ASDEX Upgrade tokamak. Moreover, a tilt angle difference of 26◦ is observed between both phases. The linear gyrokinetic stability analysis confirms a transition from an ITG to a more TEM dominated turbulence regime between the phases with dominant ion and dominant electron heating, respectively. The tilt angle is compared with results from gyrokinetic simulations, and the use of this new measurement as a signature of the turbulence regime is discussed. References [1] Y. Camenen et. al., Nucl. Fusion 51, 073039 (2011)

Speaker: Javier Rodrigo Pinzon

14:00 P1.1098 High-frequency edge coherent modes observation in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1098.pdf High-frequency edge coherent modes observation in ASDEX Upgrade A. Medvedeva1,2 , C. Bottereau2 , F. Clairet2 , G. D. Conway1 , L. Gil3 , P. Manz1 , F. Mink1 , V. Nikolaeva3 , D. Prisiazhniuk1 , U. Stroth1,4 , ASDEX Upgrade Team1 and EUROfusion MST1 teama) 1 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 2 CEA, IRFM, 13108 St-Paul-Lez-Durance, France 3 Instituto de Plasmas e Fusão Nuclear, IST, Universidade Lisboa, 1049-001 Lisbon, Portugal 4 Physik-Department E28, Technische Universität München, 85747 Garching, Germany a) For a list of members, see H. Meyer et al, Nucl. Fusion 57 102014 (2017) The modes which can be observed in a confined magnetized plasma are related to instabilities caused by different drives. The goal is to describe the mechanisms and to identify the basic properties of such instabilities, which can be measured in the experiment. During the I-phase of L-H confinement transitions the turbulence level, background and turbulent flows oscillate in the kilohertz range creating limit-cycle oscillations, while the turbulence frequency spectra significantly modify in the plasma edge. High-frequency edge coherent modes (ECMs) have been detected in the reflectometer signals during the experiments dedicated to the L-H transition studies on ASDEX Upgrade [1]. The role of the ECMs in the clamping of the pedestal pressure has been examined. The modes have been observed in the ultra-fast swept reflectometer (UFSR) signal [2] con- tinuously during the I-phase, after the transition to the ELM-free phase of the H-mode and in between ELMs [3]. The mode frequency is in the range of 40–200 kHz and often several branches are observed simultaneously. The UFSR data allow to locate the modes in the plasma pedestal region. Through a detailed analysis it is shown that the ECM frequency increases with plasma edge electron pressure. ECMs have low toroidal mode numbers between n = −2 and −11. From the UFSR and poloidal correlation reflectometer data it follows that the ECMs have a small radial wavenumber kr < 2 cm−1 and a poloidal wavenumber k⊥ = 0.2 − 0.4 cm−1 . The absence of the ballooning character, the propagation in the electron diamagnetic direction and the localisation close to the pedestal top indicate that the ECMs might be microtearing modes. References [1] A. Medvedeva et al., Plasma Physics and Controlled Fusion 59.12, 125014 (2017) [2] F. Clairet et al., Review of Scientific Instruments 88.11, 113506 (2017) [3] A. F. Mink et al., Nuclear Fusion 58.2, 026011 (2017)

Speaker: Anna Medvedeva

14:00 P1.1099 Gyrokinetic analysis of pedestal transport

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1099.pdf Gyrokinetic analysis of pedestal transport M. Kotschenreuther1, X. Liu1, D. R. Hatch1, L. Zheng1, S. Mahajan1, A. Diallo2, R. Groebner and the DIII-D team3, J Hughes and the C-mod team4, C. Maggi, S. Saarelma and JET Contributors*5 1 University of Texas, Austin, USA 2 Princeton Plasma Physics Laboratory, Princeton, USA 3 General Atomics, San Diego, USA 4 MIT Plasma Science and Fusion Center, Boston, USA 5 Culham Centre for Fusion Energy, Culham Science Center, United Kingdon Surprisingly, basic considerations can determine which modes are responsible for pedestal energy transport (e.g., KBM, ETG, ITG, MTM etc. ). Gyrokinetic simulations of experiments, and analysis of the Gyrokinetic-Maxwell equations, find that each mode type produces characteristic ratios of transport in the various channels: density, heat and impurities. This, together with the relative size of the driving sources of each channel, can strongly constrain or determine the dominant modes causing energy transport. MHD-like modes are not the dominant agent of energy transport - when the density source is weak as is often expected. Drift modes must fill this role. Detailed examination of experimental observations (with an emphasis on DIII-D case), including frequency and transport channel behavior, with simulations, demonstrates these points. Work supported by US DOE under DE-FC02-04ER54698, DE-FG02-04ER54742 and DE-FC02-99ER54512 and by Eurofusion under grant No. 633053 *See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001”

Speaker: X. Liu

14:00 P1.1100 Complex-eikonal methods applied to geodesic acoustic modes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1100.pdf Complex-eikonal methods applied to geodesic acoustic modes F. Palermo1 , E. Poli1 , A. Bottino1 , A. Ghizzo2 1 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 2 Institut Jean Lamour, University of Lorraine, F-54506 Vandoeuvre les Nancy, France The tokamak represents a very complex system in which several actors such as drift waves, streamers, turbulence, zonal flow, geodesic acoustic modes (GAMs)... interact each other defining the transport properties of the plasma. GAMs represent the oscillation counterpart of the zonal flow and have received much attention for their potential role in the energy confinement in plasma fusion domain. In particular they inter- act with turbulence in an inhomogeneous envi- ronment in which plasma shape and profile gra- dients strongly affects their amplitude and their position [1, 2]. Because of the complexity of the system, it is crucial to develop and to apply Figure 1: Electric field evolution of GAM in (time, methods that allow to have simple and accurate radial) plane. Overlapped it is shown the ray paths descriptions of specific properties of plasma be- predicted by using the geometrical optics methods. havior. In this way, it is possible to distinguish in an intuitive and useful manner relevant aspects of global physical systems. To this purpose, ray method or geometrical optics provides a very powerful tool that has been applied in many important problems related to wave propagation and energy transport. By using the paraxial WKB (pWKB) method [3, 4] and a complex-eikonal approach [5], we describe several GAM properties such as amplitude, shape evolution and energy flux of GAM in homogeneous and in- homogeneous equilibria. These findings allow us to predict the GAM evolution, in simulations (see Fig. 1) performed with the particle-in-cell code ORB5 [6, 7]. References [1] F. Palermo et al., Physics of Plasmas 24, 072503, (2017) [2] F. Palermo et al., 44rd EPS Conference on Plasma Physics P4.160, (2017) [3] G. V. Pereverzev, Physics of Plasmas 5, 3529, (1999) [4] E. Poli et al., Physics of Plasmas 6, 5, (1999) [5] E. Mazzuccato, Physics of Plasmas 1, 1855 (1989) [6] S. Jolliet et al., Comput. Phys. Commun. 177, 409 (2007) [7] A. Bottino and E. Sonnendrucker, J. Plasma Phys. 81, 435810501 (2015)

Speaker: Francesco Palermo

14:00 P1.1101 Test and Validation of TRANSP ”Kick”-Model Predictive Capability of Neoclassical Tearing Mode Induced Fast Ion Transport in ITER Relevant DIII-D Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1101.pdf Test and Validation of TRANSP ”Kick”-Model Predictive Capability of Neoclassical Tearing Mode Induced Fast Ion Transport in ITER Relevant DIII-D Plasmas L. Bardoczi1 , M. Podesta2 , W.W. Heidbrink3 , M. A. Van Zeeland4 1 Oak Ridge Associated Universities, Oak Ridge, Tennessee 37831, USA 2 Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA 3 University of California, Irvine, California 92697, USA 4 General Atomics, P. O. Box 85608, San Diego, California 92186-5608, USA E-mail: bardoczil@fusion.gat.com A newly available analysis tool of island structure determination [1] has been integrated for the first time with the TRANSP ”Kick” reduced transport model [2] to study Neoclassical Tearing Mode driven energetic particle transport in ITER relevant DIII-D plasmas Magnetic islands are implemented in the ”Kick”-model through the perturbed flux ψ of a 3D helical Gaussian current filament with m and n mode numbers, centered at q = m/n (rs ). The radial and helical structure is derived from first principles and the tearing amplitude is set to match the experimental island width (W ). Next, ψ is used to calculate the ”Kick” probability matrix P (∆E, ∆P ) of ∆E energy and ∆P momentum kicks experienced by energetic particles in different parts of phase space with the ORBIT code. This P is used in TRANSP’s NUBEAM module to modify the fast ion distribution. Initial TRANSP runs of ITER baseline, hybrid and steady state plasmas with the ”Kick” matrix are encouraging with the model quantitatively predicting measured neutron rates in contrast to the classical model [Fig.1.]. The level of transport varies by scenario and island size with observed neutron deficit up to 20% in hybrid plasmas. The ”Kick”-model retains all TRANSP functionality and is also able to self-consistently predict the NTM impact on beam ion torque, current drive and heating, which will also be discussed for the various scenarios. Figure 1: (a) Measured and TRANSP neutron rates with and without Kick-matrix in a hybrid DIII-D plasma with a m/n = 2/1 NTM. (b) Neutron deficit and NTM magnetic amplitude. This research was supported by the General Atomics Postgraduate Research Participation Program administered by ORAU under contract number DE-AC05-060R23100 and by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under contract numbers DE-AC02-09CH11466 and DE-FC02-04ER54698. [1] L. Bardoczi et al, PoP 23 052507 (2016), [2] M. Podestá, PPCF 56 055003 (2014)

Speaker: Laszlo Bardoczi

14:00 P1.1102 Multiscale fusion plasma simulations of varied tokamak scenarios within the ComPat framework

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1102.pdf Multiscale Fusion Plasma Simulations of Varied Tokamak Scenarios within the ComPat Framework O.O. Luk1 , O. Hoenen1 , A. Bottino1 , B.D. Scott1 , D.P. Coster1 1 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748, Garching, Germany Fully simulating the impact of turbulence on the performance of fusion devices such as ITER is challenging, especially when fusion plasmas exhibit highly disparate spatio-temporal scales. Currently, there are single-scale models developed to study turbulence (gyrokinetic models) and transport (large-scale simplified models) separately. To go beyond single-scale simulations, the Computing Patterns for High Performance Multiscale Computing (ComPat) project [1] takes the component based approach to construct multiscale simulations by connecting existing single- scale models (submodels) together into a workflow. This approach has simpler algorithm and codebase, therefore each submodel is easier to validate, verify, maintain and optimize. In addi- tion, ComPat incorporates the concept of Multiscale Computing Patterns [2] into its framework, so that applications can run efficiently when one or several submodels require computing capa- bilities at the petascale. In this work, the ComPat framework is taken to build a multiscale fusion application that brings equilibrium (fixed boundary codes), turbulence (either local flux-tube or global gyroki- netic code) and core transport (1D code) models together. Using both the unified datastructure developed in EUROfusion and the Multiscale Coupling Library and Environment (MUSCLE2), one can set up a reliable multiscale fusion plasma simulation based on existing single scale codebases. A significant advantage to such approach, is the ease with which individual sub- model can be replaced by another that offers similar functionality. However, there are major challenges arise to such framework. Several of these challenges will be addressed, including time bridging between turbulence and transport models, defining quasi-steady state of core plasma, implementing global gyrokinetic code into current simulation framework, and opti- mizing the overall simulation runtime. All the simulation results presented here are based on initial conditions from ASDEX Upgrade- and JET-sized cases. References [1] http://compat-project.eu [2] S. Alowayyed, D. Groen, P.V. Coveney, and A.G. Hoekstra, Journal of Computational Science 22, 15-25 (2017)

Speaker: Onnie On-Ying Luk

14:00 P1.1103 Turbulent fluctuations in the scrape-off-layer and edge plasma of the COMPASS tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1103.pdf Turbulent fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak J. Seidl1, K. Jirakova1,2, J. Adamek1, O. Grover1,2, J. Horacek1, M. Hron1, P. Vondracek1,3 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 FNSPE, Czech Technical University, Prague, Czech Republic 3 Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic This work brings an overview of properties of turbulent plasma fluctuations in the scrape-off layer (SOL) and the edge of confined plasma in COMPASS ohmic and L-mode discharges, measured using electrostatic probes. Amplitude and size of the structures, their ExB velocity, phase shift between plasma potential and density and/or temperature and general fluctuation statistics are studied across a range of plasma conditions (BT = 0.8-1.35 T, Ip = 80-290 kA, n = 2-10 1019m-3, κ = 1-1.8) in relation to the position and properties of the velocity shear layer and the SOL collisionality. Moreover, their impact on the formation of radial plasma profiles is discussed. Generally, two types of coherent fluctuations are observed: a) broadband high frequency branch (f ≈ 50-350 kHz) rotating in the electron diamagnetic direction and appearing mainly in the confined region, pronounced particularly at the position of the largest pressure gradient, but often protruding even to the SOL up to the near/far SOL boundary; b) low-frequency blobs, probably of interchange origin, rotating mostly in an opposite poloidal direction, formed in the vicinity of the radius of zero electric field and carrying significant particle and energy flux outwards to the SOL. Nevertheless, spectral decomposition of the radial particle flux shows that in the near SOL, where both types overlap, their contribution to the radial transport can be comparable. In the SOL, the radial transport is influenced by a short connection length that COMPASS has, L||,LFS ≈ 3 m [1], implying small SOL collisionality and possible sheath dissipation of the plasma potential [2, 3]. In the discharges with low-to-medium density the radial ExB velocity tends to be out of phase with density fluctuations, thus reducing the effective radial transport. At high densities this phase shift decreases, leading to increased radial transport. [1] K. Jirakova, et al., 45th EPS Conference on Plasma Physics, 2018, Prague [2] O.E. Garcia, et al., Physics of Plasmas 13, 082309 (2006) [3] J.R. Myra, et al., Physics of Plasmas 18, 060501 (2006)

Speaker: Jakub Seidl

14:00 P1.1104 Thermal energy confinement time scaling with Ip and BT in Globus-M H-mode

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1104.pdf Thermal energy confinement time scaling with Ip and BT in Globus-M H-mode. E.O. Kiselev1, M.I. Patrov1, G.S. Kurskiev1, N.N. Bakharev1, V.K. Gusev1, A.Yu. Telnova1, N A Khromov1, I.V. Miroshnikov1, Yu.V. Petrov1, N.V. Sakharov1, V.B. Minaev1, A D Sladkomedova1, P.B. Shchegolev1, V.V. Solokha1, V A Tokarev1, S.Yu. Tolstyakov1 1 Ioffe Institute, St. Petersburg, Russia Federation The presentation is devoted to the thermal energy confinement study at the compact spherical tokamak Globus-M. Globus-M had major radius R = 0.36 m and minor radius a = 0.24 m (R/a ~ 1.5). The lower-null magnetic configuration is characterized by moderate elongation k~1.7 and triangularity δ~0.35. Special feature of the Globus-M tokamak is the extremely high input heating power density: ~0.6 MW/m3 in pure ohmic heating (OH) and ~2.5 MW/m3 under auxiliary heating by neutral beam injection (NBI). The range of temperatures achieved in Globus-M is = 0.2 – 0.4 keV that leads to higher values of collisionality ν*=0.03-0.4 and normalized ion gyroradius ρ*~ 0.02-0.04 than in MAST and NSTX. The present study was performed in both OH and NBI heated H-mode plasmas. H-mode is the usual operational mode in Globus-M at moderate density range ne>2-2.5∙1019 m-3. The regression fit of the database indicates strong τE dependence on both plasma current Ip and toroidal magnetic field BT, while the dependence on ne and absorbed power was similar to the conventional scaling IPB98(y,2). The original technique for calculating the absorbed power using both NUBEAM [1] and 3d fast-ion tracking algorithm [2] is discussed. Obtained profiles of the absorbed power were used to estimate electron and ion heat diffusivity using ASTRA simulation. It was found that the electron heat diffusivity is strongly affected by the plasma current and the toroidal magnetic field. The BTτE dependence on ν* is found be similar to the one in NSTX and MAST, while q dependence is stronger than on MAST, but weaker than in ITER scaling. 1. A. Pankin et al., “The tokamak Monte Carlo fast ion module NUBEAM in the National Transport Code Collaboration library”, Comp. Phys. Comm. 159 (2004) 157. 2. Bakharev N.N. et al., Fast particle behaviour in the Globus-M spherical tokamak // Nucl. Fusion – 2015. – Т. 55 – 55043023.

Speaker: Evgenii Kiselev

14:00 P1.1105 Strong-flow gyrokinetic simulations with a unified treatment of all length scales

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1105.pdf Strong-flow gyrokinetic simulations with a unified treatment of all length scales A.Y. Sharma1 , B.F. McMillan1 , J. Dominski2 1 University of Warwick, Coventry, UK 2 Princeton Plasma Physics Laboratory, Princeton, US Tokamak turbulence exhibits interaction on all length scales, but standard gyrokinetic treat- ments consider global scale flows and gyroscale flows separately, and assume a separation be- tween these length scales. However, the use of a small-vorticity ordering [1, 2] allows for the presence of large, time-varying flows on large length scales, whilst providing a unified treatment including shorter length scales near and below the gyroradius. We present a numerical scheme for the solution of gyrokinetic equations using such an ordering. For simplicity, we use two-dimensional electrostatic potential perturbations in slab and cylin- drical magnetic geometries. In an analogous way to that of the vk -formulation of gyrokinetics, the partial time derivative of the E × B flow is present in our Euler-Lagrange and Poisson equa- tions. These terms must be kept to ensure energetic consistency [3]. However, these terms are small compared to all other terms, allowing for the use of an iterative numerical scheme. Our numerical implementation uses the δ f particle-in-cell method [4], and employs an arbitrary- wavelength Poisson solver [5]. We have performed code verification using basic slab instabili- ties. We present comparative weak- and strong-flow simulation results for centrifugal and drift instabilities. We simultaneously simulate supersonic fluctuating flows at large length scales and the cascade of shorter wavelength flows down to the gyroradius. References [1] A.M. Dimits, Physics of Plasmas 17, 055901 (2010) [2] B.F. McMillan and A.Y. Sharma, Physics of Plasmas 23, 092504 (2016) [3] B. Scott and J. Smirnov, Physics of Plasma 17, 112302 (2010) [4] S. Jolliet, A. Bottino, P. Angelino, R. Hatzky, T.-M. Tran, B.F. McMillan, O. Sauter, K. Appert, Y. Idomura, L. Villard, Computer Physics Communications 177, 409 (2007) [5] J. Dominski, B.F. McMillan, S. Brunner, G. Merlo, T.-M. Tran and L. Villard, Physics of Plasmas 24, 022308 (2017)

Speaker: Amil Sharma

14:00 P1.1106 Turbulence suppression by electrostatic biasing in the Texas Helimak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1106.pdf Turbulence suppression by electrostatic biasing in the Texas Helimak F. A. C. Pereira1, D. L. Toufen2, Z. O. Guimarães-Filho1, I. L. Caldas1, K. W. Gentle3 1 Institute of"Physics, University of São Paulo, São Paulo, Brazil 2 Federal Institute of Education, Science and Technology of São Paulo, Guarulhos, Brazil. 3 Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, USA. The Texas Helimak[1] is a toroidal plasma device with one-dimensional equilibrium, magnetic curvature and shear, resembling closely the border and scrape-of layer of a Tokamak. The Texas Helimak vacuum vessel has a rectangular cross section with 0.6 m of internal radius, 1.6 m of external radius, and 2 m of height and the plasma is generated by electron cyclotron resonance heating. The Helimak typical regime turbulence presents intermittent density bursts that are responsible for an asymmetrical PDF with long tails. This machine has four sets of plates, where Langmuir probes are mounted and from where is possible to impose an external electrostatic bias. The electrostatic bias modify the radial electric feld profle and change the turbulence regime, and it can even suppress the intermittent bursts[1]. In this work, we study the conditions for the intermittent turbulence suppression scenario by changing the density profle position in relation with the biasing plates. We acknowledge the fnancial support of FAPESP (grants 2014/07043-0, 2015/50122-0 and 2017/23128-3). [1] K. W. Gentle and Huang He, Plasma Sci. and Technology, 10, 284 (2008).

Speaker: Felipe Augusto Cardoso Pereira

14:00 P1.1108 Detection of filamentary structures using transfer entropy in TJ-II and W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1108.pdf Detection of filamentary structrures using transfer entropy in TJ-II and W7-X J H. Nicolau1 , L. García1 , B. A. Carreras1 , B.Ph. van Milligen2 , B.Liu3 , G. Grenfell2,4 , U. Losada2 , C. Hidalgo2 and the TJ-II Team 1 Universidad Carlos III de Madrid, 28911 Leganés, Spain 2 Laboratorio Nacional de Fusion, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain 3 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, People’s Republic of China 4 Consorzio RFX, Corso Stati Uniti 4, 35127, Padova, Italy A new method to detect filamentary structures in magnetic confined plasmas is presented. The method, transfer entropy (TE), is a technique which detects causality between signals [1][2]. It measures information flow from different signals. In this work, it is applied to probes distributed at different locations in the plasma. The results show connexions between signals with some time lag. Thus, the TE is capable of detecting when the filaments are passing through distant probes. We apply the TE to the fluctuating electrostatic potential in a resistive MHD model. Probes distributed along the poloidal direction identify the periodicity of the filament. Furthermore, knowing the periodicity allow us to calculate the length of the filament. The directionality of TE is used to obtain their poloidal velocity. Finally, the radial width of filaments is calcu- lated by probes distributed along the radial direction. Figure 1: Filamentary structure The method is applied to TJ-II and W7-X devices. Both ma- in TJ-II chines have low magnetic shear which generates low order ra- tional surfaces that dominate a wide radial region. In our simulations, filaments have the same periodicity as the rational surfaces and they are rotating with the same poloidal velocity as the plasma. This well-known characteristic helps to detect and contrast the filaments using the present method. Our results are consistent with expected values and with recent experiments in TJ-II [3]. References [1] Schreiber T. 2000 Measuring information transfer. Phys. Rev. Lett. 85 461 [2] B.Ph. van Milligen et al. Causality detection and turbulence in fusion plasmas. 2014 Nucl. Fusion 54 023011 [3] B.Ph. van Milligen et al. Filaments in the edge confinement region of TJ-II. 2018 Nucl. Fusion 58, 026030

Speaker: Javier Hernandez Nicolau

14:00 P1.1109 Investigation of the pump-out effect by resonant magnetic perturbations in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1109.pdf Investigation of the pump-out effect by resonant magnetic perturbations in ASDEX Upgrade N. Leuthold1, W. Suttrop1, M. Willensdorfer1, M. Cavedon1, M. Dunne1, L. Guimarais2, T. Happel1, A. Kirk3, the ASDEX Upgrade4 and MST15 teams 1 Max Planck Institute for Plasma Physics,Boltzmannstrasse 2, 85748 Garching, Germany, 2 Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Universidade de Lisboa, Portugal, 3 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, U.K., 4 See A. Kallenbach et al, Nucl. Fusion 57 (2017) 102015, 5 See H. Meyer et al, Nucl. Fusion 57 (2017) 102014 E-mail: nils.leuthold@ipp.mpg.de Resonant magnetic perturbations (RMPs) are considered as an efficient method to mitigate (in the sense of reduced stored energy losses) or suppress the Edge Localized Mode (ELM) instability in tokamaks. However, a clear reduction of plasma density (‘pump-out’) is often observed when RMPs are applied, which leads to deterioration of the H-mode edge pedestal pressure and therefore reduced confinement. Recent experiments in ASDEX Upgrade aimed to characterize the pump-out effect and its parameter dependencies. When magnetic perturbations penetrate to resonant surfaces, magnetic field lines and equipotential field lines get perturbed locally. This in turn can lead to enhanced radial transport by changes in the ExB drift velocity [1]. In scans of the safety factor, no singular behavior such as an increase of the RMP induced particle transport was found if rational surfaces resonant with the magnetic perturbation were moved through the zero crossings of the electron perpendicular velocity and radial electric field at the pedestal top. If cross-field flows vanish at rational surfaces, no shielding currents for the MP are induced, and therefore a resistive plasma response can develop. In ELM suppressed H-modes, however, enhanced fluctuations in the edge transport barrier region are observed with conventional reflectometers. Experiments with rigid rotations of the RMP field reveal their toroidally asymmetric amplitude, indicating that the enhanced fluctuation levels are an effect of the 3D perturbation field. Discharges with a modulation of the RMP field strength were performed in order to identify the plasma layer in which particle transport is modified by the RMPs. The phase profiles of the plasma density response to the modulation suggest that particle transport is modified in the H-mode edge transport barrier region. The implications of these observations for models of the pump-out effect will be discussed. [1] Heyn et al, Nucl. Fusion 54 (2014) 064005

Speaker: Nils Leuthold

14:00 P1.1110 Avoiding disruption via the locked mode control by the rotating RMP on J-TEXT tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1110.pdf Avoiding disruption via the locked mode control by the rotating RMP on J-TEXT tokamak Da Li1, Yonghua Ding1,*,Feiran Hu1, Tong Wang1, Lizhi Zhu1, Nengchao Wang1, Bo Rao1, Qiming Hu2, Hai Jin3, Zhuo Huang1, Mao Li1, Song Zhou1, Ruo Jia1, Lai Peng1, Zebao Song1, Ying He1, Jiaolong Dong, Chengshuo Shen1 and the J-TEXT team 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China 2 Princeton Plasma Physics Laboratory, Princeton NJ 08543-0451, USA 3 College of Electrical and Information Engineering, Lanzhou University of Technology, Lanzhou 730050, China *E-mail: yhding@hust.edu.cn In a tokamak, one of the major causes of disruptions is locked mode (LM), a static tearing mode which usually grows to large amplitudes. Therefore, the active control of the LM is an important issue for future fusion reactors. Previously, we have reported the unlocking of the LM by rotating resonant magnetic perturbation (RMP), which rotated at several kHz [1] . In Ref. [1], the m/n = 2/1 LM was too small to induce disruption, where m and n are the poloidal and toroidal mode numbers, respectively. In this paper, we will use rotating RMP to control the larger 2/1 LM and to avoid the disruption in J-TEXT tokamak. The electrode biasing (EB) could decelerate the tearing mode (TM) and cause the LM . A major disruption usually occurred within 5 ~ 20 ms [2] after the mode locking due to EB. The rotating RMP, applied once the appearance of a LM, could accelerate the LM to a few kHz and hence avoid the disruption. However, when the LM was quite large at lower qa, it is really difficult to unlock the LM by rotating RMP. To improve the performance of the rotating RMP, it was applied once the TM was decelerated by the EB to a critical value. This control strategy could accelerate the TM, avoid the appearance of LM and disruption. Further experiments showed that rotating RMP at higher frequency had better performance in controlling the disruption. [1] Hai Jin et al 2015 Plasma Phys. Control. Fusion 57 104007 [2] Hai Liu et al 2017 Nucl. Fusion 57 0160

Speaker: Da Li

14:00 P1.1111 Velocity-space tomography from synthetic FIDA measurements at EAST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1111.pdf Velocity-space tomography from synthetic FIDA measurements at EAST B. Madsen1 , M. Salewski1 , J. Huang2 , J. Zhang2,3 , C. Wu3 , J. Chang2 , S. Ding2 , W. Gao2 and the EAST team 1 Department of Physics, Technical University of Denmark, Kgs. Lyngby, Denmark 2 Institute of Plasma Physics, Chinese Academy of Sciences, P.O. 1126, 230031 Hefei, Anhui, China 3 School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026, China In the Experimental Advanced Superconducting Tokamak (EAST), a vertically viewing and a tangentially viewing fast-ion D-alpha (FIDA) diagnostics have been installed in order to in- vestigate fast-ion dynamics [1, 2, 3]. This is done by measuring the Doppler-shifted D-alpha light arising due to charge exchange between a neutral beam and the fast ions. By combining measurements from both FIDA instruments, the fast-ion velocity distribution can be obtained by velocity-space tomography [4]. To explore the possibilities and limitations of velocity-space tomography in studying the fast-ion distribution in EAST, we present the reconstruction of the fast-ion velocity distribution from synthetic FIDA measurements using EAST MHD-quiescent conditions including both a counter- and a co-current neutral beam injectors with beam energies of 55 keV and 47 keV, respectively. Acknowledgements Work at the Institute of Plasma Physics, Chinese Academy of Sciences, was supported by the National Natural Science Foundation of China 11575249 , National Magnetic Confinement Fusion Energy Research Program of China under Contract Nos. 2015GB110005, and Hefei Science Center CAS (2017HSC-IU005). References [1] J. Huang et al., Rev. Sci. Instrum. 85, 11E407 (2014) [2] J. Huang et al., Rev. Sci. Instrum. 87, 11E542 (2016) [3] Y. Hou et al., Rev. Sci. Instrum. 87, 11E552 (2016) [4] M. Salewski et al., Nucl. Fusion 56, 106024 (2016)

Speaker: Birgitte Madsen

14:00 P1.1112 X-ray crystal spectrometers based on HPC detector technology

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.1112.pdf X-ray crystal spectrometers based on HPC detector technology N. Pilet1, T. Donath1, B. Lyu2, L.F. Delgado-Aparicio3, N. Pablant3 1 DECTRIS Ltd., Baden-Daettwil, Switzerland 2 Institute of Plasma Physics, Chinese Academy of Science ASIPP, Hefei, Anhui, China 3 Princeton Plasma Physics Laboratory, Princeton, NJ, USA Hybrid Photon Counting (HPC) detector technology has advanced almost all X-ray based analytical methods used in basic research and industrial processes in the last decade. Besides their use in X-ray diffraction and scattering, HPC detectors have enabled progresses in many other fields including X-ray crystal spectroscopy. X-ray crystal spectroscopy is an essential diagnostic for monitoring plasmas owing to its capability of detecting emission lines of impurities (Be, C, O, Fe, Ni, Cu, W) and dopant (Ar, Ne). Princeton Plasma Physics Laboratory has integrated HPC technology into X-ray Imaging Crystal Spectrometers (XICS) for routinely detecting line emission from highly charged elements including Ar16+, Ar17+, Fe 24+ and Mo32+ amongst a selection of other lines. Noise-free performance, energy discrimination, a sharp point spread function, a high frame rate, a high dynamic range, in-vacuum operation, a large detectable energy range (1.8-30 keV) and radiation hardness are underlying criteria for the superiority of PILATUS3, an HPC detector developed and manufactured by DECTRIS and successfully implemented in various plasma X-ray crystal spectrometers. Here we present an overview of the usage of PILATUS3 in plasma spectroscopy and highlight the PILATUS3 900K-IPP, an instrument specifically designed for the study of fusion plasma at the EAST tokamak. We will show that the fast readout time of PILATUS3 of only 0.95 ms and its high frame rate of 500 Hz can enable real-time plasma condition feedback. PILATUS3 900K-IPP in-vacuum detector for X-ray plasma spectroscopy

Speaker: Nicolas Pilet

14:00 P1.2001 Characterization the state of laser-produced Au plasmas by measuring the X-ray emission spectra of buried Ti trace

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2001.pdf Characterization the state of laser-produced Au plasmas by measuring the X-ray emission spectra of buried Ti trace Zhimin Hu1, Zhencen He1,2, Jiyan Zhang1, Jiamin Yang1 and Baohan Zhang1 1 Laser Fusion Research Center, CAEP, Mianyang, China 2 Institute of Atomic and Molecular Physics, Sichuan Universiy, Chengdu, China Au plasma states were characterized by measuring x-ray emission spectra from the the buried Ti layer gold planar target irradiated by nanosecond laser pulses on the Shenguang-III [1] laser facility . The time-resolved x-ray emission spectra of hot titanium plasmas were measured by a streaked crystal spectrometer. The measured data were reproduced by the [2] FLYCHK code , and the temperature and density of plasmas were deduced from the simulated spectra. In order to evaluate the feasibility of the method of the x-ray emission spectra of buried Ti trace layer, laser-produce Au plasmas were simulated with the multi-1D [3] hydrodynamic simulations. Due to the simulations do not take the radial gradients into account, some deviations between the experimental and simulation results have been found. In this talk, the details of the experiment and theoretical work will be presented. [1] W. Zheng et al,. High Power Laser Sci. Eng. 4, 1(2016). [2] H.-K. Chung, M. H. Chen, W. L. Morgan, Y. Ralchenko, and R. W. Lee, High Energy Density Phys.1, 3 (2005). [5] R . Ramis, Schmaltz R and Meyer-ter-Vehn J, Comput. Phys. Comm. 49, 475(1988).

Speaker: Zhimin Hu

14:00 P1.2002 Current outflow to low-density plasma region of z-pinch with pre-embedded axial magnetic field

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2002.pdf Current outflow to low-density plasma region of z-pinch with pre-embedded axial magnetic field M. Cvejić1 , D. Mikitchuk1 , R. Doron1 , E. Kroupp1 , C. Stollberg1 , A. L. Velikovich2 , J. L. Giuliani2 , E. P. Yu3 , A. Fruchtman4 , Y. Maron1 1 Weizmann Institute of Science, Rehovot 76100, Israel 2 Plasma Physics Division, Naval Research Laboratory, Washington, D.C. 20375, USA 3 Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-1186, USA 4 Holon Institute of Technology, P.O. Box 305, Holon 58102, Israel Magnetic flux can be compressed within a conducting shell when the shell collapses by the application of an external force. In z-pinch scheme, the conductor is plasma and it is imploded by the J × B force due to a large current passed through it, see Fig.1. Compression of magnetic flux and magnetized plasma is gaining interest due to the advances in producing plasmas of high temperature and density for fusion purposes e.g.[1]. In our experiment, we employ a cylindrical configuration, in which an initial axial quasi-static magnetic flux Bz0 (up to 0.4 T) is pre-embedded in an argon gas column. A high-power electric discharge (300 kA, rise time 1.6 µs) then ionizes the gas and generates an azimuthal magnetic field, creating a pressure that compresses the plasma inward together with the axial magnetic field embedded in it. Non-invasive spectroscopic measurements of the azimuthal magnetic field (Bθ ) evolution using recently developed spectroscopic method [2, 3] are presented. Systematic measurements, performed for different initial Bz0 , show that with increasing initial values of 1 Bz0 , less current is flowing through the imploding Ar plasma shell. For Bz0 = 0.4 T, only ∼ 4 of the current if flowing through the imploding argon plasma whereas most of the current flows at large radii, through a lower-density plasma. We conclude that even in the presence of a low axial magnetic field (relative to the peak azimuthal magnetic-field) this effect is significant. Re- markably, the low-density plasma does not implode under this considerable current, suggesting a formation of a force-free configuration. Bz References [1] M. R. Gomez, et. al., Phys. Rev. Lett., 113, 155003, Fr (2014) Jz Bθ [2] D. Mikitchuk, M. Cvejic, R. Doron, E. Kroupp, C. initial phase implosion phase stagnation phase Stollberg, A. L. Velikovich and J. L. Giuliani, A. time Fruchtman and Y. Maron, submitted to PRL; [3] G. Rosenzweig, E. Kroupp, A. Fisher, and Y. Maron, Figure 1: Principle of magnetic flux compression by z- JINST 12, P09004 (2017) pinch plasma

Speaker: Marko Cvejic

14:00 P1.2003 Ionization and structural dynamics in solid hydrogen and deuterium

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2003.pdf Ionization and structural dynamics in solid hydrogen and deuterium U. Zastrau1, S. Göde1, C. Rödel2, 3, 4, M. Nakatsutsumi1, T. Feigl5, K. Appel1, B. Chen6, T. Döppner7, T. Fennel8, T. Fiedler5, L. B. Fletcher3, E. Förster2, 4, E. Gamboa3, D. O. Gericke9, C. Grote-Fortmann1, V. Hilbert10, L. Kazak8, T. Laarmann11, H. J. Lee3, P. Mabey12, F. Martinez8, K.-H. Meiwes-Broer8, A. Przystawik13, S. Roling14, S. Skruszewicz2, 4, M. Shihab8, 15, J. Tiggesbäumer8, S. Toleikis13, M. Wünsche2, 4, H. Zacharias14, S. H. Glenzer3, and G. Gregori12 1 European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany 2 Institute of Optics and Quantum Electronics, Friedrich-Schiller University Jena, Germany 3 Stanford Linear Accelerator Center (SLAC), Menlo Park, CA 94025, USA 4 Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany 5 optiX fab GmbH, Hans-Knöll-Strasse 6, 07745 Jena 6 China Academy of Engineering Physics (CAEP), Mianyang, China 7 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 8 Institut für Physik, Universität Rostock, 18051 Rostock, Germany 9 Centre for Fusion, Space and Astrophysics, University of Warwick, UK 10 Institute of Applied Physics, Friedrich-Schiller University Jena, 07745 Jena, Germany 11 The Hamburg Centre for Ultrafast Imaging CUI, Hamburg, Germany 12 Department of Physics, Clarendon Laboratory, University of Oxford, United Kingdom 13 Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany 14 Physikalisches Institut, Westfälische Wilhelms-Universität, 48149 Münster, Germany 15 Department of Physics, Faculty of Science, Tanta University, Egypt The thermodynamic properties of even the simplest element hydrogen remain elusive when it comes to extreme conditions. Knowledge of the equation of state of hydrogen and its isotope deuterium is hence critical for modeling stellar and planetary interiors, as well as for ICF experiments. Microscopic properties related to reflectivity, electrical and thermal conductivity are tied to dynamic energy transport between electrons and ions. In 2014, we reported on time-resolved XUV measurements [1] where ultra-fast electron heating is initiated by a 1013 W/cm² intense 300 fs short burst from the FLASH XUV-FEL at 13.5 nm wavelength. A second pulse probes the sample via XUV scattering at variable time delay. From the ion-ion structure factor S(k∼0), we found that the molecular ice dissociates in 0.9 ps, transitioning into a dense atomic plasma with a final ion temperature ≤ 1 eV at 0.08 g/cm3, which poses several challenges to the employed plasma models and equation-of-state tables. New unpublished data obtained in 2015 with 60 fs temporal resolution employed a Schwarzschild EUV microscope [2] capable of single-shot sub-µm imaging. We monitored the hydrogen jet’s structure by single-shot Mie scattering patterns. The time-resolved scattering suggests that 500 fs after XUV pump photo- and impact ionization have reached a maximum and subsequently the solid-plasma transition takes place due to electron-ion heat transfer, and is finished around 700 fs after excitation. First microscopic particle-in-cell simulations support this interpretation. We also present an outlook about repeating the experiment on deuterium, where the electronic excitation is comparable to hydrogen while the electron-ion energy transfer is slower due to the heavier deuteron mass. [1] U. Zastrau, P. Sperling, et al., Physical Review Letters 112, 105002 (2014). [2] U. Zastrau, C. Rödel, et al., Review of Scientific Instruments 89, 023703 (2018).

Speaker: Ulf Zastrau

14:00 P1.2004 Quantitative X-ray Phase Contrast Imaging of a laser driven shock wave

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2004.pdf Quantitative X­ray Phase Contrast Imaging of a laser driven shock wave F.Barbato1, S. Atzeni2, D. Batani3, D. Bleiner1, G. Boutoux3, C. Brabetz4, P. Bradford7, D. Mancelli3,5, P. Neumayer4, J. Trela3, L. Volpe6,8, G. Zeraouli6, N. Woolsey7, and L.Antonelli7 1 Empa Materials Science and Technology, Dübendorf, Switzerland 2 Dipartimento SBAI, Università di Roma “La Sapienza”, Rome, Italy 3 Universitè de Bordeaux, CNRS, CEA, CELIA, Talence, France 4 GSI, Darmstadt, Germany 5 University of the Basque Country, Donostia International Physics Center, Spain 6 Centro de Laseres Pulsados (CLPU), Salamanca, Spain 8 University of Salamanca, Salamanca, Spain 7 York Plasma Institute University of York, York, United Kigngdom X­ray Phase Contrast Imaging (XPCI) [1] is a technique based on the photon phase­shift caused by an intense density gradient. It is therefore particularly indicated to probe materials which present density interphases such as a biological sample. However, this technique could also present several advantages compared to standard absorption radiography in the study of high energy density (HED) physics and warm dense matter (WDM). In particular, laser­induced shock­waves present high density gradients (in particular on the shock front) and they can propagate in materials at very different densities (e.g. multi­layer targets). To prove this, we performed an experiment at GSI using the laser PHELiX. In particular we used a ns laser pulse to lunch a shock­wave in a plastic cylinder and a sub ps laser pulse to generate a short X­ray back­lighter. The X­ray source was limited in space by the dimension of the target (5 μm diameter tungsten wire) to guarantee lateral coherence. From each experimental image, the amplitude and the phase map were extracted allowing a direct comparison with a hydrodynamic simulation, demonstrating the validity of such approach in HED and WDM physics. This work benefited from the support of COST Action MP1208, the Eurofusion Project AWP17­ENR­IFECEA­01 and by LASERLAB­EUROPE (grant agreement no. 654148) 1. S. W. Wilkins et al. , Nature 384, 335–338 (1996). 2. Paganin, David, et al., Journal of microscopy 206.1 (2002): 33­40.h

Speaker: Francesco Barbato

14:00 P1.2005 Accelerator Based Fusion Reactor

See the ful Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2005.pdf Accelerator Based Fusion Reactor Keh-Fei Liu1 and Alex W. Chao2 1 University of Kentucky, Lexington, Kentucky, USA 2 SLAC, Menlo Park, California, USA A feasibility study of fusion reactors based on accelerators is carried out. We consider a novel scheme where the beam from the accelerator hits the target plasma on the resonance of the fusion reaction to increase reactivity and establish characteristic criteria for a workable reactor. The critical temperature of the plasma is determined from the stopping power. The needed plasma lifetime is determined from the width of the resonance, the beam velocity and the plasma density. We estimate the critical beam flux by balancing the energy of fusion production against the plasma thermo-energy and the loss due to stopping power. While the critical temperatures based on the d + t, d + He3 and p + B11 reactions turn out to be several times lower than the corresponding ones for the thermonuclear reactors and the triple product of plasma density, temperature and lifetime is about 50 times smaller than the Lawson criterion, the critical flux in the range of 1021 - 1023/cm^2/s for the plasma density ρ = 1014/cm^3$ can be a challenge. The above study is published*. We will present a follow up study on the conceptual designs of such reactors. *Reference K. F. Liu and A. W. Chao, ``Accelerator Based Fusion Reactor,'' Nuclear Fusion 57, 084002 (2017), doi:10.1088/1741-4326/aa7642, [arXiv:1707.03043]

Speaker: Keh-Fei Liu Liu

14:00 P1.2006 XFEL observation of shock-compressed highly oriented graphite

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2006.pdf XFEL observation of shock-compressed highly oriented graphite Norimasa Ozaki1,2 , Kento Katagiri1 , Ryo Hazama1 , Takahiro Matsuoka3 , Takeshi Matsuoka4 , Kohei Miyanishi2 , Yuhei Umeda1 , Yusuke Seto5 , Yuichi Inubushi6 , Toshinori Yabuuchi6 , Tadashi Togashi6 , Makina Yabashi7 , and Ryosuke Kodama1,2 1 Graduate School of Engineering, Osaka University, Suita, Japan 2 Institute of Laser Engineering, Osaka University, Suita, Japan 3 Graduate School of Engineering, Gifu University, Gifu, Japan 4 Open and Transdisciplinary Research Initiative, Osaka Univeristy, Suita, Japan 5 Graduate School of Science, Kobe University, Kobe, Japan 6 JASRI/SPring-8, Sayo, Japan 7 RIKEN SPring-8 Center, Sayo, Japan High power laser-driven shock is widely used to investigate the states and behaviors of ma- terial in extreme conditions associated with warm dense matter (WDM) physics, planetary sci- ences, and inertial fusion energy research[1]. At the high pressure and extremely high strain rate conditions, it is known that mechanical properties and behaviors of material can change significantly more than expected. Such properties change is influenced by the micro-structure of material. We here present experimental results on X-ray free electron laser (XFEL) observa- tions of shock-compressed highly oriented materials at the SACLA-HEDS platform [2, 3, 4]. We shock compressed highly oriented pyrolytic graphite (HOPG) samples along the [002] ori- entation using a 3-4 ns optical laser pulse and observed the lattices under the shock compression using the XFEL pulse with changing the time delay between the optical and X-ray pulses. Once the HOPG interlayers were compressed uniaxially up to ∼20% or more, and then a high pressure form of carbon was created on picosecond time scale above ∼20 GPa pressures. This sequence might be different from reported very recently [5, 6]. This work was supported by a Grant-in-Aid for Scientific Research, KAKENHI (Grant No. 15K13609 and 16H02246), the Genesis Research Institute, Inc. (Konpon-ken, TOYOTA), and XFEL Priority Strategy Program at Osaka Univ. from the MEXT. References [1] N. Ozaki, W. J. Nellis, T. Mashimo et al., Sci. Rep. 6, 26000 (2016). [2] T. Pikuz, A. Faenov, T. Matsuoka et al., Sci. Rep. 5, 17713 (2015). [3] N. J. Hartley, N. Ozaki, T. Matsuoka et al., Appl. Phys. Lett. 110, 071905 (2017). [4] B. Albertazzi, N. Ozaki, V. Zhakhovsky et al., Sci. Adv. 3, e1602705 (2017). [5] D. Kraus, A. Ravasio, M. Gauthier et al., Nat. Comm. 3, e1602705 (2017). [6] S. J. Turneaure, S. M. Sharma, T. J. Volz et al., Sci. Adv. 3, eaao3561 (2017).

Speaker: Norimasa Ozaki

14:00 P1.2007 The progress of indirect-drive implosion experiments on ShenGuang-III Proto-Type facility in china

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2007.pdf The progress of indirect-drive implosion experiments On ShenGuang-III Proto-Type facility in china Ji Yan1, Tian Xuan Huang1, Dong Guo Kang2, Feng Jun Ge2 1 Laser Fusion Research Center, Chinese Academy of Engineering Physics, Mianyang, China 2 Institute of Applied Physics and Computational Mathematics, Beijing,, China A series experiments on SG-III Proto-type facility (8beams/8kJ/351nm) were performed to study low to middle compression ratio implosion physics from 2007-2015. Meanwhile, some experimental technique were improved for high accuracy implosion experiment study such as Spherical-Bent-Crystal Radiography and KB radiography. Firstly, the low compression ratio (CR~5) DD implosion experiments were preformed to study the shock yield only implosion and examine the 1D hydrodynamic code (RDMG). The experimental results proposed highly repetitive neutron yield. The two type capsules with different scale-length produce 9.9x107(±9.7%) and 3.1x107(±6.5%) neutrons respectively. Based on RDMG simulations, the ion-flux-limit-factor (IF) from 0.05 to 1 will influence the neutron yield for shock yield process few times and had a little influence on inertial yield process. In our shock yield only experiments, the YOC1D will reached at 80%~105% with the IF equal to 1. Meanwhile, the NIF shock yield shots (Pape S.L, Phys.Rev.Lett 112, 225002(2014)) make 85% YOC1D using RDMG code with IF equal to 1. Secondly, the low-middle compression ratio (CR~10) DT implosion experiments with different ablator thickness, different gas fill and 220eV Radiation temperature were performed. For thin shell implosion, nearly all neutrons comes from shock yield, 3 x109 DT neutrons were collected and YOC1D is nearly 70%.on the other hand, for thick shell implosion, the inertial yield accounts for the main in 1D simulation, 8 x108 DT neutron were collected and YOC1D is less than 10% because of non-1D factor decreased implosion performance. At last, two advanced diagnostic technique were developed for high accuracy implosion experiments. The SBC Radiography was used for implosion stream line measurement. The uncertainty of implosion velocity was around 9% and better than traditional slit radiography which with the uncertainty of 15%; The KB radiography was used for hot-spot self-emission because of high-spatial resolution (~3μm). The uncertainty of hot-spot shape was around ±2μm and better than traditional pinhole-array radiography which with the uncertainty of around ±5μm.

Speaker: Ji Yan

14:00 P1.2008 Molecular dynamics simulations of Stark-broadened line shapes of Ar K-shell ions for plasma diagnostics applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2008.pdf Molecular dynamics simulations of Stark-broadened line shapes of Ar K-shell ions for plasma diagnostics applications M. A. Gigosos1 , R. Florido2 , R. C. Mancini3 , J. M. Martín-González2 1 Departamento de Física Teórica, Atómica y Óptica, Univ. de Valladolid, Valladolid, Spain 2 iUNAT - Departamento de Física, Universidad de Las Palmas de Gran Canaria, Spain 3 Department of Physics, University of Nevada, Reno, USA Analysis of Stark-broadened spectral line profiles is one of the most often used plasma di- agnostics techniques, especially to determine the electron density in both laboratory and astro- physical plasmas. The increasing number of applications and the wider availability of spectro- scopic measurements under extreme conditions have encouraged studies comparing different computational and analytical methods [1]. In this work we perform numerical simulations to compute Stark-broadened line shapes of several K-shell X-ray line transitions in highly charged Ar ions, i.e. Heα, Heβ and Heγ in He-like Ar and Lyα, Lyβ and Lyγ in H-like Ar, which have been extensively used for spectroscopic diagnosis of implosion cores in indirect- and direct- drive inertial confinement fusion (ICF) experiments [2]. Two different simulations are done: a) within the independent particle approximation using a Debye screened field to account for coupling effects between charges [3] and b) using a molecular dynamics code of interacting particles [4]. Specifically, an effort has been made to include full Stark-mixing of energy levels belonging to manifolds with different principal quantum numbers. Comparisons are made with line shapes calculated in the standard Stark-broadening theory approximation [5, 6]. Observed differences are discussed. Furthermore, we will assess the impact of employing line profiles computed with different methods on the diagnosis of core conditions in implosion experiments performed at OMEGA. Acknowledgements This work is supported by Research Grant No. ENE2015-67561-R from Spanish Ministry of Economy and Competitiveness and EUROfusion Project No. AWP17-ENR-IFE-CEA-02. References [1] E. Stambulchik et al., Atoms 2, 378 (2017). [2] R. C. Mancini et al., High Energy Density Phys. 9, 731 (2013), and references therein. [3] M. A. Gigosos et al., Astron. Astrophys. 561, A135 (2014), and references therein. [4] D. González-Herrero, Ph.D. Thesis, Universidad de Valladolid, Spain (2016). [5] L. A. Woltz and C. F. Hooper, Jr., Phys. Rev. A 38, 4766 (1988). [6] R. C. Mancini et al., Comput. Phys. Commun. 63, 314 (1991).

Speaker: M. A. Gigosos

14:00 P1.2009 multi-ion molecular dynamics and ion features of x-ray scattering in the warm dense matter regime

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2009.pdf multi-ion molecular dynamics and ion features of x-ray scattering in the warm dense matter regime Yong Hou1, Yongsheng Fu1, Cheng Gao1, Jiaolong Zeng1, Jianmin Yuan1,2 1 Department of Physics, National University of Defense Technology, Changsha Hunan 410073, P. R. China 2 Graduate school of China Academy of engineering Physics, Beijing 100193, P. R. China We perform multi-ion molecular dynamics (MIMD) simulation and apply to calculate the ionic structures and x-ray elastic scattering of different charge-state ions in the warm dense matter regime. Firstly, the method is self-consistently used to calculate electron structures of different charge-state ions in the ionic sphere, in which the ion-sphere radii are determined by the plasma density and their charges. And then the ionic fraction is obtained by solving the Saha equation, taking account of interactions among different charge-state ions in the system, and ion-ion pair potentials are computed by the modified Gordon-Kim method in the framework of the temperature-dependent density functional theory on the basis of the electron structures. Lastly, we perform the MIMD simulation to calculate ion features of x-ray elastic scattering for Al. 1. Yongsheng Fu, Yong Hou, Dongdong Kang, Cheng Gao, Fengtiao Jin, and Jianmin Yuan, Phys, Plasmas, 25, 012701 (2018). 2. K.Wunsch, J. Vorberger, G. Gregori, and D. O. Geriche, EPL, 94, 25001 (2011). yonghou@nudt.edu.cn, jmyuan@nudt.edu.cn

Speaker: Yong Hou

14:00 P1.2010 Plasma Physics Platform at ELI-Beamlines

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2010.pdf Plasma Physics Platform at ELI-Beamlines T. Laštovička1 (on behalf of the ELI Beamlines team) 1 Institute of Physics of the ASCR, ELI-Beamlines project, Prague, Czech Republic The plasma physics platform (P3) at the ELI Beamlines[1] facility in Prague, Czech Republic is planned to be a versatile user facility for high energy density, warm dense matter, labora- tory astrophysics and ultraintense laser-matter interaction experiments. The aluminum vacuum chamber with a volume of about 50 m3 was recently commissioned to a vacuum of less than 10−6 mbar. The chamber is designed to accommodate a large aperture (63 cm x 63 cm) 10 PW beam and multiple medium aperture PW level beams. Beam transport system for delivering the L3 laser beam (Ti:Sa, 10 Hz, 1 PW) is expected to be commissioned by the end of this year. This presentation will cover the details of commissioning the vacuum chamber. References [1] S. Weber et al, Matter and Radiation at Extremes, 2, pp 149-176 (2017).

Speaker: Tomas Lastovicka

14:00 P1.2011 Radiography of gas-gun impact experiments using an X-pinch

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2011.pdf Radiography of gas-gun impact experiments using an X-pinch P.S. Foster1, G. C. Burdiak1, H. Doyle1, S.N. Bland2, T. Ringrose1, J.W. Skidmore1, N. Hawker1 1 First Light Fusion Ltd, Yarnton, Oxfordshire, OX5 1QU 2 Institute of Shock Physics, Imperial College London, London, SW7 2AZ, UK A broadband point-projection x-ray backlighter has been commissioned at First Light Fusion Ltd for radiographing impact experiments driven by a two-stage light gas gun. X-ray energies of 10 - 20 keV are produced by a miniature electron beam diode which forms during the explosion of a tungsten X-pinch. The X-pinch source emits a 20 ns x-ray pulse from a 200 - 300 um diameter spot, and the imaging setup achieves a spatial resolution of 50 - 100 um at a magnification of 2.3, over a 29 mm field of view. The X-pinch load is made from 4 x 7.5 um tungsten wires, which are driven by the 70 kA, 70 ns rise-time current pulse from a high impedance pulsed-power machine. A 4 Ohm water-filled pulse-forming line drives a high inductance magnetically insulated transmission line, which delivers the current to the X-pinch load within the gas-gun experimental chamber. The backlighter is used to image density structures within cm-scale plastic targets during impact with a 6 km/s projectile. Here, we present radiographs from preliminary experiments together with details of the experimental setup and characterisation of the x-ray source. We demonstrate the ability of the diagnostic to image forward and reverse shocks, release waves, projectile deformation and jet density profiles.

Speaker: Peta Suzanne Foster

14:00 P1.2012 Simulation Studies of the Interaction of Laser Radiation with Additively Manufactured Foams

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2012.pdf Simulation Studies of the Interaction of Laser Radiation with Additively Manufactured Foams* J.L. Milovich1, O. S. Jones1, S. Wilks1, B. Winjum2, S. Langer1, L. Zepeda-Ruiz1, J. Biener1 and M. Stadermann1 1 Lawrence Livermore National Laboratory, Livermore CA 94551 2 University of California, Los Angeles CA 90095 In indirect drive inertial confinement fusion, a high-Z enclosure (or “hohlraum”) surrounds a low- Z capsule containing DT fuel. Laser beams irradiate the interior of the hohlraum, which creates an x-ray radiation bath compressing the fuel to ignition conditions. The irradiated hohlraum wall motion leads to dynamic drive symmetry swings that degrade the implosion. To mitigate this wall motion, hohlraums are typically filled with helium gas. A side effect is that for moderately high fill densities (> 0.6 mg/cc) experiments have shown a substantial amount of backscattered light, while for low densities the wall motion increases. Modern hohlraum designs are beginning to use foams in two ways. First, high-Z metallic foams may be effective in reducing wall motion without compromising capsule drive. Second, low-density mid-Z foams can be used as a substitute for higher density gas fills with the added advantage of possibly using embedded dopants to potentially mitigate backscatter losses. The interaction of laser radiation with foams of various porosity sizes and average densities has been the subject of several numerical and experimental studies [1]. In all cases, modelling foams using standard radiation-hydrodynamics codes have shown considerably disagreement with experimental measurements. These discrepancies have been attributed in large part to the inability of rad-hydro codes to faithfully represent the statistical nature of foams (solid ligaments of full density material and large vacuum pore sizes ~ 1-10 µm), typically modelled as a uniform gas of equivalent density. This deficiency may benefit from modern computer architectures (many processors) and newly developed equation of state models. In this work we use the rad-hydro code HYDRA and a simple foam statistical representation to show that this configuration goes a long way to bridge the modelling disparities. Further ease on modelling requirements can be leveraged from the use of structured foams. Recent developments in additive manufacturing (AM) allow for the fabrication of structured foams of specified average density. Currently, strands with ~ 500 nm diameter and pore sizes as small as several microns can be laid down in a structured pattern, but the technology is quickly evolving. We use HYDRA to survey a variety of AM foam configurations to find an optimal design for hohlraum experiments. [1] S.Y. Gus’kov et al., Quantum Electron., 24 696 (1997); S.Y. Gus’kov et al., Phys. of Plasmas 18, 103114 (2011); Ph. Nicolai et al., Phys. of Plasmas 19, 113105 (2012). * Work performed under the auspices of U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344 and supported by LDRD-17-ERD-118

Speaker: Jose Luis Milovich

14:00 P1.2013 Spectroscopic modeling of Ti K-alpha emission from planar targets irradiated at laser intensities relevant for shock-ignition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2013.pdf Spectroscopic modeling of Ti K-α emission from planar targets irradiated at laser intensities relevant for shock-ignition R. Florido1 , J. M. Martín-González1 , M. A. Gigosos2 , G. Cristoforetti3 , L. Antonelli4 , F. Baffigi3 , F. Barbato5 , D. Batani6 , L. A. Gizzi3 , Ph. Nicolai6 , O. Renner7,8 , V. Tikhonchuk6 1 iUNAT - Departamento de Física, Universidad de Las Palmas de Gran Canaria, Spain 2 Departamento de Física Teórica, Atómica y Óptica, Univ. de Valladolid, Valladolid, Spain 3 Intense Laser Irradiation Laboratory, INO-CNR, Pisa, Italy 4 Department of Physics, University of York, York, United Kingdom 5 Empa Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland 6 Centre Lasers Intenses et Applications, Université de Bordeaux-CNRS-CEA, Talence, France 7 Institute of Physics & ELI-Beamlines, Czech Academy of Sciences, Prague, Czech Republic 8 Institute of Plasma Physics & PALS Facility, Prague, Czech Republic Shock-ignition (SI) is a promising ICF scheme relying on the assembly of a deuterium-tritium mixture, and its ignition by a strong shock launched just before the end of the compression stage. One of SI major issues is the interaction of the laser pulse with a long-scale-length plasma formed by the CH ablator, and the impact of genereated hot electrons on shock formation and propagation in the compressed shell. In planar-geometry experiments performed at the Prague Asterix Laser System facility at SI-relevant laser intensities –i.e. I ∼ 1 − 3 × 1016 W/cm2 –, char- acterization of hot electrons production and its connection with the development of parametric instabilities is being investigated by application of X-ray spectroscopy [1, 2]. Here, we focus on the collisional-radiative [3] study of Ti layer located at the rear side of irradiated plastic targets and spectroscopic modeling of K-α emission produced after inner-shell ionization caused by hot electrons. Sensitivity of spectral features to total amount and energy of hot electrons is as- sessed. Also, for interpretation of observed spectra, we discuss synthetic spectra obtained from post-processing of hydrodynamics simulations of reported experiments. Acknowledgements This work is supported by Research Grant No. ENE2015-67561-R from Spanish Ministry of Economy and Competitiveness and EUROfusion Project No. AWP17-ENR-IFE-CEA-01. References [1] O. Renner et al., 10th IFSA International Conference, St. Malo (France), September 11-15 (2017). [2] G. Cristoforetti et al., Phys. Plasmas 25, 012702 (2018). [3] R. Florido et al., Phys. Rev. E 80, 056402 (2009).

Speaker: Ricardo Florido

14:00 P1.2015 Nonlinear ablative Rayleigh-Taylor instability

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2015.pdf Nonlinear ablative Rayleigh-Taylor instability L. F. Wang1, J. Q. Dong2, J. F. Wu1, W. H. Ye1, Y. K. Ding1, W. Y. Zhang1, and X. T. He1 1 Institute of Applied Physics and Computational Mathematics, Beijing 100094, China 2 Shanghai Institute of Laser Plasma, Shanghai 201800, China In ICF implosions, the final fuel assembly must consist of a low-density (tens of g/cm3), high-temperature (several keV's) DT plasma core surrounded by a high-density (hundreds of g/cm3), low-temperature (hundreds of eV's) shell to maximize the number of fusion reactions that can occur while the fuel is inertially confined. During the acceleration regime, the outer shell surface is unstable to the Rayleigh-Taylor instability (RTI), where the "bubbles" of outer light ablator plasma rise through the dense cold shell. When the compressed DT fuel begins to decelerate the imploding pusher, the inner shell surface is susceptible to the RTI, where again the bubbles of inner light DT plasma rise through the dense shell. In this report, the nonlinear evolution of the single-mode ablative Rayleigh-Taylor instability (ARTI) of an accelerated planar target is investigated in the parameter range of interest to inertial-confinement fusion implosions. Analysis method of the bubble and spike amplitude growth in nonlinear ARTI experiments was established. The bubble acceleration and target breakup in direct-drive ARTI experiments were observed for the first time using a Kirkpatrick-Baez microscope x-ray framing camera coupled with a side-on x-ray backlighting on the Shenguang-II laser facility. The analysis suggests that the bubble acceleration that is driven by the accumulation of vorticity inside the bubble transferred by the mass ablation from the spikes, contributes to the breakup of the accelerated target. Figure 1: Comparison of nonlinear evolution of the single-mode ARTI from the experiment and the simulation References [1] L. F. Wang, et al., Sci. China-Phys. Mech. Astron. 60, 055201 (2017) [2] R. Betti and J. Sanz, Phys. Rev. Lett. 97, 205002 (2006) [3] L. F. Wang, W. H. Ye, X. T. He, et al., Phys. Plasmas 19, 100701 (2012) [4] W. H. Ye, L. F. Wang, and X. T. He, et al., Phys. Plasma 17, 122704 (2010) [5] R. Yan, R. Betti, et al., Phys. Plasma 23, 022701 (2016)

Speaker: Li-Feng Wang

14:00 P1.2016 Effect of Fermi pressure and Bohm potential on Langmuir decay instability in strongly coupled degenerate plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2016.pdf Effect of Fermi pressure and Bohm potential on Langmuir decay instability in strongly coupled degenerate plasma Prerana Sharma and K. Avinash Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India Langmuir decay instability (LDI) in strongly coupled degenerate plasma is examined. In this study, the electrons are degenerate and weakly correlated, while non-degenerate ions are strongly correlated. The dynamics of weakly coupled degenerate electron fluid is governed by quantum hydrodynamics. The quantum forces associated with the quantum diffraction effects and the quantum statistical effects act on the degenerate electron fluid. The strong correlation effects of ion are embedded in generalized viscoelastic momentum equation including the viscoelasticity and shear viscosities of ion fluid. It is shown that strong correlation/coupling effects enhance the growth rate of instabilities, while the quantum effects suppress the instabilities. The results are analyzed for understanding LDI in dense white dwarfs which consist of degenerate electrons and strongly coupled ions. Keywords- Strongly coupled plasma, astrophysical plasmas, parametric instabilities and quantum plasma. References [1] P K Kaw and A Sen ,Phys. Plasmas, 5, 3552 (1998). [2] P Sharma, K Avinash and D N Gupta, Phys. Plasmas , 23 , 102704 (2016). [3] F Haas, Braz. J. Phys., 41, pp 349-363 (2011). [4] S Ghosh , N Chakarabarty and P K Shukla , Phys. Plasmas, 19, 072123 (2012).

Speaker: Prerana Sharma

14:00 P1.2018 Investigation of supersonic heat-conductivity linear waves in ablation flows

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2018.pdf Investigation of supersonic heat-conductivity linear waves in ablation flows G. Varillon1,2 , J.M. Clarisse1 , A. Couairon2 1 CEA, DAM, DIF, F-91297, Arpajon, France 2 CPHT, Ecole polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France Ablation flows relative to inertial confinement fusion (ICF) are well described by gas dynam- ics equations with non-linear radiative heat-conduction. Standard descriptions often assume an isothermal conduction region [1, 2]. However a local analysis in terms of linear propagating waves reveals that temperature stratification in this region gives rise to supersonic wave veloc- ity as a consequence of nonlinear heat-conduction [3]. Such behaviours arise in the case of high heat propagation regimes. These supersonic ‘heat-conductivity’ waves are associated with heat flux perturbation inhomogeneities that convey perturbation inhomogeneities in temperature and density. These latters may trigger radiative heat transport instabilities [4] and destabilize the ablation front. In the present work, we conduct numerical computations of linear perturbations in ablation flows. We drop the local hypothesis to address non-uniform and non-stationary realistic ablation flows. The entire deflagration region is modeled, and damping effects due to heat diffusion are exactly taken into account by contrast to [3]. This corresponds to the ealry stage of an ICF target implosion.. We focus on self-similar ablation flows presenting a large Mach number in the conduction zone, and possibly containing a Chapman–Jouguet point [5]. Numerical results are compared to those of the local analysis [3]. References [1] S. Atzeni and J. Meyer-ter-Vehn, Oxford University Press (2004) [2] Y. Saillard, P. Arnault, V. Silvert, Phys. Plasma 17, 123302 (2010) [3] J.M Clarisse, 44th EPS Conf. Plasma Physics (2017) [4] V. Yu. Bychenkov and W. Rozmus, Phys. Plasma 22, 082705 (2015) [5] J. M. Clarisse, J. L. Pfister, S. Gauthier, C. Boudesocque-Dubois, J. Fluid Mech. (submitted)

Speaker: Grégoire Varillon

14:00 P1.2019 Simulations of the laser-target interaction under the non-local energy transport conditions with high-order numerical methods

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2019.pdf Simulations of the laser–target interaction under the non-local energy transport conditions with high-order numerical methods Jan Nikl1,2 , M. Kuchařík2 , M. Holec3 , and S. Weber1 1 ELI-Beamlines, Institute of Physics, Academy of Sciences of the Czech Republic, 18221 Prague, Czech Republic 2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, 11519 Prague, Czech Republic 3 Centre Lasers Intenses et Applications, Université de Bordeaux-CNRS-CEA, UMR 5107, F-33405 Talence, France The laser–target interaction for intensities . 1015 W/cm2 takes place under the non-local en- ergy transport conditions in many cases [1]. The mean free paths of the transported species are longer than the characteristic lengths in the plasma given by the temperature gradients. Clas- sical hydrodynamic codes do not cover this important phenomenon or only low order numeri- cal methods are used for the macroscopic description, having insufficient numerical accuracy. These conditions of the interaction have crucial relevance for the PW class laser systems, where such intensities are reached by the main pulse in the context of ICF [2] or they appear in the prepulses of the ultra-high intensity pulses [3]. A combination of high-order numerical meth- ods, including fully non-local description of the heat and radiation transport, is used here to treat properly these conditions. The simulations under typical physical scenarios for the laser facilities are performed and important effects are emphasized. References [1] A. V. Brantov and V. Yu. Bychenkov. Nonlocal transport in hot plasma. Part I. Plasma Physics Reports, 39(9):698–744, 2013. [2] D. Batani, L. Antonelli, G. Folpini, Y. Maheut, L. Giuffrida, G. Malka, Ph. Nicolai, X. Ribeyre, M. Richetta, T. Levato, F. Baffigi, P. Koester, L. Labate, L.A. Gizzi, J. Nejdl, M. Sawicka, D. Margarone, A. Velyhan, M. Krus, O. Renner, M. Smid, E. Krousky, J. Skala, J. Ullschmied R. Dudzak, Ch. Spindloe, T. O’Dell, R.de Angelis, F. Consoliand T. Vinci, M. Rosinski, J. Badziak an T. Pisarczyk, Z. Kalinowska, T. Chodukowski, Y.J. Rhee, A. Marocchino, A. Schiavi, and S. Atzeni. Generation of high pressure shocks relevant to the shock-ignition intensity regime. Phys. Plasmas, 21:032710, 2014. [3] T. Zh. Esirkepov, J. Koga, A. Sunahara, T. Morita, M. Nishikino, K. Kageyama, H. Nagatomo, K. Nishi- hara, A. Sagisaka, H. Kotaki, T. Nakamura, Y. Fukuda, H. Okada, A. S. Pirozhkov, A. Yogo, M. Nishiuchi, H. Kiriyama, K. Kondo, M. Kando, and S. V. Bulanov. Prepulse and amplified spontaneous emission effects on the interaction of a petawatt class laser with thin solid targets. Nucl. Instrum. Meth., 745:150, 2014.

Speaker: Jan Nikl

14:00 P1.2020 The role of laser-produced hot electron on ultrahigh pressure generation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2020.pdf The role of laser-produced hot electron on ultrahigh pressure generation K. Shigemori1, Y. Fukuyama1, T. Kawashima1, H. Kato1, N. Fujiwara1, Y. Hironaka1, S. Lee1, T. Ueda1, H. Nagatomo1, H. Nishimura1, S. Fujioka1, K. Miyanishi1, N. Ozaki2, Y. Fujimoto2, H. Matsumura2, T. Nishikawa2, R. Hazama2, R. Ochante2, R. Kodama1,2, T. Matsuoka3, D. Batani4, J. Trela4, and P. Nicolai4 1 Institute of Laser Engineering, Osaka University, Japan 2 Graduate School of Engineering, Osaka University, Japan 3 Open and Transdisciplinary Research Initiatives, Osaka University, Japan 4 Centre Lasers Intenses et Applications, France We performed an experiment on ultrahigh pressure generation with hot electrons produced by high-intensity laser plasma interactions. Hot electrons with small temporal duration might be ultra-high pressure source by absorption of matter within very thin layer that is comparable to mean free path of hot electrons [1]. The ultrahigh-pressure generation exceeding GBar regime is very important for shock ignition scheme of ICF targets, as well as fundamental ultrahigh-pressure experiments. Experiments were done on GEKKO-HIPER laser irradiation facility at ILE, Osaka University. We irradiated three-layered foils (CH-Cu-Quartz) in order to generate the ultrahigh pressure with hot electrons, and observe shock wave into the third quartz layer. The pulse duration and the intensity were 300 ps and 1015 – 1016 W/cm2, respectively (2 or 3 light). For some data shots, we applied pre-pulse for enhancement of effects by hot electron generation and pre-compression. We estimated laser intensity on the target with a static x-ray pinhole camera. The absorption area by hot electrons was measured by a Cu-Kimager. The shock wave parameters were taken by VISAR and streaked optical pyrometer (SOP). .

Speaker: Keisuke Shigemori

14:00 P1.2021 Progress of Laser direct-drive implosions on the SGⅢ prototype facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2021.pdf Progress of Laser direct-drive implosions on the SGⅢ prototype facility J.Q. Dong 1, E.F. Guo1, Z.H. Fang1, J.W. Li 2, D.X. Liu3, M.X. Wei3, Q. Tang3, S.Z. Yi4 1 Shanghai Institute of Laser Plasma, Shanghai, P.R. China 2 Institute of Applied Physics and Computational Mathematics, Beijing, P.R. China 3 Laser Fusion Research Centre, Miangyang, P.R. China 4 Tongji University, Shanghai, P.R. China Gas-filled capsules are directly imploded by laser energies of 6.5 kJ with 8 laser beams at SG Ⅲ prototype laser facility. Nine different types of diagnostic instruments are used in the experiments, providing an understanding of the relevant target physics. The in-flight dynamics of imploding capsules is measured by streaked x-ray radiography. And a new developed 16-framed K-B x-ray framing camera is used to acquire 2D blow-off emission images of the in-flight shell and asymmetric shapes of hot spots. The measured D-D neutron yield of the gas-filled capsule is 1×108 at best shots, and decreases with the asymmetry of in-flight shell, which is meanly decided by the laser spot distribution at the capsule surface.

Speaker: Jiaqin Dong

14:00 P1.2022 Two-plasmon-decay mitigation using laser-frequency detuning

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2022.pdf Two-plasmon–decay mitigation using laser-frequency detuning R. K. Follett Laboratory for Laser Energetics, University of Rochester Three-dimensional laser–plasma interaction simulations show that laser-frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon–decay (TPD) instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, 3-D LPSE (laser-plasma simulation environment) simulations show that 0.7% laser-frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current OMEGA implosions. This allows for higher ablation pressures in future implosion designs by using higher laser intensities. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.

Speaker: Russell K. Follett

14:00 P1.2023 A laser-driven kiloTesla magnetic bottle for plasma confinement

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2023.pdf A laser-driven kiloTesla magnetic bottle for plasma confinement F. Schillaci1, M. De Marco1, L. Giuffrida1, D. Margarone1, G. Korn1 1 FZU, ELI-Bealines Project, Prague, Czech Republic The possibility to trigger the proton-boron nuclear fusion reaction (p + 11B → 8.5 MeV + 3a) by using a nsec class laser has been recently demonstrated. This is of high interest since such reaction does not produce any neutrons but just three alpha-particles, which could be used for applications in different fields. The possibility to confine the plasma fuel generated during laser-target interaction through an ultra-intense magnetic field would allow enhancing the rate of the generated alpha-particles. In last decades it has been experimentally proved that a small coil-target energized with a long pulse (nsec-class), high energy (several hundreds of J) laser can produce a quasi-static (over one nsec) magnetic field of the order of 1 kT. The combination of several laser beams with the dual purposes of producing a plasma responsible of the fusion reaction and, using a proper synchronization, energizing two multiturn coils would enhance the alpha particle rate by confining ions up to few MeV/u in a small region (less than 1mm^2 in diameter). We propose the design of an innovative magnetic bottle-like trap made of two multiturn coil targets able to produce a magnitude field of several kT, which is ideal to confine the plasma for a relatively long time (few nsec), thus increasing the number of p-B collisions and, hence, the fusion reaction rate. A complete study of the trap is here reported including magnetic field analysis, electric, thermal and mechanic behavior and also the confinement efficiency using particle tracking code simulations. Preliminary experimental result with low energy laser will also be reported.

Speaker: Francesco Schillaci

14:00 P1.2024 Efficient relativistic laser pulse absorption in a near-critical plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2024.pdf Efficient relativistic laser pulse absorption in a near-critical plasma J. Moreau1 , E. d’Humières1 , R. Nuter1 , V. Tikhonchuk1,2 1 Centre Lasers Intenses et Applications, University of Bordeaux, CNRS, CEA, Talence, France 2 Institute of Physics of the ASCR, ELI-Beamlines, 18221 Prague, Czech Republic Near-critical plasmas are promising media for the laser ion acceleration in high repetition rate systems because of their robustness and possibility of a volumetric heating. However, the physical mechanisms of an efficient collisionless laser energy absorption are not sufficiently un- derstood. An efficient relativistic laser pulse absorption in a near-critical plasma due to the stim- ulated Raman scattering (SRS) was demonstrated in Ref. [1] by using high resolution numerical simulations with a Particle-In-Cell code. Because of the relativistic plasma transparency, the SRS is excited in the density above quarter critical density and it leads to the transfer of 70% of the laser pulse energy to electrons. This instability leads to an homogeneous electron heating all along the distance of propagation of the laser pulse through the plasma. The ions are efficiently accelerated at the plasma edges and can get near 30% of the initial laser energy. A simple model is proposed, which predicts the velocity of laser pulse propagation and the energy deposition. The laser pulse propagation is accompanied by the formation of electromagnetic cavities. The process of cavity formation is studied in detail, and it consists in the following three steps. It is initiated by the modulational (Benjamin-Feir [2]) instability in the front of the laser pulse, which is split in a train of electromagnetic solitons. These solitons propagate inward, excite plasma waves in their wake, lose energy and are finally trapped in the plasma. These trapped solitons present seeds for the formation of density depressions. The depressions may develop into cavities, if they trap electromagnetic fields produced in the plasma. The cavities survive for a long time thanks to an equilibrium of the trapped field radiation pressure and the electron kinetic pressure at their borders. The cavities control the laser energy absorption, generation of acoustic solitons and acceleration of charged particles. References [1] J. Moreau et al., Phys. Rev. E 95, 013208 (2017) [2] T. B. Benjamin and J. E. Feir, J. Fluid Mech. 27, 417 (1967)

Speaker: Vladimir T. Tikhonchuk

14:00 P1.2025 High alpha particle yield in laser induced p-B fusion reaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2025.pdf High alpha particle yield in laser induced p-B fusion reaction V. Scuderi1,2, G. Milluzzo2,3, G. Petringa2, L. Giuffrida1, A. Velhyan1, A. Picciotto4, C. Verona5, R. Leanza2, F. Schillaci1, J. Dostal6, J. Krasa6, G. Cuttone2, G. Korn1, D. Margarone1 and G.A.P. Cirrone2 1 Institute of Physics ASCR, v.v.i (FZU), ELI-Beamlines project, Prague, Czech Republic Laboratori Nazionali del Sud, INFN, Catania, Italy 2 3 School of Mathematics and Physics, Queen’s University Belfast, Belfast, United Kingdom 4 Micro-Nano Facility, Center for Materials and Microsystems, Fondazione Bruno Kessler, Trento, Italy 5 Dipartimento di Ing. meccanica Università di Roma Tor Vergata, Roma, Italy 6 Czech Technical University in Prague, FNSPE, Prague, Czech Republic 6 Institute of Plasma Physics of the ASCR, PALS Laboratory, Prague, Czech Republic Laser-induced nuclear fusion reactions are nowadays widely investigated as an alternative approach for the production of fusion energy, which could potentially have a high societal impact. In particular, the proton–boron nuclear fusion reaction leading to the production of energetic alpha particles without neutron generation can be beneficial in several application in nuclear physics, as for building “ultraclean” nuclear-fusion reactor [1], and also in Medical Physics (for cancer treatments [2, 3]). Latest results obtained using a nanosecond, 16 −2 low-contrast laser pulse with a relatively low intensity (3 × 10 W cm ) and advanced boron-doped hydrogen-enriched silicon targets allowed the production of a high yield of 9 alpha particles of around 10 per steradian[4,5]. In this contribution, results from a recent experimental campaign performed at PALS laser laboratory in Prague will be presented. The main goal of the present experiment was to maximize the alpha particle yield from the proton-boron nuclear reaction (11B + p → 3α + 8.7 MeV) induced using thin multilayer SiHB targets thus validating and improving the surprising results achieved in our previous campaign [4,5]. Furthermore, since the complex geometry of the SiHB targets is expected to increase the efficiency of the pB nuclear reaction and produce a high brilliance alpha particle source propagating forward and backward with respect to the target normal direction, alpha particle angular distributions have been also measured for different target structures. Thomson Parabola spectrometers, TOF-based diagnostics using diamond and silicon carbide (SiC) detector array and nuclear track detectors (CR39 type), placed at different angles, allowed to study proton acceleration and alpha-particle emission in terms of energy and flux. Results show a strong enhancement of the alpha particle yield leading to about 1011 alpha particle/sr measured for the different target geometries. [1] H. Hora et al. Energy & Environmental Science, 3, 479 (2010) [2] L. Giuffrida et al. AIP Advances, 6, 105204 (2016) [3] G. A. P. Cirrone et al., Scientific Reports Vol. 8, 1141 (2018) [4] A. Picciotto et al., Phys. Rev. X, 4, 031030 (2014). [5] D. Margarone et al. Plasma Phys. Control. Fusion 57 (2015) 014030

Speaker: Valentina Scuderi

14:00 P1.2026 Hot-spot emission properties in a warm plastic-shell implosion on OMEGA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2026.pdf Hot-spot emission properties in a warm plastic-shell implosion on OMEGA W.L. Shang1, C. Stoeckl2, R. Betti2, S.P. Regan2, T.C. Sangster2, S.X. Hu2, A. Christopherson2, V. Gopalaswamy2, D. Cao2, W. Seka2, D.T. Michel2, A.K. Davis2, P.B. Radha2, F.J. Marshall2, R. Epstein2, A.A. Solodov2 1 Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900 China 2 Laboratory for Laser Energetics, University of Rochester, Rochester NY 14623 A warm plastic-shell implosion was performed on the OMEGA laser system. The measured corona plasma evolution and shell trajectory in the acceleration phase are reasonably simulated by the one-dimensional LILAC simulation including the nonlocal and cross-beam energy transfer models. The results from analytical thin-shell model reproduce the time-dependent shell radius by LILAC simulation, and also the hot-spot x-ray emissivity profile at stagnation predicted by Spect3D. In the Spect3D simulations within a clean implosion, a “U”-shaped hot-spot radius evolution can be observed with the Kirkpatrick-Baez microscope response (the photon energy is from 4 to 8 keV). However, a fading away hot-spot radius evolution was measured in OMEGA warm plastic-shell implosion because of mixings. The distance from the measured hot-spot radius evolution shape to the “U” shape could be a new criterion for an experimental implosion performance. To recover the measured hot-spot x-ray emissivity profile at stagnation, a non-isobaric hot-spot model is built, and the normalized hot-spot temperature, density, and pressure profiles (normalized to the corresponding target-center values) are obtained. References: [1] V. N. Goncharov, T. C. Sangster, R. Betti, T. R. Boehly et al., Phys. Plasmas 21, 056315 (2014). [2] P. B. Radha, J. Delettrez, R. Epstein, V. Yu Glebov, R. Keck et al., Phys. Plasmas 9, 2208 (2002).

Speaker: Wanli Shang

14:00 P1.2027 Progress on radiation hydrodynamics simulations of ICF at NUDT

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2027.pdf Progress on radiation hydrodynamics simulations of ICF at NUDT Y. Y. Ma1,2,*, F. Y. Wu1, Y. Z. Ge1, X. H. Yang1, B. B. Xu1, Y. Z. Ke1 and L. Meng1 1 Department of Physics, National University of Defense Technology, Changsha, China 2 IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai, China Some recent progress on radiation hydrodynamics simulations at National University of Defense Technology (NUDT) has been made. Some new code modules have been developed to improve the applications of the code MULTI. A reflection and refraction module was added into the Multi-2D for the simulations of inertial confinement fusion (ICF) driven by laser. Some modules were also added into the Multi-2D for the simulations of inertial confinement fusion (ICF) driven by Z-pinch. Physical models describing the formation of Z-pinch dynamic hohlraums were established. The magneto-hydrodynamic models were implemented as packages for the open-source code MULTI-IFE (1D) and MULTI-2D, which were initially designed for the simulations of inertial confinement fusion driven by laser or heavy ion. Z-pinch dynamic hohlraum is one of the competitive ways to drive inertial confinement fusion due to the excellent properties, such as high radiation conversion efficiency, low cost of X-ray energy and larger fusion energy gain. In order to increase the radiation conversion efficiency and improve the radiation uniformity in the dynamic hohlraum and suppress the fluid instability at the process of capsule implosion，the related factors affecting radiation temperature in dynamic hohlraum were analyzed, and the reasons of radiation non-uniformity around the surface of fusion capsule were discussed, and the fluid instabilities at the inner and outer surfaces of ablator were explored through both theoretical analysis and radiation hydrodynamics simulations.Text of the contribution. This work is financially supported by the National Natural Science Foundation (Grant Nos. 11475260 and 11474360), the National Basic Research Program of China (Grant No. 2013CBA01504). *email: yanyunma@126.com

Speaker: Yanyun Ma

14:00 P1.2028 Spherically convergent plasma fusion neutron generation by laser drive

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2028.pdf Spherically convergent plasma fusion neutron generation by laser drive Guoli Ren1, Jie Liu1, Ji Yan2, Ke Lan 1 1 Institute of Applied Physics and Computational Mathematics, Beijing, China 2 Laser Fusion Research Centre, Mianyang, China We propose a feasible scheme to acquire high ion temperature and high thermal nuclear fusion neutron yield with laser ablated spherical convergent plasmas fusion (SCPF). In our scheme, we use intense lasers (1014-1015 W/cm2) pulse of nanosecond duration to irradiate thermonuclear fuel (such as Carbonized Deuterium, CD) containing layer (~10 microns) lined inside a spherical hohlraum, the fuel layer is ablated and then expands at high speed (~500 km/s) towards the sphere center. The hot fuel plasma eventually merge at the center and convert most of their kinetic energy to the ion internal energy, raising the ion temperature to a high level of around 10 keV. We have done demonstration experiment on SGIII-prototype and SGII-upgrade facility. In the experiments, we use 6-12 kJ triple-frequency laser to irradiate a CD layer lined inside a 1.7~2.0 mm diameter spherical hohlraum with one laser entrance hole at each end, we have acquired a stable DD thermonuclear fusion neutron yield of 3-5×109 . The process is robust and neutron yield is insensitive to practical experimental environment and parameter fluctuation. The neutron ToF data shows that the ion temperature of the merged plasmas is around 7 keV-8 keV. The experiment results agree with our theoretical scaling law and hydrodynamic simulation. The experiment has demonstrated that the SCPF scheme can potentially be a high-flux laser fusion neutron generator in future. Improvement and further optimization of this scheme is undergoing. [1] G. Ren, J. Yan, J. Liu, K. Lan, et al., Phys. Rev. Lett. 118, 165001(2017)

Speaker: Guoli Ren

14:00 P1.2029 Target design with decoupled rocket model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2029.pdf Target design with decoupled rocket model Lulu Li1 , Wu Wen1 , Yingkui Zhao1 1 Institute of applied physics and computational mathematics, Beijing, China, 100094 According to traditional rocket model [1], with constant mass ablation rate, the implosion dy- namics of fusion target is determined only by one parameter, which is called implosion param- eter. While implosion parameter is determined, all properties related are certain, such as shell radius, aspect ratio, implosion speed, fractional payload mass and rocket efficiency. Therefore, only one property could be optimized during designing with traditional rocket model. By break- ing the strong coupling between implosion parameter and target properties, the rocket model is developed. And it could be used for target design with two properties restricted. The developed model is applied to target design with certain radiation source, and the results are compared with numerical simulations. References [1] M. Murakami and K. Nishihara, Jpn. J. Appl. Phys. 26, 1132 (1987)

Speaker: Lulu Li

14:00 P1.2030 Experimental and theoretical developments in shock ignition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2030.pdf Shock ignition is a promising route for laser fusion ignition; in principle high-gain can be achieved with modest driver energies and hence capital investment. This poster will outline ongoing collaborative experiments on the Omega, NIF and LMJ laser facilities which are being performed to improve our understanding of the physics of shock ignition. In parallel we are developing hydrodynamic simulation tools which contain self-consistent models of kinetic laser-plasma interaction instabilities. By extensively benchmarking these new models against the experimental data in plasma conditions of direct relevance to full-scale ignition experiments, we aim to create robust design tools to evaluate the feasibility of this new approach to laser fusion. R.H.H.Scott, K.Glize, L.Antonelli, N.Woolsey, T. Arber, K. Bennett, W. Theobald, A. Casner, D. Batani, R. Betti, V. Tikhonchuk, W. Garbett, Chikang Li, M. Wei, S. Atzeni.

Speaker: Robert Scott

14:00 P1.2031 On possibility of creating a muon-catalytic reactor based on periodic injection of ball lightnings in a chamber with D-T mixture

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2031.pdf On possibility of creating a muon-catalytic reactor based on periodic injection of ball lightnings in a chamber with D-T mixture A. G. Oreshko1, A.A. Oreshko2, T. B. Mavlyudov1 1 Moscow Aviation Institute-National Aerospace University, Moscow, Russia 2 National Scientific Research Institute of Physical-Technical and Radiotechnical Measurements, Moscow region, Mendeleevo, Russia The most perspective approach to nuclear fusion is the concept of muon-catalyzed fusion. As follows from theory, the reaction can occur at a very low temperatures. The main pro- blem of muon-catalyzed nuclear fusion lies in the fact that existing sources, such as linear accelerators, require considerable energy expenses for the production of muons. A cheap source of muons is ball lightning, which interacts with a target or a dense low-temperature deuterium-tritium mixture. Earlier in experiments, the phenomenon of anomalous passage of ball lightning through solid-state absorbing filter was discovered [1]. This phenomenon can be explained only by the multistage generation of particles at the interaction of high- energy protons of the external shell of ball lightning with a dense medium [2]. The exis- tence of muons and neutrino at the interaction of ball lightning with a thick metal absorber is confirmed by the presence of a ball lightning passed through the absorber 6 cm thick from plumbum [2]. In the ordinary state, the energy that protons of ball lightning gained in alternating fields is equal to 20-25 MeV [3]. Using the energy converter allows protons to gain energy, which is required for generation the pions. The decay of pions, as is well known, leads to generation of muons and muon neutrino. As is known, one and the same negative muon can participate in 120-150 fusion events for during of its existence. Gene- ration of muons by means of the ball lightning makes it possible to create a breakthrough technology in nuclear fusion which has no unsolvable problems. In a short time it is possi- ble to create a compact nuclear fusion reactor. The approximate cost of creating a demon- stration version of the reactor based on muon catalysis in one hundred million times less than the cost of the demo version of tokamak. Ball lightning is the key to solving the pro- blem of obtaining environmental pure energy. This key must be used. References [1] Oreshko A.G., Journal of Plasma Physics, 2015, v.81, N3, p.18. [2] Oreshko A.G., Oreshko A.A., Proc. 43rd EPS Conf. on Plasma Physics. Leuven (2016). [3] Oreshko A.G., Oreshko A.A., Mavlyudov T.B. Proton-electron model of ball lightning – in print.

Speaker: Alexander Grigor'evich Oreshko

14:00 P1.2032 Equation of state and optical reflectivity of shock-compressed C-H-N-O planetary ices

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2032.pdf Equation of state and optical reflectivity of shock-compressed C-H-N-O planetary ices M. Guarguaglini1, J.-A. Hernandez1, Y. Fujimoto2, K. Miyanishi2, P. Barroso3, F. Lefevre1, A. Benuzzi-Mounaix1, N. Ozaki2, T. Vinci1, E. Brambrink1, A. Ravasio1 1Laboratoire LULI - CNRS, École Polytechnique, CEA: Université Paris-Saclay, Palaiseau, France 2Graduate School of Engineering, Osaka University, Suita, Osaka, Japan 3Observatoire de Paris, Paris, France Water, ethanol, and ammonia are amongst the key components of Uranus and Neptune. Knowing their equation of state, conductivity, and transport properties at planetary interiors conditions (a few Mbar and a few 1000 K) is required for developing precise structure and evolution models of the two planets as well as for explaining their puzzling magnetic fields and luminosities. The physical and chemical behaviour of such mixtures at extreme pressures and temperatures is not only important for planetology but also interesting on its own, since those conditions are characterised by the coexistence of dissociated atoms, atomic clusters and chains. This regime is very difficult to study via ab initio simulations and experimental verifications are required. We studied pure water, a C-H-O and a C-H-N-O mixture, compressed up to 3 Mbar via laser-driven shock loading. The principal Hugoniot has been explored using the decaying shock technique. Moreover, off-Hugoniot states have been reached via a double-shock technique and through coupling of dynamic and static compression in diamond anvil cells. The experiments were performed at the GEKKO XII and LULI 2000 laser facilities using standard rear-side optical diagnostics (VISARs, SOP, reflectometer) to characterise the equation of state (a relation between density, pressure, internal energy, and temperature) and optical reflectivity of the shocked state. The results show that water and C-H-N-O mixtures share the same equation of state with a trivial density scaling, while the reflectivity behaves differently in both the onset pressure and the saturation value. From the reflectivity measurements an estimation of a conductivity will be given using a Drude model. The consequences for the icy giants interiors will be addressed.

Speaker: Marco Guarguaglini

14:00 P1.3001 Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Probe Method

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3001.pdf Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Probe Method A.S. Mustafaev¹, A.Y. Grabovskiy¹, V.S. Soukhomlinov² ¹St. Petersburg Mining University, St. Petersburg, Russia ²St. Petersburg State University, St. Petersburg, Russia The ion velocity distribution function (IVDF) is of interest in cases associated with the study of plasmachemical reactions occurring with the participation of ions, the determination of ion mobility in the plasma object, processes of heating of the neutral plasma component, etc. Among technical applications, we remark modern plasma nanotechnologies, fine ion purification of the surfaces, and the technology of creating reliefs on the surface owing to selective etching during bombardment by ion fluxes. This work is devoted to the experimental and theoretical determination of the ion velocity distribution function in intrinsic gas for a glow discharge in a constant field with allowance for the appearance of slow ions with atomic temperature as a result of charge exchange, which was considered the dominating process. It was assumed that the ion velocity before the collision considerably exceeds the velocity of atoms. For the first time, the ion distribution functions over energy and direction of motion for He+ in He (see Figure) and Ar+ in Ar have been measured by the method of the plane one- Figure. Comparison of IDF He+ in He in the strong field approximation [1] with experimental data: Ta=600K, sided probe [2]. Here IVDF was E/P0=20 V/cm∙Torr, P=0,2 Torr determined in the glow discharge of intrinsic gas in a constant electric field of an arbitrary value. The obtained results make it possible to conclude that, in independent gas discharge plasma, even at moderate fields, the ion distribution function can have noticeable anisotropy and can strongly differ from Maxwell distribution. References [1] A. Mustafaev, V. Sukhomlinov and M. Ainov. 2015. Tech. Phys. Vol. 60 P. 1778. [2] A.S. Mustafaev, A.A. Strakhova. Journal of Mining Institute. 2017. Vol 226. P. 462.

Speaker: A. Y. Grabovskiy

14:00 P1.3002 Origin of Electric Wind in Atmospheric-Pressure Plasma Jets

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3002.pdf Origin of Electric Wind in Atmospheric-Pressure Plasma Jets S. Park1, U. Cvelbar2, W. Choe1,3, S.Y. Moon4 1 Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea 2 Jožef Stefan Institute, Ljubljana, Slovenia 3 Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Republic of Korea 4 Department of Quantum System Engineering, Chonbuk National University, Jeonju, Republic of Korea It is essential to understand the interactions between ionized matter and neutral particles in order to discover their impact on the natural phenomena. One such phenomenon is the electric wind, which supposedly occurs because of the so-called c-n coupling, i.e. interaction between charged particles and neutral particles in systems of weakly ionized plasmas, however this mechanism remains elusive until now. We here report a direct evidence demonstrating that the electric wind is caused by an electrohydrodynamic (EHD) force generated by the charged particle drag, as a result of the momentum transfer from the electrons/ions to the neutrals. The model experiments are based on an atmospheric pressure μs-pulsed helium plasma jet. From helium gas flow trajectories observed using Schlieren photography, the electric wind speed along the jet axis is estimated. Studying the changes in the electric wind speed at different pulse parameters allows one to distinguish between the effects of streamer propagation and space charge drift causing the electric wind. In addition, the study permits to determine the role of electrons and (positive) ions in the wind generation. Our key finding is that the contribution of the moving streamer to the EHD force generation is negligible, while the EHD force is mainly caused by the residual space charges after the plasma streamer propagates and collapses. Another important finding is that electrons are also a main player as well as negative ions. This will be the first clear report of the electric wind in the atmospheric-pressure plasma jets. [1] S. Park, U. Cvelbar, W. Choe, and S. Y. Moon, Nature Communications 9, 371 (2018).

Speaker: S. Park

14:00 P1.3003 Electrical and magnetic spectrometry of ions emitted from laser-generated plasma at 10^10 W=cm^2 intensity

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3003.pdf Electrical and magnetic spectrometry of ions emitted from laser-generated plasma at 1010 W/cm2 intensity G. Costa and L. Torrisi Dipartimento di Scienze Fisiche - MIFT, Università di Messina, V.le F.S. D’Alcontres 31, 98166 Messina, Italy Plasmas were generated by 3 ns pulsed laser at 1064 nm wavelength using intensities of about 1010 W/cm2 irradiating solid targets with different composition. The ion emission was inves- tigated with time-of-flight measurements giving information of the ion velocity, charge state generation and ion energy distribution. Measurements use an electrostatic ion energy analyzer and a coil to generate a magnetic field suitable to deflect ions towards a Faraday cup and/or a secondary electron multiplier. Ion acceleration of the order of hundred eV per charge state, plasma temperature of the order of tens eV, charge states up to about 4+ and Boltzmann energy distributions were obtained in carbon, aluminum and copper targets. The presented results represent useful plasma characterization methods for many applications such as the new generation of laser ion sources, proton ion sources, pulsed laser deposition techniques and post ion acceleration systems.

Speaker: Giuseppe Costa

14:00 P1.3004 Insight into plasma polymerization of cyclopropylamine in low pressure capacitive RF discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3004.pdf Insight into plasma polymerization of cyclopropylamine in low pressure capacitive RF discharges L. Zajíčková1 , M. Michlíček1 , P. Papp2 , M. Danko2 , S. Hamaguchi3 1 Masaryk University, Brno, Czech Republic 2 Comenius University, Bratislava, Slovakia 3 Osaka University, Osaka, Japan Materials modified by thin films with amine groups are promising for many bioapplications. It requires tuning the film stability in aqueous media because nitrogen(amine)-rich PPs tend to dissolve and lose the nitrogen functionalities by hydrolysis [1]. The stability can be improved by an increase of plasma power at the expenses of amine concentration in the films [2]. Recently, we started a series of studies with PP of cyclopropylamine (CPA) in argon capacitively coupled plasma, either at the floating [3] or RF-biased potential [4]. At certain conditions, the PP-CPA films deposited at the floating and RF-biased surfaces had similar concentration of NH2 groups but better water stability was achieved at the RF electrode due to better cross-linking. The stability in water turned out to be more important than the amount of NHx groups in the studies of mouse muscle myoblasts viability [6], whereas the performance of the films deposited at the floating potential was much better in the immobilization of biomolecules [5]. This work provides insight into fundamental aspects of the CPA plasma polymerization by putting together the results from electron beam experiments with CPA molecule, molecular dynamics simulations of CPA/Ar plasma interaction with surfaces and direct investigation of the CPA/Ar plasma. The plasma phase processes were investigated by mass/ion spectrometry and optical emission spectroscopy, whereas surface processes, mainly the ion bombardment, were studied by retarding field energy analyzer. References [1] A. Contreras-García, M. Wertheimer, Plasma Chem. Plasma Process. 33, 147 (2013) [2] Z. Zhang, Q. Chen, W. Knoll, R. Foerch, R. Holcomb, D. Roitman, Macromolecules 36, 7689 (2003) [3] A. Manakhov, L. Zajíčková, M. Eliáš et al., Plasma Process. Polym. 11, 532 (2014) [4] A. Manakhov, D. Nečas, J. Čechal, M. Eliáš, L. Zajíčková, Thin Solid Films 581, 7 (2015) [5] E. Makhneva, A. Manakhov, P. Skládal, L. Zajíčková, Surf. Coat. Technol. 290, 116 (2015) [6] A. Manakhov, M. Landová, J. Medalová et al., Plasma Process. Polym. 2017 14, e1600123 (2017)

Speaker: Lenka Zajickova

14:00 P1.3005 An optically trapped microparticle as plasma probe

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3005.pdf An optically trapped microparticle as plasma probe V. Schneider, H. Kersten Institute of Experimental and Applied Physics, Christian-Albrechts-University Kiel, Kiel, Germany The idea to use microparticles for plasma diagnostic purposes was implemented during the last decades by several experiments as electrostatic or thermal probes [1]-[5]. Because of their small size (µm to nm) microparticles can be used in studies of dynamic processes [6] as well as single probes in plasma sheath diagnostics [7, 8]. In contrast to common plasma diagnos- tic tools (e.g. Langmuir probes, calorimetric probes, mass spectrometers etc.), the µPLASMA (microparticles in a discharge with laser assisted manipulation) experiment [9] uses optically trapped microparticles (SiO2) as noninvasive single probes. The displacement of the particle in the laser trap is observed to measure a force while it is moving relatively to the plasma, either deeper into the sheath or into the plasma bulk. In addition, information about the neutral gas damping of the particles is presented. Systematic measurements of the residual charges [10] on the particle after switching off the plasma are performed, depending on the position of the particle in the plasma or the sheath, respectively. Furthermore, charging of the spheres by UV radiation is investigated and discussed. References [1] A.A. Samarian, B.W. James, Plasma Phys. Control. Fusion. 47(2005), B629. [2] G. Thieme et al., Faraday Discuss. 137(2008), 157-171. [3] H. R. Maurer et al., Contrib. Plasma Phys. 51(2011), 218-227. [4] G. Schubert et al., Contrib. Plasma Phys. 52(2012), 827. [5] P. Hartmann et al., Plasma Sources Sci. Technol. 23(2014), 045008. [6] J. Schablinski et al., Phys. Plasmas 22(2015), 043703. [7] J. Carstensen et al., IEEE Trans. Plasma Sci. 41(2013), 764. [8] A. Douglass et al., J. Plasma Phys. 82(2016), 615820402. [9] V. Schneider, H. Kersten, Problems of Atomic Science and Technology. 1(2013), 164-167. [10] L. Couëdel et al., Contrib. Plasma Phys. 49(2009), 235-259.

Speaker: Viktor Schneider

14:00 P1.3006 Laser photo-detachment method for dust charging and density measurements

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3006.pdf Laser photo-detachment method for dust charging and density measurements S.H Lee1 , H.T. Oh1 , M.-K Bae1 , I.J Kang1 , I.S. Park1 , S.J Jeong1 , K.-S. Chung1 1 Department of Electrical Engineering, Hanyang University, Seoul, South of Korea Dusts in the size of 10 nm – 100 µm could be generated due to plasma surface interactions in tokamak devices. During tokamak operation, these dusts could cause power loss through Bremsstrahlung radiation and affect plasma performance. Therefore, measuring the exact density of dusts is important for fusion research. In this experiment, the methods used for negative ion measurements are to be applied to dust measurements. Available methods for measuring the density of negative ion are utilized: LPD (Laser photo-detachment method) [1], electric probe method. In this experiment, plasma was generated by DC filamented source in a cubic chamber device called CPD (24 × 24 × 24 cm3 ). Specifications of laser are as the following: Nd:YAG laser , energy = 250 mJ, repetition rate = 2 ~ 20 Hz, pulse width = 10 ns. An electric probe is located at center of CPD for receiving LPD signal, where laser beam path passes. Laser screening object is installed in front of CPD for reducing ablation effect of electric probe due to direct impact of laser [2]. To verify validity of LPD, negative ion densities in plasma would be deduced by measuring relative photo-detachment signal, which are to be compared with those measured by electric probe method and same process are repeated in different gas pressure ratio of O2 to Ar. In probe method, one large planar probe and one cylindrical probe have been used for the direct deduction of negative ion density [3] and dust charging. Tungsten dusts are to be introduced for the measurement of dust charging and density by electric probes and LPD. The effect of tungsten dust on plasma parameters is also measured. The dust temperature is also roughly estimated through the relaxation of LPD signal. By comparing both the negative ion measurement and the dust measurement, we could get more reliable measurement of dusts in terms of charging and density measurement. References: [1] M. Bacal, Rev. Sci. Instrum. 71 (2000) 3981. [2] K.-S. Chung and S. Kado, Phys. of Plasmas. 13 (2006) 104509. [3] S. Kajita, S. Kado, A. Okamoto and S. Tanaka, Phys. Rev. E 70 (2004) 066403.

Speaker: SeungHwa Lee

14:00 P1.3007 Shadowgraphy of the plasma plume expansion for Aluminum- and Mylar-foil targets under the interaction of nanosecond laser pulse

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3007.pdf Shadowgraphy of the Plasma Plume Expansion for Aluminum- and Mylar- Foil Targets under the Interaction of Nanosecond Laser Pulse Nader, Morshedian Research School of Plasma and Fusion, Nuclear Science and Technology Research Institute, P.O.Box: 14399-51113, Tehran-Iran nmorshed@aeoi.org.ir Abstract The behavior of plasma plumes expansion of two, metal and polymer foil targets have been studied by shadowgraphy technique at atmospheric ambient gas pressure. The interaction beam of a Nd:YAG laser with average 30 ns pulse width and maximum 160 – 300 mJ laser energy focused on the Aluminum- and Mylar foil target and the plasma evolution both in the front and rare of the target were investigated. A laser probe beam with 8 ns pulse width, at wavelength 532 nm scans the plasma plume expansion and the signals are registered on a CCD camera up to 400 ns after the interaction time. The plume expansion velocity has been obtained at maximum value velocity for both of front and rare side of Al foil target, as 8× 107cm/s and 3.8× 106 cm/s respectively. In addition, for Mylar foil target, these values are 1.6 × 106 cm/s and 7 × 105 cm/s respectively.

Speaker: Nader Morshedian

14:00 P1.3008 Comparison of Thomson scattering and Langmuir probes for electron property measurements in magnetised plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3008.pdf Comparison of Thomson scattering and Langmuir probes for electron property measurements in magnetised plasma P.J. Ryan, M.D. Bowden, J.W. Bradley Department of Electrical Engineering and Electronics, The University of Liverpool, Liverpool, United Kingdom Langmuir probes are routinely used to measure fundamental electron properties, such as, temperature and density in low temperature technological and fusion edge plasmas, by monitoring the current drawn from the plasma as the probe tip is biased. They have a straightforward setup and are simple to operate, however the measurement is inherently perturbing, and interpretation of the data often requires a complicated model [1]. A complete theory for ion and electron collection covering all parameter space does not exist, but there are several parameterised theories for the case of unmagnetised plasma [1,2]. The presence of a magnetic field complicates probe theory [3] by introducing anisotropic current collection, increasing the probe disturbance length and reducing the return electrode area of the circuit. It is difficult to incorporate these effects into a model because cross-magnetic-field transport mechanisms are poorly understood. The aim of this research is to assess the reliability of unmagnetised probe theories [1,2] in the weak magnetic field regime, where electrons are the only magnetised species. Probes were employed in a magnetron discharge (~5-35 mT) and several probe theories (OML, ABR, Laframboise, Boltzmann electron retardation [1,2]) were implemented to extract electron properties from the probe data. Results were compared with Thomson scattering measurements performed under identical discharge operating conditions, with and without the probe inserted. Thomson scattering has uncomplicated data interpretation, which is independent of the magnetic field, so can reliably measure bulk electron properties. Typical magnetron operating conditions has density ~1017 m-3 and electron temperature < 1 eV for argon plasma measured by the Thomson diagnostic. [1] P. M. Chung et al, “Electric Probes in Stationary and Flowing Plasmas”, Springer-Verlag, Berlin (1975). [2] F. F. Chen, “Langmuir probe analysis for high density plasmas”, Physics of Plasmas 8, 3029 (2001). [3] P.C. Stangeby, “Determination of Te from a Langmuir probe in a magnetic field by directly measuring the probe's sheath drop using a pin-plate probe”, Plasma Physics and Controlled Fusion 37, 1337 (1995).

Speaker: Peter John Ryan

14:00 P1.3009 A metastable hydrogen probe beam to measure static and oscillating electric fields in plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3009.pdf A metastable hydrogen probe beam to measure static and oscillating electric fields in plasma L. Chérigier-Kovacic1, C. Poggi2, T. Guillaume1, F. Doveil1 1 Aix-Marseille Université, CNRS, PIIM UMR 7345, FR-13397 Marseille Cedex 20, France 2 Consorzio RFX, Corso Stati Uniti, 35127 Padova, Italy A new diagnostic to measure directly an electric field in vacuum or in a plasma has been developed. It is based on the emission of the Lyman- line by a hydrogen probe-beam in the 2s state when the beam passes through a region where an electric field is present (Electric Field Induced Lyman- Emission). The electric field couples 2s and 2p atomic hydrogen levels, the 2s lifetime is shortened and this level decays via 2p to the ground state. By measuring the intensity of the subsequent Lyman- radiation, it is possible to determine the magnitude of the field in a defined region. Absolute measurements of a static electric field between two polarized metallic plates in vacuum or in the sheath between a plasma and one of the plates have been successfully performed1. We now address the case of oscillating fields: measurements of a radiofrequency field (in function of injected power and frequency in the range 800-1400 MHz) compare well to simulations of our experimental device including the measurement method. We observe a spectrum with very narrow peaks associated to resonant modes of the cavity. Signal intensity at the measurement point depends on many unknown parameters such as the transmission factor of the detection optics, the neutral beam density, and the electric field the beam encountered all along its path. Thus calibration is not straightforward. However, we can draw conclusions about possible ways to calibrate measurements in the RF case. References: 1. L. Chérigier-Kovacic et al., Review of Scientific Instruments 86, 063504 (2015)

Speaker: Laurence Cherigier-Kovacic

14:00 P1.3010 Plasma diagnostics during microwave plasma synthesis of graphene nanosheets

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3010.pdf Plasma diagnostics during microwave plasma synthesis of graphene nanosheets M. Snirer, V. Kudrle, O. Jasek, J. Toman, J. Jurmanova CEPLANT, Masaryk University, Brno, Czech Republic Graphene nanosheets possess many extraordinary properties with promising applications, e.g. in energy storage. However, suitable technique for cost effective synthesis is needed. Microwave plasma is one of the considered techniques but requires further diagnostics of the influence of different parameters to control the synthesis and to yield a high quality graphene [1]. Graphene nanosheets were synthesized by decom- position of precursor (ethanol) vapours in argon mi- crowave plasma excited by surface wave launcher (surfaguide [2]) at 2.45 GHz. The synthesis process took place in the volume, i.e. no substrate or cata- lyst was needed and the product was in a flake form. Their quality could be controlled by the flow of carrier gas, the amount of precursor and the input microwave power. We performed the synthesis in both low pres- sure and atmospheric pressure regimes. Different ar- gon flows were tested in the range 0.2-3 L/min with various ethanol percentages. The main plasma parame- ters were studied by optical emission spectroscopy and Figure 1: Emission spectra of Ar plasma microwave interferometry. Spatial evolution of the gas with ethanol admixture (top) and SEM temperature was calculated from the emission spec- image of graphene flake. Experimental tra, too. The synthesized graphene sheets were ana- conditions: 350 W argon 280 sccm, pres- lyzed by Raman spectroscopy and scanning electron sure 500 Pa, partial pressure of ethanol microscopy. vapours 66 Pa. This work was supported by the Czech Science Foundation under project 18-08520S and in part by the project LO1411 (NPU I) funded by Ministry of Education, Youth and Sports of Czech Republic. References [1] M. Aliofkhazraei, N. Ali, W.I. Milne, C.S. Ozkan, S. Mitura, J.L. Gervasconi, Graphene Science Book, 2016. [2] M. Moisan, Z. Zakrzewski, Plasma sources based on the propagation of electromagnetic surface waves. J. Phys. D: Appl. Phys. 24, 1025 (1991).

Speaker: Miroslav Snirer

14:00 P1.3011 Analysis of the tuning characteristics of low-power microwave device for generation of plasma sheet

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3011.pdf Analysis of the tuning characteristics of low-power microwave device for generation of plasma sheet R. Miotk1, M. Jasiński1 1 Institute of Fluid Flow Machinery, Polish Academy of Sciences, Gdańsk, Poland A novel, recently patented by us plasma source with unique shape of plasma (i.e. plasma sheet) is presented in this paper. The presented source generates non-thermal plasma using the 2.45 GHz microwaves in any gases under reduced, atmospheric and greater than atmospheric pressure. This plasma source is simple and the unique shape of generated plasma sheet is very convenient for surface treatment, thus it is attractive for industry The plasma source was tested for surfaces treatment. The following materials were subjected to the plasma treatment process: caoutchoucs, PC (polycarbonate) and PMMA (poly(methyl methacrylate)). The water contact angle (WCA) directly after plasma treatment dropped 1.6-4.8 times. The WCA 200 hours after plasma treatment is lower 1.7-1.5 times relative to WCA before plasma treatment. The experimental investigations proved high potential of the presented method for the surfaces activation in industrial applications. The ageing of adhesion enhancement effect indicates that water contact angle is related to the surface energy changes. Due to industrial requirements regarding low costs of generated discharge in this work we focus on analysis of the tuning characteristics of the device. The tuning characteristics is a dependence of reflected microwaves power PR to the incident microwaves power PI as a function of position of a movable plunger ls. In general the plasma source is efficient when the ratio PR/PI is close to zero and it is stable when this ratio does not depend on the position of the movable plunger ls. Our preliminary experimental tests showed that the presented device requires improvement in order to increase its power coupling efficiency from the supply line to the generated plasma. Therefore, the presented in this work research is the first stage in the process of improving this device for increasing its energy efficiency and stability performance. Acknowledgements: We are grateful to The National Science Centre, Poland (programme no. 2015/19/B/ST8/02123) and the Foundation for Polish Science (FNP programme START no. 53.2017) for the financial support of this work

Speaker: Robert Miotk

14:00 P1.3012 Automatized analysis of interferometric measurements on nanosecond pulsed discharge in liquid water

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3012.pdf Automatized analysis of interferometric measurements on nanosecond pulsed discharge in liquid water L. Kusýn1 , P. Hoffer2 , Z. Bonaventura1 , T. Hoder1 1 Department of physical electronics, Masaryk University, Brno, Czech Republic 2 Institute of Plasma Physics, Czech Academy of Sciences, Praha, Czech Republic Fundamental physics of the discharge development in dielectric liquids is still a subject of controversy. While the modern plasma physical concepts describe phenomena in low-temperature gas-discharges with relatively high precision: from microscopic charge multiplication by elec- tron avalanching to macroscopic parameters such as temperature, this is not the case for dis- charges in liquid phase. The crucial problems of primary electron multiplication in bubble-free liquid, picosecond timescales conditioned by molecular density, and dielectric properties of po- lar water molecules exposed to fast changing external electric field, constitute permanent chal- lenges for physicists. One of the method to experimentally reveal the fast micro-physics taking place in mentioned discharges is the Mach-Zehnder interferometry for evaluation of changes in refractive index of studied media. This can be further used to estimate the pressure or elec- tric field distribution which is generated by the nanosecond high-voltage pulse applied onto the metal electrode inserted in the water. In this contribution the interferograms generated for studied discharge case (see Fig.1) will be anal- ysed and appropriate methods for automatic pro- cessing will be proposed. Evaluated data will be compared to the manually prepared results and the quality critically reviewed. Such an automatized ap- proach will enable processing of large amount of experimental data using advanced statistical meth- ods. We expect that a new inside into the phenom- ena of nanosecond discharges in liquid media can be revealed. This contribution is funded by Czech Figure 1: Typical interferogram of the pulsed Science Agency grant no. 18-04676S. discharge in water media, taken from [1]. References [1] Hoffer P. 2014 Shock waves generated by corona-like discharges in water, doctoral thesis, CTU, Praha, Czech Republic

Speaker: Lukáš Kusýn

14:00 P1.3013 Development and fundamental investigation of He micro-plasma detector PLES for gas chromatography

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3013.pdf Development and fundamental investigation of He micro-plasma detector PLES for gas chromatography A. I. Saifutdinov1, S. S. Sysoev1, A. A. Kudryavtsev1,2 1 Saint Petersburg State University, St. Petersburg. Russia 2 Harbin Institute of Technology, Harbin, China In analytical chemistry, gas chromatography (GC) has been widely used because of the short measurement time and the low running costs. In this study, a new type of GC detector using atmospheric pressure He plasma was developed. He has the highest ionization (24.58 eV) and metastable (19.82, 20.62 eV) energies among the elements. This means that He plasma can effectively ionize and excite all elements. In the helium plasma ionization detector, DC-powered He plasma and ring-like electrodes were utilized for ionization of the samples. For an ionization detector, the generation of very stable plasma is important. Therefore, we used next configuration to initiation of DC He microplasma. Two layers of ceramic of a thickness of 0.15 mm are interleaved with three layers of tungsten of a thickness of 0.1 mm to fabricate the device. The discharge volume is defined by a hole through the center of the sandwiched layers, and the micro-discharge uses a ring cathode created by the hole in the outer tungsten cathode layer. A similar hole in the opposite outer tungsten layer is used as a hollow anode. Device has a hole diameter of 400 mkm. The metallic walls of the discharge volume are used as a wall probe. The anode is grounded and the cathode is connected to the negative pole of the dc voltage source via a resistor of a few hundred kOhm. The desired discharge current is chosen by adjusting the voltage and the resistor values. The device is connected to out of microchromatograph column. Samples of mixture was previously separated in a microchromatographic column and then detected in a micro-plasma PLES-detector [1]. In addition to the time-dependent detection of the impurities analyzed in helium, impurity detection was performed at the characteristic energies of the Penning electrons. The energy spectra of the Penning electrons were obtained by measuring the second derivative of the probe VA-characteristic (d2I/dV2) with respect to the scanning voltage applied, which, according to the Druyvesteyn’s relation, is proportional to the EEDF [1,2]. The Penning electrons’ energy spectra were obtained in He as the main gas with small admixtures of Ar, N2 and O2. The recorded energy spectra of Penning electrons at atmospheric He pressures are characterized by the appearance of maxima at characteristic energies corresponding to the energy of the electrons released in Penning reactions involving Ar, N2, O2 impurities. Well-expressed maxima in the electron energy spectra are easily obtained as a result of the high number of Penning electrons collected by the large sensor surface. The effectiveness of the micro-plasma PLES-detector for GC was demonstrated by these results. To further improve the analytical ability, the use of a RF power supply to PLES detector is recommended because high-density plasma can be generated without the electrode overheating. The work was supported by Russian Science Foundation (RSF, grant № 17-79-20032). REFERENCES [1] Kudryavtsev A., Pramatarov P., Stefanova M. and Khromоv N. Journal of Instrumentation 7, PO7002, 2012. [2] Kudryavtsev A. A., Saifutdinov A. I., Stefanova M. S., Pramatarov P. M., and Sysoev S. S. Physics of Plasmas 24, 054507, 2017.

Speaker: Almaz Saifutdinov

14:00 P1.3014 First characterization of ion fluxes in repetitively pulsed hydrogen plasma induced by 13.5 nm EUV radiation at the EBL2 facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3014.pdf First characterization of ion fluxes in repetitively pulsed hydrogen plasma induced by 13.5 nm EUV radiation at the EBL2 facility J. Westerhout1, M.F. Dekker1, R.P. Ebeling1, T. Huijser1, N.B. Koster1, K.L. Nicolai1, M. van Putten1, A.J. Storm1, A. Ushakov1, J. van Veldhoven1 1 TNO, Stieltjesweg 1, 2628 CK Delft, The Netherlands The current paper describes the properties of 13.5 nm extreme ultraviolet (EUV) radiation induced hydrogen plasma in the exposure chamber of the new EUV beam line (EBL2) at TNO. The introduction of higher source powers in EUV lithography systems causes increased risks for contamination and degradation of EUV photomasks and pellicles. Appropriate testing can help to make an inventory and mitigate these risks. To understand the influence of plasma produced due to gas photoionization on tooling and components, a more detailed description of such plasma is required. In EBL2 samples (including EUV photomasks) can be exposed to EUV radiation in a controlled environment. This allows for a systematic parameter study of EUV plasma. 3 kHz repetitively pulsed plasma conditions are characterized with compact a retarding field ion energy spectrometer, measuring time and space resolved ion flux and ion energy profiles on the chamber walls. Plasma profiles as a function of gas pressure, beam and chamber geometry, as well as plasma decay times are discussed.

Speaker: Jeroen Westerhout

14:00 P1.3015 Quantitative insights in to the fluid interactions downstream of an atmospheric pressure dielectric barrier plasma jet.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3015.pdf Quantitative insights in to the fluid interactions downstream of an atmospheric pressure dielectric barrier plasma jet. Y. Morabit1, J. L. Walsh1, M. I. Hasan1, R. D. Whalley2 1 Centre for plasma Microbiology, University of Liverpool, L69 3GJ, Liverpool, UK 2 School of Mechanical and Systems Engineering, Newcastle University, NE1 7RU, Newcastle, UK Low-temperature atmospheric pressure plasma jets are dielectric barrier discharges generated in thin dielectric tubes. The gas flowing through the capillary, typically Helium or Argon, is ionized, emerges into the quiescent ambient air creating a variety of reactive chemical species. The spatial separation between the region of plasma generation and species creation makes the plasma jet configuration unique, facilitating a stable source of short and long lived reactive oxygen and nitrogen species (RONS) under ambient conditions. Understanding the complex interaction between the discharge and the background gas is the key to understanding the RONS chemistry arriving at a downstream sample. Recently, considerable progress has been made in understanding the complex fluid interaction at play in a plasma jet configuration. Many studies have demonstrated dramatic changes to the structure of the flowing gas, which initiate turbulent fluctuations, both gas heating and electrohydrodynamic forces have been cited as possible mechanisms behind these observations [1, 2, 3]. In this investigation, a particle imaging velocimetry (PIV) was used to provide quantitative insights in to the complex fluid interactions at the orifice of a helium plasma jet. By capturing the velocity profile of both the flowing and background gas the impact of plasma generation parameters on the flow structure were identified. It was observed that key plasma parameters, such as the applied voltage, have little impact on the velocity of the flowing gas. This finding implies that the early onset of turbulence in the plasma jet is not attributed to an increased velocity, but is more likely a consequence of a periodic perturbation to the jet shear layer introduced by the discharge. [1] Robert, E. et al. Rare gas flow structuration in plasma jet experiments. Plasma Sources Science and Technology, 23(1), 12003 (2014). [2] Whalley, R. D., & Walsh, J. L. Turbulent jet flow generated downstream of a low temperature dielectric barrier atmospheric pressure plasma device. Scientific Reports 6, 31756 (2016). [3] Hasan, M. I., & Bradley, J. W. Reassessment of the body forces in a He atmospheric-pressure plasma jet: A modelling study. Journal of Physics D: Applied Physics, 49 055203 (2016).

Speaker: Youssef Morabit

14:00 P1.3016 Characterization of magnetron sputtering discharges used for the formation of metallic nanoparticles

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3016.pdf Characterization of magnetron sputtering discharges used for the formation of metallic nanoparticles A. Chami1, L. Couedel1, T. Acsente2, C. Arnas1 1 Aix-Marseille university, CNRS, Laboratoire PIIM, campus St Jérôme, 13397 Marseille, France 2 National Institute for Laser Plasma and Radiation Physics, PO Box Mg-36, Magurele, RO 077125, Romania The aim of our current experiments is to study the formation and transport of metallic nanoparticles (NPs) in conditions of DC magnetron discharges. Tungsten cathodes were used as sources of sputtered atoms/clusters, which are the very first NP precursors. The Argon pressure was varied between 20 to 40 Pa, a pressure range larger than that used for deposition. A grounded disc was placed 10 cm below the cathode (top of the device). The discharge current was fixed at 0.3 A or 0.5 A. NPs were collected on substrates placed in the center of the grounded disc. In such configuration, the magnetic field lines and strength were measured using a Hall probe. A cylindrical Langmuir probe allowed establishing a 2D map of the electron density and temperature between the cathode and the grounded disc. The evolution of these plasma parameters was correlated to the magnetic geometry and the forces applied to NPs can be deduced for typical sizes. The NP sizes were investigated with electron microscopy (SEM, TEM), the atomic structures and compositions with HR-TEM and EDS mapping. The produced W-NPs have a typical structure (monocrystal) showing that they have grown by deposition during their transport across the plasma. The core of these particles exhibits the beta-W crystalline phase. Oxide shells indicate likely oxidation after the chamber venting. Growth laws have been established as a function of the argon pressure (20 Pa to 50 Pa) for two discharge currents (0.3, 0.5 A) and as a function of the plasma duration for a given pressure. These results are discussed as a function of the discharge geometry as well as the discharge parameters. In a near future, the laser light scattering technics will be used to correlate the NP transport from the cathode region towards the substrates.

Speaker: Alebia Chami

14:00 P1.3017 Characterization of TiO2 thin films elaborated via atmospheric pressure plasma: influence of the plasma gas composition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3017.pdf Characterization of TiO2 thin films elaborated via atmospheric pressure plasma: influence of the plasma gas composition Seongchan kang1, Rodolphe Mauchauffé2, and Se Youn Moon1,2 1 Department of Applied Plasma Engineering, Chonbuk National University, Jeonju, Republic of Korea 2 Department of Quantum System Engineering, Chonbuk National University, Jeonju, Republic of Korea Nowadays, titanium dioxide (TiO2) is being widely investigated for its interesting physical, chemical and optical properties and for its various industrial applications, such as high refractive index coatings, anti-corrosion coatings and photocatalytic coatings. Thanks to the strong interest for TiO2 thin films deposition for industrial application, various methods of fabrication are developed. Among the several TiO2 thin films deposition methods, i.e. CVD (Chemical vapor Deposition), PVD (Physical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition) and APP-CVD (Atmospheric Pressure Plasma-Chemical Vapor Deposition), the latter one is a promising method for low-cost and in-line deposition because of its atmospheric pressure processing and fast deposition rate. Despite the successful deposition of TiO2 thin films by APP-CVD, studies on the TiO2 thin films growth mechanism using various plasma gases are still lacking and thus a thoughtful investigation is necessary. In this work, we studied the chemical composition and morphology of thin films deposited using a helium/argon/titanium isopropoxide (TTIP) gas mixture. To do so, the He/Ar/TTIP ratio is tuned and both the thin films surface chemistry, morphology and plasma chemistry are investigated using X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Optical Emission Spectroscopy (OES) respectively.

Speaker: Seongchan kang

14:00 P1.3018 The Schlieren Imaging to Investigate the Flow of a High-Power Axial Injection Plasma Torch

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3018.pdf The Schlieren Imaging to Investigate the Flow of a High-Power Axial Injection Plasma Torch B. Turkyilmaz1, E.I. Sungur1, D. Mansuroglu1,2, I.U. Uzun-Kaymak1 1 Middle East Technical University Physics Department, Ankara, Turkey 2 Canakkale 18Mart University Physics Department, Canakkale, Turkey Schileren imaging is utilized to assess dynamical properties of a high-power injection torch (AIT). The AIT system operates at atmospheric pressure using a power modulated 2.45 GHz microwave source through a surfaguide waveguide. Argon gas is feed to the system and plasma is generated inside a quartz tube of 20 mm in diameter. In AIT systems, the plasma is often surrounded by ambient nonionized gas, which is colder than the plasma. In small diameter tubing, it is observed that the interaction of these multiphase fluids leads to large eddies, which are separated into smaller ones by interactions, developing turbulent flows.1 It is vital for us to investigate the transition from laminar to turbulent flow in a relatively large diameter plasma which will be used for the purpose of plasma surface treatments in our studies. Reynolds Number is one of the important dynamical parameters to describe transition from laminar flow to turbulent flow. To investigate its effect, various amounts of Argon mass flow rates are studied. Thermal effects are also important for turbulence development; therefore, the effect of the input microwave power on the flow is investigated by repeating the same measurements at different power settings up to 2 kV. A “Z-type” Schileren imaging is used for the investigation of turbulence under the influence of various Reynolds Numbers, and Microwave (MW) powers before and after the plasma ignition. In addition to the results on various neutral flow and plasma flow rates, dynamical instabilities initiated by the plasma ignition are also identified using a time resolved analysis. 1. M. Shigeta, J. Phys. D. Appl. Phys. 49, (2016).

Speaker: B. Turkyilmaz

14:00 P1.3019 Nanoparticle formation and thin film deposition in a capacitiveley coupled discharge operated in aniline/argon mixtures

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3019.pdf Nanoparticle formation and thin film deposition in a capacitiveley coupled discharge operated in aniline/argon mixtures C. Pattyn1, J.Berndt1, U. Cvelbar2, E. Kovacevic1 1 UMR7344, CNRS/Université d'Orléans, France 2 Jozef Stefan Institute, Ljubljana, 1000, Slovenia Conductive polymers belong certainly to the most promising materials in current research. They have a high potential for a great variety of different applications as for example for super capacitors, antistatic coatings for electronic packaging, electrodes for organic LEDs or for novel types of sensors. Although conductive polymers have a long history, there is still a large need for simple, environmental friendly, scalable deposition techniques that guarantee a good adhesion and an exact control of thickness and surface morphology. This contribution will deal with plasma based polymersation processes in aniline containing discharges. Aniline (C6H7N, prototypical aromatic amine) is a monomer used in industry e.g. for the production of polyurethane precursors, but also for the production of polyaniline which was one of the first conducting polymers used in practice. This contribution will present some results concerning the formation of nanoparticles and the deposition of thin films in a capacitively coupled discharge operated in mixture of argon and aniline. Acknowledgement This work has received funding from European Union’s Horizon 2020 research and innovation program under grant agreement No. 766894.

Speaker: J. Berndt

14:00 P1.3020 Pulse Assistant RF Discharge and Its Application on NO and SO2 Removal

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3020.pdf Pulse Assistant RF Discharge and Its Application on NO and SO2 Removal Q. Wang, C. S. Sang Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian, China Nitrogen oxide (NO) and Sulphur dioxide (SO2) are the components most difficult to remove in air pollutions. As the plasma techniques, removal efficiency is determined by many factors, among which the power source is particularly important and the discharge driven by pulse assistant radio frequency (rf) source was studied in our previous work [1-5]. Then, removal of NO is investigated in capacitive atmospheric pressure discharges driven by both radio rf and trapezoidal pulse power with a one-dimensional self-consistent fluid model [6]. The results show that the number density of NO could be reduced obviously once a low duty ratio short pulse is additionally applied on the rf power. NO removal process of the pulse modulated rf discharge could be divided into three stages: the quick reaction stage, the NO removal stage, and the sustaining stage, respectively. Furthermore, the temporal evolutions of particle densities are analysed, and the key reactions in the stages are discovered. Finally, the SO2 purification with the pulse assistant RF discharge is also investigated. References [1] Wang Q, Sun J Z, Zhang J H, et al., Phys. Plasmas 17 (2010), 053506. [2] Wang Q, Sun J Z, Nozaki T, et al. Phys. Plasmas 21 (2014), 083503. [3] Wang Q, Sun J Z, Zhang J H, et al. Phys. Plasmas 20 (2013) 043511. [4] Wang Q, Sun J Z, Wang D Z, IEEE Trans. Plasma Sci. 40 (2012), 35. [5] Wang Q, Yu X L, Wang D Z, Chin. Phys. B 26 (2017) 035201. [6] Wang Q, Wang Y H, Wang H C, et al., Plasma Sci. Technol. 19 (2017) 064013. *This work was supported by “the Fundamental Research Funds for the Central Universities” with Grant No. DUT18LK31, and “National Natural Science Foundation of China” with Grant No. 11405022.

Speaker: Q. Wang

14:00 P1.4001 Bistable Hysteresis Physics in radio-frequency inductively coupled plasmas: Theory, Experiment, Modeling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4001.pdf Bistable Hysteresis Physics in radio-frequency inductively coupled plasmas: Theory, Experiment, Modeling Hyo-Chang Lee Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea Abstract Many different gas discharges and plasmas exhibit bistable states under a given set of conditions, and the history- dependent hysteresis that is manifested by intensive quantities of the system upon variation of an external parameter has been observed in inductively coupled plasmas (ICPs). When the external parameters (such as discharge powers) increase, the plasma density increases suddenly from a low- to high-density mode, whereas decreasing the power maintains the plasma in a relatively high-density mode, resulting in significant hysteresis. To date, a comprehensive description of plasma hysteresis and a physical understanding of the main mechanism underlying their bistability remain elusive, despite the many experimental observations of plasma bistability conducted under radio-frequency ICP excitation. If, in such applications, plasma undergoes a mode transition and hysteresis occurs in response to external perturbations, the process result will be strongly affected. Due to these reasons, this presentation comprehensively reviews the global understanding of the bistability and hysteresis physics in the ICPs [1-3]. [1] H-C Lee, “Review of Inductively Coupled Plasmas: Nano-Applications and Bistable Hysteresis Physics”, Appl. Phys. Rev. in-press (2018). [2] H-C Lee et al., “Effect of electron energy distribution on the hysteresis of plasma discharge: theory, experiment, and modeling”, Sci. Rep. 5, 15254 (2015). [3] H-C Lee et al., “Discharge mode transition and hysteresis in inductively coupled plasma”, 102, 234104 (2013).

Speaker: Hyo-Chang Lee

14:00 P1.4002 Excitation of a whistler mode wave packet by interacting, higher-frequency, electrostatic-wave eigenmodes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4002.pdf Excitation of a whistler mode wave packet by interacting, higher-frequency, electrostatic-wave eigenmodes M. Koepke1,2, N. Brenning2, I. Axnäs2, M. Raadu2, E. Tennfors2 1 West Virginia University, Morgantown WV, USA 2 Royal Institute of Technology, Stockholm, Sweden Infrequent, bursty, electromagnetic, whistler-mode wave packets, excited spontaneously in the laboratory by an electron beam from a hot cathode, appear transiently, each with a time duration around ~1 μs. The ensemble of wave-packet frequency f_W is broadly distributed in the range 7 MHz < f_W < 40 MHz. Wave-packet excitation takes place in the plasma volume which is filled with an ensemble of separate electrostatic (es) plasma oscillations, having frequency f_hf, 200 MHz < f_hf < 500 MHz, that are hypothesized to match eigenmode frequencies of an axially localized hf es field in a restricted subvolume attached to the cathode. Features of these es-eigenmodes that are studied include: the mode competition at times of transitions from one dominating es-eigenmode to the next, the amplitude and spectral distribution of simultaneous, independent es-eigenmodes that do not lead to a transition, and the correlation of these features with the excitation of whistler mode waves. It is concluded that transient coupling of es-eigenmode pairs having f_1,hf and f_2,hf, such that | f_1,hf - f_2,hf | = f_W < electron gyrofrequency, can explain both the transient lifetime and the frequency spectra of the whistler-mode wave packets (f_W) as observed in lab. The generalization of the results to bursty whistler-mode excitation in space from electron beams, created on the high potential side of double layers, is discussed. This research on radiation from an electron beam in magnetized plasma [1] strives to identify ways for a double layer in space to produce electromagnetic radiation that propagates over a long distance. This work was supported by the Swedish Research Council, the Alfven Laboratory Center for Space and Fusion Plasma Physics, and the US National Science Foundation (ATM-0201112, PHYS-0613238, and PHYS-1301896). 1. N Brenning et al 2006 J. Geophys. Res. 111, A11212; 2017 Plasma Phys. Control. Fusion 59 124006.

Speaker: Mark E. Koepke

14:00 P1.4003 Resonant excitation of high-order diocotron modes with rotating RF fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4003.pdf Resonant excitation of high-order diocotron modes with rotating RF fields M. Romé1,2 , G. Maero1,2 , N. Panzeri1,2 , R. Pozzoli1 1 Dipartimento di Fisica, Università degli Studi di Milano, Italy 2 INFN Sezione di Milano, Italy The ability to excite and control low-frequency diocotron (Kelvin-Helmholtz) perturbations in a magnetized nonneutral plasma goes beyond the obvious interest in the attainment of long- time, stable confinement of a charged particle species. Indeed it represents an opportunity to study dynamical properties of turbulent two-dimensional fluids [1, 2, 3], and recent investiga- tions have directed attention to the behaviour of strained flows under the action of externally imposed perturbations [4, 5]. In a Penning-Malmberg device, diocotron waves are typically excited by means of suitable multipolar radio-frequency drives applied on an azimuthally sectored electrode of the trap at the resonance frequency of the desired wavenumber. This scheme is limited by the number N of electrically insulated azimuthal sectors of the electrode, yielding modes with an order ≤ N/2. Generalizing a previous work [6], it is demostrated both theoretically with a linearized 2D drift-Poisson model and experimentally in the Penning-Malmberg trap ELTRAP [7] that it is possible to overcome this limit and selectively excite high-order diocotron modes with applied electric fields which are co- or counter-rotating with respect to the azimuthal plasma rotation direction, by properly choosing the drive frequency and the phase difference between adjacent sectors. References [1] M. Romé, S. Chen and G. Maero, Plasma Phys. Control. Fusion 59, 014036 (2017) [2] S. Chen, G. Maero and M. Romé, J. Plasma Phys. 83, 705830303 (2017) [3] M. Romé, S. Chen and G. Maero, AIP Conf. Proc. 1928, 020012 (2018) [4] N.C. Hurst, J.R. Danielson, D.H.E. Dubin and C.M. Surko, Phys. Rev. Lett. 117, 235001 (2016) [5] N.C. Hurst, J.R. Danielson and C.M. Surko, AIP Conf. Proc. 1928, 020007 (2018) [6] G. Bettega, B. Paroli, R. Pozzoli and M. Romé, J. Appl. Phys. 105, 053303 (2009) [7] G. Maero, S. Chen, R. Pozzoli and M. Romé, J. Plasma Phys. 81, 495810503 (2015)

Speaker: Massimiliano Romé

14:00 P1.4004 Electron capture in the dense semiclassical plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4004.pdf Electron capture in the dense semiclassical plasma E.O. Shalenov, M.M. Seisembayeva, K.N. Dzhumagulova, T.S. Ramazanov IETP, Department of Physics, al-Farabi KazNU, al-Farabi 71, 050040 Almaty, Kazakhstan Investigation of the interaction between particles and plasma properties is of great interest in many areas of physics such as atomic and plasma physics. It is important for the development of the plasma technologies. One of the elementary processes in plasma is the electron capture process. In this work the electron capture processes by the hydrogen atom and proton were investigated. The motion of the electron in the field of the motionless atom or proton was considered on the basis of the perturbation theory and the solving of the equation of motion. The interaction potentials between the electron and the hydrogen atom and also proton were presented in works [1-2]. These effective potentials, taking into account the quantum-mechanical effect of diffraction and plasma screening effects, have finite values at the distances close to zero. In this work the electron capture radius, which was determined by equating the kinetic energy of impacting electron and the interaction energy between the electron and the hydrogen atom or proton, was presented. The trajectories of the electron in the field of the atom and proton were simulated. Obtained results of the electron capture by the atom and proton were compared. Using the electron capture probability, the electron capture cross section was calculated. References [1] T. S. Ramazanov, K. N. Dzhumagulova, Phys. Plasmas 2002, 9, 3758. [2] T. S. Ramazanov, K. N. Dzhumagulova, Y. A. Omarbakiyeva, Phys. Plasmas 2005, 12, 092702.

Speaker: Erik Shalenov

14:00 P1.4005 Optical properties of the dense xenon plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4005.pdf Optical properties of the dense xenon plasma E.O. Shalenov1, K.N. Dzhumagulova1, T.S. Ramazanov1, G. Röpke2, H. Reinholz2 1 IETP, Department of Physics, al-Farabi KazNU, al-Farabi 71, 050040 Almaty, Kazakhstan 2 Institute of Physics, University of Rostock, A.-Einstein-Str. 23-24, 18059 Rostock, Germany Investigation of the optical plasma properties is of great interest due to the wide areas of practical application. In this work the reflectivity of the dense xenon plasma with taking into account the density profile of the shock wave front was investigated. Calculations were conducted in the framework of the effective interaction potentials [1-3] (that take into account the static and dynamic screening effects and diffraction effect). Reflectivity was calculated on the basis of the Fresnel formula using the dielectric function. Results were compared with experimental data [4]. References [1] T. S. Ramazanov, K. N. Dzhumagulova, Phys. Plasmas 2002, 9, 3758. [2] T. S. Ramazanov, K. N. Dzhumagulova, Y. A. Omarbakiyeva, Phys. Plasmas 2005, 12, 092702. [3] E.O. Shalenov, S. Rosmej, H. Reinholz, G. Röpke, K.N. Dzhumagulova, T.S. Ramazanov, Contrib. Plasma Phys. 2017, 57, 486 [4] V. B. Mintsev, Y. B. Zaporozhets, Contrib. Plasma Phys. 1989, 29, 493.

Speaker: Erik Shalenov

14:00 P1.4006 Characterization of laterally colliding plasma plumes formed by the multi-species target

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4006.pdf Characterization of laterally colliding plasma plumes formed by the multi-species target Alamgir Mondal, R. K. Singh, Ajai Kumar Institute for Plasma Research, Gandhinagar, India - 382428 Interaction between two seed plasma plumes and subsequently formed interaction zone have been investigated in vacuum and wide range of ambient conditions. Different combination of solid targets, e.g. carbon, aluminium, nickel, tungsten etc. have been used in present study. The time resolved fast imaging and optical time-of-flight techniques have been utilised to inves- tigate the formation, dynamical and spectral behaviour of the seed plasma plumes as well as interaction zone. Also optical time-of-flight technique has been employed to observe the veloc- ity distribution of both the ionic and neutral particles in both the regions. The key features, such as shape, size and dynamics of the primary plume as well as resultant interaction zone have been examined. Observed dynamical and geometrical features of the interaction zone are explained on the basis of plasma parameters and kinetic energy imbalance of the interacting seed plumes. This experimental findings have important roles in generation of multi-species plasma plume and to control their contribution in different applications. References [1] Bhupesh Kumar, R. K. Singh, Sudip Sengupta, P. K. Kaw, and Ajai Kumar, Physics of Plasmas 21, 083510 (2014)

Speaker: Alamgir Mondal

14:00 P1.4007 Study of propagation of ion acoustic soliton in multi-cusp plasma device

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4007.pdf Study of propagation of ion acoustic soliton in multi-cusp plasma device Meenakshee Sharma1, A. D. Patel1, N. Ramasubramanian1 1 Institute for Plasma Research, HBNI, Gandhinagar, India Multi-line cusp geometry has been used to confine the Argon plasma in Multi-cusp Plasma Device (MPD). This geometry has the centre of radius of curvature outside the confined plasma, that gives magneto-hydrodynamic stability and the plasma produced is very quiescent. In MPD six electromagnets on the circumference of the device, have been used for the magnetic field profile production. The experimental study of the ion acoustic soliton interaction with plasma in MPD will be presented in this paper.

Speaker: Meenakshee Sharma

14:00 P1.4008 Analysis of supersonic plasma flow under the influence of impurity with gridded-bias in DiPS-2

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4008.pdf Analysis of supersonic plasma flow under the influence of impurity with gridded-bias in DiPS-2 I.S. Park1, I.J. Kang1, M.-K Bae1, S.H. Lee1, S.J. Jeong1, K.-S Chung1 1 Department of Electrical Engineering, Hanyang University, Seoul, South of Korea Plasma flow has been an important factor to understand the formation of presheath and sheath in edge plasma region in term of transition from the subsonic to the supersonic by satisfying of Bohm criterion [1]. However, this plasma flow would be influenced by dusts and vapor which were generated by high transient heat loads such as edge localized modes (ELMs) and plasma-wall interaction in plasma edge. These dusts and vapor have slower velocity than plasma flow [2], which generates the necessing of analysing plasma flow with impurities. We generated helium plasma in a linear machine, called Divertor Plasma Simulator – 2 (DiPS - 2), which generates plasma using LaB6. DiPS – 2 has the following specification and plasma parameter : B-field = 1 - 3 kG, working pressure ~ 0.1 mTorr, Idis = 1 – 50A, ne ~ 1010 - 1011 cm-3, Te ~ 1 - 25 eV for He plasmas). Plasma flow velocity was measured according to injecting impurities (Dust, Ar and N2) in helium background plasmas. Ions were accelerated by grid system (from -100 V to 0 V) in order to generate supersonic plasma. Plasma flow velocity was analysed using various kinetic model and fluid model. A kinetic model is to be applied to analyze the experimental results. References: [1] Ph Ghendrih et al, Plasma Phys. Control. Fusion 53 (2011) 054019. [2] A.A. Shoshin et al, Fusion Eng. Des. 114 (2017) 157.

Speaker: InSun Park

14:00 P1.4009 Nonlinear characteristics of mediator and streamer in linear magnetized plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4009.pdf Nonlinear characteristics of mediator and streamer in linear magnetized plasmas F. Kin1 , A. Fujisawa2,3 , K. Itoh3,4,5 , Y. Kosuga2,3 , M. Sasaki2,3 , T. Yamada3,6 , S. Inagaki2,3 , S.-I. Itoh2,3,7 , T. Kobayashi5 , Y. Nagashima2,3 , N. Kasuya2,3 , H. Arakawa8 , K. Yamasaki2 , K. Hasamada1 1 Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Japan 2 Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan 3 Research Center for Plasma Turbulence, Kyushu University, Kasuga, Japan 4 Institute of Science and Technology Research, Chubu University, Aichi, Japan 5 National Institute for Fusion Science, Toki, Japan 6 Faculty of Arts and Science, Kyushu University, Fukuoka, Japan 7 Department of Innovative Energy Science and Engineering, Graduate School of Engineering, Chubu University, Aichi, Japan 8 Teikyo University, Omuta, Japan In magnetized plasmas, drift waves are excited by inhomogeneity of the pressure gradient and can develop into nonlinear structures, such as zonal flow and streamer. The study of these non- linearly evolved structures are important for nuclear fusion, since they affect radial transport and determine confinement. One of the cause of anomalous transport is due to the streamer, which is known as radially elongated and azimuthally localized structure. In a linear device, LMD-U in Kyushu University, streamer was found to be excited by the modulation of drift waves through low frequency fluctuations, namely mediator [1]. Up to date, the mediator has been simply treated as linear wave. However, by applying the conditional averaging, the mediator is found nonlinear wave that contains harmonic compo- nents excited from the self-couplings in the PANTA, the successor device of the LMD-U. Moreover, the envelope of the streamer also contains higher harmonic components of which frequencies are identical to that of the mediator. This indicates that the streamer should be mod- ulated through higher harmonic components of the mediator as well as through fundamental components. Furthermore, it is also found, as is commonly observed for solitons, that the am- plitude of the co-existing solitary structures, mediator and streamer, increase inversely with the square of the width of half maximum. References [1] T. Yamada et al. Nature Phys. 4, 721 (2008)

Speaker: Fumiyoshi Kin

14:00 P1.4011 Initial studies on the morphology of the exploding wire plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4011.pdf Initial studies on the morphology of the exploding wire plasma G. Rodriguez Prieto1 , Malena Milanese2 , Luis Bilbao3 1 UCLM . ETSII, Ciudad Real, Spain 2 Intituto de Física Arroyo Seco, Tandil, Argentina 3 Universidad de Buenos Aires, Buenos Aires, Argentina Exploding wire phenomenon consists initially in the transformation of a metallic wire matter from solid to plasma state by a very intense, at least kA, and short, maximum of ns, electrical current following through the wire in a controlled time. Wire metal is initially heated by joule heating, which in turn transforms the wire into liquid, metallic gas and finally a plasma that can still absorb part of the electrical energy [1]. The final stage of the system, when the surrounding medium is atmospheric air, is a non expanded plasma which shows diverse morphological instabilities, depending on the material and initial energy, among other factors. Electrical current distribution across the wire, 30 that could be approximated by a cylindrical one, W Exp. Decay fitting 25 Pt Exp. Decay fitting cannot be considered as constant, or uniform, with a Fe Exp. Decay fitting 20 large dependence on the skin depth of the material, Counts 15 a parameter that indicates the penetration deep of 10 the electromagnetic fields inside the wire. In prin- 5 ciple, it is tempting to consider that such parame- 0 ter can be related with the final morphology of the 0 200 400 600 800 1,000 Length (px, A.U.) plasma, as it sets up the initial condition for the plasma expansion. In this work we show that such Figure 1: Distance distribution for the peaks relation is not observed at a charging voltage of 20 and valleys of exploding wire plasmas. kV, based on measurements of the distance between observed peak and valleys, obtained with a fast frame camera synchronized with the exploding wire. They can be adjusted to exponential decay functions with very similar fitted values for the materials employed in these experiments. As fig. 1 shows, distribution of the distances between consecutive peaks and valleys is very similar for the three metals used. References [1] G. Rodríguez Prieto, L. Bilbao, M. Milanese, Laser and Particle Beams 34, 263 – 269 (2016)

Speaker: Gonzalo Rodríguez Prieto

14:00 P1.4012 Using biased hairpin probe for determining oxygen negative ions in a double plasma device

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4012.pdf Using biased hairpin probe for determining oxygen negative Ions in a double plasma device A K Pandey1, S K Karkari2 1 Institute for Plasma Research, Gandhinagar, India 2 Institute for Plasma Research, Gandhinagar, India The hairpin probe is a quarter-wave transmission line. The probe exhibits a resonance which is determined by the dielectric constant of the medium surrounding the hairpin. When immersed in the plasma, the observed resonance relates to the electron plasma frequency through the plasma dielectric constant. Hence the electron density, ne, can be directly found using this technique. The hairpin probe had been used as a detection probe in pulse laser photo-detachment of negative ions. In this paper we demonstrate that the hairpin probe can also act as a Langmuir probe to determine α (ratio of negative ion density and electron density). It is observed that on applying positive bias to the hairpin, the resonance frequency shifts towards higher values, reaching saturation at the plasma potential. The positive ion density is determined from the ion saturation region, based on OML theory. It has been found that the OML theory is suitable for calculating the positive ion density, showing excellent match with the electron density obtained by hairpin resonance in electro-positive argon plasma. Using this method, the value of α has been determined in oxygen discharge in a double plasma device. Experimental results show a decreasing trend in α on increasing the power levels, consistent with the previous results. Reference: [1] Stenzel R L 1976 Rev. Sci. Instrum. 47 603. [2] A. K. Pandey and S. K. Karkari, Phys. Plasmas 24, 013507 (2017).

Speaker: Avnish Kumar Pandey

14:00 P1.4013 Superdiffusive transport in plasma for a finite velocity of carriers: general solution and the problem of automodel solutions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4013.pdf SUPERDIFFUSIVE TRANSPORT IN PLASMA FOR A FINITE VELOCITY OF CARRIERS: GENERAL SOLUTION AND THE PROBLEM OF AUTOMODEL SOLUTIONS A.A. Kulichenko1, A.B. Kukushkin1,2 1 National Research Center «Kurchatov Institute», Moscow, 123182, Russian Federation 2 National Research Nuclear University MEPhI, Moscow, 115409, Russian Federation The analysis of the Green’s function of the non-stationary Biberman-Holstein equation for radiative transfer in plasmas and gases has shown [1] that there is an approximate automodel solution based on three scaling laws: for the propagation front and asymptotic solutions far beyond and far ahead of the propagation front. All these scaling laws are determined essentially by the long-free-path carriers (named Lévy flights). The validity of the suggested automodel solution was proved by its comparison with analytical solutions in the 3D case of the Biberman–Holstein equation of the resonance radiation transfer for various spectral line shapes (Doppler, Lorentz, Voigt and Holtsmark) with complete redistribution over frequency in the elementary act of the resonance scattering of the photon by an atom/ion. Scaling laws of Biberman-Holstein equation Green’s function and the implications for algorithms of numerical modeling of superdiffusive transport are considered in [2]. The results of accuracy analysis of automodel solutions for Lévy flight-based transport, including the resonance radiative transfer and a simple general model, are reported in [3]. Here, we generalize the method [1] of approximate automodel solutions of the 1D transport equation with a model, power-law step-length probability distribution function (PDF) to the case of a finite velocity of the carriers (e.g., photons in space plasmas). First, we derive general solution. Further, the analytic results for the asymptotics far ahead and far beyond the perturbation front are derived. And finally, an approximate automodel solution based on the above asymptotics is suggested, and its accuracy is analyzed via comparison with exact numerical solution. The method is of interest for a broad range of superdiffusive transport problems in physics and beyond. References [1]. Kukushkin A.B. and Sdvizhenskii P.A., J. Phys. A: Math. Theor. 2016, 49, 255002. [2]. Kukushkin A.B., Sdvizhenskii P.A., Voloshinov V.V., and Tarasov A.S., International Review of Atomic and Molecular Physics, 2015, 6 (1), 31-41. [3]. Kukushkin A.B. and Sdvizhenskii P.A., J. Phys. Conf. Series, 2017, 941, 012050.

Speaker: Andrey A. Kulichenko

14:00 P1.4014 On universal properties of the plasma–sheath transition and large-size sheath structures

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4014.pdf On universal properties of the plasma–sheath transition and large-size sheath structures L. Kos1 , N. Jelić1 , S. Kuhn1 , D. D. Tskhakaya (sr.)2,3 , T. Gyergyek4,5 1 Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia, 2 Plasma and Energy Physics Group, Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck, Austria, 3 Also at Institute of Physics, Georgian Academy of Sciences, 0177 Tbilisi, Georgia, 4 University of Ljubljana, Faculty of Electrical Engineering, Ljubljana, Slovenia, 5 Jozef Stefan Institute, Ljubljana, Slovenia, Recently a unified Bohm criterion has been formulated [1] in the form of the ion directional energy expressed as a function of fluid, kinetic and electrostatic-pressure contributions. While the famous purely kinetic criterion of Harrison and Thompson [2], is satisfied exclusively at the plasma edge and for vanishing Debye lengths, the new unified Bohm criterion holds at any point of the discharge even if the quasineutrality is not well satisfied (i.e., in vicinity of the sheath en- trance) irrespectively on the ion temperatures and Debye length, provided that the latter is small enough for the plasma criterion to be applicable. The plasma edge (PE) and the sheath edge (SE) have been identified as the points of inflection and the maximum of the charge density derivative with respect to the potential, respectively. Plasma quasineutrality is well satisfied up to the PE, with a non-negligible electrostatic pressure taking place only between the SE and the electrode/wall. The region between the PE and the SE, identified as the plasma–sheath transition (PST), turned out to be characterised by a universal value (about one third of the electron tem- perature) which is quite insensitive to ion temperature and the Debye length, while an increase in Debye length from zero to finite values causes the location of the sonic point/potential (lying inside the PST) to shift from the PE (for vanishing Debye length) towards the SE. Outside the PST, the electrostatic-pressure term and its derivatives turn out to be nearly identical with each other (independently of the particular values of the ion temperature and Debye length). In the present investigation we investigate further the features described, however under the condition that the ionisation within the sheath, and thus the kinetic contribution to the unified Bohm criterion cannot be completely neglected. This is achieved by decreasing the plasma density, so that the sheath thickness is comparable with the plasma length, and with employing a constant ion production profile (independent of position, i.e., potential). The results obtained by means of the theoretical method from Ref. [1] are compared with the results obtained here after performing a series of kinetic numerical simulations. Special attention is paid to possible universal sheath solutions of large size, under the condition of a non-negligible ion production rate inside. References [1] L. Kos et al., Introduction to the theory and application of a unified Bohm criterion for arbitrary-ion-temperature collision-free plasmas with finite Debye lengths to appear in Phys. Plasmas (2018); [2] E. R. Harrison and W. B. Thompson Proc. Phys. Soc. 74, 145 (1959);

Speaker: S. Kuhn

14:00 P1.4015 Interpolations for plasma transport properties in the first Born approximation of the linear response theory

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4015.pdf Interpolations for plasma transport properties in the first Born approximation of the linear response theory V.S. Karakhtanov Institute of Problems of Chemical Physics RAS, Chernogolovka, Russia In the work closed expressions for electron-electron correlation functions and fully ionized plasma dc electrical conductivity, heat conductivity and thermopower are presented. The ap- proach is based on the linear response theory in the formulation of the relevant statistical operator method and takes into account both dynamical screening and arbitrary degeneracy. The expressions are constructed in the form that includes the asymptotic properties for non- degenerate [1], moderate [2, 3] and strongly degenerate [4] plasma and describe more wide density-temperature region that in [5]. The role of exchange parts in electron-electron correla- tion functions is discussed. The results obtained might be useful in calculating the multicompo- nent plasma transport properties. References [1] V. S. Karakhtanov, R. Redmer, H. Reinholz, and G. Röpke, Contrib. Plasma Phys. 53, 639 (2013). [2] V. S. Karakhtanov, Contrib. Plasma Phys. 56, 343 (2016). [3] V. S. Karakhtanov, The EPS Conference on Plasma Physics, Leuven, Belgium, 2016, http://ocs.ciemat.es/EPS2016PAP/pdf/P5.102.pdf [4] V. S. Karakhtanov, The EPS Conference on Plasma Physics, Lisbon, Portugal, 2015, http://ocs.ciemat.es/EPS2015PAP/pdf/P1.406.pdf. [5] V. S. Karakhtanov, The EPS Conference on Plasma Physics, Belfast, Northern Ireland, UK, 2017, http://ocs.ciemat.es/EPS2017PAP/pdf/P5.406.pdf

Speaker: Valery Karakhtanov

14:00 P1.4016 Weak drift wave turbulence and the statistics of random matrices

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4016.pdf Weak drift wave turbulence and the statistics of random matrices F. Spineanu, M. Vlad, V. Baran National Institute of Laser, Plasma and Radiation Physics, Bucharest, Romania A statistical analysis of the drift wave (weak) turbulence necessarily starts with the linear eigenmodes. A weak nonlinearity can be seen as a vertex of an interaction where the elemen- tary propagators correspond to the set of orthogonal eigenfunction of the linear operator and a renormalization theory can be developed. The first nonlinearity is the interaction between the non-adiabatic part of the density response and the electrostatic perturbation, which requires two field calculation. We note, in the present work, the possibility of another technical approach which introduces the nonlinearity through a perturbation of the complex roots of the functions of the base. For the drift wave in sheared magnetic field the eigenfunctions are Hermite polynomials. With the order scaled by an artificial time parameter (which maintains the orthogonality) the Hermite polynomials verify an equation of diffusion with a negative coefficient of diffusion. By an inverse Hopf-Cole transformation one obtains the Burgers equation with the same negative viscosity [Blaizot&Nowak, Phys Rev E 82, 051115 (2010)]. Evolving in the artificial time, the solution of this equation exhibits a shock formation, which, due to the negative viscosity is accompanied by oscillations. There is a connection between this solution and the average resolvent of the hermitean matrix with Gaussian random entries. Now we interpret the introduction of the weak nonlinearity of the turbulent drift waves as a broken orthogonality of the modified set of functions, which depart from the linear drift wave eigenmodes. Then the diffusion with a negative coefficient is modified by an averaged term which acts as a source. However we adopt the approximative procedure to modify directly the complex singularities that define the inverse Hopf-Cole transformed function. Since this is connected with the resolvent of the hermitean random matrix set, the modification is reflected in the density of the eigenvalues. We discuss the possibility to use this technical approach in order to obtain renormalization of the drift wave propagator in weak turbulence.

Speaker: V. Baran

14:00 P1.4017 Similarity study of black aurora to tokamak boundary: electric field and vortex structure

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4017.pdf Similarity study of black aurora to tokamak boundary: electric field and vortex structure Kwan Chul Lee1 1 National Fusion Research Institute, Daejeon, Korea Three examples of electric field formations in the plasma are analysed based on a new mechanism driven by the ion-neutral collisions. Recently developed Gyro-Center Shift analysis includes perpendicular current which is induced by the momentum exchange between ion and neutral when there is asymmetry over the gyro-motion. The first example is radial electric field formation at the boundary of nuclear fusion devices which is a key player for the high confinement mode operation of future fusion reactors. The second example is reversed rotation of arc discharge cathode spot that has been a mysterious subject for more than hundred years. The third example is electric field formations in earth ionosphere which are important components of equatorial electrojet and black aurora. The black aurora has been a mysterious subject for decades since it has two interesting features which are the strong electric field and breaking into array of circular structure. The process of one method that explains various examples from different plasmas will be presented. The basic ideas of the mechanism for the vortex structure in the black aurora and the ELM formation of tokamak will be discussed.

Speaker: Kwan Chul Lee

14:00 P1.4018 Do hydrodynamical models underestimate exchange effects? Comparison with kinetic theory for electrostatic waves

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.4018.pdf Do hydrodynamical models underestimate exchange effects? Comparison with kinetic theory for electrostatic waves G. Brodin1 , R. Ekman1 , J. Zamanian1 1 Department of Physics, Umeå University, Umeå, Sweden In dense or cold plasmas with degenerate electrons, the quantum mechanical effect of elec- tron exchange can be important [1]. Quantum hydrodynamical models can include exchange through a potential derived from time-independent functional theory (TIDFT) [2], but because of the time-independence, the accuracy for dynamical problems is unclear. To investigate this accuracy, we compare with a kinetic model that includes exchange effects [3, 4], for the case of electrostatic waves [5]. Concretely, we compute the exchange correction to the electrostatic electron susceptibility for all phase velocities, at T = 0 K. We find that for low phase velocities (ion acoustic waves), the susceptibility in the kinetic model is an order of magnitude larger than the hydrodynamical one. The large discrepancy is due to wave-particle interaction that is lost in fluid models. However, for phase velocities large compared to the Fermi velocity (vϕ & 2.5vF ) the hydrodynamical and kinetic susceptibilities agree rather well. Our results have implications for model choice: for dense and cold plasmas, in addition to ex- change, particle dispersive effects can be important. Relative to classical terms, the contributions 1/3 scale as H 2 = h̄2 ω p2 /m2e v4F ∝ ne in both cases, where ω p , me , ne are the electron plasma fre- quency, mass, and number density, respectively. Because the numerical coefficient for exchange can be large in the low-frequency regime, using a model which includes particle dispersion but not exchange effects cannot be justified. As a further consequence, a quantum mechanical tre- atment including exchange may be necessary for a modest value of H 2 ∼ 0.1, i.e., even for electron densities somewhat below those of metals (for which H 2 ∼ 1). References [1] M. Bonitz, Quantum Kinetic Theory, (B.G. Teubner, Stuttgart, Leipzig, 1998). [2] N. Crouseilles, P.-A Hervieux, and G. Manfredi, Phys. Rev. B, 78, 155412 (2008). [3] J. Zamanian, M. Marklund, and G. Brodin, Phys. Rev. E 88, 063105 (2013). [4] R. Ekman, J. Zamanian, and G. Brodin, Phys. Rev. E, 92, 013104 (2015). [5] G. Brodin, R. Ekman, and J. Zamanian, in preparation.

Speaker: R. Ekman

16:00 → 16:30 COFFEE

16:30 → 18:30 BPIF

Chair: R. Scott

Convener: R. Scott

16:30 I1.201 Toward a burning plasma state using diamond ablator inertially confined fusion (ICF) implosions on the National Ignition Facility (NIF)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.201.pdf Toward a burning plasma state using diamond ablator inertially confined fusion (ICF) implosions on the National Ignition Facility (NIF) L. Berzak Hopkins1, S. LePape1, L. Divol1, A. Pak1, E. Dewald1, S. Bhandarkar1, L.R. Benedetti1, T. Bunn1, J. Biener1, J. Crippen2, D. Casey1, D. Edgell3, D. Fittinghoff1, M. Gatu-Johnson4, C. Goyon1, S. Haan1, R. Hatarik1, M. Havre2, D. D-M. Ho1, N. Izumi1, J. Jaquez2, S. Khan1, C. Kong2, G. Kyrala5, T. Ma1, A. J. Mackinnon1, A. MacPhee1, B. MacGowan1, N.B. Meezan1, J. Milovich1, M. Millot1, P. Michel1, S.R. Nagel1, A. Nikroo1, P. Patel1, J. Ralph1, J.S. Ross1, N.G. Rice2, D. Strozzi1, M. Stadermann1, P. Volegov5, C. Yeamans1, C. Weber1, C. Wild6, D. Callahan1, O. Hurricane1, R.P.J. Town1, M.J. Edwards1 1 Lawrence Livermore National Laboratory, Livermore, CA, US 2 General Atomics, San Diego, CA, US 3 Laboratory for Laser Energetics, University of Rochester, Rochester, NY, US 4 Plasma Science and Fusion Center, Mass. Institute of Technology, Cambridge, MA, US 5 Los Alamos National Laboratory, Los Alamos, NM, US 6 Diamond Materials GmbH, Freiburg, Germany Producing a burning plasma in the laboratory has been a long-standing milestone for the plasma physics community. A burning plasma is a state where alpha particle deposition from deuterium-tritium (DT) fusion reactions is the leading source of energy input to the DT plasma. Achieving these high thermonuclear yields in an inertial confinement fusion (ICF) implosion requires an efficient transfer of energy from the driving source, e.g., lasers, to the DT fuel. In indirect-drive ICF, the fuel is loaded into a spherical capsule which is placed at the center of a cylindrical radiation enclosure, the hohlraum. Lasers enter through each end of the hohlraum, depositing their energy in the walls where it is converted to X-rays that drive the capsule implosion. Maintaining a spherically symmetric, stable, and efficient drive is a critical challenge and focused ICF research effort. Our program at the National Ignition Facility (NIF)* has steadily resolved challenges that began with controlling ablative Rayleigh-Taylor (RT) instability in implosions, followed by improving hohlraum-capsule x-ray coupling using low gas-fill hohlraums, improving control of time-dependent implosion symmetry, and reducing target engineering feature-generated perturbations. As a result of this program of work, our team is now poised to enter the burning plasma regime. *This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Speaker: Laura Berzak Hopkins

17:00 I1.202 Progress in spherical hohlraum studies and experimental campaign on high energy laser facilities in China

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.202.pdf Progress in spherical hohlraum studies and experimental campaign on high energy laser facilities in China Ke Lan 1 1 Institute of Applied Physics and Computational Mathematics, Beijing, China We have made both theoretical and experimental progresses in spherical hohlraum study since we began to study the octahedral hohlraum in 2013. In the theoretical studies, we gave the configuration, the concept and the design of octahedral spherical hohlraum, compared the robustness of the octahedral spherical hohlraum with that of the cylindrical hohlraum and the rugby hohlraum, proposed a novel octahedral spherical hohlraum with cylindrical Laser Entrance Holes (LEH) and LEH shields, and gave a design triangle for determining the geometrical sizes of octahedral spherical hohlraum for ignition target design. Presently, we are developing LARED-3D, a 3D radiation hydrodynamic code to simulate the octahedral hohlraum physics. In experimental study, we have accomplished eight disintegration experiments in Spherical Hohlraum Campaign (SHC) on the SG laser facilities since 2014, including (1) improvement of laser transport by using the cylindrical LEH, (2) comparisons of LPI between the spherical hohlraum and the cylindrical hohlraum, (3) first demonstration of low LPI in the gas-filled capsule-located spherical hohlraums under high intensity laser, (4) determination of LEH size for ignition spherical hohlraum, (5) energetics of 2 LEH spherical hohlraum, (6) energetics of 6 LEH spherical hohlraum, (7) Thomson scattering diagnostic of plasma status inside the 6LEH spherical hohlraum, (8) determination of laser injection scheme for 6LEH spherical hohlraum at SGIII laser facility. As a result of our theoretical study and SPHC, the octahedral spherical hohlraum has advantages in a natural and robust high symmetry without supplementary technology, a high energy coupling efficiency, and a low LPI. Finally, we proposed to use 4 - 2 laser as ignition driven for future ignition facility with a configuration designed for the octahedral hohlraums.

Speaker: Ke Lan

17:30 I1.203 Improving Direct-Drive Implosion Symmetry Using Three-Dimensional X-Ray Tomography on OMEGA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.203.pdf Improving Direct-Drive Implosion Symmetry Using Three-Dimensional X-Ray Tomography on OMEGA R. C. Shah1, D. T. Michel1, I. V. Igumenshchev1, K. S. Anderson1, A. K. Davis2, D. H. Edgell1, C. J. Forrest, D. H. Froula1, V. N. Goncharov1, D. W. Jacobs-Perkins1, S. P. Regan1, A. Shvydky1, and E. M. Campbell1 1 Laboratory for Laser Energetics, University of Rochester, Rochester, NY, 14623, USA 2 NNSA Graduate Fellowship Program, Washington, DC, 20585, USA Reducing low-mode nonuniformities of imploding targets has been identified as a critical step to demonstrate conditions for laser-direct-drive (LDD) inertial confinement fusion implosions that are hydrodynamically scaled to ignition designs for megajoule laser energy at the National Ignition Facility.1 A series of well-diagnosed experiments were performed for the 100-Gbar campaign on OMEGA,2 where the 3-D modes λ = 1, 2, and 3 of the imploding target were tomographically recorded (within ±0.15% ) up to a convergence of 3 using four lines-of-sight x-ray measurements of the ablation front.3 Measurements of the ablation surface location show that the target modes are the result of two components: a dynamic part that varies linearly with the beam-energy balance, and an approximately constant static part, resulting from physical effects such as beam mispointing, mistiming, and uncertainties in the beam energies.4 This technique was used to reduce the low-mode nonuniformities of a low-adiabat implosion from 3.5-µm rms to 1-µm rms by adjusting the beam-energy balance to compensate these static modes, which is an important demonstration for LDD. These methods are currently applied to quantify the effect of the target offset on target modes, and will be applied to cryogenic implosions to obtain improved performances. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article. References 1. S. P. Regan et al., Phys. Rev. Lett. 117, 025001 (2016); 117, 059903(E) (2016). 2. V. N. Goncharov et al., Plasma Phys. Control. Fusion 59, 014008 (2017). 3. D. T. Michel et al., Rev. Sci. Instrum. 83, 10E530 (2012). 4. D. T. Michel et al., “Subpercent-Scale Control of 3-D Modes 1, 2, and 3 in Direct-Drive Configuration on OMEGA,” submitted to Physical Review Letters.

Speaker: Rahul C. Shah

18:00 I1.204 Experimental investigation on parametric instabilities in a regime relevant for shock ignition at PALS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.204.pdf I1.204 for shock ignition at PALS G. Cristoforetti1, L. Antonelli2, S. Atzeni3, F. Baffigi1, F. Barbato4, D. Batani5, G. Boutoux5, A. Colaitis5, F. D’Amato1, J. Dostal6,7, R. Dudzak7,6, L. Juha7,6, P. Koester1, M. Krus6, D. Mancelli5,9, O. Renner7,6, J. J. Santos5, M.M. Skoric10, S. Viciani1, L.A. Gizzi1 1 National Institute of Optics, CNR, Pisa and Florence, Italy 2 York Plasma Institute, department of Physics, University of York, UK 3 Dipartimento SBAI, Università di Roma “La Sapienza”, Roma, Italy 4 Empa Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland 5 Université Bordeaux, CNRS, CEA, CELIA, UMR 5107, Talence, France 6 Institute of Plasma Physics, Czech Academy of Sciences, Prague 8, Czech Republic 7 Institute of Physics, Czech Academy of Sciences, Prague 8, Czech Republic 8 INFN, Laboratori Nazionali di Frascati, Frascati (Roma) Italy 9 Donostia International Physics Center (DIPC), 20018 Donostia/San Sebastian, Basque Country, Spain 10 National Institutes of Natural Sciences, Tokyo, Japan A major issue in the Shock Ignition scheme for Inertial Confinement Fusion (ICF) is the relevance of parametric instabilities (LPI), as Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS) and Two Plasmon Decay (TPD), and the role of generated hot electrons. Here we present the main results of several campaigns at the PALS facility, where parametric instabilities at laser intensities (0.2-2)x1016 W/cm2 at 1 and 3 irradiation (438 and 1314 nm, 250 ps) have been investigated in planar geometry. Such an intensity settles the interaction in a regime relevant for Shock Ignition. Time-resolved spectroscopy and calorimetry of scattered light and characterization of hot electrons via K and bremsstrahlung emission spectroscopy allowed a detailed description of LPI and hot electron generation. Experimental data show that the energy transfer is limited by laser light Top: Time-resolved SRS spectrum from 3 irradiation. Below: SRS spectrum reflection and SBS rather than by SRS in all the from 1 irradiation. irradiation conditions. As expected, Backward Raman Scattering grows by 1-2 orders of magnitude passing from 3 to 1 irradiation and the region where it is driven moves toward higher density plasma, due to the higher plasma temperature obtained at 1 irradiation. Hot electron temperature (30-40 keV) and flux are compatible with a predominant generation via SRS rather than via TPD, despite the data suggest the presence of a component of high energy hot electrons (Thot>100 keV), which could be possibly generated by TPD or hybrid TPD/SRS. SRS reflectivity exhibits spikes both in the spectral and temporal domains, suggesting that the process is dominated by kinetic effects. Results are compared to hydrodynamic simulations using a code that includes self-consistent calculations of non-linear laser plasma interactions and accounts for the laser intensity statistics contained in the beam speckles. Fully kinetic simulations of laser plasma interaction at different times of irradiation are also in progress.

Speaker: Gabriele Cristoforetti

16:30 → 17:30 BSAP/ESPD/SNPD

Chair: M. Dieckmann

Convener: M. Dieckmann

16:30 I1.J101 Scaling and intermittency of the solar wind turbulence on MHD scales

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.J101.pdf Scaling and intermittency of the solar wind turbulence on MHD scales B. Hnat1, S. C. Chapman1, K. T. Osman1, K. H. Kiyani1 1 CFSA, Department of Physics, University of Warwick, Coventry, UK The solar wind magnetic Reynolds number has been estimated to be as high as 105. This makes the solar wind an effective turbulence laboratory for collisional plasma, spanning many temporal and spatial scales of interest. The last two decades have seen a rapid progress in the solar wind studies, due to many space missions providing in situ measurements, with ever increasing temporal resolution, and with multi-point spatial measurements. Quantifying solar wind fluctuations has direct implications for our understanding of MHD turbulence. Here we focus on quantification of three aspects of MHD turbulence: its anisotropy, intermittency and the role of compressive fluctuations. We review the phenomenological models of anisotropic MHD turbulence and discuss scaling properties of power spectra derived from in situ fluctuations of solar wind velocity and of magnetic field. Intermittency, considered as departure of scaling exponents of the higher order moments from mono-fractal values, can be quantified via structure functions and by examining distribution function of fluctuations on different scales. We show that this scaling can be strongly affected by the presence of long-lived coherent structures, for different quantities. Differences in the intermittent scaling of the magnetic field magnitude and density fluctuations suggest that the solar wind plasma cannot be treated as incompressible. We discuss different models for the compressible fluctuations in the inertial range of MHD fluctuations.

Speaker: Bogdan Hnat

17:00 I1.J102 Characterization of kinetic Alfven turbulence in fully kinetic simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.J102.pdf Characterization of kinetic Alfvén turbulence in fully kinetic simulations D. Grošelj1 , A. Mallet2 , S. S. Cerri3 , A. Bañón Navarro1 , C. Willmott4 , D. Told1 , N. F. Loureiro4 , F. Califano5 , R. Samtaney6 , F. Jenko1 1 Max-Planck-Institut für Plasmaphysik, Garching, Germany 2 Space Science Center, University of New Hampshire, Durham, NH, USA 3 Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA 4 Plasma Science and Fusion Center, MIT, Cambridge, MA, USA 5 Physics Department “E. Fermi”, University of Pisa, Pisa, Italy 6 King Abdullah University of Science and Technology, Thuwal, Saudi Arabia Several years of solar wind measurements have established the existence of a turbulent energy cascade beyond the inertial range, at scales below the ion gyroradius, where collisionless dissi- pation and dispersive wave physics come into play. The combined effort of observation, theory, and simulation led to much progress on the topic in recent years. However, a firm understanding of the kinetic range turbulence is still lacking. Here we give an overview of recent results from fully kinetic simulations [1, 2], dedicated to the study of kinetic-scale plasma turbulence in the solar wind. To elucidate the nature of the turbulent cascade, we compare the fully kinetic results against reduced-kinetic simulations, and against phenomenological models. The results are found to be largely consistent with theoretical expectations for a kinetic Alfvén wave (KAW) cascade [3]. In particular, employing massively parallel, 3D simulations with the OSIRIS code [4], we find spectral properties consistent with linear predictions for KAWs and a scale-dependent anisotropy in broad agreement with so- called critical balance. Furthermore, for a plasma beta of order unity, the kinetic-scale spectra from 2D simulations are in excellent agreement with gyrokinetic results, where a KAW cascade is a natural consequence of the model assumptions. We discuss the implications of our results and touch upon the aspects presently outside the scope of the KAW turbulence phenomenology, such as intermittency and the coupling to linear modes other than KAWs. References [1] D. Grošelj et al., Astrophys. J. 847, 28 (2017). [2] D. Grošelj, A. Mallet, N. F. Loureiro, and F. Jenko, Phys. Rev. Lett. (2018), accepted. [3] G. G. Howes et al., J. Geophys. Res. 113, A05103 (2008); A. A. Schekochihin et al., Astrophys. J. Suppl. Ser. 182, 310 (2009); S. Boldyrev et al., Astrophys. J. 777, 41 (2013). [4] R. A. Fonseca et al., Lecture Notes in Comput. Sci. 2331, 342 (2002).

Speaker: Daniel Groselj

16:30 → 18:30 LTDP

Chair: U. Cvelbar

Convener: U. Cvelbar

16:30 I1.301 Challenges for the development of plasma-based atomic layer processing - numerical and experimental analyses of plasma-exposed surface reactions at the atomic level

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.301.pdf Challenges for the development of plasma-based atomic layer processing − numerical and experimental analyses of plasma-exposed surface reactions at the atomic level Satoshi Hamaguchi and Kazuhiro Karahashi Center for Atomic and Molecular Technologies, Osaka University, Osaka, Japan As the sizes of semiconductor devices continue to diminish and are now approaching atomic scales, the downsizing of transistors following Moore’s law is bound to end in the near future. The continuing market demand for higher performance and lower energy consumption of large-scale integrated (LSI) circuits therefore necessitates further innovation in semiconductor technologies. For example, new device technologies such as three-dimensional (3D) device structures and devices based on non-silicon materials have been invented to circumvent the requirement of further device miniaturization. The precise control of device structures at the atomic level over a large area is crucial for the manufacturing of such devices and atomic layer processes, i.e., atomic layer deposition (ALD) and atomic layer etching (ALE), are considered to be some of the most effective means to achieve such goals. Unlike conventional deposition or etching processes, an atomic layer process requires self-limiting reactions, i.e., surface reactions that limit the process only to (essentially) a monolayer in each process cycle and therefore allow a highly uniform process over a large area. The exact surface reaction mechanisms that allow the self-limiting processes, however, have not been well understood. In this work, we discuss our recent study on molecular dynamics (MD) simulations for plasma-based ALE processes for SiO2 and SiN as well as beam-based experimental study on surface chemical reactions of low-energy incident reactive species with surfaces of Si-based materials and metals. Such analyses can give insight into the mechanisms of self-limiting surface reactions.

Speaker: Satoshi Hamaguchi

17:00 I1.302 Plasma-surface interaction studies: Development and application of advanced laser-based diagnostics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.302.pdf Plasma-surface interaction studies: Development and application of advanced laser-based diagnostics N. Lang1, A. D. F. Puth1, S.-J. Klose1, G. Kowzan2, S. Hamann1, J. Röpcke1, P. Maslowski2, J. H. van Helden1 1 Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany 2 Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, ul. Grudziądzka 5, 87-100 Toruń, Poland Understanding how plasmas interact with solid and liquid surfaces is of central importance in many fields such as microelectronics and biophysics, and industrially in environmental and biomedical technologies. Improving processes, such as the growth and etching of materials and surface modification, requires a comprehensive understanding of the kinetics of the transient intermediates involved at the plasma-substrate interface. The experimental approaches currently available provide an incomplete picture of plasma-surface interactions due to relatively low sensitivity, low time resolution, and restricted multi-species capability. We use a state of the art mid-infrared frequency comb (FC) to provide novel spectroscopic data on plasma-surface problems. Broadband direct frequency comb spectroscopy (DFCS), based on FCs as the light source, can detect many transient species simultaneously yielding comprehensive data on their kinetics in the plasma and their interactions with a surface down to the microsecond timescale. The measurement of the plasma environment close to a surface with the high sensitivity and time resolution of DFCS will provide new fundamental insights into the physics and chemistry of the interfacial region. Moreover, the sensitivity of DFCS can be further greatly enhanced by combining it with a high finesse optical cavity, suggesting unprecedented opportunities for ultra-high sensitivity plasma analysis over large spectral bandwidths. We demonstrate the capabilities of the advanced laser-based diagnostics by showing the latest results on the spectroscopic investigations of plasma nitrocarburizing processes with mid-infrared DFCS. We will discuss the workings of DFCS and the influence of process parameters, such as pressure, screen plasma power, and gas mixture, on the concentrations of the key process species such as NH3, C2H2, C2H6, HCN, and CH4 molecules.

Speaker: Jean-Pierre Hubertus van Helden

17:30 I1.303 Sensitive measurement of sheath electric field by Stark spectroscopy using the Balmer-alpha line of atomic hydrogen

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.303.pdf Sensitive measurement of sheath electric field by Stark spectroscopy using the Balmer-alpha line of atomic hydrogen K. Sasaki and S. Nishiyama Division of Quantum Science and Engineering, Hokkaido University, Sapporo, Japan The measurement of sheath electric field has focused on using high Rydberg states for a long time since they have sensitive Stark effects to weak electric fields. However, Rydberg states are difficult to detect because of their small transition probabilities. In this work, we shifted our approach from Rydberg states to lower-lying energy states. Lower-lying energy states can be detected easily because of large transition probabilities. The less sensitive Stark effects of lower-lying states are compensated by employing saturation spectroscopy which has ultrafine, Doppler-free spectral resolution. We demonstrated the measurement of sheath electric field in an inductively coupled hydrogen plasma by measuring the Stark spectra of the Balmer- alpha line of atomic hydrogen. We realized a sensitive detection limit of 10 V/cm and a fine spatial resolution of 0.2 mm by the developed method. Since the developed method utilizes an economical, maintenance-free diode laser system, it may be useful in various experiments which need the measurements of electric fields in plasmas. References [1] S. Nishiyama, H. Nakano, M. Goto, and K. Sasaki, J. Phys. D: Appl. Phys. 50, 234003 (2017). [2] S. Nishiyama, K. Katayama, H. Nakano, M. Goto, and K. Sasaki, Appl. Phys. Express 10, 036101 (2017).

Speaker: Koichi Sasaki

18:00 I1.304 Application of the PI-VM (Plasma Information based Virtual Metrology) for management of the plasma processes in OLED display manufacturing

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.304.pdf Application of the PI-VM (Plasma Information based Virtual Metrology) for management of the plasma processes in OLED display manufacturing S. Park1,2, T. Cho1, J. Lee1, Y. Jang1, J.-J. Hong1, W.-H. Jang1, and G.-H. Kim2 1 Samsung Display Co., Ltd, Chungcheongnam-do, Korea 2 Seoul National University, Seoul, Korea Plasma processes applied to the display- and semiconducting device manufacturing must be monitored by virtual metrology (VM) to maintain the process results and increase the throughput of the processes. Because these processes can be managed according to the VM results, the prediction accuracy of the VM models predicting such as etch- and deposition rate, defect particles, etc. are very important. The core algorithms of the existing VM model are based on statistical methods that analyse the correlation between sensing variables and performance variables in the widely-known big data pool of the fab. However, in identified sensing variables obtained from the engineering equipment system (EES), and other sensors, such as for I-V signal, and optical raw signals, the information about the reacting plasma in the process reactor is not efficiently included. The inclusion of a ‘good’ parameter, which efficiently contains information about the state of the process, is important for ensuring the accuracy of the VM model; therefore, the performance of a statistical VM, without consideration of the process plasma information, cannot satisfy industrial requirements of prediction accuracy for the high-definition organic light emitting diode (OLED) display manufacturing processes. To enhance the performance of the VM model, three types of reactions in the plasma were parameterized as the core variables of the VM model; therefore, plasma information (PI) parameters representing the reaction properties in the plasma volume, sheath, and surface were applied to the VM algorithm and named as the PI-VM [1]. In OLED display manufacturing processes, PI-VM has shown a noticeably enhanced performance (R2 > 90%) for the dry etching amount prediction compared to the existing statistical VM (R2 ~ 50%). In OLED manufacturing fab, various problems occurred during the mass production were predicted and analysed by the application of PI-VM algorithms modelled according to the characteristics of each process plasmas, and they would be introduced in the conference. [1] S. Park, S. Jeong, Y. Jang, S. Ryu, H. –J. Roh, G. –H. Kim, “Enhancement of the Virtual Metrology Performance for Plasma-Assisted Oxide Etching Processes by Using Plasma Information (PI) Parameters”, IEEE Trans. Semiconductor Manufacturing, vol. 28, pp. 241-246, August 2015.

Speaker: Seolhye Park

16:30 → 18:30 MCF

Chair: X. Litaudon

Convener: X. Litaudon

16:30 I1.101 The intermittent SOL: Setting plasma performance and power handling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.101.pdf The intermittent SOL: Setting plasma performance and power handling V. Naulin DTU Fysik, Plasma Physics and Fusion Energy group, Byg 309, DK 2800 Lyngby vona@fysik.dtu.dk The region of open magnetic field lines in tokamaks, which establishes the contact of the confined plasma with material surfaces, has often only been perceived as a boundary condition to the core plasma, with the main effect of providing a source of impurities. In the recent years, it has become increasingly clear that the SOL is setting the conditions for core plasma performance and confinement transitions between low and high confinement. Simulations dropping the distinction between fluctuations and background have been highly successful in reproducing crucial features of the SOL without the input of fitting parameters. Both transitions to H mode with intermittent access to the H mode have been demonstrated and selected power scalings have been recovered. More recently the fuelling of fusion plasmas and the influence of the particle source region in the plasma edge has gained vast attention. Experimental and numerical investigations are underway to understand the effects of SOL intermittency on fuelling and eventual inward pinch effects through the pedestal and via the X-point. The statistical properties of the SOL fluctuations are now well established and can be described as a super-position of uncorrelated pulses from the confinement region into the SOL domain. The saturation of the SOL profiles, that is shoulder formation and their potential connection with plasma detachment and HL back transition, has gained attention as detachment needs to be obtained to mitigate power loads in any realistic divertor operation regime with stable H-Mode operation. The theoretical explanation of the observed heat loads to the divertor and first wall elements and their extrapolation towards ITER conditions is challenging and needs support from accompanying numerical simulations. Large-scale kinetic simulations give stimulating input, but ultimately systematic scans of the parameter space in operating tokamaks are mandatory. The inclusion of finite temperature ion dynamics and neoclassical effects were successful for connecting empirical results to physics interpretation, revealing the role of zonal flows for the initial access to H mode and reproducing SOL fall off lengths, While much progress has been obtained in understanding the non-local and intermittent nature of the SOL, large gaps in our understanding remain, specifically the interaction with neutrals and plasma facing components especially divertor regions. Many species plasmas and most certainly geometry effects will be the areas where most development is expected. We here review recent experimental findings and contrast them with present simulation results including the effects of neutral turbulence interaction.

Speaker: Volker Naulin

17:00 I1.102 Impact of flow poloidal asymmetries on transport in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.102.pdf Impact of flow poloidal asymmetries on transport in tokamaks X. Garbet1, Y. Asahi1 , E. Caschera1, P. Donnel1, G. Dif-Pradalier1, P. Ghendrih1, V. Grandgirard1, Ö. Gürcan2, G. Latu1, P. Hennequin2, Y. Sarazin1, A. Smolyakov3, L.Vermare2, D. Zarzoso4 1 CEA, IRFM, F-13108 St. Paul-lez-Durance cedex, France 2 LPP, Ecole Polytechnique, CNRS, F-91128 Palaiseau, France 3 University of Saskatchewan, Saskatoon, Canada 4 Aix-Marseille Université, CNRS, PIIM, UMR 7345 Marseille, France Physics of turbulent transport in tokamaks has long relied on the paradigm of helical fluctuations on top of a fully symmetrical equilibrium. Symmetry is still preserved whenever zonal fields or zonal flows are generated by turbulence, since these structures are left invariant by rotations in both poloidal and toroidal directions. However it turns out that turbulence generates flows that are not poloidally symmetric, while still zonal in the toroidal direction. These structures are dubbed “poloidal convective cells”. These cells affect transport, via several processes - some similar to those at play for neoclassical transport. It appears in particular that poloidal convective cells contribute to a significant fraction of heavy impurity fluxes [1] and stress tensors [2]. Mechanisms for the formation and sustainment of these cells have been clarified and will be presented. Their impact on transport will be illustrated with results from GYSELA gyrokinetic simulations where neoclassical and turbulent fluxes are computed simultaneously. Evidence of flow poloidal asymmetries has been found in measurements by Doppler backscattering in the Tore Supra tokamak [3]. Possible explanations for these flow asymmetries, including convective cells, will be discussed. Finally turbulence self-regulation via asymmetrical flow generation and feed-back due to flow shear will be discussed. [1] D. Estève et al., https://hal-insu.archives-ouvertes.fr/cea-01380649/, to appear in Nucl. Fusion. [2] X. Garbet et al., New J. Phys. 19, 015011 (2017). [3] L. Vermare et al., 44th EPS conference on plasma physics (2017), submitted to Physics of Plasmas.

Speaker: Xavier Garbet

17:30 I1.103 The effect of triangularity on plasma turbulence and transport in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.103.pdf The effect of triangularity on plasma turbulence and transport in tokamaks Z. Huang, M. Fontana, S. Coda, L. Porte, and the TCV team∗ 1 École Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland The effects of plasma shaping, in particular of the triangularity δ , on plasma turbulence in terms of relative density and temperature fluctuations, have been studied in the Tokamak à Configuration Variable (TCV) using the Tangential Phase Contrast Imaging (TPCI) [1] and the Correlation Electron Cyclotron Emission (CECE) [2] diagnostics, respectively. It has been found that for inner wall limited L-mode plasmas, negative triangularity leads to a substantial reduction of turbulence amplitude, as well as of the decorrelation time and radial correlation length, consistent with the beneficial effect on energy confinement. Crucially, this reduction extends deepin the core, where the local triangularity becomes vanishingly small. Additionally, the electron temperature profile of negative triangularity plasmas features a narrower and less stiff core region [3], as well as a higher value of critical electron temperature gradient for the onset of turbulence. A stabilizing effect of effective collisionality νeff = 0.1ne Zeff /Te2 on TEM- type turbulence was also observed. The increase of turbulence amplitude with decreasing νeff is slower with negative triangularity, while the triangularity effect vanishes at high νeff . These observations are consistent with previous experimental results on the triangularity effect on electron heat transport [4], as well as with global gyrokinetic GENE simulation results [5]. It is also observed that the GAM frequency and wavenumber increases with the triangularity. Experiments are ongoing on the effects of varying electron to ion temperature ratio in plasmas with positive and negative triangularity to investigate the transition between TEM and ITG dominated turbulence regimes. References [1] A. Marinoni, et al., Review of Scientific Instruments 77, 10E929 (2006) [2] M. Fontana, et al., 44th EPS conference on plasma physics (2016) [3] O. Sauter, et al., Physics of Plasmas 21, 055906 (2014) [4] Y. Camenen, et al., Nuclear Fusion 47, 510 (2007) [5] G. Merlo, PhD thesis (2016) ∗ See author list of S. Coda et al 2017 Nucl. Fusion 57 102011

Speaker: Zhouji Huang

18:00 I1.104 Measuring fast ions in fusion plasmas with neutron diagnostics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.104.pdf Measuring fast ions in fusion plasmas with neutron diagnostics J. Eriksson1, F. Binda1, M. Cecconello1, S. Conroy1, G. Ericsson1, C. Hellesen1, V.G. Kiptily2, M. Mantsinen3, M. Nocente4, A. Sahlberg1, M. Salewski5, S. Sharapov2 and JET Contributors † 1 Dept. of physics and astronomy, Uppsala University, Sweden 2 CCFE, Culham Science Centre, Abingdon, Oxfordshire, UK 3 BCS and ICREA, Barcelona, Spain 4 Dipartimento di Fisica and Istituto di Fisica del Plasma, Milano, Italy 5 Department of Physics, Technical University of Denmark, Kgs. Lyngby, Denmark A high-performance fusion plasma inevitably contains a population of supra-thermal ions, with energies in the range from ∼100 keV to a few MeV, that are produced either in the fusion reactions or by the plasma heating systems. Such “fast ions” can drive plasma instabilities, and their confinement in the plasma is important to maintain the high temperature required for fusion. Fusion plasmas consisting of deuterium (D) or a deuterium-tritium mixture (DT) are sources of intense neutron emission due to the D+D and D+T fusion reactions (at the JET tokamak neutron rates of 5.5⋅1016 s-1 and 5.7⋅1018 s-1 have been achieved in D and DT plasmas, respectively), and fast ions often leave characteristic signatures in the neutron emission. In this presentation, we will show how neutron measurements can be used to study fast ions and give examples of results obtained at JET and other present day tokamaks. It is often possible to determine the fast D energy distribution from neutron spectroscopy measurements. With this technique it is possible to study energy dependent interactions between the fast ions and MHD activity, as well as the fast ion dynamics in plasmas heated with neutral beam injection (NBI) and ion cyclotron radio-frequency heating (ICRH). An even more detailed picture of the fast ion distribution can be obtained by combining several different diagnostics. We show how the fast ion distribution can be resolved in both energy and pitch angle by combining neutron and gamma-ray measurements obtained along several different sightlines using velocity-space tomography. Finally, we give an outlook about neutron-based fast ion measurements at the next generation fusion experiment, ITER. † See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001”

Speaker: Jacob Eriksson

17:30 → 18:30 BSAP

Chair: C. Dougados

Convener: C. Dougados

17:30 I1.401 Forecasting space weather: modern community simulation tools and frameworks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.401.pdf Forecasting space weather: modern community simulation tools and frameworks S. Poedts1, J. Pomoell2 1 CmPA / KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium 2 University of Helsinki, Helsinki, Finland Solar Coronal Mass Ejections (CMEs) are large-scale eruptive events in which large amounts of plasma (up to 1013-1016 g) and magnetic field are expelled into interplanetary space at very high velocities (typ. 450 km/s, but up to 3000 km/s). When sampled in situ by a spacecraft in the interplanetary medium, they are termed Interplanetary CMEs (ICMEs). They are nowadays considered to be the major drivers of “space weather” and the associated geomagnetic activity. The detectable space weather effects on Earth appear in a broad spectrum of time and length scales and have various harmful effects for human health and for our technologies on which we are ever more dependent. Severe conditions in space can hinder or damage satellite operations as well as communication and navigation systems and can even cause power grid outages leading to a variety of socio-economic losses. Therefore, the International Space Environment Service (ISES) has set up a collaborative network of 16 space weather service-providing warning centres around the globe, delivering coordinated operational space weather services for the benefit of the extensive user community. In order to improve the forecasts and predictions, NASA, ESA and other agencies have set-up space weather modelling frameworks. We will discuss how such frameworks enable to run and couple different space weather models, and to validate their results by comparing them with those of other similar models and, where possible, to in-situ data. Examples of such frameworks are the Community Coordinated Modeling Center (CCMC, NASA GSFC), the Space Weather Modeling Framework (SWMF) at the Center for Space Environment Modeling (CSEM) at the University of Michigan, and ESA’s novel Virtual Space Weather Modeling Centre (VSWMC) that is being developed. The latter one includes space weather models that are geographically distributed and will be demonstrated.

Speaker: Stefaan Poedts

18:00 I1.402 Characteristics of various high-density helicon sources and their application to electrodeless plasma thruster

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I1.402.pdf Characteristics of Various High-Density Helicon Sources and their Application to Electrodeless Plasma Thruster Shunjiro Shinohara Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan Because of high-density (~1013 cm-3) and low electron temperature (from a few to several eV) available with a broad range of external operating parameters, helicon plasma sources [1,2], using an rf frequency range, are very useful. Various kinds of the sources have been developed and characterized by us to control plasmas as required: e.g., very large- [3,4] (up to 74 cm in diameter with an axial length of 486 cm) or very small-area [5,6] (down to 0.1-0.3 cm in diameter) sources can be found. Particle production efficiency in a wide range of plasma size showed an excellent performance [4], close to a classical diffusion coefficient. High-beta (~ 1) plasma can be easily achieved, showing an importance of neutrals effect [7]. Therefore, these sources can be expected to be utilized in vast areas from fundamental to application fields. Applying these sources to a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between a plasma and electrodes/antennas) [4,6] has been executed, due to a longer life operation expected. Here, we will overview our studies on various-sized, helicon plasma sources and their application to the electrodeless thrusters under the Helicon Electrodeless Advanced Thruster (HEAT) project [4,6]: Characteristics of very large or small (diameter) sources, and plasma thrust performance [6,8]. Here, a broad range of excitation frequency, 7-435 MHz, was used for optimization of plasma sources. In addition, some trials of electrodeless, additional acceleration methods are introduced, such as Rotating Magnetic Field (RMF) and m = 0 half cycle schemes [6], emphasizing the importance of some diagnostics. [1] R. W. Boswell, Phys. Lett. 33A, 457 (1970). [2] S. Shinohara, Adv. Phys.:X 3, 185 (2017) (Review Paper), and references therein. [3] S. Shinohara and T. Tanikawa, Rev. Sci. Insturm. 75, 1941 (2004). [4] S. Shinohara, T. Hada, T. Motomuta, K. Tanaka, T. Tanikawa, K. Toki, Y. Tanaka, and K. P. Shamrai, Phys. Plasmas. 16, 057108 (2009). [5] D. Kuwahara, A. Mishio, T. Nakagawa, and S. Shinohara, Rev. Sci. Instrum. 84, 103502 (2013). [6] S. Shinohara, H. Nishida, T. Tanikawa, T. Hada, I. Funaki, and K. P. Shamrai, IEEE Trans. Plasma Sci. 42, 1245 (2014). [7] S. Shinohara, D. Kuwahara, K. Yano, and A. Fruchtman, Phys. Plasmas 23, 122108 (2016). [8] D. Kuwahara, S. Shinohara, and K. Yano, J. Propul. Power 33, 420 (2017).

Speaker: Shunjiro Shinohara

19:30 → 20:00 RECEPTION

Tuesday, 3 July

09:00 → 09:35 PLENARY SESSION: Innovation Prize

Chair: J. Berndt

Convener: J. Berndt

09:00 I2.005 High Power Impulse Magnetron Sputtering - the Age of Adolescence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.005.pdf High Power Impulse Magnetron Sputtering - the Age of Adolescence A. P. Ehiasarian, National HIPIMS Technology Centre - UK, Materials and Engineering Research Institute, Sheffield Hallam University, Howard St., Sheffield, S1 1WB, UK High power impulse magnetron sputtering (HIPIMS) is one of the youngest sputtering technologies for thin film deposition. It provides a new deposition parameter space which is unattainable by conventional technologies and results in unique material properties. Magnetron sputtering devices confine plasmas in an E×B field where the cathode is planar and the magnetic field is arranged in a closed loop tunnel along the solid surface. The plasma sputter-erodes the cathode to produce a deposition vapour. HIPIMS is operated in a magnetron sputtering configuration but utilises a short (impulse) quasi-stationary gas discharge with duration of ~100 µs and duty cycles of <1% reaching high peak power densities of 3000 Wcm-2 at the cathode at voltages of several hundred volts. Within each HIPIMS pulse the discharge is ignited through an electron ionisation wave and then develops into a cold metal plasma. The properties of the target material such as sputter yield, atomic mass and ionisation potential determine film growth conditions at the substrate. The timescales are sufficient to produce dense metal plasma of 1013 cm-3 whilst avoiding excessive heat buildup and glow-to-arc transitions on the cathode. The plasma pressure may exceed the confinement fields causing localised rupture and intense particle emission. The emission points organise themselves on the crests of a wave propagating in the E×B direction whose velocity is related to the ionisation degree. HIPIMS plasmas can induce a metal implantation zone of a few nanometres to promote adhesion of the coating to the substrate by producing a crystalline interface and a chemical environment for better wetting during film nucleation which result in local epitaxial growth. At highly ionised conditions Nb films have better crystallinity and superconducting properties. Better coverage of meshes and high aspect ratio vias is achieved. In reactive conditions, deposition flux contains highly dissociated nitrogen which promotes a 200 crystallographic texture and fully dense column boundaries in TiN monolithic films. Nanolayered CrN/NbN and CrAlN/CrN developed with low roughness and enhanced density making them suitable for biological and high-temperature oxidation environments. Industrial uptake is rife in the fields of hard coatings and microelectronics with a number of vendors providing turn-key solutions and products made with HIPIMS technology.

Speaker: Arutiun P. Ehiasarian

09:35 → 10:10 PLENARY SESSION

Chair: J. Berndt

Convener: J. Berndt

09:35 I2.006 Opacity data for stellar models and its uncertainties

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.006.pdf Opacity data for stellar models and its uncertainties J.E. Bailey1, T. Nagayama1, G.P. Loisel1, G.A. Rochau1, C. Blancard2, J. Colgan3, Ph. Cosse2, G. Faussurier2, C.J. Fontes3, F. Gilleron2, I. Golovkin4, S.B. Hansen1, G. Hazak5, C.A. Iglesias6, D.P. Kilcrease3, Y. Kurzweil5, J.J. MacFarlane4, R.C. Mancini7, R.M. More8, S.N. Nahar9, C. Orban9, J.-C. Pain2, A.K. Pradhan9, M. Sherrill3, and B.G. Wilson6 1 Sandia National Laboratories, Albuquerque, New Mexico 2 CEA, DAM, DIF, F-91297 Arpajon, France 3 Los Alamos National Laboratory, Los Alamos, New Mexico 4 Prism Computational Sciences, Madison, Wisconsin 5 Nuclear Research Center Negev, Israel 6 Lawrence Livermore National Laboratory, Livermore, California 7 University of Nevada, Reno, Nevada 8 RMorePhysics, Pleasanton, California 9 Ohio State University, Columbus, Ohio Laboratory experiments have found iron opacity predictions are notably different from measurements performed at conditions similar to the boundary between the solar radiation and convection zones [Bailey et al., Nature (2015)]. The measurements help resolve discrepancies between helioseismology and solar models. However, it is essential to understand the differences between opacity predictions and measurements. New measurements with chromium, iron, and nickel are providing a systematic study of how opacity changes with temperature, density, and atomic number. Additional experiments are underway to extend the accessible temperature and density range and to measure the time- resolved temperature and density evolution. These experiments help further evaluate experiment error possibilities and constrain hypotheses for opacity model refinements. ++ Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Speaker: James Bailey

10:10 → 10:40 COFFEE

10:40 → 12:40 BSAP/BPIF

Chair: T. Grismayer

Convener: T. Grismayer

10:40 I2.J201 Particle acceleration in astrophysical and laser-driven plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J201.pdf Particle acceleration in astrophysical and laser-driven plasmas F. Fiuza1 1 SLAC National Accelerator Laboratory, Menlo Park, USA The acceleration of non-thermal particles is critical for our understanding of explosive astrophysical phenomena, from solar flares to gamma ray bursts. Collisionless shocks and magnetic reconnection are often invoked as the dominant acceleration mechanisms, depending on whether the system energy is stored in flows or magnetic fields, respectively; however the microphysics underlying these processes and their ability to efficiently accelerate particles is not yet fully understood. The combination of first principles simulations and high-energy-density laser-driven plasma experiments can play an important role in the exploration of the microphysics of particle acceleration in collisionless plasmas. By performing for the first time 3D particle-in-cell simulations of the interaction of both magnetized and unmagnetized laser-driven plasmas it was possible to identify the optimal parameters for observation of particle acceleration in the laboratory with current laser systems. I will show that efficient non-thermal acceleration of both electrons and ions can be reached in near-future laser-driven studies of collisionless shocks and magnetic reconnection [1-2]. The dominant mechanisms associated with energy dissipation and particle acceleration are identified as a function of the plasma conditions. Finally, I will discuss the requirements on the diagnostics to probe the microphysics of particle acceleration. These results open the way for the first experimental characterization of these important processes in the laboratory [3]. [1] S. Totorica, T. Abel, F. Fiuza, Physical Review Letters 116, 095003 (2016); [2] S. Totorica, T. Abel, F. Fiuza, Physics of Plasmas 24, 041408 (2017); [3] C. M. Huntington, F. Fiuza et al, Nature Physics 11, 173(2015);

Speaker: Frederico Fiuza

11:10 I2.J202 Equation of state and transport properties of water plasmas from ab initio simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J202.pdf Equation of state and transport properties of water plasmas from ab initio simulations M. French1 , R. Redmer1 1 Universität Rostock, Rostock, Germany The equation of state (EOS) and transport properties of dense water plasmas are of fun- damental importance for understanding the interior structure and magnetic-field generation in water-rich giant planets like Uranus and Neptune. Ab initio molecular dynamics simulations based on density functional theory (DFT-MD simulations) have proven to be an efficient and accurate method to calculate such thermodynamic and transport properties of water plasmas. This method also allows for a consistent description of transformations from the plasma state to dissociated or molecular fluid states as well as to a superionic solid at high density [1]. This talk will give an overview about the phase diagram, the EOS and the electrical conduc- tivity of warm dense water as derived from DFT-MD simulations. It is shown that the results for the EOS and optical conductivity are in good agreement with shock-wave compression ex- periments [2]. The description of low-density states ≤ 0.1 g/cm3 is still hardly feasable with DFT-MD due to computational limitations. Therefore, we also report on investigations on finding a possible region of overlap between DFT-MD data and results from a partially ionized plasma model for low densities [3, 4]. It will be shown that both approaches share a region of reasonable, albeit not perfect overlap, so that the construction of wide-range models for the EOS and conductivity remains yet a challenge. This work is supported by the DFG within the FOR 2440 "Matter under Planetary Interior Conditions - High Pressure, Planetary, and Plasma Physics." References [1] R. Redmer, T.R. Mattsson, N. Nettelmann, M. French, Icarus 211, 798 (2011) [2] M.D. Knudson, M.P. Desjarlais, R.W. Lemke, T.R. Mattsson, M. French, N. Nettelmann, R. Redmer, Phys. Rev. Lett. 108, 091102 (2012) [3] M. Schöttler, R. Redmer, M. French, Contrib. Plasma Phys. 53, 336 (2013) [4] M. French, R. Redmer, Phys. Plasmas 24, 092306 (2017)

Speaker: Martin French

11:40 I2.J203 New radiative shock experiments with high power lasers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J203.pdf New radiative shock experiments with high power lasers F. Suzuki-Vidal1, C. Stehlé2, T. Clayson1, J.M. Foster3, P. Graham3, C. Danson3, R.L. Singh4, M. Kozlova5, U. Chaulagain5, J. Dostal5, R. Rodriguez6, J.M. Gil6, G. Espinosa6, and P. Velarde7 1 Blackett Laboratory, Imperial College London, UK 2 LERMA, Observatoire de Paris, France 3 AWE Aldermaston, UK 4 Queen’s University Belfast, UK 5 Extreme Light Infrastructure (ELI), IPP, Czech Republic 6 Universidad de las Palmas de Gran Canaria, Spain 7 Universidad Politecnica de Madrid, Spain The formation of ‘radiative shocks’, shocks in which the structure of the density and temperature is affected by radiation from the shock-heated matter, is ubiquitous in many astrophysical scenarios. They are present, for instance, in Supernovae remnants, accretion disks, and in supersonic jets from young stars. The study of these extreme shocks in controlled laboratory conditions has been possible due to the development of high-power lasers, which allow producing plasmas with the right physical conditions for radiative shock formation. I will present results from experiments performed at the Orion (UK) and PALS (Czech Republic) lasers, in which new geometries have been investigated particularly the collision between two counterpropagating shocks. The investigation benefits from the plasma diagnostics available at each laser facility, for instance point- projection X-ray backlighting and 4-frame optical self-emission imaging at Orion, and optical laser interferometry with fs-exposure at PALS. The results are also investigated with numerical simulations using radiation-hydrodynamic codes such as NYM/PETRA and ARWEN. [1] F. Suzuki-Vidal et al., “Counterpropagating Radiative Shock Experiments on the Orion Laser”, Physical Review Letters 119, 055001 (2017) [2] R.L Singh et al., “Experimental study of the interaction of two laser-driven radiative shocks at the PALS laser”, High Energy Density Physics 23, 20-30 (2017)

Speaker: Francisco Suzuki-Vidal

12:10 O2.J201 Relativistic magnetic reconnection driven by a laser interacting with a micro-scale plasma slab

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.J201.pdf Relativistic magnetic reconnection driven by a laser interacting with a micro-scale plasma slab Longqing Yi1, Baifei Shen2, Alexander Pukhov3, and Tünde Fülöp1 1: Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden 2: Department of Physics, Shanghai Normal University, Shanghai, 200234, China 3: Institut für Theoretische Physik I, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, 40225, Germany Magnetic reconnection is a fundamental plasma process associated with conversion of embedded magnetic field energy into kinetic and thermal plasma energy, via bulk acceleration and Ohmic dissipation. In many high-energy astrophysical events, magnetic reconnection operating in the relativistic regime, i.e. with magnetic energy per particle exceeds the rest mass energy, is usually invoked to explain the non-thermal signatures. However, due to the difficulty in making direct measurements in remote high-energy astrophysical systems and/or achieving the extreme energy density conditions that are necessary to observe relativistic reconnection in laboratory environments, the process by which field energy is transferred to the plasma to power the observed emission are still not properly understood. In this work 1, we propose a novel scenario where the relativistic reconnection is accessed via the interaction of a readily available (TW-mJ- class) laser with micro-scale plasma slab. By means of fully-kinetic 3D particle-in-cell simulations, we show that when the electron beams excited on both sides of the slab approaches the end of the plasma structure, ultra-fast relativistic reconnection occurs in a magnetically-dominated (low-β) plasma. As the field topology changes, the explosive release of magnetic energy results in the emission of relativistic electron jets with cut-off energy ~ 12 MeV. In the meantime, various signatures of magnetic reconnection are observed, including a hard power-law electron energy distribution (with index p ~ 1.8), out-of-plane quadrupole fields pattern, and quantified agyrotropy peaks in the reconnection site. The proposed scenario can be straightforwardly implemented in experiments, and the significant field dissipation process (0.1-TW-class) makes it a promising platform to study the non-thermal signatures and energy conversion in the relativistic regime of reconnection. [1] L. Q. Yi, B. F. Shen, A. Pukhov, and T. Fülöp, Relativistic magnetic reconnection driven by a laser interacting with a micro-scale plasma slab, under consideration in Nat. Commun. (2017) https://arxiv.org/abs/1708.07676

Speaker: Longqing Yi

12:25 O2.J202 Studying the mechanisms of sub-mm wave emission from plasma due to two-stream instability of relativistic electron beam

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.J202.pdf Studying the mechanisms of sub-mm wave emission from plasma due to two-stream instability of relativistic electron beam A.V. Arzhannikov1,2 , V.S. Burmasov1,2 , I.A. Ivanov1,2 , A.A. Kasatov1,2 , S.A. Kuznetsov1,2 , M.A. Makarov1, K.I. Mekler1, S.V. Polosatkin1,2 , S.S. Popov 1,2 , A.F. Rovenskikh1, D.A. Samtsov1,2 S. L. Sinitsky1,2 , V.F. Sklyarov1,2, V.D. Stepanov1,2 , I.V. Timofeev1,2 1 Institute of Nuclear Physics, SB RAS, Novosibirsk, Russia 2 Novosibirsk State University, Novosibirsk, Russia Studying the mechanisms of electromagnetic wave emission from magnetized plasma due to the development of two-stream instability of a high-current relativistic electron beam (REB) is considerably important. The two-stream instability is a fundamental process occurring in both cosmic and laboratory plasmas. In laboratory experiments, the beam-plasma interaction allows one to generate high-power sub-mm waves with the promptly varying frequency1 that is important for practical applications. In this paper, we present the novel results on studying the mechanisms of sub-mm wave emission produced in a REB-plasma system as a result of the two-stream instability development. Experimental investigations are carried out at the GOL-PET device. In these experiments, the high-power REB (0.7 MeV/ 20kA/ 10 μs) is transported through a plasma column of 2 m length with the density np= (0.5÷2)1015 см-3 which is confined in corrugated magnetic field with average induction Bm= 4.2 T and corrugation factor 1.5. We have measured the temporal dynamics of the radiation spectra by a 8-channel polychromator with semiconductor diodes for the frequency range 0.1÷0.5 THz and by an additional 2-channel system of cryogenic sensors for 0.5÷0.9 THz one. It is found that the high level of spectral power density of the radiation is mainly concentrated in two clearly distinct regions of spectrum. For the plasma with density near 11015 см-3, the first frequency region is located from 0.25 up to 0.35 THz, the second one  from 0.6 up to 0.8 THz. The emission power in these regions depends essentially on the radial profile of the plasma density in the cross section of the plasma column. This profile is measured by Thomson scattering system during the beam injection in eight points over the plasma column diameter. We have compared the experimental results with existing theoretical models describing the conversion of the beam-driven plasma oscillations into electromagnetic radiation for the typical conditions of our experiments. It is found that for the first frequency region the observed emission can be interpreted by the linear mode conversion2 of the upper-hybrid branch of plasma oscillations to the electromagnetic radiation in the regions of strong plasma density gradients. For the second frequency region the emission is occurred due to merging of these oscillations at a high level of plasma turbulence3. 1. A.V. Arzhannikov, A.V. Burdakov, V.S. Burmasov, et al., IEEE Transactions on Terahertz Science and Technology, Vol. 6, No. 2, P.245 (2016) 2. I.V. Timofeev, V.V. Annenkov, A.V. Arzhannikov, Physics of Plasmas 22, p.113109 (2015), http://dx.doi.org/10.1063/1.4935890 3. A.V. Arzhannikov and I. V. Timofeev. Plasma Phys. Controlled Fusion 54, 105004 (2012). http://dx.doi.org/10.1088/0741-3335/54/10/105004.

Speaker: Andrey Vasil'evich Arzhannikov

10:40 → 12:40 LTDP

Chair: H. Thomas

Convener: H. Thomas

10:40 I2.305 Influence of plasma pulsing on active species kinetics in low pressure radiofrequency ICP plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.305.pdf Influence of plasma pulsing on active species kinetics in low pressure radiofrequency ICP plasmas A. Granier1, A. Bousquet2, M. Mitronika1, L. Stafford3, S. Bulou4, M. Richard-Plouet1, A. Goullet1 1 Institut des Matériaux Jean Rouxel, IMN, Nantes, France 2 Institut de Chimie de Clermont-Ferrand, ICCF, Clermont-Ferrand, France 3 Université de Montréal, Montréal, Québec, Canada 4 Luxembourg Institute of Science and Technology, LIST, Belvaux, Luxembourg There is an increasing interest in developing surface treatment processes close to room temperature, for instance for flexible electronics. Pulsed Plasma Enhanced Chemical Vapor deposition (PECVD) is one route to reduce the deposition temperature of thin films. Thin films generally deposited above 300°C were shown to be successfully deposited on thermally sensitive substrates such as polymeric films. The challenge is to control the density and kinetics of active species (ions and radicals) so that thin films with the properties of films usually deposited at high temperature may be obtained at much lower temperature. Radiofrequency inductively coupled plasmas (ICP) operated in pulse mode (at a frequency in between 200 Hz and 5 kHz) were previously shown to deposit dense SiO2 films at low temperature. It was furthermore recently shown to allow the deposition of nanocrystallized anatase TiO2 photocatalytic films on polymeric substrates at T < 80°C, whereas anatase is usually obtained above 300°C. The density and kinetics of charged species (electrons and positive ions) and oxygen atoms have been investigated by Langmuir probe and time resolved optical emission spectroscopy in pulsed low pressure rf ICP plasmas created in pure oxygen and oxygen/organometallic vapour mixtures. Hexamethyldisiloxane (HMDSO) and titanium isopropoxyde (TTIP) organometallic precursors, used for SiO2 and TiO2 deposition respectively, are investigated. The respective roles of electrons and oxygen atoms in the dissociation of the organosilicon precursor are discussed in detail.

Speaker: Agnes Granier

11:10 I2.306 Extraction of positive and negative ion beams from large area plasma sources

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.306.pdf Extraction of Positive and Negative Ion Beams from Large Area Plasma Sources S. Radovanov1, A. Samolov1 1 Applied Materials, SPG, Gloucester, Massachusetts, USA Energetic ion beams, extracted from large area radio frequency (RF) plasma sources, are used for material modifications in the leading-edge technologies. One example is the large area inductively coupled plasma (ICP) source used in flat panel plasma vapour deposition (PVD) system, where an ion beam sputter etch is used to reduce the contact resistance prior to depositing an oxide layer. While implantation and deposition are mainly utilizing positive ions, etching and beam neutralization can be done with negative ions, as well. Negative ions are extracted from the afterglow phase of pulsed plasmas, while positive ions can be extracted from both the DC and pulsed plasmas. In the case of pulsed plasma, extraction electrodes and a treated surface are biased synchronously with the discharge modulation for positive/negative ion transport to the target. The energy of extracted ions closely follows the amplitude of the applied bias voltage and it ranges from few hundreds of electron volt to 20 keV. The peak beam current density can reach 100 A/m2. In this paper we review the production and extraction of positive and negative ions from the DC and pulsed RF plasma sources. The experimental verification of the ion angular distribution (IAD), ion current and ion composition is reported. The extraction physics requires correlating the positive and negative ion and electron densities near the extraction opening with the extracted currents. This system is modelled using the CRTRS, 2D/3D code, a plasma fluid code that self-consistently solves for ICP power deposition, electrostatic potential and plasma dynamics in the drift-diffusion approximation. The focus is on the transport of low energy beams. A new perspective on the possible production of angled ion beams on surfaces is discussed. The authors acknowledge Dan Distaso and Joseph Dzengeleski for their expertise in control systems and Shahid Rauf for the development of CRTRS code.

Speaker: Svetlana Radovanov

11:40 O2.301 Design and performance of solid-state microwave plasma sources for lab and industrial applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.301.pdf Design and performance of solid-state microwave plasma sources for lab and industrial applications K. Achkasov1, L. Latrasse1, J. Lo2 and P. Guillot2 1 SAIREM SAS, 12 Porte du Grand Lyon, 01700, Neyron, France 2 Diagnostic Research Team, CUFR Jean François Champollion, Place de Verdun, 81012, Albi, France Microwaves (MW) are frequently used to produce high density plasmas for industrial and laboratory applications presenting several advantages when compared to RF and DC discharges such as high reactive species density and no need for electrodes. Technological advances over the last few years calls for large-scale processing with high density and uniform plasma at reduced pressure. To meet these industrial requirements Aura-Wave [1], an electron cyclotron resonance coaxial plasma source and Hi-Wave, a collisional plasma source, have been designed. Multiple sources can be distributed together in the same reactor. Using the solid-state technology allows the sources to be self-adapted [2] on a wide range of operating conditions: gas type, pressure, MW power. Atmospheric plasma sources are widely requested in applications such as surface functionalization, elementary analysis, creation of radicals and reactive species as well as a broad use in medicine (sterilization/disinfection, treatment of chronic wounds, etc.). For these purposes, a compact plasma source S-Wave has been developed. It can operate in the range of a few 10-2 mbar to atmospheric pressure and is able to create and maintain plasma columns with variable lengths. An ignition system based on dielectric barrier discharge allows to breakdown easily even at atmospheric pressure. Fig. 1. (a) Aura-Wave ECR MW plasma source; (b) Multisource reactor with 8 off × Aura-Waves. Argon, total MW power 160 W, 1 Pa. (c) Photo of the atmospheric plasma created by S-Wave (without incorporated ignition system). Argon, MW power 200 W. References 1. S. Béchu, S., Bès, A., Lacoste, A., Pelletier, J, Device and method for producing and/or confining a plasma, Patent WO 2010049456. 2. Latrasse, L., Radoiu, M., Jacomino, J.-M., Grandemenge, A., Facility for microwave treatment of a load, Patent WO 2012146870.

Speaker: Kostiantyn Achkasov

11:55 O2.302 Current Status of Etching Process Diagnostics and Simulations Based on Atomic and Molecular Data

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.302.pdf Current Status of Etching Process Diagnostics and Simulations based on Atomic and Molecular Data Jung-Sik Yoon1, Mi-Young Song1, Deuk-Chul Kwon1 1 Plasma Technology Research Center, National Fusion Research Institute, Gunsan, Korea The semiconductor industry’s continued trend of manufacturing device features on the nanometer scale requires increased plasma processing control and improved understanding of plasma characteristics and plasma-material interactions. As interest has increased, the role of simulation and diagnostics of processing plasmas become more important in understanding the effects of charged particles and radicals in plasma applications. Also, in order to understand the behavior and properties of chemically active plasma, scientific data such as atomic and molecular data have become a rapidly growing area of scientific endeavor that holds great promise for practical applications for industrial application fields. Thus, in this presentation, we review the current status of plasma diagnostics and simulation based on atomic & molecular data aspect and identify the most important data needs in future plasma research.

Speaker: Jung-Sik Yoon

12:10 O2.303 Glow Discharges with Gridded Electrodes: Models and Applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.303.pdf Glow Discharges with Gridded Electrodes: Models and Applications S. I. Eliseev1, A. I. Saifutdinov1, S. S. Sysoev1, A. A. Kudryavtsev2 1 Saint Petersburg State University, St. Petersburg. Russia 2 Harbin Institute of Technology, Harbin, China Low pressure glow discharges with gridded electrodes can be efficiently used to create electron beams and sustain low-temperature plasma in large volumes. Such electrode configurations are now used as plasma sources in experiments on electromagnetic wave propagation in plasma. Besides, the properties of such plasma – weak electric field and low electron temperature – are similar to those of the negative glow region of DC discharge in planar or hollow configurations [1]. Plasma in this region is characterized by nonlocality of electron energy distribution function (EEDF), and several electron groups which behave almost independently can be distinguished. Greater dimensions of plasma created in configurations with gridded electrodes allows obtaining better spatial resolution of probe measurements, which opens doors for experimental investigation of electron kinetics, implementation of selective control of plasma parameters and gas analysis. Discharges with gridded electrodes require low pL values (product of pressure and intereletrode gap), which corresponds to the left branch of Paschen curve. In this case a cathode sheath is formed between the electrodes which accelerates electrons up to high energies and injects them through the electrode grid into the space where they lose acquired energy on ionization of neutral atoms [2]. This way plasma is created outside the interelectrode gap, and its size depends on the range of beam electrons. The ionization rate induced by these beam electrons depends on parameters of the sheath and can be expressed analytically. In this work such formulation of ionization source was used to create clear models of such discharges, both for purposes of carrying out efficient numerical simulations and writing simple expressions for dependence of discharge parameters from external conditions, i.e. scaling laws. Comparison of results obtained using both methods with each other and with data obtained from probe measurements is presented. Self-sustainment of discharges in various electrode configurations, especially the role of ions coming into the cathode sheath from plasma, is investigated. The work was supported by Russian Science Foundation (RSCF, grant № 17-79-20032) and Saint Petersburg State University (grant № 11.37.212.2016). REFERENCES [1] Yuan, C., Kudryavtsev, A. A., Saifutdinov, A. I., Sysoev, S. S., Tian, R., Yao, J., & Zhou, Z. IEEE Transactions on Plasma Science, 45(12), 3110-3113, 2017. [2] Yuan, C., Yao, J., Eliseev, S. I., Bogdanov, E. A., Kudryavtsev, A. A., & Zhou, Z., Journal of Applied Physics, 122(14), 143304,2017.

Speaker: Stepan Eliseev

12:25 O2.304 Features of forming atmospheric pressure plasma jet in helium and argon flows

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.304.pdf Features of forming atmospheric pressure plasma jet in helium and argon flows O. Stepanova1 , M. Pinchuk2 , A. Astafiev2 , Z. Chen3 1 Saint Petersburg State University, St. Petersburg, Russia 2 Institute for Electrophysics and Electric Power of Russian Academy of Sciences, St. Petersburg, Russia 3 Anhui University of Technology, Maanshan, China Argon and helium gases are the main common substances to generate cold atmospheric pressure plasma jets (APPJ) for biomedicine applications. We studied the features of forming APPJ in helium and argon. An electrode system assembled as a high-voltage inner electrode inside a quartz tube and a grounded electrode – ring was used. The quartz tube served as a dielectric barrier to initiate dielectric-barrier discharge (DBD). The developing discharge inside the tube и propagation of APPJ along the helium and argon flows (guided streamers) into an ambient air was registered by an intensified charge coupled device (ICCD) camera Andor Tech. To supply the discharge a power with a tunable frequency and controlled duty cycle was applied. The discharge in argon differs from the discharge in helium because of a high inhomogenuity with the formation of the bright filaments and broken straightly defined streamers (Fig. 1(a)). They pass out into the surrounding air from the tube and form a luminous image of the jet that we can see. Fig. 1 Images of DBD structure in argon (а) and helium (b) The discharge in helium has a diffuse nature (Fig. 1(b)). Nevertheless, with the increase in the gas flow rate, filaments structure with a greater brightness occurs. The rates of development of streamer structures for both types of discharge are of the s ame order of magnitude ~ 1 cm/µs.

Speaker: Olga Stepanova

10:40 → 12:40 MCF

Chair: L. Frassinetti

Convener: L. Frassinetti

10:40 I2.105 Isotope effects on turbulent transport and confinement in helical and tokamak plasmas: theory and experiment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.105.pdf Isotope effects on turbulent transport and confinement in helical and tokamak plasmas: theory and experiment M. Nakata1,2, M. Nunami1,2, H. Sugama1,2, T. –H. Watanabe3, S. Satake1,2, M. Yokoyama1,2, K. Tanaka1, H. Takahashi1,2, and K. Nagaoka1,3 1 National Institutes of Natural Sciences / National Institute for Fusion Science, Toki, Japan 2 The Graduate University for Advanced Studies, Toki, Japan 3 Department of Physics, Nagoya University, Nagoya, Japan Impacts of the hydrogen isotope ion mass on the energy confinement, which are observed in earlier tokamak and helical plasma experiments, have been a long-standing issue in plasma and fusion research, despite its broad interests and importance. One of the scientific goals in new deuterium plasma experiments in Large Helical Device (LHD) is to explore such “isotope effects” on transport and confinement. In this talk, we present a recent progress in gyrokinetic turbulence simulation studies and the related experiments in LHD. Gyrokinetic Vlasov simulations of trapped-electron-mode (TEM) and ion-temperature-gradient (ITG) driven turbulence in LHD plasmas with hydrogen isotope ions and real-mass kinetic electrons are carried out. It has been clarified that combined effects of the collisional TEM stabilization by the isotope ions and the associated increase of the steady zonal flows at the near-marginal linear stability lead to the transport reduction [1, 2], which is distinct from the ion mass dependence in the conventional gyro- Bohm scaling. On the other hand, the gyro-Bohm like dependence is found for the ITG case without the effect of poloidal rotations by equilibrium radial electric fields. The universal nature of the isotope effects on the TEM-driven turbulence and zonal flows is theoretically verified also for tokamak plasmas. In addition, by using PCI and HIBP/CXS measurements in LHD, TEM-like fluctuations propagating to the electron diamagnetic direction have been identified in high-Te/Ti deuterium and hydrogen experiments with ECRH. A moderate isotope mass dependence in the global energy confinement is also found. [1] M. Nakata, M. Nunami et al., Physical Review Letters 118, 165002 (2017) [2] M. Nakata, M. Nunami et al., Plasma Physics and Controlled Fusion 58, 074008 (2016)

Speaker: Motoki Nakata

11:10 O2.101 Isotope identity experiments in JET-ILW

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.101.pdf Isotope identity experiments in JET-ILW CF Maggi1, H Weisen2, L Horvath3, F Auriemma4, R Lorenzini4, E. Delabie5, D King1, D Keeling1, S Menmuir1 and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CCFE, Culham Science Centre, Abingdon OX14 3DB, UK 2 SPC, Ecole Polytechnique Federale de Lausanne, Switzerland 3 York Plasma Institute, Department of Physics, University of York, York YO10 5DD, UK 4 Consorzio RFX, Corso Stati Uniti 4, I-35127 Padova, Italy 5 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America (*) See the author list of X Litaudon et al. 2017 Nucl. Fusion 57 102001 Dimensionless identity experiments test the invariance of plasma physics to changes in the dimensional plasma parameters, e.g. ne and Te, when the dimensionless parameters are conserved [1] [2]. However, conditions at the plasma boundary, such as influx of neutral particles, may introduce additional physics. An isotope identity experiment was carried out in the JET tokamak with C wall (JET-C), in which ELMy H-modes were obtained with different hydrogenic isotopes, H and D, but with the same profiles of *, *,  and q [3]. The thermal energy confinement times, ELM and sawtooth frequencies scaled as expected, suggesting that the invariance principle was satisfied in JET throughout the plasma radius, despite the different physical processes in the plasma centre, core confinement and edge regions [3]. The isotope identity technique was revisited in recent experiments with H and D plasmas in JET with the ITER-like Be/W wall materials (JET-ILW) and with improved edge profile diagnostics. In L-mode, an isotope identity pair was achieved at IP/BT of 2.5MA/3.0T (D) and 1.48MA/1.78T (H), q95 = 3.4, with D-NBI and H-NBI, respectively, delivering very similar scaled power density profiles (TRANSP/NUBEAM). The line averaged Zeff, the scaled thermal energy confinement times, B E,th /A, and core plasma effective heat diffusivities, A eff/ B, were matched within experimental uncertainties, suggesting that the invariance principle is satisfied in the L-mode core confinement region. In type I ELMy H- modes the experiments were conducted at 1.7MA/1.7T (D) and 1.0MA/1.0T (H), q95 = 3, with D-NBI and H-NBI, varying input power (Pabs ~ B5/3) and injected gas rate to achieve the match in density and temperature profiles (n ~ A and T ~ A1/2). The scaled ELM frequencies, A fELM/B, and the scaled E,th were not matched simultaneously in H and D discharge pairs, unlike the JET-C case. Scaled E,th and core eff were also not matched simultaneously, unlike the L-mode case. When the pre-ELM profiles of *, *,  and q are matched in H and D, the ELM averaged profiles are not matched and the scaled thermal energy confinement times and ELM frequencies are larger in D than in H, suggesting that in JET-ILW H-modes the invariance principle is not satisfied simultaneously in the core and edge regions. Atomic physics of the edge recycling neutrals, thought to play an important role on pedestal confinement and stability in JET-ILW [4], may invalidate the isotope identity technique in the pedestal region. [1] Connor J W and Taylor J B 1977 Nucl. Fusion 17 1047; [2] Luce T C, Petty C C and Cordey J G 2008 Plasma Phys. Control. Fusion 50 043001; [3] Cordey J G et al. 2000 Plasma Phys. Control. Fusion 42 A127; [4] Maggi C F et al. 2015 Nucl. Fusion 55 113031.

Speaker: Costanza Federica Maggi

11:25 O2.102 Isotope-mixing at JET: experiments and modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.102.pdf Isotope-mixing at JET: experiments and modelling M. Marin1 , J. Citrin1 , A. Ho1 , C. Bourdelle4 , Y. Camenen3 , F. J. Casson2 , F. Koechl5 , M. Maslov2 and JET contributors6 1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands 2 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 3 CNRS, Aix-Marseille Univ., PIIM UMR7345, Marseille, France 4 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 5 OAW/ATI, Atominstitut, TU Wien, 1020 Vienna, Austria 6 See the authors list of X. Litaudon et al 2017 Nucl. Fusion 57 102001 Accurate modelling of particle transport is crucial to interpret and predict tokamak experi- ments. Multiple-isotope experiments at JET have allowed a detailed investigation of ion particle transport, providing a valuable test of the underlying theory. These experiments varied the core isotope sources by scanning the relative contribution of peripheral gas injection (edge source) and neutral beam injection (core source). The isotope density peaking followed the electron density peaking, and was found to be insensitive to the core isotope source [1]. This is con- sistent with ion particle transport coefficients being significantly larger than electron particle transport coefficients. This interpretation is supported by recent analytical, nonlinear and quasilinear analysis in the Ion Temperature Gradient (ITG) dominated regime [2]. We show that the experimental observa- tions of the mixed-isotope experiments are well reproduced by first-principle-based flux-driven transport modelling using the quasilinear turbulent transport model QuaLiKiz [3] within the JINTRAC integrated modelling suite [4]. This encompasses the successful reproduction of ion and electron temperature profiles, electron density profiles, and the insensitivity of isotope pro- files to core sources. This result has implications for multi-isotope core fuelling and burn con- trol, where in the ITG regime we predict both fast isotope mixing and peaked isotope profiles. References [1] M. Maslov et al. 2018 Submitted to Nucl. Fusion. [2] C. Bourdelle et al. 2018 Submitted to Nucl. Fusion. [3] Citrin, et al. 2017 Plasma Phys. Control. Fusion, 59(12):124005. [4] M. Romanelli et al. 2014 Plasma and Fusion Research Volume 9.

Speaker: Michele Marin

11:40 O2.103 Isotope mixture control in the high density regime by pellet injection at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.103.pdf Isotope mixture control in the high density regime by pellet injection at ASDEX Upgrade P.T. Lang1, A. Drenik1, R. Dux1, T. Jackson2, O.J.W.F. Kardaun1, A. Mlynek1, B. Ploeckl1, M. Prechtl3, V. Rohde1, R.R. Ruess3, P.A. Schneider1, M. Schubert1, ASDEX Upgrade Team 1) MPI für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 2) CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 3) Hochschule für angewandte Wissenschaften, Friedrich-Streib-Str. 2, 96450 Coburg The all-metal-wall tokamak ASDEX Upgrade is equipped with a versatile pellet launching system. Offering an injection set up similar to that foreseen for EU-DEMO, one of its major tasks is to investigate reactor relevant aspects of core particle fuelling. A future fusion power plant has to operate at high core densities with a D:T isotope mixture of about 1:1 in order to harvest a maximum of fusion power. To access accordingly high densities beyond the Greenwald density nGw fuelling by pellets, mm-sized bodies of solid fuel, is required. This approach must happen in a controlled manner, raising the core density while keeping edge density sufficiently low to avoid confinement degradation. Hence, the challenge of the task is to develop both suitable plasma scenarios and effective tools capable of simultaneously controlling the density profile and the isotope fraction in the core. ASDEX Upgrade deploys a sophisticated control system, providing full feedback control of the pellet launcher. The reactor relevant D/T scenario was mimicked by using H/D. To enable for isotope fraction control, the pellet lauching system was modified to produce H2/D2 pellets, delivering pellet trains with a constant H/(H+D) fraction of 0.5 ± 0.03. Pellet injection can alter the isotope mixture in plasma as requested; after equilibration a 1:1 H:D ratio was established in the plasma, as confirmed by spectroscopy and residual exhaust gas analysis. In addition, pellet actuation allows for operation at high core densities. Hence, our experiments proved pellet actuation can yield access to the high density regime while simultaneously establishing and maintaining the requested H/D isotope ratio. A database containing key parameters was created for the set of experiments dedicated to pellet based isotope fraction control and their pure D reference discharges. It covers plasmas with a H/(H+D) fraction in the range 0 – 0.8 and core densities up to 1.8 x nGw. For the energy confinement, degradation with increasing core density was observed. An increasing H fraction correlates with lower energy confinement. However, the latter correlation does not fit well to the smooth transition with the average ion mass M as predicted by e.g. the scaling H98(y,2) ∼ M0.19. Conversely, small fractions of H were found to cause a significant reduction. This observation demands further consideration for its potential consequences since e.g. for the engineering design of the H removal system in the EU-DEMO fuel cycle a 2 % contribution of H to the plasma particles has been mooted as acceptable. From our data, there is also strong indication of an increasing H content significantly reducing the particle confinement. The same pellet actuation shows a pronounced lower density build up in cases with a significant H fraction in comparison to their pure D counterparts. In addition, analysis of the density evolution after pellet injection shows a distinct shortening of the pellet particle sustainment time for the HD compared to the D pellets.

Speaker: Peter Thomas Lang

11:55 O2.104 The confinement of helium tokamak plasmas, impact of electron heating, turbulent transport and zonal flows

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.104.pdf The confinement of helium tokamak plasmas, impact of electron heating, turbulent transport and zonal flows P. Manas1 , C. Angioni1 , A. Kappatou1 , F. Ryter1 , P. A. Schneider1 and the ASDEX Upgrade Team 1 Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany Helium plasmas in tokamaks are regularly observed to have a reduced confinement with respect to deuterium plasmas [1, 2], inconsistent with the gyro-Bohm scaling of turbulent trans- port. A theoretical explanation of this confinement reduction is required to reliably predict the plasma confinement in the initial non-nuclear phases of ITER operation and also extend the understanding of the isotope effect, hydrogen and helium having the same Larmor radius. Pairs of L- and H-mode plasmas in He and D have been produced in ASDEX Upgrade, where a large variation of the electron to ion heating fraction is obtained with the ECRH and NBI systems. While all the D plasmas exhibit good confinement, the stored energy in He plasmas is observed to increase from 70% to 100% of that of D with increasing ratio of the electron to ion heating. Two regimes are identified, one characterised by strong ECRH heating and low electron density where He shows confinement as good as D, and one characterised by strong NBI heating, where He shows a significant degradation of the confinement. These two regimes were analysed with the transport code ASTRA, and the microinstabilities and the saturated turbulence were simulated with the gyrokinetic code GKW. When ion heating is dominant, in the edge region, ETGs are found to be strongly unstable in the simulations, and thermal coupling limits the increase of the ion temperature when moving from D to He. In the core, the electron and ion temperatures are very similar, but lower in He compared to D, due to increased transport in He. Nonlinear electromagnetic simulations of the D plasma show strong zonal flow activity in ion temperature gradient (ITG) turbulence whereas for a companion simulation where D is replaced by He, a factor of 2 increase of the ion heat flux is observed, with relatively weaker zonal flow levels. When electron heating is dominant, in the edge region the electron temperature largely exceeds the ion temperature and allows an increase of the ion and electron temperatures when moving from D to He due to reduced thermal coupling and relatively stable ETGs. In the core, strong TEM turbulence is obtained in the simulations, with weak zonal flow activity and heat fluxes lower in He than in D. These results confirm a weaker impact of zonal flows in TEM turbulence and for the first time relate them to the different properties of He confinement. The strong impact of zonal flows coupled to electromagnetic effects on the turbulent transport level and on the breaking of the gyro-Bohm scaling presents analogies with recent results on the isotope effect of H [3]. References [1] D. C. McDonald et al, Plasma Physics and Controlled Fusion 46, 519 (2004) [2] F. Ryter et al, Nuclear Fusion 49, 062003 (2009) [3] J. Garcia et al, Nuclear Fusion 57, 014007 (2017)

Speaker: Pierre Manas

12:10 O2.105 CXRS measurements of energetic helium ions in ASDEX Upgrade plasmas heated with a three-ion species ICRH scheme

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.105.pdf CXRS measurements of energetic helium ions in ASDEX Upgrade plasmas heated with a three-ion species ICRH scheme A. Kappatou1, M. Weiland1, Ye. O. Kazakov2, B. Geiger1, R. Bilato1, V. Bobkov1, R. Dux1, T. Pütterich1, R.M. McDermott1, the EUROfusion MST1 team* and the ASDEX Upgrade team 1 Max-Planck-Institut für Plasmaphysik, Garching, Germany 2 Laboratory for Plasma Physics, LPP-ERM/KMS, Brussels, Belgium Fast ion physics is an active field of research in the fusion community, but the studies mostly focus on deuterium fast ions. The generation and investigation of energetic helium in present devices, however, provide significantly more insight on how fast alpha particles, produced from fusion reactions, will behave in future reactor plasmas. Apart from the fusion-produced helium studies carried out at TFTR [1], such investigations have been conducted in non-nuclear devices simulating the fast helium ion population either by helium neutral beam injection [2], or by accelerating either 4He-beam ions [3] or 3He ions [4] with ion cyclotron resonance heating (ICRH). Fast helium ion populations can be measured with charge exchange recombination spectroscopy (CXRS) in the wings of the helium spectral line (HeII n=4-3, 468.6nm), as was done in [1, 2, 4], providing information on their distribution function. In the present work, we present CXRS measurements of energetic 3He ions, obtained for the first time at ASDEX Upgrade. These measurements were part of experiments investigating the feasibility of a novel ‘three-ion’ ICRH scheme at ASDEX Upgrade [5, 6], namely heating hydrogen-deuterium plasmas with a small amount of energetic 3He ions generated with ICRH (energies on the order of 1MeV). The challenges of interpreting the complex CXRS spectra are discussed. The information obtained is compared with the theoretical predictions obtained with the TORIC-SSFPQL code [7]. Possible applications of these measurements for energetic helium transport studies are considered. [1] G.R. McKee et al, Nucl. Fusion 37, 501 (1997) [2] M.G. von Hellermann et al, Plasma Phys. and Control. Fusion 35, 799 (1993) [3] M.J. Mantsinen et al, Phys. Rev. Lett. 88, 105002 (2002) [4] B.C. Stratton et al, Nucl. Fusion 34, 734 (1994) [5] Ye.O. Kazakov et al, Nat. Phys. 13, 973 (2017) [6] Ye.O. Kazakov et al, contribution submitted to the 27th IAEA Fusion Energy Conference (2018) [7] R. Bilato et al, Nucl. Fusion 51, 103034 (2011) * See the author list of H. Meyer et al., Nucl. Fusion 57, 102014 (2017)

Speaker: Athina Kappatou

12:25 O2.106 Isotope wall content control strategy in the upcoming D, H and T experimental campaigns in JET-ILW

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.106.pdf Isotope wall content control strategy in the upcoming D, H and T experimental campaigns in JET-ILW I. Borodkina1,2, D. Douai3, D. Borodin1, S.Brezinsek1, D.Alegre4,5, E.de la Cal5, Y. Corre3, A.Drenik6 J. Gaspar3, C.C. Klepper7, T. Loarer3, G.Sergienko1, S. Vartanian3, T. Wauters8, and JET Contributors* 1 , IEK – Plasmaphysik, TEC , Germany 2 National Research Nuclear University MEPhI, 31, Kashirskoe sh., 115409, Moscow, Russia 3 CEA, IRFM, F-13108 Saint Paul Lez Durance, France 4 D p d I í E é , UNED, C/ d R 1 , 80 0 M d d, Sp 5 Laboratorio Nacional de Fusion, CIEMAT, Avda. Complutense 22, 28040 Madrid, Spain 6 Max-Planck-I f p y k, D-85748 Garching, Germany 7 Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6169, USA 8 Laboratory for Plasma Physics, ERM/KMS, 1000 Brussels, Belgium, TEC Partner * See the author list of X. Litaudon et al., Nucl. Fusion 57 (2017) 102001 JET is the largest tokamak in use and currently the only one capable of handling tritium (T). Equipped with the ITER-like wall (ILW), a tungsten (W) divertor and beryllium (Be) main chamber, JET will soon operate with pure hydrogen isotopes in order to prepare scenarios for ITER [1]. The total budget of 1020 14 MeV fusion neutrons for the upcoming isotope campaigns in JET being consumed in 250 high power plasma pulses (40MW/5s) with only 1%D in the T campaign (or 1%T in the following D campaign), a strategy for reducing the D (T) wall inventory below this level before the T (D) campaign is mandatory. In this paper, we present the elaborated strategy to control and measure the D wall inventory. The efficiency of the different methods which are composing it are evaluated, as well as their combination aiming at maximizing access to different D retention areas in the JET-ILW. We also discuss the review of experimental data and diagnostics (divertor spectroscopy, sub- divertor Rest Gas Analysis) undertaken in order to reliably assess the isotope ratio and thus the strategy efficiency. The strategy includes one week vacuum vessel baking at 320°C, combined with isotopic exchange by hydrogen Glow Discharge and Ion Cyclotron Wall Conditioning, preferentially accessing D retained in the main chamber. Post-mortem analysis of JET PFCs after the first two ILW campaigns revealed however that the majority of the fuel is retained in Be deposited layers at the inner divertor top [2] with thickness up to 40µm, and that complete thermo-desorption of the co-deposited fuel requires surface temperatures beyond 550°C [3]. Analysis of IR measurements in plasma discharges with inner strike point raised to the inner divertor top shows that such temperatures and beyond can be reached. Whereas spectroscopy in these shots reveals the enhancement of Dα, Be I and Be II emission intensities at the strike point, BeD emission intensity is almost absent, consistently with the fact that chemical sputtering of the co-deposited layers is inhibited if surface temperature is higher than 270ºC [4]. Similarly, another scenario designed with strike points on vertical targets will aim at depleting D stored in the outer divertor. [1] X. Litaudon et al. Nucl. Fusion 57 (2017) 102001; [2] A. Widdowson et al, Nucl. Fusion 57 (2017) 086045 [3] K. Heinola et al. Nucl. Fusion 57 (2017) 086024; [4] R.P. Doerner et al, J. Nucl. Mater.681 (2009) 390–391

Speaker: Irina Borodkina

10:40 → 12:40 MCF

Chair: E. Wolfrum

Convener: E. Wolfrum

10:40 I2.106 Phase Space Visualization and Validation of 3D Field Operating Windows for ELM Suppression in KSTAR

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.106.pdf Phase Space Visualization and Validation of 3D Field Operating Windows for ELM Suppression in KSTAR J.-K. Park1 , Y. M. Jeon2 , Y. In2 , J.-W. Ahn3 , N. C. Logan1 , Z. Wang1 , G. Y. Park2 , J. Kim2 , H. H. Lee2 , W. H. Ko2 , H. S. Kim2 , E. A. Feibush1 , R. Nazikian1 , J. E. Menard1 , and M. C. Zarnstroff1 1 Princeton Plasma Physics Laboratory, Princeton, NJ 08540, USA 2 National Fusion Research Institute, Daejeon 34133, South Korea 3 Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA A small degree of 3D relaxation is a key component of tokamaks in the path towards fu- sion burning plasmas, as it provides the great means to control various instabilities such as edge-localized-modes (ELMs). However, the number of choices available for a 3D magnetic field is virtually unlimited and most of them will only destabilize or degrade plasmas by global symmetry-breaking, presenting a major challenge to the concept of 3D tokamaks. Here, we present a complete visualization of 3D field operating windows for ELM suppression in a toka- mak, and its remarkable validation with a complex 3D coil system. The Korean superconducting tokamak advanced research (KSTAR) facility is presently unique by its versatile 3 rows of in- vessel coils, which enabled KSTAR to suppress the type-I ELM crashes using an n = 1 resonant magnetic perturbation (RMP) without triggering core MHD instabilities [1] in high-β plasmas and for a duration longer than ∼ 90τE [2]. This stable RMP window exists only within a small fraction of the total phase space volume that the KSTAR 3D coils can access, as predicted based on local 3D response metrics and validated by a special group of RMPs [3]. The phase space visualization of RMP windows offered excellent opportunities to navigate all available 3D fields and optimize new RMPs, such as the ones only accessible by dynamic passages, the off-midplane RMPs for the first time in KSTAR, and the potentially favorable RMPs for higher toroidal shaping or wider q95 windows. The method and principle adopted in this study is also being used to optimize 3D fields in DIII-D and ITER, and to develop innovative 3D coils feasi- ble for a reactor where long-range ex-vessel RMP solutions are necessary. References [1] Y. M. Jeon, J.-K. Park et al., Physics Review Letters 109, 035004 (2012) [2] Y. In, J.-K. Park et al., Nuclear Fusion 57, 116054 (2017) [3] J.-K. Park, Y. M. Jeon et al., Nature Physics, Under Review (2018) This work was supported by US DOE Contract DE-AC02-09CH11466, and also by the Ko- rean Ministry of Science, ICT and Future Planning.

Speaker: Jong-Kyu Park

11:10 I2.107 Modification of the local edge stability by the plasma response to non-axisymmetric magnetic perturbations in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.107.pdf Modification of the local edge stability by the plasma response to non-axisymmetric magnetic perturbations in ASDEX Upgrade M. Willensdorfer1 , T.B. Cote2 , C. Hegna2 , W. Suttrop1 , S.S. Denk1 , M. Dunne 1 , R. Fischer1 , L. Giannone1 , C.J. Ham3 , A. Kirk3 , F. Orain1 , D.A. Ryan3 , Strumberger1 , N. Wang4 , H. Zohm1 , the EUROfusion MST1 Team[*] and the ASDEX Upgrade Team 1 Max Planck Institute for Plasma Physics, 85748 Garching, Germany, 2 University of Wisconsin-Madison, Madison, Wisconsin 53706, USA 3 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK, 4 AEET, SEEE, HUST, Wuhan 430074, P R China The application of externally applied non-axisymmetric magnetic perturbation (MP)-fields is a promising method to mitigate or even suppress the repetitive impulsive energy loss due to edge localised modes (ELMs) which is expected to be intolerable in low-collisionality H-mode plasmas of future fusion devices. The mitigation of ELMs and the consequent reduction of the pedestal pressure (density ’pump-out’) are strongly related to the amplification of the externally applied MP-field by marginally stable ideal kink modes at the edge. The 3D boundary displacement from these kink modes is characterised by toroidally localised diagnostics with high radial resolution in combination with toroidally rotating n=2 MP-fields. The important role of these kink modes in the ELM mitigation is supported by the following findings [1]: 1. Same dependence of the measured displacement and ELM behaviour on the applied poloidal mode spectrum, 2. Agree- ment of the measured displacements with ideal 3D magnetohydrodynamic (MHD) code predic- tions (e.g. MARS-F, VMEC), 3. Calculated displacements from the vacuum field approximation clearly underestimate the experimental observations. We also demonstrate experimentally that the induced 3D MHD geometry modifies the lo- cal stability at the edge. An additional ideal MHD mode with ballooning structure in-between ELMs is observed only at certain field-lines (helical position) within the 3D geometry in the H-mode edge barrier region [2]. Infinite-n ballooning stability analysis using a realistic 3D equilibrium from VMEC shows that the dominant reason for the local ballooning destabilisa- tion is the 3D distortion of the local magnetic shear. Our investigations suggest that the observed reduction of the edge pedestal pressure in H-mode due to the application of MPs results from a change of the edge stability boundary introduced by the 3D perturbation of the local mag- netic shear. Additionally, not only the observed ballooning mode before the ELM, but also the dynamics of the following ELM crashes are influenced by the local lower stability. [*] H. Meyer et al, Nucl. Fusion 57,102014 (2017) [1] M. Willensdorfer et al, Nucl. Fusion 57, 116047 (2017) [2] M. Willensdorfer et al, Phys. Rev. Lett. 119, 085002 (2017)

Speaker: Matthias Willensdorfer

11:40 O2.107 Experimental conditions for suppressing Edge Localised Modes by magnetic perturbations in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.107.pdf Experimental conditions for suppressing Edge Localised Modes by magnetic perturbations in ASDEX Upgrade W Suttrop1 , A Kirk2 , V Bobkov1 , M Cavedon1 , M Dunne1 , R M McDermott1 , H Meyer2 , R Nazikian3 , C Paz-Soldan4 , D A Ryan2 , E Viezzer1,5 , M Willensdorfer1 , the ASDEX Upgrade∗ and MST1† Teams 1 Max Planck Institute for Plasma Physics, Boltzmannstrasse 2, 85748 Garching, Germany 2 CCFE Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 3 Princeton Plasma Physics Laboratory, PO Box 451, Princeton, NJ 08543-0451, USA 4 General Atomics, PO Box 85608, San Diego, CA 92186-5608, USA 5 Dept. of Atomic, Molecular and Nuclear Physics, University of Seville, 41012 Seville, Spain Full suppression of Edge Localised Modes (ELMs) by magnetic perturbations (MP) in high- confinement mode (H-mode) plasmas has been obtained in ASDEX Upgrade (AUG) in a shape- match experiment with DIII-D [Nazikian, IAEA FEC 2016]. In contrast to previous scenarios where ELMs were mitigated by MP, full ELM suppression in AUG requires stronger shaping. This finding has been attributed to larger pedestal plasma pressure, which in turn lead to stronger amplification of the external MP by marginally stable, edge localised, kink-peeling modes. Re- cent experiments in AUG aimed to identify critical parameters for accessing ELM suppression: Safety factor, plasma rotation, plasma edge density and collisionality. Edge safety factor scans in the range of q95 = 3.6 − 4.2 showed a window q95 = 3.57 − 3.95 for ELM suppression with n = 2 MP. In the ELM suppression scenario used so far, there is a clear maximum edge density (3.3 × 1019 m−3 ) for ELM suppression, which can also be expressed as a collisionality limit at ν∗i,ped = 0.36. Our present data set is still too sparse to discriminate between these quantities. In H- modes with ELM mitigation or ELM suppression, the pedestal pressure is typically 30% below that of ELMy H-mode with MP switched off and still somewhat below that of phases with MP-mitigated ELMs. The resonant, field-aligned MP components near the top of the H-mode edge gradient region are believed to be essential for ELM suppression [Wade, Nucl. Fus. 2015] and their strength in turn depends (in two-fluid MHD) on absence or presence of electron flow across the magnetic field (ve,⊥ ) which can induce helical currents that shield the MP. In our experiment we find that the toroidal rotation at the pedestal top, measured by charge exchange recombination spec- troscopy on B5+ impurities, varies widely, vB5+ tor = 0−40 km/s. There is also significant variation of ve,⊥ , despite ELM suppression being maintained. This includes cases with zero-crossing in the pedestal region (weak shielding) and cases where ve,⊥ (in electron drift direction) in the entire pedestal region is sufficiently large to shield the resonant plasma response everywhere. ∗ See A Kallenbach et al, Nucl Fus 57 (2017) 102015 † See H Meyer et al, Nucl Fus 57 (2017) 102014

Speaker: Wolfgang Albert Suttrop

11:55 O2.108 CASTOR3D: linear stability studies for tokamak and stellarator configurations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.108.pdf CASTOR3D: linear stability studies for tokamak and stellarator configurations E. Strumberger, S. Günter Max Planck Institute for Plasma Physics, 85748 Garching, Germany Three-dimensional tokamak and stellarator equilibria are in the focus of present fusion re- search. While stellarators are characterized by a complex 3D magnetic field topology, 3D toka- maks are devices with weakly broken axisymmetry. Reasons for the asymmetry of tokamak configurations are e.g. three-dimensional resistive wall structures which can reduce the growth rates of external modes, and magnetic perturbation fields. The latter are applied to mitigate or even to suppress edge localized modes (ELMs). The design of 3D fusion devices, as well as the analysis and interpretation of the corresponding plasma discharges require appropriate nu- merical tools that are able to handle their geometry. The newly developed, linear stability CAS- TOR3D code [1] is such a tool. It is a hybrid of the linear stability CASTOR_3DW code [2] and the resistive wall mode STARWALL code [3]. Numerous modifications and extensions of both code parts led to a synergistic effect. The possible applications of the CASTOR3D code exceed easily the possibilities of both of them. The code has a number of significant advantages. It al- lows: (i) to choose between various kinds of flux coordinates, (ii) to perform ideal and resistive stability studies for 3D equilibria, (iii) to take plasma inertia and resistive walls simultaneously into account, (iv) to study the effects of plasma rotation and viscosity on the stability properties, (v) to investigate vertical instabilities, and (vi) to deal with coils and multiply-connected wall structures. The MPI parallelization of the code including the implementation of a parallel eigen- value solver for non-hermitian eigenvalue problems (SLEPc [4]), allows an efficient solution of large eigenvalue problems. Stability studies demonstrating the large variety of possible application of the CASTOR3D code will be presented for a 3D tokamak and a quasi-axisymmetric stellarator configuration. References [1] E. Strumberger and S. Günter,Nuclear Fusion 57, 016032 (2017) [2] E. Strumberger et al., 38th EPS Conf. on Plasma Phys. (Strasbourg, France) vol 35G, (ECA) P5.082 (2011) [3] P. Merkel and E. Strumberger (2015) http://arxiv.org/abs/1508.04911 [4] J.E. Romin et al., SLEPc users manual, Technical Report dsic-ii/24/02, Universidad Politecnica de Valencia (2014), www.grycap.upv.es/slepc

Speaker: Erika Strumberger

12:10 O2.109 L-H transition dynamics with applied n=3 resonant magnetic perturbations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.109.pdf L-H Transition Dynamics with Applied n=3 Resonant Magnetic Perturbations* L. Schmitz,1 M. Kriete,2 R. Wilcox,3 Z. Yan,2 T.L. Rhodes,1 C. Paz-Soldan,4 A. Marinoni,5 G.R. McKee,2 P.Gohil,4 L. Zeng,1 and C.C. Petty.4 1 University of California-Los Angeles, Los Angeles, CA 90095-7799, USA 2 University of Wisconsin-Madison, Madison, WI 53706, USA 3 Oak Ridge National Laboratory, Oak Ridge, TN 37831-0117, USA 4 General Atomics, PO Box 85608, San Diego, CA 92186-5608, USA 5 PFSC, Massachusetts Institute of Technology, Cambridge, MA 02139, USA In ITER-similar plasmas in DIII-D (=1.5- 5x1019m-3, Bt=1.9-2T, Ip=1.5MA, q95~3.6), the L-H threshold power PLH with n=3 Resonant Magnetic Perturbations (RMP) is found to increase strongly with decreasing collisionality, a concern for H-mode access in primarily ECH-heated ITER plasmas since RMP may be applied before the L-H transition in ITER to safely suppress the first ELM. Low edge collisionality is thought to lead to substantial additional thermal losses across the last closed flux surface in ITER, potentially increasing the L-H power threshold [1]. Figure 1 clearly shows that PLH increases at low collisionality, and that the collisionality dependence of PLH is much more Fig. 1: L-H transition power threshold PLH pronounced with applied RMP [PLH~(ν*)-0.3] vs. collisionality ν* (ρ = 0.95) without and compared to non-RMP plasmas [PLH~(ν*)-0.1]. with applied n=3 RMP (3.3×10-4 ≤ δB/B ≤ -4 Pronounced non-axisymmetric modifications of the 4.6×10 The expected ITER L-mode edge collisionality range is shaded. L-mode shear layer with RMP include a substantial local reduction of the Er well and ExB shear [in particular the outboard ExB shear layer is locally “eroded” for flux tubes connecting to high I-coil perturbation field]. Two-fluid modeling with the M3D-C1 code [2] shows that the normalized radial density gradient a/Ln is toroidally modulated and periodically increased on the outboard midplane with RMP. Low- wave-number turbulence is spatially modulated with RMP and increases substantially in amplitude on field lines connecting to high RMP perturbation field. We conjecture that the increase in PLH with RMP results from the combined effects on locally enhanced instability drive (via increased normalized density gradient) and reduced ExB shear. Theoretically, increased Reynolds stress would be required to initiate the L-H transition with RMP active [3], as the Reynolds stress [4] is counteracted by radial forces related to the RMP field structure. The observed increase of the L-H power threshold may be consistent with this picture, as the observed local turbulence increase with applied RMP may not substantially increase the flux-surface-averaged Reynolds stress. Non-resonant n=3 perturbations do not affect PLH significantly, and the modifications in turbulence level and ExB shear are minimal. [1] F. Ryter et al. Nucl. Fusion 54 083003 (2014). [2] R.S. Wilcox et al. Nucl. Fusion 57 116003 (2017). [3] M. Leconte et al, Nucl. Fusion 54 013004 (2014); G. Choi and T.S. Hahm, Nucl. Fusion 58 026001 (2018). [4] Z.Yan et al. Nucl. Fusion, 57, 126015 (2017); Z. Yan, et al. Phys Rev. Lett. 107, 055004 (2014). *This work was supported by the US Department of Energy under DE-FG02-08ER54984, DE-FG02- 89ER53296, DE-FG02-08ER 54999, and DE-FC02-04ER54698.

Speaker: Lothar Schmitz

12:25 O2.110 Modelling of the effects of divertor recycling conditions and toroidal field direction on divertor power and particle flux asymmetries between and during ELMs with PARASOL for COMPASS-like plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.110.pdf Modelling of the effects of divertor recycling conditions and toroidal field direction on divertor power and particle flux asymmetries between and during ELMs with PARASOL for COMPASS-like plasmas M. Hosokawa1, A. Loarte1, G.T.A. Huijsmans2, T. Takizuka3, N. Hayashi4, J. Adamek5, J. Seidl5, J. Horacek5, M. Komm5 1 ITER Organisation, Route de Vinon sur Verdon, 13067 St Paul Lez Durance Cedex, France 2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3 Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan 4 National Institutes for Quantum and Radiological Science and Technology, Naka, Ibaraki 311-0193, Japan 5 Institute of Plasma Physics AS CR, Prague, Czech Republic Particle and energy fluxes to the plasma facing components (PFCs) during edge localized modes (ELMs) are expected to unacceptably shorten the lifetime of PFCs in ITER [1]. Non-linear MHD simulations of ELMs for ITER have shown that some aspects of empirical extrapolations, such as the broadening of the ELM power footprint at the divertor plate, may not apply at the ITER scale [2]. However, these findings are questionable because the particle and energy transport along the field lines in these MHD simulations are modelled in a fluid approximation. The ELM transport in the ITER SOL-divertor plasma is essentially collisionless given the high pedestal plasma temperature. In order to understand the consequences of kinetic effects on the power and particle fluxes to PFCs by ELMs, particle simulations with PARASOL [3] have been carried out. Initial 1-D simulations for ITER showed that the in/out asymmetry of the ELM divertor power/particle fluxes is strongly affected by the magnitude of the ELM energy loss and by the thermoelectric current flow [4]. In order to understand the 2-D aspects of the ELM energy flow to the divertor, initial PARASOL-2D simulations for COMPASS-like tokamak plasmas were carried out in stationary conditions and during ELMs including both the effects of drifts and divertor recycling [5]. It was found that: (i) the directions of the ion B drift “normal” and “reversed” had a strong effect on the steady-state in/out heat/particle flux divertor asymmetries Ein/Eout ~ 0.3 and 1.0 respectively, (ii) the energy load was generally larger during an ELM at the inner divertor for “normal” B and at the outer divertor for “reversed” B. This finding is robust to modelling assumptions (recycling ratio, ELM energy loss magnitude) and in good qualitative agreement with experiment. The paper will report on improved simulations of COMPASS-like plasmas and the comparison of the results with previous COMPASS experimental results [6] and those of more recent experiments. Consequences regarding the comparison between kinetic and fluid modelling for ELMs will be described in the paper. [1] A. Loarte, et al., Nucl. Fusion 54 (2014) 033007. [4] M. Hosokawa, et al., Proc. 41st EPS Conf. P5.003. [2] G.T.A. Huijsmans, et al., Nucl. Fusion 53 (2013) [5] M. Hosokawa, et al., 16th PET Workshop, O-07. 123023. [6] J. Adamek, et al. Nucl. Fusion 57 (2017) 022010. [3] T. Takizuka, Plasma Sci. Technol. 13 (2011) 316.

Speaker: Masanari Hosokawa

12:40 → 14:00 LUNCH

Women in Plasma Physics Lunch

14:00 → 16:00 POSTER SESSION

Mánes Exhibition Hall: MCF P2.1x, BSAP P2.4x
Mánes Multifunctional Hall: BPIF P2.2x, LTDP P2.3x

14:00 P2.1001 Nonlinear wave interactions explain high-harmonic cyclotron emission from fusion-born protons during a KSTAR ELM crash

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1001.pdf Nonlinear wave interactions explain high-harmonic cyclotron emission from fusion-born protons during a KSTAR ELM crash R O Dendy1,2, B Chapman2, S C Chapman2, K G McClements1, G S Yun3, S G Thatipamula3 and M H Kim3 1 CCFE, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK 2 Centre for Fusion, Space and Astrophysics, Department of Physics, Warwick University, Coventry CV4 7AL, UK 3 Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea During ELM crashes in deuterium plasmas in the KSTAR tokamak, the emitted electromagnetic radiation includes features with sharp spectral structure in the frequency range up to ~900MHz. Cases where the spectral peaks below ~500MHz correspond to proton cyclotron harmonics at the outer midplane edge are explained (B Chapman et al., Nucl. Fusion 57 124004 (2017)) as ion cyclotron emission (ICE) driven by a subset of the 3MeV protons born in deuteron-deuteron fusion reactions in KSTAR plasmas. This subset is confined because it lies on deeply passing drift orbits which carry the protons from the core to the outer plasma edge and back. Its sharply defined non-Maxwellian distribution in velocity space means that this energetic proton minority can undergo the magnetoacoustic cyclotron instability (MCI) in the edge plasma. The MCI drives waves on the fast Alfvén-cyclotron harmonic wave branch, which are observed as ICE. During KSTAR ELM crashes, the duration of the proton ICE features is brief, typically a few microseconds. The chirping results from rapid changes in the density of the ambient plasma in which the energetic ions are embedded. Some chirping ICE features below ~500 MHz are accompanied, after a time delay < 1μs, by a fainter detached (“ghost”) chirping feature in the range 500MHz to 900MHz. This frequency range exceeds the local lower hybrid frequency, and cold plasma waves propagating quasi-perpendicular to the magnetic field are expected to be evanescent here. Nevertheless, we show that the “ghost” chirping ICE feature is a real physical phenomenon. It is generated by strong nonlinear wave-wave coupling between different spectral peaks within the primary chirping ICE feature below ~500MHz. We demonstrate this by bicoherence analysis of: first, KSTAR data files for ICE field magnitudes; and, second, the fields generated from direct numerical solution, using a particle-in-cell code, of the self-consistent Maxwell- Lorentz system of equations for fully kinetic electrons and thermal deuterons, together with a minority ring-beam distribution representing the fusion-born 3MeV protons. This work was supported in part by the RCUK Energy Programme [grant number EP/P012450/1], NRF Korea grant no. 2014M1A7A1A03029881 and Euratom. The views and opinions expressed herein do not necessarily reflect those of the European Commission. ROD and GSY acknowledge the hospitality of Kyushu University during this collaboration. SCC acknowledges a Fulbright-Lloyd’s of London Scholarship and US AFOSR grant FA9550-17-1-0054.

Speaker: Richard Dendy

14:00 P2.1002 Study on ion cyclotron emission excited by DD fusion produced ions on JT-60U

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1002.pdf Study on ion cyclotron emission excited by DD fusion produced ions on JT-60U S. Sumida1, K. Shinohara2, R. Ikezoe1, M. Ichimura1, M. Sakamoto1, M. Hirata1, S. Ide2 1 Plasma Research Center, University of Tsukuba, Tsukuba, Japan 2 National Institutes for Quantum and Radiological Science and Technology, Naka, Japan On JT-60U, ion cyclotron emissions (ICEs) which are related to deuterium-deuterium (DD) fusion produced fast 3He (ICE(3He)), T and H ions were detected [1]. The previous work shows that toroidal wavenumber and frequency of the ICE(3He) observed in JT-60U are close to those based on the dispersion model of the magneto-acoustic cyclotron instability [2]. In this study, to understand its excitation mechanism, we have evaluated and compared the fast 3He ion velocity distribution between the cases with and without the ICE(3He) in a similar condition by using fast ion transport code OFMC [3]. To evaluate the velocity distribution of the beam-thermal fusion produced ions properly, we take into account effects of scattering-angle dependence of the fusion products on their birth energies and pitch angles. On JT-60U, the ICE(3He) tended to become weak and disappear when negative-ion-sourced NB (N-NB) was injected [1]. Figure 1 shows evaluated energy and pitch angle distributions of the fast 3He ions at the plasma edge on the low field side in the cases (a) without and (b) with the N-NB injection. In the case without the N-NB injection, the distribution has a bump-on tail structure in the energy direction. On the other hand, the distribution does not have the structure in the case with the N-NB injection. Relatively low energy 3He ions that can reach the plasma edge are produced due to the N-NB injection. As a result, they eliminate the bump-on tail structure. Hence, the comparison implies that the ICE(3He) is excited by the bump-on tail structure in the energy direction. Fig.1. Energy and pitch angle distribution of fast 3He ions (a) without and (b) with N-NB injection in E45335. [1] M. Ichimura et al., Nucl. Fusion, 48, 035012 (2008). [2] S. Sumida et al., J. Phys. Soc. Jpn., 86, 124501 (2017). [3] K. Tani et al., J. Phys. Soc. Jpn., 50, 1726 (1981).

Speaker: Shuhei Sumida

14:00 P2.1003 Nonlinear gyrokinetic investigation of energetic particle driven geodesic acoustic modes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1003.pdf Nonlinear gyrokinetic investigation of energetic particle driven geodesic acoustic modes A. Biancalani1 , A. Bottino1 , N. Carlevaro2 , A. Di Siena1 , T. Görler1 , G. Montani2 , I. Novikau1 , and D. Zarzoso3 1 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 2 ENEA C.R. Frascati - ENEA for EUROfusion, C.P. 65 - 00044 Frascati, Italy 3 Aix-Marseille Université, PIIM, UMR 7345, 13397 Marseille, France Geodesic acoustic modes [1] (GAM) are zonal, i.e. axisymmetric oscillations of the radial electric field, typically observed in tokamaks in the presence of turbulence. GAMs can be driven unstable by the presence of energetic particles (EP), i.e. fast ions which can be present as the product of fusion reactions or external heating mechanisms. A possible role of these EP-driven GAMs (EGAM) [2] in the nonlinear saturation of turbulence, has been recently emphasized by means of gyrokinetic (GK) semi-lagrangian simulations [3]. In this work, the nonlinear dy- namics of EGAMs is investigated with the GK particle-in-cell code ORB5 [4, 5]. The EGAM saturation due to wave-particle nonlinearity [6] and wave-wave nonlinearity is compared. The radial structure of EGAMs is also investigated. Finally, the nonlinear interaction of EGAMs and turbulence is studied. Comparisons with reduced models and with the GK codes GENE and GYSELA, are presented. References [1] N. Winsor, J. L. Johnson and J. M. Dawson, Phys. Fluids 11, 2448, (1968) [2] G. Y. Fu, Phys. Rev. Letters 101 (18), 185002 (2008) [3] D. Zarzoso, et al. Phys. Rev. Letters 110 (12), 125002 (2013) [4] S. Jolliet, et al. Comput. Phys. Commun. 177, 409 (2007) [5] A. Bottino, et al. Plasma Phys. Controlled Fusion 53, 124027 (2011) [6] A. Biancalani, et al. J. Plasma Phys. 83 725830602 (2017)

Speaker: Alessandro Biancalani

14:00 P2.1004 Performance of the Imaging Motional Stark Effect diagnostic at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1004.pdf Performance of the Imaging Motional Stark Effect diagnostic at ASDEX Upgrade A. Burckhart, O. Ford, A. Bock, R. Fischer, M. Reich, D. Rittich and the ASDEX Upgrade team Max-Planck Institut für Plasmaphysik, Garching / Greifswald, Germany Motional Stark Effect (MSE) diagnostics provide important information on the safety factor in magnetically confined fusion plasmas. The method utilizes the polarisation of Stark-split D-alpha light emitted by injected neutral particles. In a traditional MSE system, the light, after being led through a set of two photo-elastic modulators that modulate its intensity in time, is collected via optical components defining individual lines of sight. Imaging MSE systems (IMSE), on the other hand, guide the light through a series of birefringent plates, combined with a linear polariser, before focusing it onto a camera without reducing the spatial resolution or coverage. This leads to a spatial modulation that takes the form of an interference pattern in the image, containing both spatial and polarisation information in each frame. While conventional MSE systems filter out the π- or σ-lines of the Stark spectrum, the IMSE approach utilizes all the lines, increasing the signal to noise ratio and eliminating the need for narrow-band filters. Furthermore, IMSE is not disturbed by polarized, broadband background light and provides a 2D image of the polarisation angle, significantly increasing the quality of the equilibrium reconstruction compared to 1D MSE systems. The ASDEX Upgrade IMSE diagnostic has a wide field of view, extending from the outer separatrix across the magnetic axis. The optics are designed for low Faraday rotation, which is monitored, together with possible drifts, using in-vessel light sources with known polarisation. In the 2016 campaign a prototype “back-end”, which is the set of lenses and crystals creating the interference pattern, was mounted to the new in-vessel system. It was possible to resolve polarization changes of 0.1° with a time resolution of 5.6 ms, enabling the study of current redistribution during sawteeth. This prototype back-end was replaced by a fully optimized system at the start of the 2017 campaign. The new design features larger birefringent plates yielding a larger étendue, higher stability and improved calibration possibilities. The signal to noise level was significantly increased by the upgrade. The details of the new IMSE back-end will be presented, together with a comparison with the conventional MSE system and the benefit of the IMSE data for the reconstruction of magnetic equilibria. Furthermore, a calibration method using specially designed forward and reversed magnetic field discharges will be described, as well as results from discharges with modified q- profiles.

Speaker: Andreas Oliver Burckhart

14:00 P2.1005 Assessment of the fast particle spectra for Tangential Spectrometer for H/He and DT ITER operation.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1005.pdf Assessment of the Fast Particle Spectra for Tangential Spectrometer for H/He and DT ITER Operation T.M. Kormilitsyn1, A.R. Polevoi2, L. Bertalot2, M.I. Mironov3, V. Krasilnikov2, A. Serikov4, R. Barnsley2, Yu. A. Kashchuk5, A. Loarte2, S.D. Pinches2, M. Walsh2 1 Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700, Russia 2 ITER Organization, Route de Vinon sur Verdon, CS 90 046, 13067 St Paul-lez-Durance Cedex, France 3 Ioffe Institute, St. Petersburg 194021, Russia, 4Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany, 5Project Center ITER, Moscow, Russia The study of fast ion behaviour in reactor conditions is among the major goals of the ITER project. Additional heating by NBI and ICH creates population of suprathermal ions with an anisotropic distribution in velocity space. The energy spectrum measurements of CX neutrals and neutrons made by the Tangential Neutron Spectrometer (TNS) contribute to the reconstruction of the fast ions’ distribution function in combination with the radial measurements by the NPA, RNC, and HRNS diagnostics. It will help determine the consequences of instabilities which cause the redistribution of fast ions in the plasma and to the assessment of their impact on plasma heating and current drive. Assessing the capabilities of diagnostics at different phases of ITER operation is an essential part of ITER research planning. Simulations of the signals that will be measured at different phases of ITER operation require computational tools, so called synthetic diagnostics (SD), with realistic geometry and parameters corresponding to the ITER diagnostic design. To assess the accuracy and resolution of the measurements of the TNS in all ITER scenarios we have developed a TNS SD compatible with the ITER IMAS suite of codes. The module developed enables simulation of the anisotropic spectra of the charge-exchange (CX) neutrals and neutrons originated from interactions between suprathermal and thermal ions together with the background spectra. Simulations of realistic signals require appropriate approximations for the processes which produce the main and background signals. In our simulations the distribution of the suprathermal ions is calculated by solving the 3D Fokker-Plank equation for the different scenarios foreseen in the ITER research plan. This includes the pre-DT and DT phases of ITER operation with different orientations of the NBI as foreseen in the ITER design. Simulations of the spectrum of the CX neutrals are based on the DOUBLE-MC code extended to simulate anisotropic sources and neutrons. Background spectra at the location of the TNS detectors for neutrons were calculated on the basis of a parameterisation of the MCNP simulations with realistic ITER geometry and features of the machine components. Assessment of the CX neutrals and DT neutrons spectra is carried out for H-NBI during the pre-DT phase and D-NBI heated baseline DT scenarios. The impact of the fast particle distribution on the spectra is studied.

Speaker: Timofey Kormilitsyn

14:00 P2.1006 Simulation of trajectories of runway electrons for supprort diagnostics at the COMPASS tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1006.pdf Simulation of trajectories of runaway electrons for support diagnostics at the COMPASS tokamak J. Cerovsky1,2 , O. Ficker1,2 , J. Mlynar1 , J. Urban1 , E. Macusova1 , V. Weinzettl1 , M. Farnik1,2 , J. Zebrowski3 , M. Jakubowski3 , M. Rabinski3 , M. J. Sadowski3 , R. Panek1 , M. Hron1 and the COMPASS team1 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 FNSPE, Czech Technical University in Prague, Prague, Czech Republic 3 National Centre for Nuclear Research (NCBJ), Otwock, Poland The Cherenkov detector is one of the few runaway electron diagnostics, which do not rely on a detection of secondary radiation caused by an impact of high energetic particles on the limiter or the first wall of the tokamak. The capability of a direct observation of runaway electrons together with a possibility of setting energy thresholds for incoming particles makes the Cherenkov detector a useful diagnostics tool for an investigation of runaway electrons dynamics. In the past years experiments focused on observation of runaway electrons by the Cherenkov-type detector were performed at the COMPASS tokamak. One of features of the Cherenkov detector is a measurement in the well defined location of the tokamak with high temporal resolution. Due to safety reasons, the Cherenkov detector is placed in the shadow of the low field side protection limiter in most discharges performed on the COMPASS tokamak. The open question is whether runaway electrons can reach the detection head of the Cherenkov detector or are preferably lost at the protection limiter. The aim of this work is a simulation of trajectories of escaping runaway electrons and finding the location of their impact in order to determine possible parameters of runaway electrons, which can be detected by the Cherenkov detector. For these purposes, the pushers for tracking of relativistic particles were implemented in the Python environment and particles are tracked in the reconstructed axisymmetric magnetic field of the COMPASS tokamak (calculated by the EFIT code). References [1] Panek R. et al. 2016 Plas. Phys. Contr. Fusion 58 014015 [2] Mlynar J. et al. invited, this conference

Speaker: Jaroslav Cerovsky

14:00 P2.1007 Automatic Robust Regression Analysis of Fusion Plasma Experiment Data based on Generative Modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1007.pdf Automatic Robust Regression Analysis of Fusion Plasma Experiment Data based on Generative Modelling K. Fujii1 , C. Suzuki2 , and M. Hasuo1 1 Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Japan 1 National Institute for Fusion Science, Gifu 509-5292, Japan The first step to realize an automatic data analysis for fusion plasma experiment is automat- ically fitting noisy data measured routinely. A textbook example of fitting procedures is the minimization of the squared difference between the measured data and some parameterized functions such as polynomial. This model implicitly assumes that both the noise distribution and the latent function form are already known, however, it is frequently not the case for the real world data analysis. Using the conventional model in such situatiln easily results in over- or under-fitting, and therefore some human supervision has been usually necessary. In this work, we propose to optimize a model itself to stabilize the analysis. Based on Bayesian statistics, the goodness of a model M for particular (k-th) data y(k) can be measured by the merginal likelihood, ∫ p(y(k) |M ) = p(y(k) |θ , M )p(θ |M )d θ (1) where, p(y(k) |θ ) is likelihood of data y(k) with given fitting parameter θ . The form of the likeli- hood (noise distribution and form of the latent function) is implicitly included in the likelihood and the prior distribution p(θ |M ). The robustness of the model M might be measured by an expectation of this merginal like- lihood, E p(y) [log p(y|M )], where p(y) is the true distribution of y that will generate data in the future. We show that the maximization of this expectation is identical to the minimization of Kullback-Leibler divergence between the true data distribution p(y) and the modeled data distribution p(y|M ), and therefore the unbiased generative modeling is essential. A strategy we propose here is to construct a flexible generative model, i.e. the latent function form and the noise distribution, with neural networks and optimize their weights to fit our gen- erative model to a large amount of data. We applied this strategy to Thomson scattering data in Large Helical Device and found that our model outperforms the conventional analysis methods that does not take into account the data distribution, especially in terms of the robustness.

Speaker: Keisuke Fujii

14:00 P2.1008 Neutron monitoring and in-situ detector calibration at the Wendelstein 7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1008.pdf Neutron monitoring and in-situ detector calibration at the Wendelstein 7-X stellarator W. Schneider1, C. Biedermann1, R. Burhenn1, F. Grünauer2, T. Richert1, H. Schuhmacher3, B. Wiegel3, M. Zboril3, A. Zimbal3 and the W7-X Team1 1 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 2 Physics Consulting, Zorneding, Germany 3 Physikalisch-Technische Bundesanstalt, Braunschweig, Germany The neutron monitor system of the W7-X stellarator consists of three sets with up to five neutron detector tubes of different sensitivities to thermal neutrons in a dedicated moderator geometry in order to realize a nearly constant response independent of the neutron energy. The monitors have been designed to cover the expected neutron yields in deuterium plasmas from 1011 up to 1016 neutrons per second with a time resolution of 5 ms and a statistical uncertainty of better than 15 %. This corresponds to neutron fluence rates from 103 cm−2 s−1 to 109 cm−2 s−1 at the location of the monitors. The central monitor is located 3.9 m above the equatorial mid-plane of W7-X, the two peripheral monitors are placed outside the cryostat at a distance of 0.8 m from the vessel at a height of 1.6 m above the equatorial plane directed towards the plasma axis. The monitors have been characterized in the neutron reference fields of the Physikalisch-Technische Bundesanstalt (PTB) to validate the specified properties. The objectives of the neutron monitors of W7-X combine the documentation of the total neutron emission per year and the monitoring of the maximum neutron emission rate as well as the determination of the neutron flux rates measured at different positions around the W7- X verifying physical plasma parameters such as the ion temperature and deuterium density. In order to determine the neutron emission produced by D(d,n)3He fusion reactions in the plasma an in-situ calibration with a neutron source of known source strength is required. The results of such a calibration procedure depend on the entire scattering behavior of the neutrons by all W7-X materials and its environment, starting inside the plasma up to the detector tubes inside the neutron monitors. This is why we have performed two in-situ calibrations, one before the first operation of W7-X in a limiter configuration without graphite tiles in January of 2015 and one after the installation of the divertor targets including uncooled graphite tiles in March of 2017. The procedures of these in-situ calibrations will be described and the results compared to predictions of Monte-Carlo calculations (using the MCNP code) of the neutron propagation from the location of the neutron source to the neutron monitors using a simplified model of W7-X.

Speaker: Wolfgang Schneider

14:00 P2.1009 2-D ECE imaging diagnostic for comparative study of MHD instabilities in WEST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1009.pdf 2-D ECE imaging diagnostic for comparative study of MHD instabilities in WEST tokamak Y. B. Nam1, R. Sabot1, D. Elbeze1, M. Kim2, M. Choi3, H. K. Park2, 3, G. S. Yun4, W. Lee3, P. Lotte1 and WEST team1 1 CEA, IRFM, Saint-Paul-lez-Durance, France 2 Ulsan National Institute of Science and Technology, Ulsan, Korea 3 National Fusion Research Institute, Daejeon, Korea 4 Pohang University of Science and Technology, Pohang, Korea An electron cyclotron emission imaging (ECEI) diagnostic for WEST (W Environment for Steady state Tokamak) is on the last stage of the development under Korean-French collaboration, and the system will be installed before the 2018 autumn experimental campaign. The WEST ECEI diagnostic will initially provide 2-D ΔTe images from the core to the low-field side (LFS) edge of the plasma (R= 2.4 ~ 3m) [1], and the detectable radial range will be extended to high-field side (HFS) edge in future. The WEST ECEI system is specially designed to overcome the limited accessibility and indirect beam direction: Two metallic mirrors, which can endure 400°C during long discharges, will be installed inside the vacuum vessel for beam focusing and redirection in the vicinity of the plasma. The detection element and focus control optics are vertically aligned in an optical enclosure of 2.7 m height installed in a narrow area behind the man-access port. The laboratory characterization with the integrated imaging optics had confirmed that the system can provide well-focused images from any radial location on the LFS of the plasma, with high spatial (≤1.7 cm) resolution. A synthetic image reconstruction tool for XTOR code is on development for numerical validation of the WEST ECEI measurement. The tool will provide synthetic images from XTOR result, taking into account the spatial resolution, instrumental effect and broadening effect of the ECEI system. The direct comparability of the 2-D images obtained from WEST ECEI and the synthetic images from XTOR, along with the core reflectometry measurements [2], synthetic images from JOREK and/or the ECE images from KSTAR and other tokamaks will provide deep understanding of the phenomena affected by tungsten impurities. *Work supported by NRF of Korea (grant No. NRF- 2014 M1A 7A1A03029865). References [1] Y. B. Nam, et al, Rev. Sci. Instrum. 87, 11E135 (2016) [2] R. Sabot et al, Comptes rendus de physique, 17, 1018-1026 (2016)

Speaker: Yoonbum Nam

14:00 P2.1010 Characterization of a Cherenkov diagnostic for fast electrons measurements in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1010.pdf Characterization of a Cherenkov diagnostic for fast electrons measurements in tokamak plasmas F. Bagnato1,2, A. Romano1, D. Pacella1, P. Buratti1, A. Doria1, L. Gabellieri1, E. Giovenale1, A. Grosso1, L. Jakubowski3, V. Piergotti1, M. Rabinski3, G. Rocchi1, A. Sibio1, B. Tilia1, J. Zebrowski3 1 ENEA, Fusion and Nuclear Safety Department, Via E. Fermi 45, 00044 Frascati (RM), Italy 2 Swiss Plasma Centre, EPFL, CH-1015 Lausanne, Switzerland 3 National Centre for Nuclear Research, 7 Andrzeja Soltana Str., 05-400 Otwock, Poland Predicting and controlling plasma disruptions in tokamaks is one of the key features for a reliable application of nuclear fusion [1]. In particular, measurements of fast electrons produced in the plasma core and escaping from it are of interest to study processes occurring inside the plasma itself. A Cherenkov diagnostic detector was installed on FTU and its performances have been under investigation to explore these phenomena [2]. In this work, a laboratory characterization of the Cherenkov probe is presented. The contribution of visible light and X-rays up to 85 keV was explored confirming that soft and hard X-rays do not affect the measurement of the probe (about 1%). A first calibration of the Cherenkov probe with an intense electron beam of 2.3 MeV and at high fluxes (1012 e−, much higher than the 104 e− of the radioactive sources) was done at ENEA’s Microtron source facility [3]. The characterization was performed together with a spectrometric analysis, which gave a deeper insight of the phenomena occurring inside the detectors. The results show an ionization spectrum, confirming the suspects that the signals observed during plasma discharges are due mainly to luminescence. Nevertheless the validity of the Cherenkov probes as diagnostic tool is not compromised, considering the good correlation with plasma instabilities and runaway electrons (REs) production measured by different diagnostics. Moreover, the direct detection of fast electrons with high time resolution showed interesting features not present in other diagnostics. This configures the Cherenkov as a very promising diagnostic for real time control and monitoring of RE beams for future machines. Thanks to this calibration, REs have been estimated in 8x107 e- of about 2.3 MeV corresponding to a signal of 2 V in FTU. A more detailed calibration at INFN Laboratory’s Beam Test Facility is planned, to test the detector response in a wide range of fluxes and with better precision. [1] B. Esposito, et al., Plasma Physics and Controlled Fusion 59 (2017) 014044. [2] F. Causa, et al., Nuclear Fusion 55 (2015) 123021. [3] M. Perenzoni, et al., Physics and Appl. of Terahertz Radiation, 23 Springer Series in Opt. Sci. 173, Chap. 5.

Speaker: Danilo Pacella

14:00 P2.1011 Application of Optical Emission Spectroscopy to Hydrogen plasmas for proton rich plasmas generation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1011.pdf Application of Optical Emission Spectroscopy to Hydrogen plasmas for proton rich plasmas generation M. Mazzaglia1, G. Castro1, D. Mascali1, R. Reitano1,2, L.Celona1, E. Naselli1,2, L.Neri1, G. Torrisi1 and S. Gammino1 1 INFN – Laboratori Nazionali del Sud, Catania, Italy 2 Università degli studi di Catania, Catania, Italy The evaluation of the electron density and proton fraction of hydrogen plasmas has a relevant importance for plasma traps used as sources of intense proton, H2+ or H3+ beams. Optical Emission Spectroscopy (OES) enables to evaluate simultaneously and on-line the H/H2 relative abundances together with plasma and electron temperature. In this work, the experimental results of the OES measurements on the Proton Source of the European Spallation Source plasma has been related to the properties of the ion beam extracted by the source (proton fraction and beam intensity, in particular). Benefit of the diagnostics and the further improvements foreseen in next future will be highlighted.

Speaker: Maria Mazzaglia

14:00 P2.1012 Stochastic clustering of material surface under high-heat plasma load in fusion devices

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1012.pdf Stochastic clustering of material surface under high-heat plasma load in fusion devices V. P. Budaev 1,2 1 National Research University “MPEI”, Moscow, Russia 2 National Research Center “Kurchatov Institute”, Moscow, Russia Materials of various chemical composition and initial crystalline virgin structure (tungsten, carbon materials and stainless steel) have been studied after the irradiation by high heat plasma fluxes in nuclear fusion facilities [1]. High-temperature plasma load on the plasma facing material in fusion devices during transients (disruption, ELMs, VDE etc.) produces several multiscale effects including surface erosion, redeposition of eroded materials, melting and melt motion over the surface, inhomogeneous solidification leading to specific surface clustering conditions which are strictly different from any other conditions of solidification and clustering of materials previously analysed. This study has demonstrated evidences of inhomogeneous stochastic clustering of the surface with properties of the self-similarity of granularity from nano- to macroscale. In particular, the hierarchical granularity and self-similarity with cauliflower-like shape of tungsten surface have been revealed for the first time. The clustering of materials irradiated by high-temperature plasma qualitatively differs from the ordinary Brownian surface roughness and from clustering under other conditions. This difference is shown by comparing the results with those for the molybdenum sample after exposure in the magnetron plasma discharge and for the industrial steel casting with the ordinary roughness formed typically at solidification after melting. The specific property of material solidification and clustering under plasma influence in fusion devices is due to a material’s (ions, clusters, melt on the surface etc.) motion under the influence of stochastic electromagnetic field formed by the near-wall turbulent plasma. This field ensures memory effects, long-term correlation and conditions for the growth of agglomerates with a self-similar structure [2, 3]. In addition to such a process, effects of irregular motion and relaxation of the material (melt) on the surface contribute to the process of clustering at the extreme heat load on the material surface. These multiple effects are responsible for the fractal growth mechanism at scales from several tens of nanometers to hundreds of microns [2, 3]. Collective (synergistic) effects, rather than the specific physical and chemical properties of the virgin materials, dominate in such stochastic clustering. The reported experimental results possibly indicate universal mechanisms of stochastic clustering of materials under the high-heat plasma load in a fusion device. The quantitative characteristics of the statistical inhomogeneity of such surface structure, in particular, the broadening of the multifractal spectrum by 0.5–1.2, are in the range observed for typical multifractal objects in nature. The work was supported by the Grant RSF № 16-19-10531. [1] V.P. Budaev, Physics Letters A 381, 43, (2017) 3706 [2] V.P. Budaev, JETP Letters 105, 5 (2017) 307 [3] V.P. Budaev, et. al., JETP Letters 95, 2 (2012) 78

Speaker: Viacheslav Petrovich Budaev

14:00 P2.1013 A one-dimensional scrape-off layer model in the reactor systems code 'PROCESS'

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1013.pdf A one-dimensional scrape-off layer model in the reactor systems code ‘PROCESS’ M. Kovari1, A. Kallenbach2, M. Siccinio2,3 1 CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK 2 Max-Planck Institute for Plasma Physics, Garching, Germany 3 EUROfusion Consortium, Garching, Germany * Tel.: +44 (0)1235-46-6427. E-mail address: michael.kovari@ccfe.ac.uk We have implemented a one-dimensional scrape-off layer (SOL) model in the PROCESS fusion reactor systems code. It allows reactor scenarios to be obtained while limiting both the plasma temperature of the SOL at the entrance to the sheath at the divertor target, and the power density on the target. The following physical processes are included: convected heat flux; thermal conduction; momentum conservation; radiation by deuterium, tritium and impurities; charge exchange; electron impact ionisation; and surface recombination. The isotropic emission of fast neutrals due to charge exchange from the part of the SOL adjacent to the target dominates the total power density on the target when the plasma temperature is reduced below 5 eV. As the seeded impurity concentration is increased a discontinuous transition is observed between an attached state where the plasma temperature at the target is high, and an approximately detached state in which the temperature at the target hits the lower bound of the simulation. The inclusion of a simple divertor model restricts the PROCESS optimisation to a more realistic subset of parameter space. 300 250 200 Plasma temperature at eV outer midplane [eV] 150 100 50 Plasma temperature near target [eV] 0 0 0.0005 0.001 0.0015 0.002 Argon number density fraction

Speaker: Michael Kovari

14:00 P2.1014 Effects of magnetic perturbations on axisymmetric divertors

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1014.pdf Effects of magnetic perturbations on axisymmetric divertors Alkesh Punjabi1, Allen Boozer2 1 Hampton University, Hampton, VA 23668, USA 2 Columbia University, New York, NY 10227, USA The behavior of the magnetic turnstiles that depart plasma from axisymmetry to strongly perturbed is studied. An analytic model is derived in which the width and nature of the intersection of points of magnetic flux tubes can be studied. This exact model is based on the Boozer-Rechester two wire model [A. H. Boozer and A. B. Rechester, Phys. Fluids 21, 682 (1978)]. Boozer and Rechester represented the magnetic field using the complete elliptic integrals and the Jacobi elliptic functions, but they did not place the equations in terms of an explicit magnetic field line Hamiltonian. In our model this is done and the magnetic field lines are modified by the addition of a fixed small radial spiraling velocity. The lines eventually cross the outermost confining magnetic surface and form flux tubes that strike the surrounding walls. The width and nature of the intersection of points of these flux tubes are studied in the limit as the spiraling velocity vanishes. This is done for both an axisymmetric divertor and for an axisymmetric divertor subjected to a quadrupole perturbation that has an orientation that rotates with the toroidal angle. The flux escaping through the turnstiles must exactly equal the returning flux. The scaling of the loss time and the size of intersection with the spiraling velocity are studied. General universal scaling laws characterizing the effects of perturbation on the axisymmetric divertors are sought. This work is supported by the US DOE grants DE- FG02-01ER54624 and DE-FG02-04ER54793 to Hampton University and DE-FG02- 95ER54333 to Columbia University. This research used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-05CH11231.

Speaker: Alkesh Punjabi

14:00 P2.1015 Scaling of ELM crash parameters

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1015.pdf Scaling of ELM Crash Parameters A.F. Mink1,2 , E. Wolfrum1 , M. Hoelzl1 , M. Maraschek1 , B. Vanovac1,3 , G.F. Harrer1,4 , M. Cavedon1 , E. Trier1 , A. Cathey1 , U. Stroth1,2 and the ASDEX Upgrade team 1 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 2 Physik Department, E28, TUM, 85748 Garching, Germany 3 DIFFER — Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands 4 Institute of Applied Physics, TU Wien, Fusion@ÖAW, 1040 Vienna, Austria In the pedestal region, which is characterized by steep pressure gradients, mode structures are observed during crashes of edge localized modes (ELMs) and in the phase between them. Recent observations showed that the crash phases are dominated by low toroidal mode numbers (n = 1–7) on the ASDEX Upgrade tokamak, which fits to comparisons to the nonlinear magne- tohydrodynamic code JOREK [1]. In order to understand the dominant physical mechanisms, the comparison of modeling and experiment for cases with a significant variation of critical parameters is essential. A parameter scaling conducted on ASDEX Up- grade shows that the toroidal mode numbers of ELM crashes increase with decreasing the edge safety factor q95 , see figure 1. Other peeling- ballooning relevant parameters such as bootstrap current, normalized pressure gradient or triangular- ity do not show a clear trend. In addition to that it is shown that the ELM duration and intensity also varies with q95 , which is in line with previous stud- ies on different machines [2, 3]. Figure 1: Average toroidal mode numbers hni of mode structures during the ELM crashes Starting from the results of the ASDEX Upgrade of 30 ASDEX Upgrade H-mode discharges parameter scaling an intuitive geometric model is against the edge safety factor q95 . presented that can explain the q95 scaling of the toroidal structure by the dominance of one poloidal structure. Furthermore, experimental scal- ings are compared to modelling results from advanced JOREK simulations [4]. References [1] A. F. Mink et al., Nuclear Fusion, 58, 2 (2018) [2] L. Frassinetti et al., Nuclear Fusion, 55, 2 (2015) [3] T. Eich et al., Nuclear Materials and Energy, 12, 84–90 (2017) [4] M. Hoelzl et al., Contributions to Plasma Physics, accepted (2018).

Speaker: Alexander Felician Mink

14:00 P2.1016 Intermittent fluctuations in the Alcator C-Mod

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1016.pdf Intermittent fluctuations in the Alcator C-Mod A. Theodorsen1 , O. E. Garcia1 , R. Kube1 , D. Brunner2 , B. LaBombard2 , J. L. Terry2 1 UiT - The Arctic University of Norway, Tromsoe, Norway 2 Plasma Science and Fusion Center, MIT, Cambridge, US In the far scrape-off layer (SOL), radial motion of filamentary structures leads to excess trans- port of particles and heat. Single point dwell probe measurements from the SOL of several tokamaks [1, 2, 3] reveal order unity relative fluctuations with positively skewed histograms with exponential tails towards high amplitudes. Conditional averaging of fluctuations reveal the large-amplitude bursts to have two-sided exponential structures, with a sharp rise and trailing wake. This is consistent with the power spectral density and autocorrelation function of the time series. Investigations of SOL fluctuations in the Alcator C-Mod using both the mirror Langmuir probe (MLP) [4] and gas puff imaging (GPI) [5] conform well to these general results. However, there are discrepancies: the MLP time series generally has lower fluctuation levels and larger filament width than those taken with GPI. In this contribution, we investigate measurements taken with a conventional Langmuir probe using both the well known techniques listed above as well as a new deconvolution method for unambiguously revealing filament arrival times and amplitudes [6]. With measurements from plasmas with different parameters as well as in both upper and lower single null configurations, the Langmuir probe data set is well suited to address this discrepancy and reveal universality in the behavior of SOL fluctuations. References [1] A. Theodorsen, O. E. Garcia, J. Horacek, R. Kube and R. A. Pitts, Plasma Physics and Controlled Fusion 58, 044006 (2016) [2] R. Kube, A. Theodorsen, O. E. Garcia, B. LaBombard and J. L. Terry, Plasma Physics and Controlled Fusion 58, 054001 (2016) [3] O. E. Garcia, R. Kube, A. Theodorsen, J.-G. Bak, S.-H. Hong, H.-S. Kim, the KSTAR Project Team and R. A. Pitts, Nuclear Materials and Energy 12, 36-43 (2017) [4] R. Kube, O. E. Garcia, A. Theodorsen, D. Brunner, A. Q. Kuang, B. LaBombard and J. L. Terry, ’Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer’, submitted to Plasma Physics and Controlled Fusion [5] O. E. Garcia, R. Kube, A. Theodorsen, B. LaBombard and J. L. Terry, ’Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas’, submitted to Physics of Plasmas [6] A. Theodorsen, O. E. Garcia, R. Kube, B. LaBombard and J. L. Terry, ’Universality of Poisson-driven plasma fluctuations in the Alcator C-Mod scrape-off layer’, submitted to Physical Review Letters

Speaker: Audun Theodorsen

14:00 P2.1017 Measurement and modeling of tungsten sources in WEST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1017.pdf Measurement and modeling of tungsten sources in WEST C.C. Klepper1, O. Meyer2, E.A. Unterberg1, A. Sepetys2 , Y. Marandet3, R. Guirlet2 ,H. Bufferand2, G. Ciraolo2, J.H. Harris1, P. Lotte2 and the WEST Team 1 Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169, USA† 2 CEA, IRFM, F-13108 Saint Paul Lez Durance, France 3 PIIM, CNRS-Université de Provence, Marseille, France WEST is the first superconducting tokamak to have begun operations with all tungsten (W) plasma-facing components (PFCs) [1]. To fully benefit from the opportunity to study W sources in this all W environment, including the relative contributions from divertor and wall regions, as well as synergy between them, dedicated experimental sessions are planned for the upcoming campaigns. In anticipation of these dedicated pulses, relevant measurement and modeling capabilities are discussed, together with the experimental plan. For source characterization, all regions of interest are accessible by means of in vessel periscopic optics and optical fiber assemblies, thus overcoming the direct access limitations imposed by the cryostat [2]. Two spectrally resolving instruments are supplemented by an ORNL Filterscope [3] system, to resolve sources at ELM-relevant timescales. This is necessary, as intra-ELM sources can have a different dependence on plasma parameters than inter-ELM sources [4], thus also potentially affecting the relative weight between divertor and wall sources in ELMing H-mode discharges. All optics and instruments are optimized for transmission and detection at and near the W I line at 400.9nm, while the Filterscope also includes continuum emission monitoring from a (line free) region spectrally offset from the W I line, to correct for bremsstrahlung or blackbody radiation. Dα is simultaneously detected. Spectral filtering is optimized to avoid the parasitic lines from e.g. diagnostic argon injections. Early spectra and Filterscope commissioning data will be shown and discussed. Progress in the simulation of W sources from WEST will be also discussed in the context of interpretation of the spectroscopic data. Earlier studies had revealed the divertor baffle to be a potentially significant source region outside the divertor targets [5]. Refinements in these calculations, including the effect of impurities will be presented. Longer term plans, including long-pulse W migration studies will also be briefly discussed in the context of measurement and modeling capabilities. [1] J. Bucalossi et al., Fusion Eng. Des. 86 (2011) 684; [2] O. Meyer et al., RSI 87, 11E309 (2016); [3] E.A. Unterberg et al., RSI 83, 10D722 (2012); [4] N. Den Harder et al., NF 56, 026014 (2016)); [5] M. Marandet, JNM 463, p. 629, 2015) †Work supported, in part, by US DOE under Contract DE-AC05-00OR22725 with UT-Battelle, LLC.

Speaker: C. Christopher Klepper

14:00 P2.1018 Preliminary investigation of the helical current induced by electrode biasing in the SOL on the J-TEXT tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1018.pdf Preliminary investigation of the helical current induced by electrode biasing in the SOL on the J-TEXT tokamak Zebao Song1,*, Nengchao Wang1,*, Y. Liang1, 2, 3, Jie Yang1, Tong Wang1, Huaxiang Zhang3, Yunong Wei1, Da Li1, Y. H. Ding1 and the J-TEXT team 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, Huazhong University of Science and Technology, Wuhan, China 2 Forschungszentrum Jülich, Jülich, Germany 3 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China *E-mail: zb_song@hust.edu.cn, wangnc@hust.edu.cn An essential problem for future burning plasma is that the Edge-Localized Modes (ELMs) could erode and melt the plasma-facing components. Therefore, the effective control of ELMs is of great importance. Extensive experiments have demonstrated that the resonant magnetic perturbations (RMPs) generated by in-vessel or ex-vessel saddle coils can change the edge magnetic topology and hence mitigate or even suppress the ELMs. Similar as the RMPs, the helical current filaments (HCFs) induced by lower hybrid waves has been observed to change the magnetic topology and strongly mitigate ELMs in EAST [1]. The HCFs could be a new attractive method to apply RMPs. According to analytical calculation, the sufficient SOL helical current could be produced by biasing the divertor plates asymmetrically in order to control ELMs in ITER [2]. In this paper, we will present the recent results on the HCFs actively driven by a moveable biased electrode in the SOL of J-TEXT. Once the biasing voltage (e.g. +200V) was applied to the electrode, significant current (~150 A) was induced through the electrode. The perturbed magnetic fields produced by the biasing current were measured at two poloidal cross-sections. The total magnetic fields, generated by the helical currents flowing both along and against the magnetic field lines at the location of the electrode, were calculated at the same cross-sections. The measured and calculated magnetic fields are highly consistent, which confirmed that the current induced by the electrode flowed helically along and against the local magnetic field lines. In addition, the radiation of the HCFs were observed from the images captured by a fast frame visible camera with the CIII filter. The spectrum of the magnetic field generated by the HCFs were calculated, which resonate with the edge rational surfaces and hence modify the edge magnetic topology significantly. References: [1] Y. Liang, et al. Physical Review Letters 110 (2013) 235002. [2] Joseph I, et al. Physics of Plasmas 16 (2009) 052511.

Speaker: Ze Bao Song

14:00 P2.1019 Edge-SOL stability: a two-layer approach

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1019.pdf Edge-SOL stability: a two-layer approach F. Wilczynski1 , D.W. Hughes1 , S. Van Loo1 , F. Millitelo2 , W. Arter2 1 University of Leeds, United Kingdom 2 Culham Centre for Fusion Energy, Abingdon, United Kingdom In magnetic confinement devices, the boundary turbulence is characterised by intermittent ejection of coherent filamentary structures. These filaments transport plasma from the well- confined core region, through the Scrape-Off Layer (SOL), towards the material surfaces. This results in increased plasma-wall interaction, which has the potential to damage plasma-facing components and shorten the lifetime of the device. It is therefore essential to develop full un- derstanding of the mechanisms behind the transport in the edge of the plasma. Study of the formation and expulsion of filaments requires consideration of both the core and the SOL region. The two regions exhibit distinct dynamics parallel to the magnetic field. In the core, field lines are considered periodic in the parallel direction, while in the SOL the field lines end with a Debye sheath at a material surface. The presence of the sheath provides a sink for plasma particles and energy. Mathematically, this is represented by inclusion of parallel loss terms in the SOL region. The resulting sharp transition between the two regions imposes a number of continuity conditions that need to be satisfied at the separatrix. In this contribution, we study the stability of the boundary plasma by considering a two di- mensional interchange model that includes a simple description of open and closed field line regions based on the sheath dissipation closure. We calculate the linear stability threshold and characterise the onset of instability. Furthermore, we discuss how the stability threshold is af- fected subject to changes in our model, such as varying the separatrix location, or different choices of boundary conditions.

Speaker: Fryderyk Wilczynski

14:00 P2.1020 Modulation of the strike line position using control coils in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1020.pdf Modulation of the strike line position using control coils in Wendelstein 7-X M. Śl˛eczka1 , A. Ali2 , P. Drewelow2 , Y. Gao3 , M. Jakubowski1,2 , H. Niemann2 , A. Puig Sitjes2 , G. Wurden4 and W7-X team 1 Faculty of Mathematics and Physics, University of Szczecin, Szczecin, Poland 2 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 3 Forschungszentrum Jülich GmbH, IEK-4, Jülich, Germany 4 Los Alamos National Laboratory, Los Alamos, USA The stellarator Wendelstein 7-X (W7-X) restarted operation in 2017 with ten divertor modules made of inertially cooled graphite plasma-facing components (PFCs)[1]. They serve a purpose of testing the heat and power exhaust concept of so-called island divertor before installation of water-cooled divertor planned for 2020. The island divertor, developed at Wendelstein 7-AS, uses large magnetic islands to remove heat and particles from the plasma boundary. As W7-X in near future will operate as a quasi steady state device, it is crucial to control the power loads to the divertor to avoid overheating. Therefore W7-X is equipped with ten 3D-shaped control coils which, by creating additional magnetic fields, can be used to modulate position and geometry of strike line and island divertor [2, 3]. This extra field can also correct symmetry of the field, sweep the strike line on the target in order to avoid local overheating or change the X-point position to control detachment. We will present changes in the geometry of the island divertor as measured by the thermographic diagnostics. Ten infrared cameras, one per each divertor, collected the temperature distribution at the divertor surface. The THEODOR code was used for data analysis in order to extract geometry and movement of the strike line on the horizontal and vertical elements of the diver- tor during the discharge. Apart of small deviations due to error fields, the measured strike line shows good agreement with predicted by field line tracing codes. To observe the effect of the correction field on the strike line position and island divertor geom- etry several discharges with different amplitude of the control coils DC currents (from -2000 A to 2000 A) have been performed. Moreover, AC current of 600 A and frequency of 5 Hz was used to sweep the strike line and caused its movement by a few centimeters. References [1] Wolf, R. C. et al. Nucl. Fusion 57, 102020 (2017) [2] McCormick, K. et al. J. Nucl. Mater. 313, 1131-1140 (2003) [3] Jauregi, E. et al. Fusion Eng. Des. 66-68, 1125-1132 (2003)

Speaker: Marcin Sleczka

14:00 P2.1021 Amelioration of plasma-material interactions and ELMs, and improvement to plasma performance with lithium injection and conditioning in EAST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1021.pdf Amelioration of Plasma-Material Interactions and ELMs, and Improvement to Plasma Performance with Lithium Injection and Conditioning in EAST R. Maingi1, J.S. Hu2, D. Andruczyk3, J.M. Canik4, A. Diallo1, K.F. Gan5, E. Gilson1, X.Z Gong2, T.K. Gray4, M. Huang2, R. Lunsford1, D.K. Mansfield1, X. C. Meng6, T.H. Osborne7, D.N. Ruzic3, Z. Sun2, K. Tritz8, W. Xu2, G.Z. Zuo2, Z. Wang9, B.D. Wirth9, K. Woller10, S.J. Zinkle9, and the EAST Team 1 Princeton Plasma Physics Laboratory, 100 Stellarator Road, Princeton, NJ 08540, USA 2 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China 3 University of Illinois, Urbana-Champaign, Champaign IL 61820, USA 4 Oak Ridge National Laboratory Oak Ridge, TN 37830 USA 5 University of Tennessee, Knoxville TN 37996, USA 6 Department of Applied Physics, Hunan University, Changsha 410082, China 7 General Atomics, San Diego, CA 92121, USA 8 Johns Hopkins University, Baltimore MD 21211, USA 9 Los Alamos National Laboratory, Los Alamos NM 87545, USA 10 Massachusetts Institute of Technology, Cambridge MA 02139, USA We present new results from a US-PRC boundary physics collaboration where 1) lithium (Li) powder was injected to eliminate ELMs in upper-single null (USN) shape that used the ITER-like tungsten monoblock divertor; 2) a 2nd generation flowing liquid lithium limiter was inserted into the EAST midplane and used to mitigate plasma-materials interactions (PMI); and 3) Li granule injection was used for ELM triggering studies. Li powder was injected into upper-single null H-modes using the ITER-like tungsten monoblock divertor. At constant injection rates, the ELM elimination became progressively easier, suggesting a cumulative wall conditioning effect. An edge coherent mode was evident, as typical with Li conditioning. Normalized energy confinement HH98y2 was maintained ~ 1.2, above the previous ELM elimination with Li injection on the lower C divertor with HH98y2 ~ 0.75. A 2nd generation flowing liquid Li limiter inserted into EAST was found to be compatible with H-modes, even when placed within 1cm of the separatrix in RF heated discharges. A Cu plate is used for the heat sink, with a thin stainless steel coating for Li compatibility. This limiter had several design improvements over the 1st generation limiter. The heat flux exhausted by the 2nd generation limiter was up to 4 MW/m2. Also, short-lived ELM-free phases were observed for the first time in EAST with increasing τE and transient HH98y2 < 2 when the 2nd generation limiter was inserted. Finally ELM triggering studies with a four-chamber Li granule injector showed a size threshold for ELM triggering probability, as qualitatively predicted by theory. *Research sponsored by the U.S. DoE under a US-PRC PMI collaboration, and by a few agencies in the People’s Republic of China.

Speaker: Rajesh Maingi

14:00 P2.1022 Physics of the Super H-Mode Regime: Record Performance on C-Mod and DIII-D, and Prospects for JET and ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1022.pdf v>

Physics of the Super H-Mode Regime: Record Performance on C-Mod and DIII-D, and Prospects for JET and ITER P.B. Snyder1, J.Hughes2, T. Osborne1, C. Paz-Soldan1, W. Solomon1, C-Mod/DIII-D teams 1 General Atomics, San Diego CA, USA 2 MIT PSFC, Cambridge MA, USA High fusion performance in tokamaks is enabled via the spontaneous formation of a transport barrier, or “pedestal.” While many open issues remain, progress in gyrokinetic, neoclassical and MHD theory and simulation [eg 1] has enabled a significant degree of predictive capability for the pedestal height and width, embodied in models such as EPED [2], which have been compared to hundreds of observations on several tokamaks (σ~0.25) [eg 2,3]. Notably, EPED predicts that, at very strong shaping, above a critical density, the pedestal solution bifurcates into multiple roots, including the usual H-mode pedestal root, and a “Super H-mode” (SH) root at very high pedestal pressure [Fig 1a]. Guided by predictions, the SH regime was discovered on DIII-D [4]. More recently, in the final two weeks of Alcator C-Mod operations, SH experiments achieved world record pedestal pressure (~80 kPa) [5], finding, as predicted, ITER-like pedestal pressure at ITER-like toroidal and poloidal field. New DIII-D SH experiments in 2017-18 have achieved high pedestals [Fig 1a] and fusion performance [Fig 1b], including what appears to be the highest QDD (and QDT_equiv~0.5) ever achieved on a medium scale tokamak (R<2m). Sustained high performance operation at low and high separatrix density has been achieved, using 3D magnetic perturbations to control density and achieve stationary profiles. Normalized metrics of fusion performance such as Q/IaB, or

W/PheatIaB, reach very high values in SH [Fig 1b]. Achieving similar levels of normalized performance could allow Q>1 in JET, or Q=10 in ITER at currents below 15MA. However, there are many challenges in achieving such performance, including methods for sustainment, impurity and ELM control, and compatibility of high triangularity shapes with nearby metal walls. We present SH theory compared to results on C-Mod and DIII-D, and predictions and challenges for SH on JET, ITER , JT-60SA and DEMO concepts. Access to High Performance Super H-Mode Regime on DIII-D 35 Pedestal Pressure [2*pe,ped, kPa] 30 t=2.4s 25 t=2.2s 20 15 t=1.9s 10 H-Mode 5 Near Super H Super H 0 3 4 5 6 7 8 9 10 11 12 Pedestal Density [ne,ped(Zeff/2)1/2,1019m-3] Figure 1: (a) Recent DIII-D experiments have achieved very high pedestal pressure, deep into the SH regime, simultaneously achieving high fusion performance. (b) A simple metric of normalized fusion performance (

W/PhIaB) illustrates the fusion benefit of Super H (solid symbols are existing data from cases with

> 50kPa). Approximate required values of this metric for various levels of ITER performance are also shown. [1] G.T.A. Huysmans PPCF 47 (2005) B165; D. Dickinson et al. PPCF 53 (2011) 115010; S. Saarelma et al. PPCF 59 (2017) 064001. [2] P.B. Snyder et al NF 51 (2011) 103016; PoP 16 (2009) 056118. [3] M.N.A. Beurskens et al NF 54 (2014) 043001; R.J. Groebner et al NF 53 (2013) 093024; M.G. Dunne et al PPCF 59 (2016) 025010; M. Komm et al NF 57 (2017) 056041. [4] W. Solomon et al PRL 113 (2014) 135001; P.B. Snyder et al NF 55 (2015) 083026. [5] J.W. Hughes 2018 to appear in Nucl. Fusion. Acknowledgment: Supported by the US DOE under DE-FG02-95ER54309, FC02-06ER54873, DE-FC02-04ER54698, DE-FC02-99ER54512.

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Speaker: Phil B. Snyder

14:00 P2.1023 Signatures of the magnetic configuration observed with the video diagnostic at Wendelstein 7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1023.pdf Signatures of the magnetic configuration observed with the video diagnostic at Wendelstein 7-X stellarator C. Biedermann1, G. Cseh2, G. Kocsis2, T. Szepesi2, M. Otte1 and the W7-X Team 1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 2 Wigner RCP RMI, Budapest, Hungary Wendelstein W7-X is a highly optimized stellarator experiment with a modular superconductive coil system operating at a magnetic field of 2.5 T. Commissioning started in 2015 with plasmas up to 20s. W7-X is stepwise upgraded: beginning from uncooled fine-grain graphite limiters, then installing uncooled divertor units, and finally implementing actively water-cooled high-heat flux divertor structures made of graphite. At W7-X the island divertor concept is applied, with intrinsic island chains at the plasma edge producing multiple X-points directing the out flowing plasma in the scrape-off layer to dedicated target plates of the divertor. To verify the magnetic field configuration and measure magnetic field errors, which cause asymmetries in the heat flux to the island-divertor, a set of 10 1.3MPixel-CMOS cameras has been installed [1]. These cameras give a toroidal overview of the magnetic field lines and flux surfaces visualized by an adjustable electron gun and a fluorescent rod [2] and further of the light emission from the edge plasma in the visible spectral range. The main objective of the video diagnostic is to visualize plasma shape, position as well as plasma-wall interaction during the discharge operation for supervision and scientific exploration. During the first operational phase with the uncooled divertor unit a variety of magnetic configurations have been executed and the emission of visible light during extensive external as well as intrinsic gas fuelling was observed. To help the understanding of the recorded radiation distributions a synthetic diagnostic including the viewing geometry of different magnetic field configurations has been developed. The set of 10 camera channels with Event Detection Intelligent Camera (EDICAM) sensors allows coverage of the whole torus interior and visualization of the island structure. In this contribution we present an overview of the camera system and capabilities and summarize the observed signatures of the different magnetic field configurations. [1] G. Kocsis et al. Fusion Engineering and Design 96-97 (2015) 808. [2] M. Otte et al. Plasma Phys. Contr. Fusion 58 (2016) 064003.

Speaker: Christoph Biedermann

14:00 P2.1025 Study of the Impact of High Neon Radiation on Pedestal and Divertor in JET Experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1025.pdf Study of the Impact of High Neon Radiation on Pedestal and Divertor in JET Experiments S. Glöggler1,2 , M. Wischmeier1 , M. Bernert1 , G. Calabrò3 , A. Huber4 , C. Lowry5 , M. Reinke6 , S. Wiesen4 , X. Bonnin7 , E. Fable1 , S. Henderson8 , JET Contributors† 1 Max Planck Institute for Plasma Physics, Boltzmannstraße 2, 85748 Garching, Germany 2 Physik-Department 28, Technische Universität München, 85747 Garching, Germany 3 Department of Economics, Engineering, Society and Business Organization (DEIm), University of Tuscia, Largo dell’Università snc, 01100 Viterbo, Italy 4 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, 52425 Jülich, Germany 5 European Commission, 1049 Brussels, Belgium 6 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 7 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St-Paul-lez-Durance, France 8 CCFE Fusion Association, Culham Science Centre, Abingdon, AX143DB, UK † See the author list of "X. Litaudon et al 2017 Nucl. Fusion 57 102001" Impurity radiation is a major requirement to protect the divertor targets of future fusion de- vices, such as ITER and DEMO, from power loads beyond the material limit of 5−10 MW/m2 . Such radiation is induced by deliberate puffing of impurity gases into the plasma. In order to extrapolate the impact of neon on the plasma confinement of DEMO, where in an ITER-like geometry around 70% of the induced radiation must originate from inside the separatrix, recent experiments and numerical simulations have been carried out. At JET dedicated experiments with high heating powers (over 15 MW), high line-averaged densities (over 5 · 1019 m−3 ), BT = 2.6 T, Ip = 2.5 MA were carried out. In particular, measure- ments of bolometry, spectroscopy, target Langmuir probes, and HRTS were analyzed. With the seeding of neon the radiation in the pedestal region rises, which leads to a strong reduction of the target power flux. It was found that with neon the temperature and density at the pedestal top position degrade by up to 30% but recover towards the core. Despite this degradation, an increase of the global energy confinement time of about 10% is observed. The 1D transport code ASTRA is used to determine a possible impact of the radiation on the energy transport coefficients. In addition, these experimental measurements were used to validate numerical sim- ulations performed with the code package SOLPS-ITER. The details of this validation will be explained.

Speaker: Stephan Glöggler

14:00 P2.1026 Impact of He admixture on the ammonia formation in N2 seeded D2 plasmas in the GyM facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1026.pdf 45 EPS Conference on Plasma Physics 13326 Impact of He admixture on the ammonia formation in N2 seeded D2 plasmas in the GyM facility L. Laguardia1, A. Cremona1, G. Gatto1, G. Gervasini1, F. Ghezzi1, G. Granucci1, V. Mellera1, D. Minelli1, R. Negrotti2, M. Pedroni1, M. Realini2, D. Ricci1, N. Rispoli1, A. Uccello1, E.Vassallo 1 1 Istituto di Fisica del Plasma - CNR, Via R. Cozzi 53, 20125 Milan, Italy 2 Istituto per la Conservazione e la Valorizzazione dei Beni Culturali - CNR, Via R. Cozzi 53, 20125 Milan, Italy Impurity seeding with nitrogen is routinely used to reduce the power load to divertor target plates by radiation in front of the target plates as demonstrate in JET-ILW and AUG [1]. As a side product of the use of nitrogen as metallic plasma-facing surface, ammonia in significant amounts can develop. The ammonia formation is a critical issue because, being ammonia hazardous, could have a significant implication on the operation of the ITER tritium plant which is prepared to process titrated ammonia in small amounts. In this context, it is important to try and identify means to reduce/prevent ammonia formation during experiments with nitrogen seeding in present day devices. In N2 seeded D2 plasmas, ammonia formation proceeds on the surface of the wall by adsorption of the ND radicals produced by ion- molecules reactions in low temperature plasmas [2]. Taking into account the mechanism before mentioned, helium has been identified as the species that could reduce the ammonia formation because it can potential occupy surface trapping sites in the metallic surface at which surface reactions leading to ammonia formation take place. The effects on the ammonia formation of the helium admixture to N2 seeded D2 plasmas were evaluated in GyM linear device [3]. ND3 produced during the experiments was monitored by optical emission spectroscopy, through observation of the ND emission band. Ammonia quantification was obtained by operations involving the collection of the exhaust in LN2 trap and liquid ion chromatography (LIC) analysis [5]. Results by LIC reveal a decrease in ND3 formation proportional to the increase of the He ion flux. [1] M. Oberkofler et al., Journal of Nuclear Materials 438 (2013) S258–S261 [2] L. Laguardia et al., Nuclear materials and Energy 12 (2017) 261-266 [3] G. Granucci, et al., Proceedings of the 36th EPS Conference on Plasma Physics (EPS 2009), 2009, Sofia, Bulgaria, 2009 ECA 33E, P- 4.148. [5] L. Laguardia et al., Journal of Nuclear Materials 463 (2015) 680–683

Speaker: Laura Laguardia

14:00 P2.1027 Relative shift in pedestal position during power and gas scans at the COMPASS tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1027.pdf Relative shift in pedestal position during power and gas scans at the COMPASS tokamak P. Bílková1, L. Frassinetti2, M. G. Dunne3, J. Havlíček1, M. Komm1, M. Peterka1,4, T. Markovič 1, P. Böhm1, E. Štefániková2, M. Šos1,5, J. Seidl1, O. Grover1,5, K. Mitošinková1,4, J. Varju1, P. Vondráček1,4, J. Urban1, V. Weinzettl1, M. Hron, R. Pánek1 and the EUROfusion MST1 team6 1 Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic 2 KTH, Div Fus Plasma Phys, SE-10044 Stockholm, Sweden 3 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, Germany 4 Fac. Math & Phys., Charles Univ., V Holešovičkách 2, 180 00 Prague 8, Czech Republic 5 FNSPE, Czech Technical University in Prague, Břehová 7, Czech Republic 6 See the author list (H. Meyer et al 2017 Nucl. Fusion 57 102014 Recent analysis performed on ASDEX Upgrade, NSTX and DIII-D suggest that the density profile position plays an important role in pedestal stability [1,2,3]. On JET and on ASDEX Upgrade, it has been observed that the electron temperature and electron density profiles can have a different relative pedestal positions (so-called relative shift). As shown in [4], the increase of the relative shift is correlated with the reduction in the normalized pressure gradient, leading to a weakening of the pedestal stability. Systematic measurements of pedestal structure were performed during Ohmic and NBI-assisted H-modes at the COMPASS tokamak [5]. For PNBI exceeding 200 kW the electron pedestal temperature ∗ reached 300 eV, allowing to achieve pedestal collisionality 𝜈𝑝𝑒𝑑 < 1 at q95 ~3. Measurements during the last 30% of the ELM cycle were considered for analysis and were processed as described in [6]. First results on analyses of pedestal shift on COMPASS were published in [7]. A linear trend between the shift and Psep was observed similarly as on JET [8]. Dependence of αcrit on pedestal shift was more complex - it followed the trend observed previously on JET only for low collisionalities. The pedestal stability was analysed with the peeling-ballooning model [9]. In this contribution, analyses on an extended dataset was performed. Particularly, data from power and gas scans are included. The experimental data are compared to EPED. [1] T.H. Osborne et al., Nucl. Fus. 55,063018 (2015) [6] L. Frassinetti et al., Rev. Sci. In. 83, 013206 (2012) [2] R. Maingi et al., Nucl. Fus. 52 083001 (2012) [7] P. Bilkova et al., 44th EPS C. on Pl. Phys., P2.120 [3] M. Dunne et al., Plas. Phys. Contr. Fus.59 (2017) [8] E. Stefanikova et al., 43rd EPS C. Pl. Phys., O4.117 [4] E. Stefanikova et al, 2018 Nucl. Fus. in press [9] P. Wilson et al., Phys. Plasmas 9, 1277 (2002) [5] M. Komm et al., Nucl. Fus. 57, 5 (2017), 056041

Speaker: Petra Bilkova

14:00 P2.1028 Characterisation of power flux reduction in the Wendelstein 7-X divertor plasma with Langmuir probes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1028.pdf Characterisation of power flux reduction in the Wendelstein 7-X divertor plasma with Langmuir probes L. Rudischhauser1, K.C. Hammond1, M. Endler1, H. Niemann1, M. Krychowiak1, T. Barbui2, B.D. Blackwell3, F. Effenberg2, Y. Feng1, R. König1, M. Jakubowski1 and the W7-X Team1 1 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 2 University of Wisconsin-Madison, Madison, USA 3 Australian National University, Canberra, Australia During the first divertor operation phase (OP1.2a) of the stellarator Wendelstein 7-X strong reductions in heat load by a factor of five or more on the graphite divertor targets were observed for periods of time within numerous discharges. During these we recorded substantial drops in temperature by an order of magnitude to below 6 eV and increases in density with the 40 Langmuir probes embedded in the divertor. The probe results support the ongoing discussion on this power detachment [1] with measurements over a range of poloidal distances, sampling the magnetic island divertor field inside the island, in the strike line and in the private flux region. Design, capabilities and limitations of the Langmuir diagnostic as well as the data analysis model are briefly introduced. The Langmuir probe data are compared with observations of other relevant diagnostics such as the infrared and spectroscopic observation systems, and the thermal helium beam diagnostic [2, 3, 4]. In addition to discussing the indications for detachment in detail we characterise the general behaviour of the divertor plasma under different global plasma conditions and present evidence of up-down asymmetry and active scrape-off layer cooling by impurity seeding and edge fuelling. [1] D. Zhang et al., First observation of a stable highly-radiative divertor regime at stellerator W7-X, EPS 2018, to be published [2] M.W. Jakubowski et al., Infrared Imaging Systems for wall protection in the W7-X stellarator, HTPD 2018, to be published [3] M. Krychowiak et al., Overview of diagnostic performance and results for the first operation Phase in Wendelstein 7-X, RSI 87, 2016 [4] T. Barbui et al., Feasibility of line-ratio spectroscopy on helium and neon as edge diagnostic tool for Wendelstein 7-X, RSI 87, 2016

Speaker: Lukas Rudischhauser

14:00 P2.1029 Gyrokinetic simulation of turbulence at the FT-2 tokamak egde

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1029.pdf Gyrokinetic simulation of turbulence at the FT-2 tokamak egde L. Chôné1, A. D. Gurchenko2, E. Z. Gusakov2, T. P. Kiviniemi1, S. I. Lashkul2, S. Leerink1, P. Niskala1 1 Department of Applied Physics, Aalto University, Espoo, Finland 2 Ioffe Institute, St. Petersburg, Russia Predicting the dynamics of edge plasma is of particular importance for magnetic fusion devices. Indeed, the scrape-off layer (SOL) dynamics governs the power exhaust and plasma-surface interaction, which entails that it controls the influx of impurities, as well as the transition to improved confinement regimes via the formation of edge transport barriers (ETB) [1-5]. Because of the non-linear nature of the edge and SOL plasma dynamics, predictions have to rely on numerical simulations from first principle. In this work, we use the global full-f particle-in-cell (PIC) gyrokinetic code ELMFIRE [6] to simulate circular limited tokamak plasmas from the magnetic axis to the SOL, including a simple PWI model. In order to simulate the FT-2 SOL, ELMFIRE uses the logical boundary condition to faithfully reproduce recover the sheath-limited SOL [7]. Here we characterise the dynamics of turbulence in the SOL of FT-2 and it’s interaction with the confined plasma across the last-closed flux surface (LCFS). [1] E. J. Doyle et al., Nucl. Fusion 47 (2007) S18 [2] A. Loarte et al., Nucl. Fusion 47 (2007) S203 [3] P. C. Stangeby, The Plasma Boundary of Magnetic Fusion Devices, IOP, 2000 [4] F. Wagner, Plasma Phys. Control. Fusion 49 (2007) B1 [5] F. Ryter et al., Nucl. Fusion 54 (2014) 083003 [6] J. A. Heikkinen et al., J. Comput. Phys. 227 (2008) 5582‒5609 [7] L. Chôné et al., Contrib. Plasma Phys. to be published

Speaker: Laurent Chôné

14:00 P2.1030 RMP reduces effective particle confinement time during RMP application at MAST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1030.pdf RMP reduces effective particle confinement time during RMP application at MAST K. Flesch1, H. Frerichs1, J. Harrison2, A. Kirk2, O. Schmitz1, I. Waters1 1 Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI, USA 2 Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxfordshire, UK The application of resonant magnetic perturbations (RMPs) on plasma discharges at MAST leads, in many cases, to reduced particle confinement of the core plasma, known as density pump-out. This can be described by the characteristic particle confinement time p obtained from a global, single reservoir particle balance analysis. During all discharges with pump-out, the ionization source increased as the RMPs are turned on, but the confinement time decreased substantially enough to cause an overall density decrease. In L-mode plasma, up to a 15% reduction in p is measured, and in H-mode plasma, a similar level of p reduction is seen, however, the exact value depends on the RMP mode number and phasing. The results presented in this paper relate this pump out for the first time for MAST to the neutral fueling and exhaust fluxes using a single reservoir, global particle balance. This particle balance was assembled using the plasma density and Dα emission measured by filter-scopes and a calibrated 1-D camera, as well as local values of S/XB coefficients determined by edge plasma parameter measurements, to infer the particle flux loss from the plasma and the incoming neutral recycling flux maintaining the plasma density. In order to resolve the underlying effects in the neutral fueling and exhaust household inside the recycling and ionization layer, a multi-reservoir particle balance model [1] was revived, which includes both molecular and atomic species as well as the plasma and wall inventory. This model allows for experimental inputs such as fueling from gas puffing and neutral beam injection and estimates of parameters like the probability of particles adsorbing on the wall and the efficiency with which ionized particles are confined. Using the previously determined confinement time p, the model is able to accurately reproduce the time evolution of the plasma density, vacuum vessel neutral pressure, and Dα emission that would be measured by the filterscope. The results from this experimental analysis with both particle balance models are compared to results from numerical analysis with the EMC3-EIRENE code. Initial results from this comparison supports increased fueling efficiencies and reduced particle confinement times as a reason for the observed particle pump out. [1] G.P. Maddison, et al., Plas. Phys. & Contr. Fus. 48 (2006) 71-107 Acknowledgement: This work was funded in part by the U.S. DoE under grant DE-SC0012315.

Speaker: Kurt Flesch

14:00 P2.1031 Redistribution of three-dimensional divertor footprint induced by time-varying resonant magnetic perturbations on EAST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1031.pdf Redistribution of three-dimensional divertor footprint induced by time-varying resonant magnetic perturbations on EAST M. Jia1,2 , Y. Sun2 , Y. Liang1,2 , L. Wang2 , J. Xu2 , S. Gu2 , Y. Q. Liu3 , S. Xu1,2 , K. Gan2 , B. Zhang2 , B. Lyu2 , W. Feng2 , H. H. Wang2 , T. Shi2 , J. Qian2 , B. Shen2 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung-Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Institutes of Plasma Physics, Hefei Institutes of Physical Sciences, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China 3 Culham Centre for Fusion Energy, Abingdon, OX14 3DB, United Kingdom The application of time-varying resonant magnetic perturbations (RMPs) is recently pro- posed for its promising abilities of both edge localized mode (ELM) control and divertor power load control in tokamak H-mode discharges[1]. These effects are all closely related to the three- dimensional magnetic topology changes induced by magnetic perturbations, which can be stud- ied with both experiments and numerical analyses. It needs to be examined on various devices as references for future ITER operation[2]. Recently two kinds of time-varying RMPs, the rigid rotating and up-down differential phasing RMPs, with toroidal mode number n=1 and 2 have been examined in the EAST H-mode discharges. The observed power load distributions on the divertor target are rotated synchronously with the rotating or phasing RMP fields. Numerical modelings of magnetic topology, which takes into account the plasma responses calculated by the toroidal magnetohydrodynamics code MARS-F, are carried out by the field line tracing code TOP2D. The topology modelings show that the magnetic footprint pattern has a qualita- tive consistency with the experimental observations[3]. The plasma response is found to play an important role in magnetic edge topology changes as well as in the ELM-control effect[4]. With different spectra by changing the up-down phase difference, it shows an amplifying or screening effect, which means it changes the field line penetration depth rather than the general footprint shape. These results show the potential of making a scheme using both rotating and phasing RMP fields with minimum current changes to achieve an even power load distribution on divertor targets while keeping a good ELM-control effect. References [1] A. Loarte et al., Nuclear Fusion, 47, S203 (2007) [2] C. J. Ham et al., Nuclear Fusion, 56, 086005 (2016) [3] M. Jia et al., Nuclear Fusion, Accepted, (2018) [4] Y. Sun et al., Physical Review Letters, 117(11), 115001 (2016)

Speaker: Manni Jia

14:00 P2.1032 Impurity seeding and divertor fueling effects on the plasma surface interaction of Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1032.pdf Impurity seeding and divertor fueling effects on the plasma surface interaction of Wendelstein 7-X V. R. Winters1, T. Barbui1, S. Brezinsek2, F. Effenberg1, K. Hammond3, J. Harris4, M. Jakubowski3, R. König3, P. Kornejew3, T. Kremeyer1, M. Krychowiak3, L. Rudischhauser3, O. Schmitz1, E. Wang2, G. Wurden5 and the W7-X team 1 University of Wisconsin-Madison, Madison WI 53706 USA 2 Forschungszentrum Jülich GmbH, IEK-4, D-52425 Jülich, Germany 3 Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald, Germany 4 Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA 5 Los Alamos National Laboratory, Los Alamos, NM 87545 USA The method and efficiency of plasma fueling at Wendelstein 7-X (W7-X) is shown to have a direct impact on the level of carbon erosion during the first experimental phase with the carbon-covered Test Divertor Unit (OP1.2a). Two approaches to manipulate the plasma fueling were taken: (a) cooling the scrape-off layer (SOL) via the seeding of radiative impurities (Ne, N2) in order to make it more transparent for fueling H neutrals or (b) fueling the plasma through a gas valve located directly in the island divertor. A set of ORNL Filterscopes [1] was used to directly characterize the C erosion from these changes in fueling by observing the C-III line (465.0nm, 2nm FWHM) in the divertor where both seeding impurities and hydrogen were introduced. Combination of these spectroscopic data with plasma parameter data from the Langmuir probes located in that divertor, data from the thermal helium beam diagnostic [2], and temperatures inferred from H line ratios, allow the extraction of C particle fluxes using S/XB coefficients. With direct fueling into the island at the divertor target, a decrease of the C erosion yield from the divertor surface was measured. This most likely is due to ionization cooling from the fueling gas, which directly can affect the PMI through reduced physical sputtering rates. This is promising as the localized fueling seems to reduce C erosion at the same time. The seeded impurities have, depending on the species chosen, a more complex interaction with the PMI, which is being investigated. Depending on the actual ion temperatures, physical sputtering can be increased due to the higher mass and/or charge state of seeding ions and a change to chemical erosion is likely for species like N2. Acknowledgements: This work was funded in part by U.S. DoE grant DE-SC0014210. References [1] Colchin, R J et al, Rev. Sci. Instrum. 74 (2003) [2] Barbui, T et al, Rev. Sci. Instrum. 87 (2016)

Speaker: Victoria Robin Winters

14:00 P2.1033 Density profiles and fluctuations in front of the ICRF antenna on the ASDEX Upgrade using X-mode reflectometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1033.pdf Density profiles and fluctuations in front of the ICRF antenna on the ASDEX Upgrade using X-mode reflectometry E. Seliunin1 , C. Silva1, P. Manz2, D. Aguiam1, G.D. Conway2, L. Gil1, L. Guimarãis1, C. Moon2, T. Pütterich2, A. Silva1, U. Stroth2,3, E. Wolfrum2, W. Zhang2, the ASDEX Upgrade team and the EUROfusion MST1 team*. 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Lisboa,PT 2 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 3 Physik-Department E28, Technische Universität München, 85747 Garching, Germany *See the author list of Meyer H. et al 2017 Nucl. Fusion 57 102014 A new multichannel reflectometer diagnostic (RIC) was recently installed in an ICRF antenna of ASDEX Upgrade (AUG), aiming mainly for ICRF coupling and operation studies [1]. However, this system also opens up research opportunities in the area of scrape- off layer (SOL) physics by exploring the high temporal and spatial resolution of the diagnostics and by taking advantage of the three channels installed at different poloidal locations. This reflectometry diagnostic was designed to measure density profiles up to 2 × 1019 m−3 in X-mode in the typical 1.5 T–2.7 T magnetic fields of AUG. The full frequency range is swept in 15 μs, generating an electron density profile every 25 μs simultaneously in 3 different poloidal positions. Besides its high sensitivity to density fluctuations, reflectometry also provides localized measurement. Therefore, taking into account its high temporal resolution, the RIC diagnostic can be potentially used to observe SOL density fluctuations. In this contribution, the capabilities of the RIC diagnostic are demonstrated in selected examples. The SOL density profiles and fluctuations are measured in density ramp up discharges where the amplitude of the fluctuations is observed to increase with the near SOL profiles becoming flatter, which is consistent with the expected enhancement in radial transport. A good agreement between the average density profiles obtained from lithium beam, Langmuir probes, and reflectometry diagnostics is demonstrated. Statistical properties of the density fluctuations such as the standard deviation and skewness obtained from Langmuir probes and reflectometry are also compared. Fluctuations levels ranging from 40 to 60% are found, in reasonable agreement with the Langmuir probe results. Although a good agreement is found with respect to the density standard deviation, RIC measurements typically underestimate the skewness of the density fluctuations most probably due its lower temporal resolution that prevents the detection of the largest amplitude fluctuations. The dependence of the density profiles and fluctuations characteristics measured by the RIC on parameters such as plasma current, density, and magnetic configuration will be explored for L and H-mode conditions. [1] D. Aguiam et al, Rev. Sci. Instrum. 87 11E722 2016

Speaker: Egor Seliunin

14:00 P2.1034 Investigating the outer magnetic field of Wendelstein 7-X using the magnetic probe

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1034.pdf Investigating the outer magnetic field of Wendelstein 7-X using the magnetic probe A. Knieps1, P. Drews1, S. Liu1, C. Killer2, Y. Liang1, J. Geiger2, K. Rahbarnia2, D. Nicolai1, G. Satheeswaran1 and the W7-X team2 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany During the first phase of the second experimental campaign OP1.2a of Wendelstein 7-X (W7-X) – featuring for the first time an island divertor – measurements of the edge magnetic field profiles were conducted using the combined probe [1] mounted on the Multi-Purpose-Manipulator (MPM) with its 3D coil array. The measurements with the combined probe have been performed in different magnetic configurations as well as with varying heating scenarios. While the measured vacuum profiles matched the predictions quite well, it was observed that the measurements with plasma deviated noticeably. This is in contrast to the first operational campaign where the considerably lower pressures did not cause such a difference between the vacuum fields and those with plasma. The measurements have been performed in different magnetic configurations and for different plasma heating scenarios which allows a dedicated comparison. Although W7-X has been optimized for small bootstrap currents, finite toroidal plasma currents were present in the scenarios and have been measured with Rogowski coils. It is currently not yet clear whether the differences in the measurements have to be attributed to the toroidal plasma current connected with the bootstrap current, to pressure-related effects or to a combination. To address this uncertainty in future works the measured data will be compared with MHD equilibrium models. [1]: P. Drews et al. (2017). Measurement of the plasma edge profiles using the combined probe on W7-X. Nuclear Fusion. 57. . 10.1088/1741-4326/aa8385.

Speaker: Alexander Knieps

14:00 P2.1035 GDB flux-driven turbulence simulations of the IWL Alcator C-Mod L-mode boundary plasma compared with experiment and stochastic model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1035.pdf GDB flux-driven turbulence simulations of the IWL Alcator C-Mod L-mode boundary plasma compared with experiment and stochastic model M. Francisquez, B. Zhu, B. Rogers Dartmouth College, Hanover, NH, USA Prior to predicting confinement regime transitions in tokamaks one may need an accu- rate description of L-mode profiles and turbulence properties. These features determine the heat-flux width upon which wall integrity depends, a topic of major interest for re- search aid to ITER. To this end our work uses the Global Drift Ballooning (GDB) model [1] to simulate the Alcator C-Mod edge and contributes support for its use in studying criti- cal edge phenomena in current and future tokamaks. We carried out 3D electromagnetic flux-driven two-fluid turbulence simulations of inner wall limited (IWL) C-Mod shots spanning closed and open flux surfaces [2]. These simulations are compared with gas puff imaging (GPI) and mirror Langmuir probe (MLP) data, as well as the stochastic fluctuation model [3], examining global features and statistical properties of turbulent dynamics. GDB reproduces important qualitative aspects of the C-Mod edge regarding global density and temperature profiles, within reasonable margins, and though the tur- bulence statistics of the simulated turbulence follow similar quantitative trends questions remain about the model’s difficulty in exactly predicting quantities like the autocorrela- tion time. A proposed breakpoint in the near SOL pressure and the posited separation between drift and ballooning dynamics it represents are examined. This experimental- stochastic comparison helps us assess the reliability of GDB as a physics and a predictive tool for other studies. [1] B. Zhu, et al., submitted to Comp. Phys. Comm. (2017) [2] M. Francisquez, et al., Nucl. Fusion 57 (2017) 116049 [3] O. E. Garcia, et al., Phys. Plasmas 23 (2016) 052308 1

Speaker: Manaure Francisquez

14:00 P2.1036 Filament representation of the plasma in the tokamak disruption studies

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1036.pdf Filament representation of the plasma in the tokamak disruption studies V.D. Pustovitov U National Research Centre Kurchatov Institute and National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia It is well known that the plasma-produced poloidal field outside the tokamak plasma can be quite accurately approximated by the field of a set of the distributed toroidal currents (filaments or circular loops) [1]. This is justified by referring to the fact that the tokamak plasma looks like a toroidal current and needs a proper electromagnetic treatment for suppressing the outward expansion. An additional argument in favour of such image is that, with a desirable axisymmetry, the magnetic field due to the plasma poloidal current always remains completely ‘hidden’ inside. The force balance requires that this current must vary reacting on the plasma changes. It will inevitably generate the poloidal electric field outside, which is not accounted for in the models with plasma replaced by current filaments. Such models are often used in calculations of the disruption-induced forces on the tokamak wall [2–5]. Here we analyze the accuracy of this approach. We treat the problem within the standard large-aspect-ratio tokamak model assuming that both the plasma and the wall are circular in the perpendicular cross-sections. The magnetic pressure on the wall during thermal quench (TQ) and current quench (CQ) is analytically calculated by following the approach described in [6]. The rapid events are considered when the penetration of the plasma-driven perturbation through the vessel outwards is weak due to the skin effect in the wall. The derived formulas allow comparison of the disruption-induced forces calculated differently: with plasma described by the MHD equilibrium equations as opposed to the plasma modelled by a set of filaments. The differences in the results are discussed and explained. It is explicitly demonstrated that the filamentary model of the plasma (or disregard of the poloidal current in the plasma) gives unacceptably large errors in the simulated forces for both TQs and CQs. [1] B. J. Braams, Plasma Phys. Control. Fusion 33, 715 (1991). [2] R. Albanese, et al., Fusion Eng. Des. 94, 7 (2015). [3] V. Rozov and A. Alekseev, Nucl. Fusion 55, 083022 (2015). [4] S. N. Gerasimov, et al., Nucl. Fusion 55, 113006 (2015). [5] R. Roccella, et al., Nucl. Fusion 56, 106010 (2016). [6] V. D. Pustovitov and D. I. Kiramov, submitted to Plasma Phys. Control. Fusion (2018).

Speaker: Vladimir D. Pustovitov

14:00 P2.1037 Non-linear interplay between edge localized infernal mode and plasma flow

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1037.pdf Non-linear interplay between edge localized infernal mode and plasma flow G. Q. Dong,1 Y. Q. Liu,2,1 Y. Liu,1 S. Wang,1 N. Zhang,1 G. Z. Hao,1 and G. L. Xia1 1 Southwestern Institute of Physics, Chengdu, People’s Republic of China 2 General Atomics, PO Box 85608, San Diego, California 92186-5608, USA Quiescent H-mode (QH-mode) was first discovered in DIII-D as an ELM-free H-mode regime, which is usually achieved at relatively low plasma density and found to be accompanied by the presence of edge harmonic oscillations (EHOs). EHOs are believed to provide necessary transport to eliminate ELMs by dynamics of the plasma itself. The saturated kink-peeling mode has been suggested as a possible candidate for EHO. In this work, we consider another instability – the edge localized infernal mode (ELIM) – as a possible candidate, for plasmas where the large edge bootstrap current causes local flattening of the plasma edge safety factor, or even the magnetic shear reversal in the pedestal region. An ELIM is a low-n (n is the toroidal mode number) instability similar to the conventional infernal mode, but being localized at the plasma edge where safety factor is locally flattened. Finite plasma pressure in the pedestal region drives this mode. A saturated ELIM, due to non-linear interaction with toroidal plasma edge flow, can be responsible for EHO. A systematic numerical investigation, utilizing the free boundary MARS-F/K codes, shows that both plasma resistivity and toroidal flow shear destabilize the ELIM. The drift kinetic effects, due to mode resonance with precessional and bounce motions of trapped thermal particles, are found to be stabilizing for the mode, albeit not dramatic. We also find that the low-n ELIM instability is strongly affected by a close-fitting resistive wall. The presence of a resistive wall can fully stabilize an otherwise flow-shear destabilized ELIM. The ELIM instability, like other MHD instabilities, generates toroidal torques which in turn can affect the plasma flow. The non-linear interplay between the ELIM and the plasma flow, by running initial value simulations with the quasi-linear code MARS-Q, is investigated. We start simulations at a prescribed rotation speed. Compared to the linear runs, the quasi-linear run shows partial saturation of the mode. Meanwhile, the toroidal rotation profile especially that near the plasma edge where the mode is located, is significantly reduced, together with the local flow shear near the q=4 surface. It is this reduction of the local flow shear that leads to the eventual mode saturation in this simulation.

Speaker: Guanqi Dong

14:00 P2.1038 External kink mode stability in a tokamak with a finite current density in the SOL

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1038.pdf External kink mode stability in a tokamak with a finite current density in the SOL A.A. Martynov1,2, S.Yu.Medvedev1,2, S.V. Konovalov2, A.S. Kukushkin2,3, A. Loarte4, A. R. Polevoi4, J.C. Hillesheim5, S. Saarelma5 and JET Contributors* 1 Keldysh Institute of Applied Mathematics, Moscow, Russia 2 National Research Centre Kurchatov Institute, Moscow, Russia 3 National Research Nuclear University MEPhI, Moscow, Russia 4 ITER Organization, 13067 St. Paul Lez Durance Cedex, France 5 CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom A conducting plasma outside the separatrix affects the stability of the external kink modes in tokamaks with a divertor. Large values of the pressure gradient and current density in the scrape-off layer (SOL) region driven by both the thermoelectric current between the divertor plates with different plasma temperatures and the bootstrap current can be expected according to the transport simulations [1]. Here we apply the equilibrium and stability codes CAXE-SOL/KINX-SOL [2] to study in a systematic way the dependence of the stability of the peeling-ballooning (PB) mode localized in the pedestal region on the plasma parameters in the SOL. We show that the limiting pressure pedestal height is not very sensitive to the pressure gradient distribution over the SOL and pedestal region, but a high current density parallel to the magnetic field in the SOL leads to the instability of the external kink modes localized at the conducting plasma edge. The development of such instabilities can be an alternative trigger for the ELMs, in addition to the standard model based on destabilization of the Peeling-Ballooning (PB) modes. For reconstructed JET H-mode equilibria including the pedestal, the possibility of ELMs being triggered due to the existence of currents in the SOL has been studied and found to be a viable mechanism, particularly for the cases when the pedestal height is insufficient to destabilize the PB modes [3]. The same finding is reproduced for typical NSTX H-mode plasma conditions. Since accurate measurements and estimates of the current density in the SOL are not available, the stability limits and their sensitivity to variations of the current profiles and of the width of the conducting plasma layer outside the separatrix are investigated. This analysis will also be performed in the paper for ITER plasma equilibria in reference H-mode operational conditions including various levels of SOL current density. ITER is a Nuclear Facility INB-174. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. [1] A. Loarte, F. Liu, G.T.A. Huijsmans, A.S. Kukushkin and R.A. Pitts. J. Nucl. Mater. 463 (2015) 401. [2] S.Yu. Medvedev et al. Plasma Phys. Control. Fusion 59 (2017) 025018. [3] C. Bowman et al. Nucl. Fusion 58 (2018) 016021. * See the author list of “X. Litaudon et al. 2017 Nucl. Fusion 57 102001”

Speaker: Alexander Martynov

14:00 P2.1039 Effect of externally applied resonant magnetic perturbations on the stability of magnetic island

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1039.pdf Effect of externally applied resonant magnetic perturbations on the stability of magnetic island Q. Yu, S. Günter and K. Lackner Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany The effect of externally applied resonant magnetic perturbations (RMPs) on the stability of magnetic island is investigated based on two-fluid equations. The growth of the m/n=2/1 magnetic island (m and n are the poloidal and toroidal mode numbers), driven by an unfavorable plasma current density profile and bootstrap current perturbation, is found to be suppressed by static RMPs of the same helicity and of moderate amplitude (~ 10-4 of the toroidal field), if the local bi-normal electron fluid velocity at the resonant surface is sufficiently large. While without applying RMPs, the 2/1 island saturates at a width of 0.2a (a is the plasma minor radius) in the nonlinear phase even when neglecting the bootstrap current perturbation. A significant change in the local equilibrium plasma current density gradient by small amplitude RMPs is also found for realistic ASDEX Upgrade plasma parameters, which together with the diamagnetic drift and the associated ion polarization current affect the island stability. The two-fluid effects, including the electron inertia, on the island stability are found to be larger for a lower plasma resistivity and expected to be more important for a fusion reactor like ITER. Our results indicate that error field can be stabilizing for the island growth, if the error field amplitude is not too large and the local bi-normal electron fluid velocity is not too low, and that applied rotating RMPs with an appropriate frequency can be utilized to change the local plasma current density gradient around the resonant surface and to suppress the 2/1 island growth in high temperature plasmas even for a low bi-normal electron fluid velocity. It is known that the 2/1 mode can lead to significant decreases in plasma confinement or even disruptions in tokamak discharges and should be stabilized.

Speaker: Qingquan Yu

14:00 P2.1040 Influence of stiff temperature profile on island stabilization by RF heating

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1040.pdf Influence of stiff temperature profile on island stabilization by RF heating Patrick Maget, Fabien Widmer, Olivier Février1 , Hinrich Lütjens2 , Xavier Garbet CEA, IRFM, F-13108 Saint Paul-lez-Durance, France. 1 SPC, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. 2 Centre de Physique Théorique, Ecole Polytechnique, CNRS, France. Theory and experiments show that turbulent transport in tokamaks is triggered above a critical temperature gradient, and leads to resilient (also refered to as stiff) profiles above this threshold [1]. Inside magnetic islands, where the temperature profile is flattened, a reduced diffusivity is expected and indeed measured [2]. The consequences of profile stiffness on island stabilization by RF heating has recently been investigated analytically and numerically [3], using a character- re f σ −1 istic form for heat diffusivity as χ⊥ = χ⊥ T 0 /Teq 0 , with σ the stiffness parameter and Teq the equilibrium temperature. This formulation reproduces the low diffusivity below a threshold in temperature gradient, and the large diffusivity above this threshold, with an actual equilib- rium temperature gradient that lies in the turbulent transport dominated regime. We find that the stabilization efficiency varies as (PRF /Peq )1/σ , with Peq the power injected inside the island position and PRF the additional heat source centered at the O-point of the island. For non-stiff profiles (σ = 1), we find a good agreement with known results [4]. In the most common case where the ratio (PRF /Peq ) is small, the stabilization can be much larger than anticipated when assuming non-stiff profiles. Numerical simulations with the XTOR code [5], where a RF heat source is deposited at the O-point of a (2,1) island, shows a good agreement with the analyti- cal model. The stabilization of Neoclassical Tearing Modes by the combined effect of heat and current drive can then be addressed in more realistic conditions [6]. References [1] A. M. Dimits et al., Physics of Plasmas 7, 969 (2000); X. Garbet et al., Plasma Physics and Controlled Fusion 46, B557 (2004). F. Imbeaux et al, Plasma Physics and Controlled Fusion 43, 1503 (2001); P. Mantica et al., Phys. Rev. Lett. 102, 175002 (2009); [2] W. A. Hornsby et al., Physics of Plasmas 17, 092301 (2010); K. Ida et al., Phys. Rev. Lett. 109, 065001 (2012); Bardòczi et al., Physics of Plasmas, 24(12), 122503 (2017) [3] P. Maget et al., Physics of Plasmas 25, 022514 (2018) [4] C. C. Hegna et al., Physics of Plasmas 4, 2940 (1997); D. D. Lazzari et al., Nuclear Fusion 49, 075002 (2009). [5] H. Lütjens and J.-F. Luciani, Journal of Computational Physics 229, 8130 (2010). [6] F. Widmer et al., Neoclassical Island Control with Stiff Temperature Model (European Physical Society, Prague (Czech Republic), 2018).

Speaker: Patrick Maget

14:00 P2.1041 Real-time equilibrium reconstruction integration into the ASDEX Upgrade control system

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1041.pdf Real-time equilibrium reconstruction integration into the ASDEX Upgrade control system L.Giannone, B.Sieglin, R.Fischer, J.C.Fuchs, P.J.McCarthy1 , K.H.Schuhbeck and the ASDEX Upgrade Team Max Planck Institute for Plasma Physics, EURATOM Association, 85748 Garching, Germany 1 Department of Physics, University College Cork, Association EURATOM-DCU, Cork, Ireland The real-time equilibrium reconstruction code for the ASDEX Upgrade tokamak, JANET [1], is in the process of migration to a Linux based C11++ code. This is motivated by the need for closer integration into the control system and the long term goal of replacing the currently used function parameterisation based control when upper divertor coils for studying advanced magnetic configurations are installed [2]. The benchmarks of the individual elements are presently being optimised. The parameters for the position and orientation of the magnetic probes and flux loops, the position of the poloidal field coils and limiters and the surface locations of the 7 rows of ferromagnetic tiles installed in 2017 are input from an XML based machine description file. The setting up of the 12 basis current functions on the flux matrix from the previous time step requires 105 µs. On a 65x129 grid, the Grad-Shafranov solver then calculates a solution in 130 µs that is a best fit to the magnetic probe measurements. Contour integrals at 10 normalised radii required for input to the RAPTOR code [3] and at the separatrix to calculate beta poloidal and plasma inductance are carried out in 100 µs. Integrators for magnetic probe arrays at 4 additional toroidal locations have been developed. The 16 bit ADC’s of the integrators can acquire data with a sample frequency up to 100 kHz and with a software selectable integration time. There are 16 channels in a crate with an interface card and four crates are connected to a PXIe 7821 FPGA. The recorded data is transmitted in real-time by an optical bus extender (MXI Express x4) to the computing node with an 8 core Intel Xeon E5-2667 v3 running at 3.2 GHz. References [1] L. Giannone, R. Fischer, P. McCarthy, et al., Improvements for real-time magnetic equilib- rium reconstruction on ASDEX Upgrade, Fusion Eng. Des. 100 (2015) 519. [2] T. Lunt, H. Zohm, A. Herrmann, et al., Proposal of an alternative upper divertor in ASDEX Upgrade supported by EMC3-EIRENE simulations, Nucl. Mat. and Energy 12 (2017) 1037. [3] F. Felici, O. Sauter, S. Coda, et al., Real-time physics-model-based simulation of the current density profile in tokamak plasmas, Nucl. Fusion 51 (2010) 083052.

Speaker: Louis Giannone

14:00 P2.1042 Characterization of plasma major disruption in the Globus-M spherical tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1042.pdf Characterization of Plasma Major Disruption in the Globus-M Spherical Tokamak N.V. Sakharov1, V.K. Gusev1, S. N. Kamenshchikov2 A.A. Kavin2, K. M. Lobanov2, A.B. Mineev2, M.I. Patrov1, Yu.V. Petrov1 1 Ioffe Institute, St. Petersburg, Russia 2 JSC D.V. Efremov Scientific Research Institute of Electrophysical Apparatus, Saint Petersburg, Russia In this presentation we describe the characteristics of the plasma current quench during disruptions in the Globus-M spherical tokamak. The process of current quench is accompanied by the loss of the vertical stability of the plasma column. The plasma boundary during the disruption is reconstructed using the algorithm of movable filaments. In comparison with the International Disruption Database for conventional tokamaks [1] the analysis of the data obtained in the stage of plasma current quench demonstrates a favorable, almost linear dependence of the normalized current quench time tCQ/S on the plasma current density Ip/S before the disruption [2]. The current induced in the vessel also increases linearly with increasing plasma current. The data on the current quench time and the toroidal current induced in the tokamak vessel are compared for hydrogen and deuterium plasmas. It is shown that the disruption characteristics depend weakly on the ion mass. The main current quench characteristics are compared for different values of the toroidal magnetic field and different values of the plasma safety factor before the disruption. The distribution of the toroidal current induced in the vessel wall is determined from magnetic measurements, and the electromagnetic loads on the vessel wall during the current quench are calculated [3]. It is shown that the current quench results in the appearance of bending stresses in the vessel domes of near momentless shape. References: [1] N. W. Eidietis, S. P. Gerhardt, R. S. Granetz et al, Nucl. Fusion 55, 063030 (2015). [2] N. V. Sakharov, V. K. Gusev, A. D. Iblyaminova et al, Plasma Phys. Rep. 43, 422 (2017). [3] N. V. Sakharov, V. K. Gusev, A. A. Kavin et al, Plasma Phys. Rep., to be published in 2018.

Speaker: Nikolai Vladimirovich Sakharov

14:00 P2.1043 NIFS-SWJTU joint project for Chinese First Quasi-axisymmetric Stellarator (CFQS)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1043.pdf NIFS-SWJTU joint project for Chinese First Quasi-axisymmetric Stellarator (CFQS) M. Isobe1,2, A. Shimizu1, H. Liu3, S. Okamura1, and Y. Xu3 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 2 SOKENDAI (The Graduate University for Advanced Studies), Toki, Japan 3 Institute of Fusion Science, Southwest Jiaotong University, Chengdu, People’s Republic of China National Institute for Fusion Science (NIFS) established an international academic cooperation agreement with Southwest Jiaotong University (SWJTU) in July, 2017, for moving towards the first helical plasma experimental research in the People’s Republic of China. NIFS and SWJTU initiated the implementation of physics and engineering designs of the new helical device called Chinese First Quasi-axisymmetric Stellarator (CFQS) collaboratively. From now, the two institutes will undertake construction of the CFQS, plasma heating and diagnostics technical development, and plasma experiments jointly. The CFQS will be constructed in SWJTU. The magnetic configuration of CFQS is quite different from that of the Large Helical Device (LHD). Although the CFQS is tokamak-like in the magnetic configuration, it does not require a net plasma current to confine a high- temperature plasma as its name suggests. It is characterized by low-aspect ratio, weak magnetic shear, and significantly reduced neoclassical transport and toroidal viscosity. By implementing plasma experimental research based upon a device designed using new concepts in new collaborative design and construction, we can complement experimental research performed on the LHD. NIFS is going to utilize existing resources of Compact Helical System (CHS) of NIFS effectively, i.e., vacuum pumping system, gyrotron for electron cyclotron resonance heating, and key diagnostics such as heavy ion beam probe. Relocation of a neutral beam injector of CHS will be also considered after the commissioning stage.

Speaker: Mitsutaka Isobe

14:00 P2.1044 Operational diagrams for MHD instabilities limiting plasma performances in JET D-T Scenarios with ILW

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1044.pdf Operational diagrams for MHD instabilities limiting plasma performances in JET D-T Scenarios with ILW E. Alessi1, P. Buratti2, E. Giovannozzi2, T. O'Gorman3, G. Pucella2, M.Baruzzo4, E.Joffrin5, S.Nowak1, F.G. Rimini3 and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 IFP-CNR, via R. Cozzi 53, Milano, Italy 2 ENEA C. R. Frascati, via E. Fermi 45, Frascati (Roma), Italy 3 CCFE, Culham Science Centre, Abingdon, United Kingdom 4 Consorzio RFX, Corso Stati Uniti 4, Padova, Italy 5 CEA, IRFM, Saint Paul Lez Durance, France (*) See the auhor list of X. Litaudon et al 2017 Nucl. Fusion 57 102001 One of the major aims of nowadays JET experimental campaigns is the execution of D-T experiments with a metallic tokamak (ILW, ITER-like wall) wall [1-2]. At present, experiments are devoted to develop scenarios capable of sustaining high performances for >5s. Two scenarios are considered with this aim: the Baseline H-mode Scenario, and the Hybrid Scenario. High performances and duration can be limited by the onset of MHD modes or by the influx of high Z impurities in the plasma core [3,4,5]. MHD modes can foster the accumulation of impurities [4] and, on the other hand, an excess of impurities in the core plasma degrades the current density profile providing the conditions to lower the thresholds for triggering MHD instabilities. Then, to identify the conditions under which NTMs are the main cause limiting the plasma performances, the statistical analysis of the MHD onset conditions has been undertaken distinguishing between the trigger causes (e.g., Sawteeth) and the presence or not of impurities in the plasma. The latter condition has been found effective in indicating that cases of n=2 onsets (not Sawtooth triggered) at low ßN in the Hybrid scenario are mainly due to plasma profiles already degraded by impurity influx. The analysis here presented takes into account all pulses performed in Hybrid scenario during the 2015-2016 JET campaign (~250 pulses), and a selected list of ~90 pulses for the Baseline scenario. References: [1] X. Litaudon et al 2017 Nucl. Fusion 57 102001 [2] L. Horton et al 2016 Fusion Eng. Des. 109–11 925 [3] P. Buratti et al 2015 42nd EPS Conf. on Plasma Physics (Lisbon) P2.115 [4] T. Hender et al. 2016 Nucl. Fusion 56 066002 [5] I Nunes and the JET Contributors 2016 Plasma Phys. Control. Fusion 58 014034

Speaker: Edoardo Alessi

14:00 P2.1046 Kinetic modeling of plasma response to RMPs for a tokamak in full toroidal geometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1046.pdf Kinetic modeling of plasma response to RMPs for a tokamak in full toroidal geometry C. G. Albert1 , M. F. Heyn1 , S. V. Kasilov1,2 , W. Kernbichler1 , the EUROfusion MST1 Team∗ 1 Fusion@ÖAW, Institut für Theoretische Physik - Computational Physics, TU Graz, Petersgasse 16, A–8010 Graz, Austria 2 Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics and Technology”, Akademicheskaya Str. 1, 61108 Kharkov, Ukraine ∗ See the author list “H. Meyer et al 2017 Nucl. Fusion 57 102014” The successful application of external non-axisymmetric magnetic perturbations (resonant magnetic perturbations or RMPs) for the mitigation and suppression of edge-localized modes in medium-sized tokamaks [1] has left a number of open questions with regard to models that include plasma response currents in a 3D equilibrium. Kinetic modeling in straight cylindrical geometry [2] shows a collisionality-dependent difference of plasma response currents compared to predictions of commonly used MHD models, in particular a shift of electron fluid resonances depending on the temperature gradient. Therefore a predictive model should include kinetic effects. Because cylindrical geometry cannot account for poloidal mode coupling and guiding- center orbit effects pertinent to a toroidal configuration, a model in full toroidal geometry is necessary. Since resonant plasma response localized around resonant flux surfaces and non- resonant (NTV) response in the whole plasma volume cannot be decoupled, a predictive model should take both of them into account. Here results from a kinetic Monte-Carlo model in full toroidal geometry and with realistic magnetic perturbations [3] are presented for the case of ASDEX Upgrade with ELM mitigation coils. Namely the perturbed pressure tensor and current density are compared to results from a corresponding MHD model. It is shown that the pressure perturbation is strongly anisotropic not only in vicinity of resonant surfaces, but in the whole plasma volume. While parallel pressure agrees well with ideal MHD predictions, perpendicular pressure might be affected by orbital resonances, which are usually important for ion NTV at low-collisional reactor-relevant conditions [4, 5]. This means that perturbations of diamagnetic currents caused by external non-axisymmetric perturbations cannot always be described by ideal MHD theory, and kinetic modeling may be required for the calculation of perturbed plasma equilibria even in absence of resonant flux surfaces. References [1] A. Kirk, W. Suttrop, et al., Nucl. Fusion 55, 043011 (2015) [2] M. F. Heyn et al., Nucl. Fusion 54, 064005 (2014) [3] C. G. Albert et al., Varenna-Lausanne Workshop, J. Phys. Conf. Ser. 75, 012001 (2016) [4] K. C. Shaing et al., Nucl. Fusion 55 125001 (2015) [5] A. F. Martitsch et al., Plasma Phys. Contr. Fusion 58, 074007 (2016)

Speaker: Christopher Georg Albert

14:00 P2.1047 Dynamic evolution of runaway electron energy distribution during tokamak disruptions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1047.pdf Dynamic evolution of runaway electron energy distribution during tokamak disruptions L. Zeng1, Y. Liang1, 2, H.R. Koslowski2, S. Lin1, B. Zhang1, X. Zhu1, T. Tang1, R. Zhou1, H. Liu1, J. Qian1, S. Zhang1, Y. Jie1, X. Gong1, X. Gao1 1 Institute of Plasma Physics, Chinese Academy of Sciences, 230031 Hefei, China 2 Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research -Plasma Physics (IEK-4), Association EURATOM-FZJ, 52425 Jülich, Germany E-mail: zenglong@ipp.ac.cn The dynamics of runaway electron energy distribution during tokamak disruptions is described by a 0D model taking collision, bremsstrahlung, synchrotron radiation and also electric field into account. It is shown that the collision term is sensitive to the low energy range of runaway electrons but the bremsstrahlung and synchrotron radiation terms are more effective on the high energy runaway electrons. Contribution from the external electric field mainly affect the relatively medium energy runaways. This model introduces new features in the test equations describing dynamic evolution of runaway electron energy distribution: 1) During massive gas injection into post-disruption runaway electron plateaus, it is shown that for a massive injection of a low-Z gas such as helium and hydrogen to the RE beam generated by argon injection during the disruptions, the dependence of bremsstrahlung on the injection amount is non-monotonous. When the injection amount is less than a threshold, the bremsstrahlung will decrease and then the maximum RE energy increase, which can even improve RE generation. For a massive injection of a medium-Z gas such as neon and argon, the bremsstrahlung will increase continually leading to more RE losses and a decrease of the maximum RE energy. 2) During a large negative loop voltage applied on post-disruption runaway electron plateaus, it is shown that the electric field de-accelerates REs and mainly decrease the RE energy in the medium-energy range. When the added electric field is large enough, it can possibly drive an energetic electron instability, causing the anomalous runaway losses.

Speaker: Long Zeng

14:00 P2.1048 The rapid response of 2/1 tearing mode to electrode biasing in J-TEXT experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1048.pdf The rapid response of 2/1 tearing mode to electrode biasing in J-TEXT experiments Tong Wang1, Zhipeng Chen1,*, Qiming Hu2,*, Q. Yu3, Hai Liu4, Mingxiang Huang1, Jie Yang1, Da Li1, Yuan Huang1, Daojing Guo1, Zhuo Huang1, Zhifeng Cheng1, Lizhi Zhu1, Zhoujun Yang1 and J-TEXT Team 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China 2 Princeton Plasma Physics Laboratory, Princeton NJ 08543-0451, USA 3 Max-Planck-Institut für Plasmaphysik, 85748, Garching, Germany 4 Institute of Fusion Science, Southwest Jiaotong University, Chengdu, 610031, China *Corresponding author E-mail: zpchen@hust.edu.cn and qhu@pppl.gov The effects of electrode biasing (EB) on the m/n = 2/1 tearing modes(TM) have been experimentally studied in J-TEXT tokamak, where m and n are the poloidal and toroidal mode numbers. According to the response time, the response of 2/1 tearing mode to EB can be divided into two processes, the rapid response and the slow response. In the rapid response, what needs to be noted is that the variation of EB current is proportional to the variation of tearing mode frequency, regardless of the EB current rise time, position of electrode, and bias voltage. On the base of that EB can supply a torque to change the tearing mode frequency quickly, the EB has been applied to unlock the locked mode. The experimental results show that the mode locking can be avoided by the negative bias voltage. While, it’s unfortunately that the EB can’t unlock the locked mode in recent experiments, which is different from our conjecture. In summary, the experimental results suggest that applied electrode biasing is a possible method for the avoidance of mode locking and disruption.

Speaker: Tong Wang

14:00 P2.1049 A machine learning approach towards a disruption prediction and avoidance system: developments and perspectives

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1049.pdf A machine learning approach towards a disruption prediction and avoidance system: developments and perspectives A. Pau1, A. Fanni1, B. Cannas1, S. Carcangiu1, G. Sias1, P. Sparapani1, E. Alessi2, C. Sozzi2, M Baruzzo3, E. Joffrin4, P.J. Lomas5, A. Murari3, F. Rimini5, and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 Electrical and Electronic Eng. Dept. University of Cagliari, Italy 2 IFP-Consiglio Nazionale delle Ricerche, Milano, Italy 3 Consorzio RFX-Associazione - EURATOM ENEA per la Fusione, Padova, Italy 4 CEA, IRFM, F-13108 St Paul Les Durance, France. 5 CCFE, Culham Science Centre, OX14 3DB Abingdon, UK * See X. Litaudon et al. Nucl. Fusion 57, 102001 Disruptive events still represent one of the main concerns for the protection of in-vessel components of large size tokamaks, imposing several constraints on the design of the next step experimental devices such as ITER and DEMO. This work aims to summarize the efforts in the development of an innovative machine learning approach, based on a generative model, towards the implementation of a disruption prediction and avoidance system. [1] In the proposed approach the first step is the construction of a reliable database and to the proper selection of the discharge phases of interest for the study: the analysis, in particular, will be mainly focused on the flat-top phase of the plasma current. In order to effectively extract the information contained in the raw signals, a feature engineering approach has been combined with the definition of physics-based indicators related to more structured spatial and/or temporal information, such as the time evolution of kinetic plasma profiles, the spatial distribution of the radiation and MHD rotating modes. In this framework, the potential of a machine learning tool [2] built upon the Generative Topographic Mapping [3] algorithm will be discussed emphasizing the effectiveness of the tool for the investigation of the operational [4] space where the relevant physics takes place . Typical patterns, describing different processes and characterizing different types of disruption, will be compared for different scenarios developed at JET with the ILW, extending the analysis presented in [5] to the recent high power experimental campaign carried out in 2016. The paper will discuss how the operational boundaries appearing in the considered parameters space are potentially modified and how this could affect the definition of robust disruption avoidance schemes. [1] A Pau et al 2017 “A tool to support the automatic construction of reliable disruption databases”, FED http://dx.doi.org/10.1016/j.fusengdes.2017.10.003. [2] A Pau 2014 “Techniques for prediction of disruptions on TOKAMAKS”, http://paduaresearch.cab.unipd.it/6664/ [3] Bishop C., Svensén M., Williams C. (1998), Neural Comp.10 215–34. [4] B Cannas et al 2015 “Automatic disruption classification in JET with the ITER-like wall”, PPCF 57 125003 [5] A Pau et al 2017 “A first analysis of JET plasma profile-based indicators for disruption prediction and avoidance”, 27th IEEE Symposium on Fusion Engineering, Shanghai, China, under review on IEEE TPS

Speaker: Alessandro Pau

14:00 P2.1050 Kinetic equilibrium reconstruction on TCV: towards a self-consistent approach

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1050.pdf Kinetic equilibrium reconstruction on TCV: towards a self-consistent approach F. Carpanese1 , O.Sauter1 , A. Merle1 , J-M.Moret and the TCV team 1 EPFL-SPC, Switzerland The equilibrium reconstruction of TCV plasmas is usually performed making use of only external magnetic measurements. Not using internal measurements from the confined plasma, such as those provided by an MSE diagnostic, results in an ambiguous reconstruction of the current and pressure profiles, which ultimately reflects on the q profile. Moreover, the limited number of basis functions used to represent the plasma profiles when computing the equilibrium makes the latter inaccurate particularly in the presence of steep pressure gradients or a peaked current density profile. When kinetic plasma measurements (ne, Te, Ti) are used in the reconstruction one refers to kinetic equilibrium reconstruction: the pressure is constrained by measurements while the current density profile is constrained by solving the time-dependent flux surface averaged Ohm’s law. We tackled this problem by coupling the free-boundary equilibrium reconstruction code LIUQE [1] to the transport code ASTRA [2] solving just for the flux surface averaged Ohm’s law. The coupling is performed by taking the pressure and current density profiles from ASTRA as basis functions for LIUQE but allowing them to be scaled in order to minimize the error between the equilibrium solution and magnetic measurements. This scheme was chosen with the purpose of re-using existing, well benchmarked tools as much as possible with the smallest possible number of modification so that their future individual upgrades will not affect the coupling. The scheme has proven to converge and to produce more realistic evolution of internal inductance in the presence of central and off-axis current drive. It will also be used to study H- mode plasmas in the presence of NBI heating and the effects of strong pressure flattening due to NTMs. The tool can be run autonomously (without human interaction) and is aimed at being used routinely for experimental data analysis of TCV discharges. [1] Pereverzev, G. V., & Yushmanov, P. N. (2002). ASTRA. Automated System for TRansport Analysis in a tokamak. [2] Moret, J. M., Duval, B. P., Le, H. B., Coda, S., Felici, F., & Reimerdes, H. (2015). Tokamak equilibrium reconstruction code LIUQE and its real time implementation. Fusion Engineering and Design, 91, 1-15.

Speaker: Francesco Carpanese

14:00 P2.1051 Application of the free-boundary SIESTA MHD equilibrium code to bootstrap control scenarios in the W7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1051.pdf Application of the free-boundary SIESTA MHD equilibrium code to bootstrap control scenarios in the W7-X stellarator R. Sanchez1 , H. Peraza-Rodriguez1 , J.M. Reynolds-Barredo1 , V. Tribaldos1 , J. Geiger2 1 Universidad Carlos III de Madrid, SPAIN 2 Max-Planck-Institut für Plasmapyhsik, Greifswald, GERMANY SIESTA [1] is an MHD equilibrium code designed to perform fast and accurate calculations of ideal MHD equilibria for three-dimensional magnetic configurations. SIESTA is an iterative code that uses the solution previously obtained by the VMEC code [2] for the same problem to provide an Eulerian background coordinate system and an initial guess of the equilibrium solution. In contrast to VMEC, SIESTA does not assume closed magnetic surfaces. Thus, the final equilibrium solution can include magnetic islands and stochastic regions. In its original implementation, the SIESTA code addressed only fixed-boundary problems. That is, the shape of the plasma edge, assumed to be a magnetic surface, was the same obtained by the VMEC code and it was kept fixed as the solution iteratively converges to equilibrium. This fixed boundary condition has somewhat restricted the possible applications of SIESTA in the past, limiting it to problems in which a possible variation of the plasma boundary was not of interest. To circumvent these limitations, SIESTA has been recently extended [3] being now able to deal with free-plasma-boundary problems, opening up the possibility of addressing situations in which the plasma boundary is perturbed either externally or internally. The compu- tational domain of the new version of SIESTA can now be extended all the way to the vacuum vessel if desired. This is made possible by several techniques that extend the background coor- dinate system and provide suitable initial guess for the equilibrium solution over the extended volume. As an illustration of its new capabilities, SIESTA is applied in this contribution to the study of bootstrap control scenarios to avoid undesired distortions of the island chain that insulates the plasma edge from the divertor of the W7-X stellarator [4]. References [1] S.P. Hirshman, R. Sanchez and C.R. Cook, Phys. Plasmas 18 062504 (2011) [2] S.P. Hirshman and JC Whitson, Phys. Fluids 26 3553 (1983) [3] H. Peraza-Rodriguez, J.M. Reynolds-Barredo, R. Sanchez, V. Tribaldos, J. Geiger, S.P. Hirshman and M. Cianciosa, Phys. Plasmas 24 082516 2017) [4] H. Peraza-Rodriguez, J.M. Reynolds-Barredo, R. Sanchez, V. Tribaldos and J. Geiger, Plasma Phys. Contr. Fus. 60, 2018 (2018)

Speaker: Raul Sanchez

14:00 P2.1052 Modelling of TAE mode excitation with an antenna in X-point geometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1052.pdf Modelling of TAE mode excitation with an antenna in X-point geometry A. Dvornova1,2,3, G.T.A. Huijsmans2,3, S. Sharapov4, M. Hoelzl5, J. Artola1, S. Pamela4 1 Aix-Marseille Universite, CNRS, PIIM UMR 7345, 13397 Marseille, France 2 Eindhoven University of Technology, Eindhoven, The Netherlands 3 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 4 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 5 Max-Planck-Institut fur Plasmaphysik, 85748 Garching, Germany In magnetic fusion devices, excitation of Toroidal Alfven Eigenmodes (TAEs) can be caused through wave-particle resonance by fusion-born alpha-particles or fast ions generated by ion cyclotron resonance and neutral beam heating. TAEs may affect fast particle confinement, reduce heating and current drive efficiency, cause damage to the first wall, and decrease overall plasma performance. In the absence of fast ions, TAEs can be investigated by launching electromagnetic waves by an external antenna and sweeping the antenna frequency across the TAE frequency range in order to detect a high-quality peak in the plasma response marking the weakly-damped TAE resonance. Excitation of TAE modes with an external antenna has been very successful [1]. It was found, however, that TAEs, probed with an external antenna in the limiter phase of the discharges, disappear when the X-point forms in the magnetic configuration. This effect was thought to be likely due to an increase in the TAE damping rates. More detailed studies [2] show that the damping rates increase significantly with elongation and ellipticity. The aim of the present work is to investigate in detail the effect of the X-point geometry on the efficiency of the TAE excitation with an external antenna and on the TAE damping rate. An equilibrium from a JET discharge with a clear effect of the X-point on the TAE (pulse #42870) just before and after the X-point phase was analysed with the CASTOR linear resistive MHD code including the external TAE antenna [3]. As the plasma boundary of the simulation domain approaches the separatrix from the core, the amplitude of the excited TAE mode is strongly reduced, in agreement with observations. Damping rates of 0.5 to 10% are found, consistent with the previous results [1]. However, in the castor code the X-point geometry can be only closely approximated. The JOREK-STARWALL nonlinear MHD code has been extended to include the active TAE coils [4]. This does allow the simulation of the excitation of TAE modes with an external antennas in full X-point geometry, including the scrape-off layer. The simulations of antenna excitation of TAE modes is challenging due to the low dissipation (i.e. resistivity, viscosity) that is required to avoid a strong damping. Results in a limiter plasma with the time evolution code JOREK-STARWALL are in good agreement with the steady state solution from CASTOR. Simulations of the JET case in x-point geometry are compared to the linear MHD results to identify the cause for the absence of antenna excited TAE mode in this configuration, as observed in the experiments. [1] A. Fasoli et al 2010 Plasma Phys. Control. Fusion 52 075015 [2] D. Testa et al 2001 Nucl. Fusion 41 809 [3] G.T.A. Huysmans et al Physics of Plasmas 2, 1605 (1995) [4] M. Hoelzl et al 2012 J. Phys.: Conf. Ser. 401 012010

Speaker: Anastasia Dvornova

14:00 P2.1053 Multi-branch resistive wall instabilities in a resistive plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1053.pdf Multi-branch resistive wall instabilities in a resistive plasma G. Z. Hao1, S. X. Yang2, Y. Q. Liu3, Z. X. Wang2 1 Southwestern Institute of Physics, Chengdu, People’s Republic of China 2 Dalian University of Technology, Dalian People’s Republic of China 3 General Atomics, San Diego, California 92186-5608, USA Most of the theory and the modelling efforts on the resistive wall mode (RWM) instability are based on the ideal plasma assumption (i.e., without plasma resistivity). Previous works shown that toroidal favorable average curvature (i.e. GGJ) effect associated with the resistive layer has a stabilization effect on the RWM [1]. In this work, we apply the full toroidal stability code MARS-F to investigate the GGJ effect on the RWM stability in a toroidal resistive plasma. An important conclusion is that there are two instability branches of the RWM, when the GGJ effect is taken into account as shown in Fig. 1. The behavior of these two branches (both mode growth rate and mode real frequency) rather different while varying both the Lundquist number and the toroidal plasma rotation frequency. However, only one branch can be found when GGJ effect is excluded. Qualitatively similar results can be obtained by numerically solving the RWM dispersion relation, which includes the resistive layer physics associated with the GGJ effect. Fig.1 The normalized growth rate (a) and real frequency (b) of resistive wall mode versus the normalized plasma pressure β𝑁 with different choices of Lundquist number S. In order to successfully control RWM instability in high performance plasmas such as in ITER, the possible multi-branches of RWM induced by non-ideal effects (e.g. resistivity discussed in this work and the kinetic effect from thermal particles [3]) should be considered. References [1] Y. L. He, Y. Q. Liu, Y. Liu, G. Z. Hao, and A. K. Wang, Phys. Rev. Lett. 113, 175001 (2014). [2] Y. L. He, Y. Q. Liu, Y. Liu, C. Liu, G. L. Xia, A. K. Wang, G. Z. Hao, L. Li, and S. Y. Cui, Phys. Plasmas 23, 012506 (2016). [3] G. Z. Hao, S. X, Yang, Y. Q. Liu, Z. X. Wang, A. K. Wang, and H. D. He, Phys. Plasmas, {23, 062105 (2016)

Speaker: Guangzhou Hao

14:00 P2.1054 First experiments on helical mirror device SMOLA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1054.pdf First Experiments on Helical Mirror Device SMOLA A.V. Sudnikov1,2, A.D. Beklemishev1,2, A.V. Burdakov1,3, I.A. Ivanov1,2, A.A. Inzhevatkina2, V.V. Postupaev1,2 1 Budker Institute of Nuclear Physics, Novosibirsk, Russia 2 Novosibirsk State University, Novosibirsk, Russia 3 Novosibirsk State Technical University, Novosibirsk, Russia Plasma confinement in modern open magnetic traps features high relative pressure (β ≈ 60%), mean energy of hot ions of 12 keV and electron temperature ~ 1 keV [1]. At the same time, the confinement efficiency is limited by the achievable magnetic field; the mirror ratio is supposed to be 15–20 in neutron source concepts [2]. Higher fusion gain in linear plasma devices is possible with improved confinement. The existing technique of multiple-mirror suppression of the axial heat flux combined with gas-dynamic central cell [3] can provide effective mirror ratios >100, which gives feasible fusion gain appropriate for hybrid systems. This report presents the first experimental results on the new method of active plasma flow suppression in a helical magnetic field [4]. This method renews the idea of a plasma flow control with moving mirrors. Plasma rotation in E×B fields can be utilized to create periodical variations of helicoidal magnetic field moving upstream in plasma’s frame of reference. These variations transfer momentum to trapped particles and lead to plasma pumping towards the central trap. Theory predicts exponential dependence of the flow suppression on the magnetic structure length, that is more favorable then the power dependence in passive mirrors [5]. Plasma biasing or natural ambipolar potential can drive the rotation. The first case also leads to plasma pinching that counteracts the collisional radial diffusion. Concept exploration device SMOLA with a helical mirror system [6] started operation in a start configuration in BINP in the end of 2017. Major aims of the first experiments were preliminary observations of plasma behaviour at changes of the magnetic configuration, regardless of the confinement efficiency. Plasma stream modification with the helical plugging was clearly shown. In this report, the main results of the experiments are discussed. [1] P. A Bagryansky, et al., Phys. Rev. Lett. 114, 205001 (2015). [2] A. V. Anikeev, et al., Materials. 8, (No. 12), 8452 (2015), DOI: 10.3390/ma8125471. [3] V.V. Postupaev, et al., Nuclear Fusion, 57, 036012 (2017). [4] A. D. Beklemishev, Fusion Sci. Technol. 63 (No. 1T), 355 (2013). [5] A. D. Beklemishev, AIP Conference Proceedings. 1771, 040006 (2016). [6] A. V. Sudnikov, Fusion Engineering and Design. 122, 85 (2017), DOI: 10.1016/j.fusengdes.2017.09.005],

Speaker: Anton Vyacheslavovich Sudnikov

14:00 P2.1055 Evaluation of core beta effects on pedestal MHD stability in ITER and consequences for energy confinement

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1055.pdf Evaluation of core beta effects on pedestal MHD stability in ITER and consequences for energy confinement W. Oosterbeek1, T. Weyens2, A. Loarte2, G.T.A. Huijsmans1,3. F.J. Artola2,4 1 Eindhoven University of Technology, Eindhoven, The Netherlands 2 ITER Organization, 13067 St. Paul Lez Durance, France 3 CEA, IRFM, 13108 St. Paul Lez Durance, France 4 Aix-Marseille Université, CNRS, PIIM UMR 7345, 13397 Marseille, France High confinement mode (H-mode) in fusion plasmas is characterized by a steep pressure gradient, or pedestal, that is limited by Peeling-Ballooning instabilities driven by pressure gradients and edge currents. Ideal MHD studies of the pedestal stability have shown that the maximum stable pedestal pressure increases with more peaked core pressure profiles through the effect of the Shafranov shift. Because of stiffness of the core pressure profile this can lead to a positive feedback between core and edge pressure but this is found to saturate beyond given values of core beta [1]. Such positive feedback has been found to lead to a more favourable scaling of the plasma energy with input power in tokamak experiments of that expected from the ITER-H(98,y2) scaling (e.g. [2]) but the extrapolation of this experimental results remains uncertain. This paper deals with the ideal MHD pedestal stability aspects of this positive feedback for ITER, which may differ from present experiments given the larger levels of bootstrap current expected in ITER (due to low Figure 1. Stable (empty circles) and plasma collisionality). Ideal MHD stability studies have unstable (mode number given by colour) equilibria for different core (normalized been performed for a range of ITER plasmas in which beta) and pedestal (pedestal beta) ITER the stability boundary for the pedestal pressure has been 7.5MA/2.65T plasmas pressure. identified for a range of plasma betas. This is done by self-consistently changing the pressure profile and scaling the corresponding bootstrap current and modelling the corresponding equilibrium with HELENA and calculating the ideal MHD stability with the MISHKA code (an example with the results of such analysis is shown in Fig. 1 for a 7.5 MA/2.65T H-mode plasma). The modelled pedestal marginal stability relation obtained (ped = f (N)) will be used to determine the  parameter global energy confinement 𝛼 scaling 𝛽𝑁 ~ 𝑃𝑖𝑛𝑝𝑢𝑡 , for a range of assumptions on core pressure profile changes with additional 𝛽𝑐𝑜𝑟𝑒 𝛾 heating power ~𝑃𝑖𝑛𝑝𝑢𝑡 , where characterizes the stiffness of the core pressure profiles. 𝛽𝑝𝑒𝑑 [1] Wolfrum, E., et al., Nuclear Materials and Energy 12 (2017) 18. [2] Challis, C. D., et al., Nuclear Fusion 55 (2015) 053031.

Speaker: Wouter Oosterbeek

14:00 P2.1056 Modification of Alfvén eigenmodes in tokamaks by pellet injection

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1056.pdf Modification of Alfvén eigenmodes in tokamaks by pellet injection H. J. C. Oliver1,2, S. E. Sharapov2, B. N. Breizman1, D. A. Spong3, and JET contributors* 1 Institute for Fusion Studies, University of Texas, Austin, Texas, 78712, USA 2 CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK 3 Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831-6169, USA * See the author list of “X. Litaudon et al., Nucl. Fusion, 57, 102001 (2017)” Alfvén eigenmodes driven unstable by energetic particles are routinely observed in tokamak plasmas. The most frequently observed Alfvén eigenmodes are gap modes, where two poloidal harmonics are coupled by geometric effects. Further coupling of harmonics can transiently result from the injection of frozen deuterium pellets. Once injected, pellets break down on timescales of several milliseconds. In JET, we observe a significant change in the Alfvén eigenmode spectrum during this short period. This phenomenon may be explained by the transient breaking of the toroidal and poloidal symmetry of the density profile by the material deposited by the pellet. These inhomogeneities couple additional poloidal and toroidal harmonics, modifying the Alfvén continuum and eigenmode spectrum. We have generalised the 3D MHD codes Stellgap [1] and AE3D [2], which characterise Alfvén waves in stellarators, to incorporate 3D density profiles generated from analytical expressions for pellet deposition profiles. We thereby obtain the Alfvén mode spectrum and structure in tokamak plasmas with pellet injection. We compare these calculations with analytical predictions of mode coupling due to density inhomogeneities. These results complement the ongoing efforts to use Alfvén eigenmodes for MHD spectroscopy [3]. From changes in the mode frequency and amplitude – both of which are affected by the density-related coupling of harmonics – information can be inferred about the pellet deposition dynamics and fast particle response to pellet injection. This work has received funding from the U.S. Department of Energy under Grant No. DE-FG02-04ER54742 (IFS) and DE-AC05-00OR22725 (ORNL). References [1] D. A. Spong, R. Sanchez, and A. Weller, “Shear Alfvén continua in stellarators”, Phys. Plasmas, 10, 3217 (2003); [2] D. A. Spong, E. D’Azevedo, and Y. Todo, “Clustered frequency analysis of shear Alfvén modes in stellarators”, Phys. Plasmas, 17, 022106 (2010); [3] S. E. Sharapov, H. J. C. Oliver, B. N. Breizman, M. Fitzgerald, L. Garzotti, and JET contributors, “MHD spectroscopy of tokamaks with pellets via Alfvén Eigenmodes”, submitted to Nucl. Fusion (2018)

Speaker: Henry James Oliver

14:00 P2.1057 Momentum-space analysis of suprathermal electrons generation under conditions of gas puffing during runaway tokamak discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1057.pdf Momentum-space analysis of suprathermal electrons generation under conditions of gas puffing during runaway tokamak discharges I.M. Pankratov1,2, V.Y. Bochko1 1 Department of Physics and Technology, V.N. Karazin Kharkiv National University Svobody Sq.4, 61022 Kharkiv, Ukraine 2 Institute of Plasma Physics, NSC “Kharkiv Institute of Physics and Technology” Akademicheskaya str., 1, 61108 Kharkiv, Ukraine The energy of disruption generated runaway electrons can reach as high as tens of mega- electron volt energy and they can cause a serious damage of plasma-facing-component surfaces in large tokamaks like International Thermonuclear Experimental Reactor [1]. At the same time, the quiescent runaway electron generation during the flat-top of DIII-D low density Ohmic discharges allows accurate measurement of all key important parameters to runaway electron excitation [2]. Using a test particle description (like [3]) that includes acceleration in the toroidal electric field and collisions with the plasma particles the generation of suprathermal electrons is analyzed under conditions of gas puffing. In presented modeling, the plasma parameter behavior close to the DIII-D quiescent runaway shot #152895 parameters is used. For this puffed discharge the growth and decay of high-frequency ECE signal was in disagreement with the HXR and synchrotron emission signals. Possibility of formation of the suprathermal electron population with v  v|| , which is trapped in a uniform magnetic field, is shown ( v|| and v are the velocities parallel and perpendicular to the magnetic field, respectively). The growth and decay of high-frequency ECE signal may be explained by occurrence of this suprathermal population. [1] Progress in the ITER physics basis: MHD stability, operational limits and disruptions. Nuclear Fusion, 47, 128 (2007). [2] C. Paz-Soldan, N. W. Eidietis, R. Granetz et al. Phys. Plasmas 21, 022514 (2014) [3] V. Fuchs, R. A. Cairns., C. N. Lashmore-Davies et al. Phys. Fluids., 29, 2931 (1986)

Speaker: Volodymyr Bochko

14:00 P2.1058 Modelling of NTM stabilization by RF heating and current drive in Plasma with stiff temperature profile

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1058.pdf Modelling of NTM Stabilization by RF Heating and Current Drive in Plasma with a Stiff Temperature Profile F. Widmer1 , P. Maget1 , O. Février2 , X.Garbet1 , H.Lütjens3 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2 EPFL-SPC, CH-1015 Lausanne, Switzerland. 3 CPhT, Ecole polytechnique, CNRS, Université Paris-Saclay, Palaiseau, France. Neoclassical Tearing Modes (NTM) are a class of MHD instability whose non-linear growth is driven by the perturbation of the bootstrap current. Such instabilities must be controlled or suppressed to prevent a degradation of the energy confinement for future devices. This can be done applying RF-current (ECCD) or -heating (ECRH) at the rational surface where the instabi- lity appears. We report on the modelling of NTM stabilization by the combined effects of ECCD and ECRH depositions using the XTOR-2F code [1]. To consider the impact of the ECRH on the NTM decay rate, it is necessary to take into account the Tokamaks turbulent transport pro- perties related to a critical temperature gradient [2, 3]. Such properties are considered through a heat diffusivity model depending on the stiffness σ only [4]. The stiffness and the ECRH consequence on the NTM decay rate is highlighted by a scan in PRF /Peq with PRF the additi- onal heat source centered at the O-point and Peq the power injected inside the island position. Numerical simulations show that the island response to ECRH is on a short time scale. Also, 1/σ the ECRH contribution to the NTM decay rate decreases as PRF /Peq . On the contrary, the NTM reaction to ECCD acts during a longer time scale with a lasting effect on the island decay rate. A good agreement between the ECRH and ECCD efficiencies deduced from the simulati- ons and the theoretical predictions is found. Furthermore, the results show that the ECCD and ECRH effects add up to contribute to the island decay. Finally, a generalized criteria for NTMs stabilization by RF that integrates the heating effect in a plasma with stiff temperature profile is derived. References [1] H. Lütjens and J.-F. Luciani, Journal of Computational Physics 229, 8130 (2010); O. Février, P. Maget, H. Lütjens, et al., Plasma Physics and Controlled Fusion 58, 045015 (2016). [2] W.A. Hornsby et al.,Physics of Plasmas 17, 092301 (2010); K. Ida et al., Phys. Rev. Lett. 109, 065001 (2012); [3] A. M. Dimits et al., Physics of Plasmas 7, 969 (2000); X. Garbet et al., Plasma Physics and Controlled Fusion 46, B557 (2004). F. Imbeaux et al, Plasma Physics and Controlled Fusion 43, 1503 (2001). [4] P. Maget et al., Physics of Plasmas (1994-present) accepted, (2018); P. Maget et al., (European Physical Society, Prague (Czech Republic), 2018).

Speaker: Fabien Widmer

14:00 P2.1059 Non-linear 3D hybrid kinetic-MHD simulations of Alfven eigenmodes in the ASDEX Upgrade tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1059.pdf Non-Linear 3D Hybrid Kinetic-MHD Simulations of Alfven Eigenmodes in the ASDEX Upgrade Tokamak J. Gonzalez-Martin1,3, M. Garcia-Munoz2,3, Y. Todo4, S. E. Sharapov5, M. Dunne6, V. Igochine6, R. Fischer6, P. Oyola2, L. Sanchis-Sanchez1,3, A. Jacobsen6, J. Ayllon-Guerola1,3, J. Galdon-Quiroga2,3, J. Rivero-Rodriguez1,3, J. Dominguez-Palacios2, M. Rodriguez-Ramos2,3, J. Dominguez-Abascal1,3, AUG and MST1 Teams 1 Department of Mechanical Engineering and Manufacturing, University of Seville Spain. 2 Department of Atomic, Molecular and Nuclear Physics, University of Seville, Spain. 3 Centro Nacional de Aceleradores (CNA) (Universidad de Sevilla, CSIC, Junta de Andalucía). 4 National Institute for Fusion Science, Toki, Japan. 5 Culham Science Centre, Abingdon, UK. 6 Max-Planck-Institut für Plasmaphysik, Garching, Germany. Recent experiments in the ASDEX Upgrade (AUG) tokamak have shown that externally applied 3D fields may be used to control Toroidally Induced Alfven Eigenmodes (TAE) in neutral beam heated discharges with elevated q-profile and low collisionality. TAEs have been fully suppressed or excited in identical discharges with n=2 3D fields by varying their poloidal spectrum. The non-linear 3D hybrid kinetic-MHD MEGA code has been applied to these discharges to identify the underlying mechanism in a fully 3D geometry. MEGA simulations reproduce some key aspects of the experiments such as the mode frequency, radial structure and the dependence of the AE activity on the poloidal spectrum of the externally applied 3D fields. The wave-particle resonances responsible for the TAE drive and affected by the externally applied 3D fields have been identified using full orbit simulations. A synthetic Fast-Ion Loss Detector (FILD) diagnostic has been included in MEGA by implementing the AUG 3D wall for numerical particles.

Speaker: Javier Gonzalez-Martin

14:00 P2.1060 Helical self-organization in 3D MHD modelling of fusion plasmas: plasma flow effects and Alfvén waves detection

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1060.pdf Helical self-organization in 3D MHD modelling of fusion plasmas: plasma flow effects and Alfvén waves detection M. Veranda1, D. Bonfiglio1, S. Cappello1, L. Chacòn2, D. F. Escande3, A. Kryzhanovskyy1, M. Zuin1 1 Consorzio RFX (CNR, ENEA, INFN, Università degli Studi di Padova, Acciaierie Venete SpA), Padova, Italy 2 Los Alamos National Laboratory, Los Alamos, New Mexico, USA 3 Aix-Marseille Univ, CNRS, PIIM, UMR 7345, Marseille, France Self-organized helical states are a ubiquitous feature in astrophysical and magnetic confinement current carrying plasmas. In the reversed-field pinch toroidal plasmas quasi-helical states are observed both in high current experiments [1] and in nonlinear magnetofluid numerical simulations [2]. In the tokamak helical self-organization is an essential part of the dynamics in advanced regimes [3]. In this work we show two main advancements in our 3D nonlinear visco-resistive magnetohydrodynamic (MHD) studies. First, we study the effect of a macroscopic plasma rotation on helical states, to model both reversed-field pinches and tokamaks: in particular, we analyze the interaction between an external momentum source and/or seed magnetic perturbations (MPs), both static and rotating. We find the expected interplay between plasma rotation and applied MPs in tokamaks [4] confirming MPs screening over a threshold in normalized plasma rotation. We then focus on the reversed-field pinch case: starting from previous works [5,6,7], where it is shown that a mean flow arises from and interacts with nonlinearly coupled kink/tearing modes, and then introducing a momentum source, we analyse the impact of mean plasma flow on self-organized helical regimes. Our modelling indicates that an external momentum source of sufficiently high intensity can prevent the formation of a helical state, while a moderate one is compatible with a slight enhancement of the intensity of the helical state. We present a novel study in the realistic cases [2] of experimental-like helical states stimulated by MPs: the presence of a plasma flow, previously not considered, introduces quantitative changes to their properties. As a final novelty, we here also show (for the first time) that the typical intermittency with reconnection events displayed in the RFP helical self-organization process is accompanied by the excitation of both compressional and shear Alfvén waves, in reasonable agreement with experimental measurement [8]. References: 1 R. Lorenzini, E. Martines, P. Piovesan, et al, Nature Physics 5, 570 (2009) 2 M. Veranda, D. Bonfiglio, S. Cappello, et al., NF 57, 116029 (2017) 3 P. Piovesan, D. Bonfiglio, M. Cianciosa, et al., NF 57, 076014 (2013) 4 R. Fitzpatrick, NF 33, 1049 (1993) 5 S. Cappello, M. Viterbo, 26th EPS Conference, Maastricht (1999) 6 K. Kusano, T. Tamano, T. Sato, NF 31, 1923 (1991) 7 F. Ebrahimi, V.V. Mirnov, S.C. Prager et al., PoP 15, 055701 (2008) 8 S. Spagnolo, M. Zuin et al., NF 51 083038 (2011)

Speaker: Marco Veranda

14:00 P2.1061 Motivations and perspectives of RFX-mod2, the challenge of the upgraded RFX-mod device

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1061.pdf Motivations and perspectives of RFX-mod2, the challenge of the upgraded RFX-mod device M. Spolaore, R. Cavazzana, L. Marrelli, S. Peruzzo, M.E. Puiatti, P.Zanca and the RFX-mod team Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA) Corso Stati Uniti 4 - 35127 Padova, Italy In recent years the RFX-mod device has been operated as a Reversed Field Pinch (RFP) and as a low-q Tokamak. In both configurations the capability and flexibility of its active control system of MHD instabilities have been exploited to control RWMs and tearing mode wall locking (RFP) and to stabilize the m/n=2/1 mode to operate at q(a)≤2 (Tokamak). The dynamics of the tearing modes has been fully characterized experimentally and simulated by the RFXLocking code [Zanca P. 2009 Plasma Phys. Control. Fusion 51 015006]. At high current, RFP plasmas have been observed to self-organize into quasi single helicity (QSH) states, where a single m=1 modes dominates the spectrum of all the other secondary modes and magnetic chaos is reduced. In particular, in QSH the best plasma performance is observed at the lowest amplitude of the secondary modes, which on the other hand also affect wall recycling and impurity content. The beneficial effect expected from reducing the amplitude of tearing modes and increasing their dynamics, motivated the plasma moving closer to the conductive shell and as a consequence a modification of the device load assembly. The present inner Inconel vacuum vessel, which is surrounded by a copper shell, both enclosed in a stainless steel support structure, will be removed. The support structure will be modified in order to ensure vacuum tightness. In this way, the conductive shell will approach the plasma, whose minor radius will increase from 0.459m to 0.49m. According to RFXLocking simulations, discussed in this contribution, the deformation related to m=1 modes will decrease by a factor ≈3. The expected improvement in confinement will be at least by a factor ≈35%. In addition, the plasma current threshold for tearing mode locking will increase from ≈120 kA to ≈400-600 kA. This contribution also describes the challenges in the design of the upgraded RFX-mod (RFX-mod2) and the innovative solutions found to solve the main issues, in particular to fulfill vacuum and electrical requirements of the in-vessel components.

Speaker: Monica Spolaore

14:00 P2.1062 Modelling the NTM evolution directly from JET experimental data

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1062.pdf Modelling the NTM evolution directly from JET experimental data I.G. Miron1 , S. Nowak2 and JET Contributors∗ 1 National Institute for Lasers, Plasma and Radiation Physics, Magurele-Bucharest, Romania 2 Istituto di Fisica del Plasma, CNR, Milano, Italy ∗ See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001" A quasi-analytic model [1] and appropriate code are built in order to calculate the evolution of the NTM delta prime stability index and subsequent island width. The former is an explic- itly time dependent derived quantity whereas the latter satisfies a modified Rutherford equation having the previously derived analytic delta prime term and a heuristic quantity for the boot- strap term. To obtain explicitly dynamic quantities, the following strategy is used: the involved perturbed equations are Laplace transformed in order to get rid of intrinsic time derivatives. The Laplace transformed perturbed equations are solved and the solutions are arranged via partial fraction decomposition method in order to be easily inverse Laplace transformed, the latter pro- cedure being the final step to be achieved. JET hybrid discharge experimental data are used to test the model accuracy regarding the evo- lution of a 3/2 NTM triggered by a sawtooth. No triggering sawtooth is considered in our ap- proach, which would pointlessly complicate the model. Instead, a resonant external perturbation is considered to replace the sawtooth as a trigger for the NTM. Despite the fact that the theoret- ical model is built in order to describe the behavior of the small perturbations from the equilib- rium state, therefore seeking for constant equilibrium quantities in order to be valid, the model uses stepwise varying JET data tables for the latter quantities and seems to simply work. The equilibrium quantities time growth rates are smooth enough in order to not break the perturbed model validity and to not significantly affect the NTM evolution during the period of interest. The NTM amplitude and frequency behavior are finally shown along with its corresponding magnetic island evolution. References [1] I.G. Miron, P2.060, 43rd EPS Conference on Plasma Physics, 4-8 July 2016, Leuven, Belgium.

Speaker: Iulian Gabriel Miron

14:00 P2.1063 Synchrotron radiation of relativistic runaway electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1063.pdf Synchrotron radiation of relativistic runaway electrons D. del-Castillo-Negrete, L. Carbajal Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-8071, USA The understanding of runaway electrons (RE) in magnetically confined plasmas is key for the success of the controlled fusion program. If not avoided or mitigated, high energy relativistic RE can significantly damage the plasma facing components of ITER. The study of synchrotron radiation (SR) of RE in these plasmas is important because it provides a limiting mechanism for the maximum energy that RE can reach, and because it can be used as an experimental di- agnostic to infer RE parameters including energy and pitch-angle distributions. Here we report recent results on SR taking into account full-orbit effects and the details of the SR camera ge- ometry. The results were obtained using the recently developed SR synthetic diagnostic [1] for the Kinetic Orbit Runaway electrons Code (KORC) [2] that computes the full-orbit relativis- tic dynamics in electric and magnetic fields including radiation damping and collisions. SR is studied in axisymmetric fields and in 3-D magnetic configurations exhibiting magnetic islands and stochasticity [3]. For passing particles in axisymmetric fields, neglecting orbit effects might underestimate or overestimate the total radiation power depending on the direction of the radial shift of the drift orbits. For trapped particles, the spatial distribution of synchrotron radiation exhibits localized “hot" spots at the tips of the banana orbits. The spatial distribution of syn- chrotron radiation in stochastic magnetic fields, obtained using the MHD code NIMROD, is strongly influenced by the presence of magnetic islands. 3-D magnetic fields also introduce a toroidal dependence on the SR spectra, and neglecting orbit effects underestimates the total ra- diation power. In the presence of magnetic islands, the radiation damping of trapped particles is larger that the radiation damping of passing particles. Results modeling synchrotron emission by RE in DIII-D quiescent plasmas are also presented. The computation uses EFIT reconstructed magnetic fields and RE energy distributions fitted to the experimental measurements. Quali- tative agreement is observed between simulations and experiments for simplified pitch angle distributions. However, it is noted that to achieve quantitative agreement it is necessary to use pitch angle distributions that depart from simplified 2-D phase-space Fokker-Planck models. References [1] L. Carbajal and D. del-Castillo-Negrete, Plasma Phys. Control. Fusion, 59, 124001 (2017). [2] L. Carbajal, D. del-Castillo-Negrete, D. Spong, S. Seal, and L. Baylor, Phys. Plasmas, 24, 042512 (2017). [3] D. del-Castillo-Negrete, L. Carbajal, D. Spong, and V. Izzo, Accepted for publication Phys. Plasmas (2018).

Speaker: Diego del-Castillo-Negrete

14:00 P2.1064 Tearing mode control with electron cyclotron resonant heating and current drive on EAST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1064.pdf Tearing mode control with electron cyclotron resonant heating and current drive on EAST tokamak Y. Zhang1, Q. Yu2, X. J. Wang1, H. D. Xu1, H. H. Wang1, T. H. Shi1, S. Gu1, Y. Liu1, L. Q. Hu1, Y. W. Sun1, F. K. Liu1 , X. Z. Gong1, X. D. Zhang1 and EAST team 1 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China 2 Max-Planck Institute for plasma physics, EURATOM Association, D-85748 Garching, Germany The experiments of m/n = 2/1 classical tearing mode suppressed by the ECRH/ECCD have been performed on EAST tokamak. The continuous EC beam with different power is injected perpendicularly into the L-mode plasma and deposited at the radial position of the magnetic island, i.e. ρ = 0.5. It is found that the magnetic island size is reduced gradually as the ECRH power increases from 100 kW to 250 kW, and then it goes to a saturated value (60% of initial size) even if its power increases further, indicating that the classical tearing mode cannot be suppressed completely. This can be explained by the stabilization mechanism which comes only from the temperatures inside the island separatrix. The smaller the island size is, the less the heating area is. The minimum power for the effective stabilization of the tearing mode is 100 kW, which is only about 6% of background plasma. The deposition position of the EC beam is moved from plasma core to edge shot by shot with fixed power of 320 kW. The results shows that the stabilization effect of ECRH/ECCD can be observed in a wide region of ρ = 0.3 - 0.6, however the destabilization effect is enhanced at the plasma core. This can be explained by the fact that the current density profile tailored by ECRH/ECCD changes the magnetic shear and therefore decreases the classical stability index Δ'. It is supposed that the heating rather than the current driver plays an more important role in the des-/stabilization of the 2/1 mode in these low beta discharge. Moreover, the RMP is further applied to control the island rotating slowly, and the stabilization effect of ECRH/ECCD on the island's O and X points with either an inward or outward misalignment allows to be investigated deliberately. The preliminary analysis presents that a good stabilization effect is achieved by ECRH with an inward misalignment of 3 cm relative to the radial location of the magnetic island rather than by ECCD with the almost alignment.

Speaker: Yang Zhang

14:00 P2.1065 Toroidal magnetic field increase in the Globus-M spherical tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1065.pdf Toroidal magnetic field increase in the Globus-M spherical tokamak N.N. Bakharev, F.V. Chernyshev, V.K. Gusev, N.A. Khromov, E.O. Kiselev, G.S. Kurskiev, A.D. Melnik, V.B. Minaev, I.V. Miroshnikov, M.I. Patrov, Yu.V. Petrov, N.V. Sakharov, P.B. Shchegolev, A.D. Sladkomedova, V.V. Solokha, A.Yu. Telnova, V.A. Tokarev, S.Yu. Tolstyakov Ioffe Institute, St. Petersburg, Russia Globus-M spherical tokamak (ST) was a compact machine (R ≈ 36 cm, a ≈ 24 cm, plasma-wall distance of a several centimeters) with toroidal magnetic field Btor = 0.4 T and unique features such as high normalized Larmor radius ( ) and high heating power density. This year a new Globus-M2 ST with the same vacuum chamber, 2.5 times increased Btor and Ip, and upgraded heating and diagnostic systems will be launched. A significant expansion of the experimental parameter range will provide an opportunity to get closer to the operating conditions of the compact fusion neutron sources (CFNS) and, hopefully, answer the question, if the pros of the ST configuration outweigh the cons when used as a basis for a CFNS . In the final Globus-M experimental campaign [1] Btor and Ip were raised by 25% up to 0.5 T and 250 kA respectively. As a result an overall improvement in plasma performance was observed. Plasma total stored energy and energy confinement time grew by about 30% in the discharges with density up to 6·1019m-3. D-D beam-plasma neutron rate increased significantly at the same NB heating power. The main reasons for this effect, in order of importance, are the electron temperature rise and the fast ion confinement improvement. Decrease of first orbit, sawtooth-induced and TAE-induced fast ion losses was recorded. Energy confinement time growth proportional to toroidal magnetic field was observed. Acquired in the experiments energy confinement time scaling and power decay length scaling, based on the Langmuir probe measurements, were in a reasonable agreement with scalings, based on MAST [2] and NSTX [3] data. References: 1. Minaev V.B. et al. 2017 Nucl. Fusion 57 066047 2. Valovic M. et al 2009 Nucl. Fusion 49 075016 3. Kaye S M et al 2006 Nucl. Fusion 46 848–57

Speaker: Nikolai Bakharev

14:00 P2.1066 Fueling DEMO: required flux and pellet injection parameters

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1066.pdf 45 EPS EPSConf. on Plasma Conference Physics,Physics on Plasma Prague, 2018 P2.1066 Fueling DEMO: required flux and pellet injection parameters B. Pégouriéa, J.-F. Artauda, J. Garciaa, C. Dayb, P.T. Langc (a) CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France (b) Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany (c) Max Planck Institute for Plasma Physics, 85748 Garching, Germany Pellets have demonstrated their capacity for depositing matter in the plasma core and will be mandatory for DEMO fueling. In a previous work [1], both the poloidal domain for an optimal launching and corresponding range in the injection velocity were estimated, taking into account the technical constraints due to the available injectors and possible interaction of the guide tube with the different coils and machine structure elements. This was done using an ad hoc pellets size (ITER-like pellet: cylinder L = D = 5 mm, 61021 at.). But designing practically the fueling system (injector type and characteristics, guide tube trajectory) for DEMO requires an accurate definition of (i) the optimal launching point, (ii) the pellet size and velocity and (iii) the injection frequency. This can be done through a closed loop modeling process, where the residence time of the pellet deposited material in the plasma core is calculated self-consistently with the plasma transport reaction to the pellet induced changes in the density and temperature profiles. This requires a parametric study for determining the injection frequency and possible changes in the plasma response as a function on the pellet size. For the present study, we use the CRONOS code [2] and GLF23 transport model [3], the pellet deposition profiles being calculated with the HPI2 pellet ablation/deposition code [4] using a preliminary design of the HFS guiding tubes [1]. DEMO parameters are those given in ref. [5]. This paper summarizes the main results of this study, showing that an injection frequency of ~ 3-8 Hz is required, depending on the pellet size (~ 6 Hz for ITER-like pellets). ELMs are only taken into account through simple assumptions (they play a role on two sides: (i) the fueling pellets must replace the material ejected from the pedestal by the ELMs and (ii) if ELM-pacing through pellet injection is used, the latter can contribute to the core fueling since – depending in their injection location - these pellets have probably to penetrate up to half the pedestal). Attention is paid to the simplification made in the simulation, namely that the SOL-core interaction is not taken into account (the density is assumed to be constant at the separatrix, which means that no fueling of the core from the SOL is considered). The work is complemented by a study of the influence of the dispersion in the pellet injection angle and velocity on the source profile. References: [1] P.T. Lang et al., Fusion Eng. Des. 96–97 (2015) 123 - B. Pégourié et al., ECA, Vol.40A (2016) P4-076 [2] J.-F. Artaud et al., Nucl. Fusion 50 (2010) 043001 [3] R. E.Waltz et al., Phys. Plasmas 4 (1997) 2482 [4] B. Pégourié et al., Plasma Phys. Control. Fusion 47 (2005) 17 & Nucl. Fusion 47 (2007) 44 [5] DEMO1 Reference Design, (2015 April) Document EFDA_D_2LBJRY v1.0

Speaker: Bernard Pégourié

14:00 P2.1067 Monte Carlo ion cyclotron heating and fast ion loss detector simulations in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1067.pdf Monte Carlo ion cyclotron heating and fast ion loss detector simulations in ASDEX Upgrade S. Sipilä1, J. Varje1, T. Johnson2, T. Kurki-Suonio1, J. Galdón Quiroga3, J. González Martín3, the ASDEX Upgrade Team and the EUROfusion MST1 Team* 1 EUROfusion-VTT, Dept. of Applied Physics, Aalto University, FI-00076 AALTO, Finland 2 EUROfusion-VR, Fusion Plasma Physics, EES, KTH, Stockholm, Sweden 3 Dept. of Atomic, Molecular and Nuclear Physics, University of Seville, 41012 Seville, Spain The orbit-following simulation tool ASCOT-RFOF consists of the orbit-following Monte Carlo code ASCOT [1] interfaced to the radiofrequency heating Monte Carlo code library RFOF [2]. In the present work, ASCOT-RFOF is applied to simulate fundamental mode ion cyclotron (IC) heating of hydrogen in ASDEX Upgrade discharge #33147 at t = 1.0 s and the related fast ion loss detector (FILD) signal. This discharge was chosen because it is well diagnosed and provides the possibility of further, more challenging simulations due to an observed FILD signal oscillation attributed to a beat effect between MHD modes, which is expected to be within ASCOT’s simulation capabilities. In the two-stage simulation scheme, the IC-heated hydrogen population is first created by an ASCOT-RFOF simulation, starting with 500.000 ion markers that represent a Maxwellian hydrogen population making up 3% of the total ion density, which consists mainly of deuterium. The IC-heated hydrogen distribution is then used as input for ASCOT’s distribution-sampling marker source module, and 500.000 sampled hot ion markers are used in a simulation of the hot ion wall load and fast ion loss detector (FILD) signal in the presence of AUG’s toroidal field ripple of about 0.5%. The simulation results are compared to FILD signal measurements from the modelled discharge [3]. [1] E. Hirvijoki et al., “ASCOT: Solving the kinetic equation of minoriy particle species in tokamak plasmas”. Computer Physics Communications 185 (2014) 1310-1321. [2] T. Johnson et al., “Library for RF Interactions in Orbit Following Codes”. AIP Conference Proceedings 1406 (2011) 373. [3] M. García-Muñoz and S. Sharapov, at MST1 AUG 1.7-2 Meeting, Seville, Spain, 28 July 2016. * See the author list of H. Meyer et al., Nuclear Fusion 57 (2017) 102014

Speaker: Seppo Sipilä

14:00 P2.1068 Nonlinear contribution of neutral beam injection in TCV EC-heated advanced tokamak scenarios

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1068.pdf Nonlinear contribution of neutral beam injection in TCV EC-heated advanced tokamak scenarios M. Vallar1, M. Agostini1, T. Bolzonella1, S. Coda2, J. Garcia3, B. Geiger4, T. Goodman2, A. Karpushov2, T. Kurki-Suonio5, C. Piron1, L. Pigatto1, O. Sauter2, N. Vianello1, P. Vincenzi1, M. Yoshida6 the TCV team and the MST1 team 1. Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy 2. Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH- 1015 Lausanne, Switzerland 3. CEA, IRFM, 13108 Saint-Paul-lez-Durance, France 4. Max Planck Institute for Plasma Physics, Garching, Germany 5. Aalto University, P.O. Box 14100, FI-00076 AALTO, Finland 6. National Institutes for Quantum and Radiological Science and Technology, Naka, Ibaraki 311-0193, Japan TCV (Tokamak à Configuration Variable) is a tokamak device capable of many different plasma shapes and positions, equipped with a flexible system of Electron Cyclotron (EC) antennas and a new Neutral Beam (NB) injector [1]. The auxiliary power from the beam can reach 1 MW and it is injected tangentially co-current, coupling mostly with ions. This heating system allows new insights on advanced tokamak scenarios in TCV which, up to now, have been performed only with EC heating (ECH). These scenarios have high βN, high non- inductive current fraction and a relevant energetic particle (EP) population fraction (≈10 %). An internal transport barrier can be generated by reversing the q-profile using EC current- drive (ECCD) [2]. In this work we show that the effect of the sum of the two heating sources (NBI and ECH) in TCV high βN plasmas is not linear, and interpretative modelling is carried out to understand the behaviour of the NB EPs when ECH is present. A statistical study on a set of experiments with both ECH and NBI is presented to show the effect of NB injection (NBI) on plasma performance: βN and the plasma stored energy do not increase linearly with NB power. Furthermore, the contribution to the total plasma current from ohmic transformer, bootstrap current and current drive are respectively estimated, showing that EC has a strong impact on Zeff, modifying therefore the plasma resistivity and the ohmic contribution to the current. This effect is taken into account when applying the Monte Carlo interpretative NBI code NUBEAM. It results that with the combined application of ECRH and ECCD, the electron temperature and plasma equilibrium change significantly, impacting on the NB power deposition: CX and orbit losses tend to increase, reducing by 20% the power deposited on plasma species. Modelling suggests that the variation in Te changes the EP power redistribution among the species, transferring more power to the ions. The impact on EPs orbit given by ECCD equilibrium modification is performed with the Monte Carlo ASCOT code for NBI modelling, capable of solving the EP full gyro-motion. [1] A.N.Karpushov, et al., FED 123 (2017) [2] T P Goodman et al., PPCF 47 (2005)  See the author list "H. Meyer et al 2017 Nucl. Fusion 57 102014"

Speaker: Matteo Vallar

14:00 P2.1069 Spectrum broadening and degradation of the O-X mode coupling efficiency due scattering of a microwave beam on plasma density fluctuations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1069.pdf Spectrum broadening and degradation of the O-X mode coupling efficiency due scattering of a microwave beam on plasma density fluctuations E. Gospodchikov1, T. Khusainov1, A. Shalashov1, A. Köhn2 1 Institute of Applied Physics RAS, Nizhniy Novgorod, Russia 2 IGVP, University of Stuttgart, Stuttgart, Germany We discuss the tunnelling of quasi-optical wave beams through the evanescent region near the plasma cut-off in magnetized plasmas with density fluctuations: so called ordinary(O) and extraordinary(X) mode coupling. The primary influence of density fluctuations on the O-X mode coupling efficiency is due to a small-angle scattering of a microwave beam along the whole trace of its propagation, while the influence of the fluctuations inside the localised coupling region may be neglected [1]. In this paper model is proposed that describes the effect of a random modulation of a wave phase induced by the fluctuations along the propagation path on the efficiency of linear O-X mode coupling in a two- dimensional geometry that suits well the toroidal magnetic conditions [2]. An analytical formula is derived that relates the mean coupling efficiency and the phase correlation function of a random wave beam. Thresholds are found for the correlation length of the random phase and the length of the beam path, above which the density fluctuations become the dominant effect. The peculiar effects of two-dimensional geometry of mode coupling region [3], including the magnetic field-line curvature [4] and the magnetic surface curvature [5] are shown to be important even in the presents of fluctuations. The results of the analytical study are verified with full-wave numerical simulations. [1] A. G. Shalashov, E. D. Gospodchikov, PPCF 56 125011 (2014). [2] T. A. Khusainov, E.D. Gospodchikov, A.G. Shalashov, JETP 126 366 (2018). [3] E.D. Gospodchikov, A.G. Shalashov, E.V. Suvorov, PPCF 48 869 (2006). [4] A.G. Shalashov, E. D. Gospodchikov, PPCF 52 115001 (2010). [5] E. D. Gospodchikov, T. A. Khusainov, A. G. Shalashov, PPCF 54 045009 (2012).

Speaker: Egor Dmitrievich Gospodchikov

14:00 P2.1070 Anomalous absorption in ECRH experiments due to parametric excitation of localized UH waves

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1070.pdf Anomalous absorption in ECRH experiments due to parametric excitation of localized UH waves E.Z. Gusakov, A.Yu. Popov, A.N. Saveliev Ioffe Institute, St. Petersburg, Russia Electron cyclotron resonance heating (ECRH) is widely used in toroidal plasmas and is considered for application in ITER for heating and neoclassical tearing mode control. In contradiction to the theory predictions [1] during the last decade many experiments have demonstrated excitation of the anomalous phenomena at the ECRH. The clearest evidence of the nonlinear effects was obtained at TEXTOR [2] where the strong backscattering signals down–shifted in frequency and amplitude modulated by the magnetic island were observed. A demonstration of the anomalous ion heating during the ECRH pulse was obtained at TCV [3]. In the present paper we develop further the theoretical model [4] taking into account, as distinct from the standard theory [1], the presence of a non-monotonous density profile, which always exists on the discharge axis or is often present due to the magnetic island or the density pump-out effect. The model interprets the generation of backscattering signal and the anomalous ion heating, as a result of secondary nonlinear processes that accompany a primary low – threshold two–upper-hybrid (UH) – plasmon PDI of the pump X mode. The threshold of the primary PDI is shown to be smaller than the one predicted in [1] due to the trapping of one UH wave in the presence of the non-monotonous density profile. The primary PDI is absolute due to the finite-size of the pump beam. Its growth enhancing the UH wave fluctuations from the thermal noise level is saturated in our theory due to both the pump wave depletion and the decay of the trapped daughter UH wave that leads to excitation of the secondary UH wave, which is also localized and ion Bernstein (IB) wave. The coupling of different daughter UH waves is responsible in the theory for generation of the backscattering signal. This mechanism appears capable of reproducing the fine details of the frequency spectrum of the anomalously reflected X wave and the absolute value of the observed backscattering signal in TEXTOR experiment. It also predicts substantial (up to 20%) anomalous absorption in the electron channel and explains the anomalous ion heating at TCV by the generation of the secondary IB waves which directly transfer the pump power to the ion component. The possibility of anomalous absorption of the O-mode pump in the ECRH experiment due to parametric excitation of the trapped UH wave is discussed as well. [1] M. Porkolab, B.I. Cohen 1988 Nucl. Fusion 28 239 [2] E. Westerhof, S. Nielsen, J. W. Oosterbeek et al. 2009 Phys. Rev. Lett. 103 125001 [3] A. N. Karpushov et al. 2013 33rd EPS Conference on Plasma Physics, 2006 30I P–1.152 [4] E. Z. Gusakov and A. Yu. Popov 2016 Physics of Plasmas 23, 082503

Speaker: Evgeniy Z. Gusakov

14:00 P2.1071 ECRH H-mode Experiments in the HL-2A Tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1071.pdf ECRH H-mode Experiments in the HL-2A Tokamak S. D. Song1, J. Rao1, M. Huang1, X.L.Zou2, H. Wang1, D. H. Xia3, Z. H. Kang1, K. Feng1, M. W. Wang1, Y. N. Bu1, B. Lu1, C. Wang1, X. Y. Bai1, X.M. Song1, B.B. Feng1, C.Y. Chen1, W. L. Zhong1, Z.Y. Cui1, Z.B. Shi1, D.L. Yu1, M. Jiang1, Y. Zhou1, Y.G. Li1, M. Xu1, Yi Liu1, Z. Cao1, L. Y. Yao1, W. M. Xuan1, L.W. Yan1, Q.W. Yang1, L.H. Yao1, X.T. Ding1, J.Q. Dong1, X. R. Duan1 and Yong Liu1 1 Southwestern Institute of Physics, P.O. Box 432, Chengdu, Sichuan, 610041, China 2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3 Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, Hubei, China Heating in electron and ion channel plays different role in the scope of L-H transition [1]. In HL-2A tokamak 5MW ECRH system [2, 3] and 1.5MW NBI system have been equipped. The first H-mode on HL-2A was obtained in 2009 [4], with both NBI and ECRH. After that H-mode was also obtained with purely NBI. Although the total ECRH power is much higher than the NBI power, steady H-mode on HL-2A with purely ECRH has not been realised. However, clear evidence of limit cycle oscillation (LCO) and ELMy like phenomena on D signal in purely ECRH discharges has been observed, which indicates the plasma has entered into the intermediate phase (I-phase) toward steady H-mode. Shot 21886 (Bt = 1.32T, Ip = 155kA, PECRH = 1.6MW) gives an example for such ECRH I-phase discharges. In the experiments, SMBI is employed to mitigate the density pump out [5, 6] effect during ECRH phase. Oscillation at frequency 2~3 kHz on D signal in t = 730~750ms and formation of edge density pedestal support the assertion of plasma confinement mode transition. However, the I-phase does not last long since the plasma density keep decreasing which improves the L-H transition threshold. Employing feedback control of density using SMBI to keep density constant, quasi-continuous LCO has also been clearly observed as in the case of shot 23065(Bt = 1.31T, Ip = 172kA, PECRH = 1.6MW, ne ~ 1.7×1019/m3). However, transition to steady ELMy H-mode has not yet been realised. The reason may be due to the enhancement of TEM instabilities and turbulence in ECRH phase. References [1] F. Ryter T. Pütterich, M. Reich, et al., 2009 Nucl. Fusion 49 062003 [2] M. Huang, J. Rao, B. Li, et al. 3MW ECRH system and experiments on HL-2A. 37th EPS conference, Dublin, Ireland. 2010. [3] M. Huang et al. Development of a 140 GHz steerable launcher for the HL-2A ECRH system. Plasma Sci. Technol. 15 (2013) 1247-1253 [4] X.R. Duan, J.Q. Dong, L.W. Yan, et al., Nucl. Fusion 50, 095011(2010) [5] X.L. Zou, W.W. Xiao, S.D. Song, et al. Particle Transport Investigation in HL-2A Using ECRH and SMBI, 23rd IAEA Fusion Energy Conference, Daejeon. (2012) [6] C. Angioni, A.G. Peeters, X. Garbet, et al., Nucl. Fusion 44, 827 (2004)

Speaker: Shaodong Song

14:00 P2.1072 ICRF antenna coupling in ASDEX Upgrade 3D plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1072.pdf ICRF antenna coupling in ASDEX Upgrade 3D plasmas G. Suarez Lopez1,2 , R. Ochoukov1 , M. Willensdorfer1 , H. Zohm1,2 , D. Aguiam3 , V. Bobkov1 , M. Dunne1 , H. Faugel1 , H. Funfgelder1 , J.-M. Noterdaeme1,4 , E. Strumberger1 , W. Suttrop1 , ∗ † the ASDEX Upgrade Team , and the EUROfusion MST1 Team. 1 Max Planck Institute for Plasma physics, Garching b. Munchen, Germany 2 Ludwig-Maximilians-University of Munich, Munich, Germany. 3 Instituto de Plasmas e Fusao Nuclear, Universidade de Lisboa, Lisboa, Portugal 4 Applied Physics Department, University of Ghent, Ghent, Belgium The excitation of the fast branch of the ion cyclotron (IC) plasma wave by an antenna is a method for efficient energy transport to the plasma core used for ionic heating. The amount of power coupled to the plasma by the antenna is a function of the radiation impedance, which is characterized by the plasma parameters, such as plasma density, the magnetic field, and the antenna strap phasing for multiport networks. Antenna coupling has been extensively studied under the assumption of axisymmetry in the plasma. Non-axisymmetric scenarios have become more relevant in view of the gas puff tech- niques used for coupling improvement and the usage of magnetic perturbations (MPs) for edge localized modes control. The application of MPs produces a plasma kink-peeling response that amplifies the vacuum field perturbation and leads to significant non-axisymmetric field-aligned displacements of the flux surfaces. These displacements create a 3D density profile in front of the IC antenna. Dedicated discharges in the ASDEX Upgrade tokamak have been performed to study the ef- fect of MP-induced boundary displacements on IC coupling. Different phasings between the upper and lower row of MP coils with n=2 toroidal periodicity were applied. The MP field is rotated in order to diagnose the effect of the rotating 3D profiles on the antenna performance. Strap loading resistance oscillations, coherent with the rotating density profile, of the order of |∆RL | ≈ ±0.2 Ω have been recorded. Embedded reflectometry in one of the 3-strap antennas is used to correlate the density distribution to the observed antenna behavior. NEMEC ideal MHD modeling is performed, allowing a direct comparison of the measured loading resistance oscillations with the computed plasma deformation in the confined region. ∗ For a complete list of authors, see A. Kallenbach et al, Nucl Fus 57 (2017) 102015 † For a complete list of authors, see H. Meyer et al, Nucl Fus 57 (2017) 102014

Speaker: Guillermo Suarez Lopez

14:00 P2.1073 Modeling of plasma position and shape control during termination of T-15 discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1073.pdf Modeling of plasma position and shape control during termination of T-15 discharges M.L. Dubrov1, R.R. Khayrutdinov1, V.E. Lukash1, M.M. Sokolov1 1 National Research Centre «Kurchatov Institute», Moscow, Russia The aim of the work is to simulate the magnetic control of the plasma position and shape of the T-15 tokamak currently being modernized [1] at the current ramp down stage using the plasma-physical code DINA [2] and the developed regulators [3]. At the stage of the current ramp down, additional heating is turned off, the temperature and density of the plasma drop rapidly. This leads to abrupt changes in the values of βp, li, q95 [4], which directly affects the stability of the plasma and the possibility of its stabilization by the magnetic control system. During the whole period of current ramp down, the plasma should be in a limited region on the diagram li - q95 [5] to avoid the development of instabilities and disruption, and maintain the divertor configuration to the minimum values of the plasma current. Several discharge termination scenarios that satisfy these criteria and take into account the actual characteristics of the poloidal magnetic field coil supplies are simulated in the work. The results of the simulation are used to determine the maximum achievable current ramp down rate in the T-15 tokamak. References 1. Azizov E.A. et al. Status of project of engineering-physical tokamak. — In: 23rd IAEA Fusion Energy Conf. Daejeon, Republic of Korea, 11—16 October 2010, FTP/P6-01. 2. R.R. Khayrutdinov and V.E. Lukash. Journal of Computational Physics, 109, No. 2 (1993) 193-201. 3. M.L. Dubrov et al. Modeling control of diverted plasma of the T-15 tokamak, 44th Conference on Plasma Physics, Belfast, Northern Ireland (UK), 26—30 June 2017, P4.154. 4. P.C. de Vries et al. Multi-machine analysis of termination scenarios with comparison to simulations of controlled shutdown of ITER discharges, Nucl. Fusion 58 (2018) 026019 5. J. Wesson et al. Nucl. Fusion 29 (1989) 641

Speaker: Maksim Dubrov

14:00 P2.1074 Validation of a real-time model-based approach for ITER first wall heat flux control on the TCV tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1074.pdf Validation of a real-time model-based approach for ITER first wall heat flux control on the TCV tokamak H. Anand1, R. A. Pitts1, J. A. Snipes1, P. C. De Vries1, L. Kos3, L. Zabeo1 ,Y. Gribov1, S. Coda2, C. Galperti2, M. Brank3, and G. Simic3 1 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St.-Paul-lez-Durance Cedex, France 2 Ecole Polytechnique Fédérale de Lausanne (EPFL), SPC, CH-1015 Lausanne, Switzerland 3 University of Ljubljana, Aškerčeva 6, 1000 Ljubljana, Slovenia A real-time (RT) first wall (FW) heat load control system will be required at a very early stage of ITER plasma operations. The long pulse nature of the device imposes active cooling of all plasma-facing components (PFCs) and thus strict control of surface power flux density at all times. A 2-D physics-based and control oriented heat flux estimation model, based on real time (RT) equilibrium reconstruction has already been successfully implemented into the ITER Plasma Control System Simulation platform (PCSSP). However, an additional module accounting for 3-D geometrical structure of the FW panels is essential to estimate a more realistic value of true heat flux on the plasma facing components. The evaluation of an improved RT approach to first wall heat flux control accounting for shaping of the FW panels on the TCV tokamak will be reported. For a given magnetic equilibrium, the integration of the 3-D effect into the algorithm is performed by offline determination of the heat load distribution on the inner FW panels of the TCV tokamak using a new utility, SMITER GUI, developed at the ITER Organization. A comparison of surface power flux density with the infra-red measurements of the TCV central column tiles is also presented. The associated weights with respect to the position in the poloidal plane and magnitudes of the peak heat flux are extracted for implementation into the 2-D approach. The implementation and experimental performance of the new improved RT model based approach on the TCV digital control system will be reported.

Speaker: Himank Anand

14:00 P2.1075 Shallow pellet fuelling under conditions of RMP ELM mitigation or divertor detachment in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1075.pdf Shallow pellet fuelling under conditions of RMP ELM mitigation or divertor detachment in ASDEX Upgrade M Valovič1, P T Lang2, A Kirk1, W Suttrop2, M Bernert2, M Cavedon2, M Dunne2, R Fischer2, L Garzotti1, L Guimarais2, F Janky2, N Leuthold2, PJ Mc Carthy3, A Mlynek2, B Plőckl2, G Tardini2, E Viezzer2, E Wolfrum2, the ASDEX Upgrade team2 and the EUROfusion MST1 team4 1 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK; 2Max-Planck-Institut fűr Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching, Germany; 3Department of Physics, University College Cork, Cork, Ireland; 4See H. Meyer et al., Nucl. Fusion 57 (2017) 102014 Pellets are used in ASDEX Upgrade [1] to control plasma density under conditions of ELM control or divertor detachment. In experiments presented here direct fuelling by gas is negligible. Relative pellet size and pellet deposition are aimed to approach those in ITER but differences still remain. ELMs are controlled by n=2 RMPs in feed forward mode [2]. Divertor detachment is controlled by nitrogen gas in feedback mode. In low upper triangularity plasmas with ELM control by RMPs, pellets can refuel the RMP pump out using both gradual [3] and prompt [4] application of pellet trains. With application of pellets promptly after activation of the RMP fields the duration of the density transient can be reduced to 3 energy confinement times. The required pellet particle throughput to restore pre-RMP density is about pel~5.6×1021at/s~0.07Paux/Tped (Paux is the auxiliary heating power and Tped is the pedestal temperature) which is comparable to the RMP pump out rate RMP~1.7×1021at/s determined from the time derivative of the plasma density after the RMP is switched on. The density increase by pellets approximately preserves ion pedestal pressure in the RMP phase. An unwanted side effect of pellet refuelling is the transition from ELM suppression to an ELMy regime, triggered by the first pellet. A favourable observation is that ELMs with pellet fuelling are still smaller than those without RMPs, and the ELM frequency is not modulated by pellets. At elevated upper triangularity the ELM suppression is restored after an ELM-like events triggered by the pellets [4]. With increasing density plasma eventually transitions to ELMy regime, similarly as in low triangularity case. In plasmas with divertor detachment, density control by pellets without gas is demonstrated. The required particle throughput is about pel~19×1021at/s. When normalised to heat flux the throughput is pelTped /Paux~0.1 which is broadly agreeing with ITER prediction [5]. With detachment, an unwanted side effect is the pellet induced modulation of the plasma temperature (~2x) at the outer strike point and a consequential modulation of the nitrogen gas due to feedback control. This is caused by the modulation of the ELM frequency by pellets and not by a pellet induced cooling wave as one might expect. [1] Lang P T et al 2012 Nucl. Fusion 52 024002; [2] Suttrop W et al 2017 Plasma Phys. Control. Fusion 59 014050, [3] Valovič M et al 2015 Nucl. Fusion 55 013011, [4] Valovič M et al 2018 Plasma Physics Contr. Fusion to be submitted, [5] Polevoi A R et al 2017 Nucl. Fusion 57 022014

Speaker: Martin Valovic

14:00 P2.1076 The next step in systems modelling: The integration of a simple 1D transport and equilibrium solver

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1076.pdf The next step in systems modelling: The integration of a simple 1D transport and equilibrium solver K.V. Ellis* 1, H. Lux1, E. Fable2,, R. Kembleton1,3, M. Siccinio2, 4 1 CCFE, UKAEA, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 2 Max-Planck Institute for Plasma Physics, Garching, Germany 3 EUROfusion PMU, Culham Science Centre, Abingdon, OX14 3DB, UK 4 EUROfusion PMU, Garching, Germany *Corresponding author. Tel.: +44 (0)1235-46-6993. E-mail address: katy.ellis@ukaea.uk Systems codes are used in the conceptual phases of fusion reactors design. They employ a multitude of simplified models to simulate an entire power plant and ensure that designs are self-consistent, viable and optimised with respect to a given figure of merit. Their strength is the fast determination of an overall design. However, their output should be viewed with caution due to model simplicity and requires verification via more detailed physics and engineering analysis. The PROCESS systems code is predominantly used to model the European demonstration power plant, DEMO. As such, it is under constant development to improve its capabilities. In this work, we describe the integration of a simple, 1D transport and equilibrium model known as PLASMOD [1] into PROCESS. This represents a significant step up in physical realism with the creation of self-consistent radial profiles including electron density and temperature. PLASMOD is a time-independent transport model combined with an equilibrium solver from ASTRA. It has been benchmarked against both a standalone version of ASTRA and running within PROCESS. We present initial results from PLASMOD integrated with PROCESS, highlighting the impact on the calculated power plant design and performance of the newly implemented transport model. References: [1] E. Fable et al., submitted to Fus Eng and Design (2018)

Speaker: Katy Ellis

14:00 P2.1077 ST Path to Fusion: First Results from ST40

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1077.pdf ST Path to Fusion: First Results from ST40 M Gryaznevich for the Tokamak Energy Ltd team Tokamak Energy Ltd, Culham Science Centre, Abingdon, OX14 3DB, UK Spherical Tokamak (ST) path to Fusion has been proposed by R Stambaugh [1] and experiments on STs since then demonstrated feasibility of this approach. Advances in the high temperature superconductor technology [2] allows significant increase in the toroidal field which was found to improve confinement in STs. The combination of the high , which has been achieved in STs [3], and the high TF that can be produced by HTS TF magnets, opens a path to lower- volume fusion reactors, in accordance with the fusion power scaling proportional to 2Bt4V. Feasibility of a low-power compact ST reactor and physics and engineering challenges of the ST path to Fusion Power will be discussed. Several devices have been built by Tokamak Energy on the development of this path. A small tokamak ST25 (R/a=0.25/0.125m, Ipl<10kA, Bt<0.2T, pulse up to 30sec, circular and D-shaped vessels) is operational since 2012, testing EBW pre- ionisation and current drive. 29h discharge has been demonstrated in a similar small tokamak, but with all-HTS magnets [4], Results from these STs will be overviewed. High field spherical tokamak ST40 (R=0.4-0.6m, R/a=1.6-1.8, Ipl=2MA, Bt=3T, k=2.5, pulse~1- 10sec, 2MW NBI, DD and DT operations) is now operating. Plasma current of 300kA has been already achieved at Bt=0.72T during first weeks of operations. The Figure shows magnetic reconstruction and visible light image of the plasma obtained using merging-compression plasma formation, as used on START and MAST tokamaks [7]. Results of numerical simulations on the energy, fast ions and alpha particle confinement, stability and equilibrium [5,6] will be discussed. According to simulations, due to low collisionality, high field and low ion neoclassical transport, a hot ion mode with Ti ~ 10-15keV may be achieved in ST40 even with moderate confinement. We will undertake experiments on ST40 to demonstrate the performance of high field ST in burning plasma regimes and to support designs of next step devices on the ST path to Fusion. Details of engineering design and experimental plans will also be presented. [1] R Stambaugh et al, Fus. Tech. 33 (1998) 1; [2] M Gryaznevich et al, Fus. Eng. & Design 88 (2013) 1593; [3] M Gryaznevich et al, Phys Rev Lett 50 (1998) 3972; [4] M Gryaznevich et al, Nucl. Fus. 55 (2015) 104019; [5] A Salmi et al, Fus. Eng. & Design 117 (2017) 14; [6] A Dnestrovskij, J W Connor and M Gryaznevich, submitted to NF (2017); [7] M Gryaznevich, A Sykes, NF 57 (2017) 072003.

Speaker: Mikhail Gryaznevich

14:00 P2.1078 Statistical analysis of edge-localized mode timing in JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1078.pdf Statistical analysis of edge-localized mode timing in JET G. Verdoolaege1,2 and JET Contributors* 1 Department of Applied Physics, Ghent University, Ghent, Belgium 2 Laboratory for Plasma Physics, Royal Military Academy, Brussels, Belgium Probability distributions of edge-localized mode (ELM) properties in tokamaks under stationary plasma conditions contain information about ELM variability that can potentially be exploited for scenario optimization and ELM control purposes [1–4]. Such information complements averages taken over multiple ELM bursts and enables calculation of occurrence probabilities of specific ELM events. In this work, the distributions of inter-ELM time and ELM duration are studied in a database of JET carbon wall (CW) and ITER-like wall (ILW) plasmas. A new algorithm has been developed, based on gamma mixture modelling for robustly extracting the ELM timing under a wide variety of plasma conditions, with minimal user input. The Weibull distribution is seen to be a good model for the probability density function of the inter-ELM time, as well as the ELM duration [1, 3]. It allows to distinguish between type I ELMs (representing the majority of ELM activity in the database) and small type III ELMs, for similar ELM frequencies. Different distribution shapes are observed throughout the database, characterized by a variety of widths and tail lengths. The typical width of the distribution quantifies the regularity of the ELM timing, while long tails point to intermittent ELM activity. The distribution parameters are visualized using a projection based on a faithful similarity measure between the distributions (Rao geodesic distance), allowing to discern several clusters, including those corresponding to plasmas from baseline and hybrid scenarios in JET ILW [5]. Several trends with the main plasma parameters are observed and quantified. The database is being extended with additional plasmas from JET and other devices, aiming at a systematic characterization of statistical ELM properties and their dependences under various conditions. [1] A. Shabbir, et al., Nucl. Fusion 57, 036026, 2017. [2] A. Shabbir, et al., Rev. Sci. Instrum. 87, 11D404, 2016. [3] B.J. Fritch, A. Marinoni and A. Bortolon, 59 th APS DPP 69(12), JP11.28. [4] A.J. Webster et al., Phys. Rev. Lett. 110, 155004, 2013. [5] G. Verdoolaege and J.-M. Noterdaeme, Nucl. Fusion 55, 113019, 2015. * See the author list of X. Litaudon et al., Nucl. Fusion 57, 102001, 2017.

Speaker: Geert Verdoolaege

14:00 P2.1079 Disruption prediction with sparse modeling by exhaustive search

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1079.pdf Disruption Prediction with Sparse Modeling by Exhaustive Search Tatsuya Yokoyama1 , Takamitsu Sueyoshi1 , Yuya Miyoshi2 , Ryoji Hiwatari2 , Yasuhiko Igarashi3 , Masato Okada1 , and Yuichi Ogawa1 1 Graduate School of Frontier Science, The University of Tokyo, Kashiwa, Japan 2 Rokkasho Fusion Institute, QST, Rokkasho, Japan 3 Japan Science and Technology Agency, PRESTO, Saitama, Japan Plasma disruption is one of crucial phenomena in a tokamak fusion reactor. To realize nuclear fusion reactor, it is necessary to elucidate and control it. However, its physical mechanism is not clearly identified yet, so there are some studies trying to predict occurrence of disruptions based on experimental data. In this research, we constructed disruption predictor using a support vector machine(SVM) based on the large experimental data in JT-60U and feature extraction by sparse modeling was carried out. The concept of sparse modeling exploits the inherent sparseness that is common to all high-dimensional data and enables us to efficiently extract the maximum amount of informa- tion from data. For the sparse modeling, we used exhaustive search with SVM, assuming that the optimal combination of explanatory variables is K-sparse [1]. We have obtained some results showing that feature extraction can contribute to improvement of disruption prediction performance and understanding of the physical background of disrup- tion. As a variable before narrowing down, we chose 17 parameters from physical knowledge. We selected normalized beta and plasma internal inductance because we use results of high- beta experiment. We also selected safety factor 95% of minor radius, and these parameters are obtained from MHD equilibrium calculation. We use not only those parameters’ value, but also time derivative value. In our results, 6 parameters including mode lock amplitude and its time derivative are extracted as the optimal combination of parameters. We will try to specify dangerous parameter area where disruption is likely to occur using sparse modeling. References [1] Y. Igarashi, H. Takenaka, Y. Nakanishi-Ohno, M. Uemura, S. Ikeda, and M. Okada. Exhaustive search for sparse variable selection in linear regression, 2017.

Speaker: Tatsuya Yokoyama

14:00 P2.1080 Transport hysteresis and zonal flow stimulation in magnetized plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1080.pdf Transport hysteresis and zonal flow stimulation in magnetized plasmas E. Gravier, M. Lesur, T. Reveille, T. Drouot, J. Médina, M. Idouakass Institut Jean Lamour - UMR 7198 CNRS-University of Lorraine, Nancy, France A study of zonal flows generated by trapped-electron mode (TEM) and trapped-ion mode (TIM) micro turbulence is presented as a function of the temperature ratio Te /Ti . For this purpose the gyrokinetic code TERESA (Trapped Element REduction in Semi lagrangian Ap- proach) considering only trapped particles is used [1, 2, 3, 4, 5, 6]. The model enables the study of a full f problem for ion and electron trapped particles at low numerical cost. A hysteresis in the relationship between zonal flows and electron heating is observed. As the electron temperature increases, a first transition occurs, at a given electron/ion temperature ratio, above which zonal flows are much weaker than before the transition, leading to a poorly confined plasma [6, 7]. Beyond this transition, even if the electron temperature is lowered to a moderate value, the plasma fails to recover a dynamic state with strong zonal flows. Then, as the electron temperature decreases further, a new transition appears, at a temperature lower than the first transition, below which the zonal flows are stronger than they were initially [8]. The confinement of the plasma and the heat flux are thus found to be sensitive to the history of the magnetized plasma. These transitions are associated with large exchanges of energy between the modes corresponding to instabilities (m > 0) and zonal flows (m = 0). We also observe that up to the first transition it is possible to use a control method to stimulate the appearance of zonal flows and therefore the confinement of the plasma. Beyond that transition, this control method is no longer effective. References [1] G. Depret, X. Garbet, P. Bertrand, A. Ghizzo, Plasma Phys. Cont. Fusion 42, 949 (2000) [2] Y. Sarazin, V. Grandgirard, E. Fleurence, X. Garbet, Ph. Ghendrih, P. Bertrand and G. Depret, Plasma Phys. Control. Fusion 47, 1817 (2005) [3] A. Ghizzo, D. Del Sarto, X. Garbet, Y. Sarazin, Phys. Plasmas 17, 092501 (2010) [4] T. Cartier-Michaud, P. Ghendrih, Y. Sarazin, G. Dif-Pradalier, T. Drouot, D. Esteve, X. Garbet, V. Grandgi- rard, G. Latu, C. Norscini, C. Passeron, J. Phys.: Conf. Series 561, 012003 (2014) [5] M. Lesur, T. Cartier-Michaud, T. Drouot, P. Diamond, Y. Kosuga, T. Reveille, E. Gravier, X. Garbet, S.-I. Itoh, K. Itoh, Phys. Plasmas 24, 012511 (2017) [6] T. Drouot, E. Gravier, T. Reveille, M. Sarrat, M. Collard, P. Bertrand, T. Cartier-Michaud, P. Ghendrih, Y. Sarazin, X. Garbet, Phys. Plasmas 22, 082302 (2015) [7] E. Gravier, M. Lesur, T. Reveille, T. Drouot, Phys. Plasmas 23, 092507 (2016) [8] E. Gravier, M. Lesur, T. Reveille, T. Drouot, J. Médina, Nuclear Fusion (2017)

Speaker: Etienne Gravier

14:00 P2.1081 Turbulence Regulation with Radial Wavenumber Spectral Shift Caused by LHCD Induced Velocity Shear during ELM Mitigation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1081.pdf Turbulence Regulation with Radial Wavenumber Spectral Shift Caused by LHCD Induced Velocity Shear during ELM Mitigation X.L. Zou1, G.L. Xiao2,3, W.L. Zhong2, S.D. Song2, X.R. Duan2, A.D. Liu4, X.Y. Bai2, J. Cheng2, Z.Y. Cui2, L. Delpech1, X.T. Ding2, J.Q. Dong2,5, A. Ekedahl1, B.B. Feng2, G. Giruzzi1, J.M. Gao2, M. Goniche1, G.T. Hoang1, X.Q. Ji2, M. Jiang2, B. Lu2, D. Mazon1, Y. Peysson1, X.M. Song2, Z.B. Shi2, M. Xu2, D.L.Yu2, B.Y. Zhang2, Y.P. Zhang2, Y. Zhou2 and HL-2A team2 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 2 Southwestern Institute of Physics, P.O. Box 432, Chengdu, China 3 Department of Engineering physics, Tsinghua University, Beijing, China 4 KTX Laboratory and Department of Modern Physics, University of Science and Technology of China, Anhui Hefei 230026,China 5 Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China Email: xiao-lan.zou@cea.fr ELM mitigation with LHCD has been achieved in the HL-2A tokamak for high plasma density (ne ≥ 2.5×1019 m-3) and large LHCD absorbed power (PLHCD ≥ 300 kW) [1]. The divertor peak heat load induced by ELM has been significantly reduced during the mitigation phase. A severe decrease of the pedestal velocity shear has been observed with LHCD switch on, while the kr-spectrum of the pedestal turbulence is shifted toward the origin (Fig.1(d)). It has been found that the ELM mitigation is desynchronized with LHCD pulse, but it is closely correlated to the pedestal turbulence enhancement (Fig.1(e)). In order to understand the mechanism of the turbulence enhancement during ELM mitigation, a theoretical model, based on the regulation of the turbulence amplitude by its radial wavenumber spectral shift caused by external velocity shear, has been developed. A critical growth rate for the turbulence regulation has been identified in this model. It has been found that the turbulence enhancement and ELM mitigation occur Fig.1 ELM mitigation with LHCD. when the decrease of LHCD driven velocity shear exceeds a threshold value, which directly depends on . Good agreement has been found between experiment and theory for the regulation of the turbulence amplitude with its averaged radial wavenumber. Reference [1] G.L. Xiao et al., Phys. Plasmas 24 (2017) 122507

Speaker: Xiaolan Zou

14:00 P2.1082 Electron temperature gradient (ETG) turbulence induced particle transport in finite beta laboratory plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1082.pdf Electron Temperature Gradient (ETG) Turbulence Induced Particle Transport in Finite Beta Laboratory Plasma Prabhakar Srivastav1, Rameswar Singh1, L. M. Awasthi1, A. K. Sanyasi1, P. K. Srivastava1, R. Sugandhi1 and R. Singh2 1 Institute for Plasma Research, HBNI, Gandhinagar, India 2 Advance Technology Center, NFRI, Daejeon, Rep. of Korea Abstract Plasma transport across confining magnetic field continues to bother fusion fraternity, engendering numerous efforts on experimental, theoretical and computational studies. Although, over recent times, problem concerning ion scales is greatly resolved but success on containing electron scale contribution to plasma loss still eludes. The reason for this may be the inability of carrying out direct measurements in fusion devices due to extremely small scale lengths and unfavorable conditions [1]. Prompted by recent success of successful demonstration of unambiguous excitation of Electron Temperature Gradient (ETG) turbulence, by introduction of a Electron Energy Filter (EEF) in Large Volume Plasma Device (LVPD)[2]. This helped in tailoring plasma for satisfying threshold condition of ETG i.e., e  Lne LTe , where Lne and LTe are plasma density and electron temperature gradient scale lengths respectively. We investigated particle transport, classified as either electrostatic or magnetic in origin, in finite beta (  0.01  0.4 ) plasma of LVPD and observed particle flux follow the beta scaling for ETG turbulence. Detailed Results on effect of plasma beta scaling on electrostatic and electromagnetic components of particle flux and their respective dominance towards contributing plasma loss will be presented in the conference. References: 1. P. C. Liewer, Nucl. Fusion 25, 543 (1985). 2. S.K. Mattoo, et.al Phys. Rev. Lett. 108, 255007(2012)

Speaker: Prabhakar Srivastav

14:00 P2.1083 Spectral modeling of tungsten transport based on a compact advanced extreme ultraviolet spectrometer system for KSTAR and WEST plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1083.pdf Poloidal asymmetry of perpendicular velocity of the density fluctuations L. Vermare1, Y. Asahi2, F. Clairet2, G. Dif-Pradalier2, X. Garbet2, J-C. Giacalone2, V. Grandgirard2, O. Gürcan1, P. Hennequin1, C. Honoré1, P. Morel1 and the TORE SUPRA team2 1 LPP, Ecole Polytechnique, CNRS, 91128 Palaiseau, France 2 CEA, IRFM, F-13108 Saint Paul Lez Durance, France Simultaneous measurements of binormal velocity of density fluctuations using two separate Doppler backscattering systems at the low field side and at the top of the plasma show significant poloidal asymmetry [1]. The measurements are performed in the core region between the radii (0.7

Speaker: Wonho Choe

14:00 P2.1084 Radial structure of vorticity in the plasma boundary of tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1084.pdf Radial structure of vorticity in the plasma boundary of tokamak plasmas B. Gonçalves1, I. Henriques1, C. Hidalgo2, C. Silva1, H. Figueiredo1, V. Naulin3, A. H. Nielsen3 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal. 2 Euratom-Ciemat, Madrid, Spain 3 Technical University of Denmark, Department of Physics, 2800 Kgs. Lyngby, Denmark The first experimental measurement of vorticity and vorticity flux divergence in a fusion device is presented. This is an important achievement since vorticity plays a key role in the transport of energy and particles in plasmas and fluids. The measurements were performed in the plasma edge of the small tokamak ISTTOK, with an array of Langmuir probes, specifically designed for the purpose, allowing for the first time a direct comparison with theoretical models. Plasma profiles and turbulence have been investigated using the probe head, located on the equatorial plane of the device. It consists of two parallel arrays of Langmuir probes separated by Dr~3 mm allowing the simultaneous investigation of the radial structure of fluctuations on vorticity, Reynolds stress and turbulence in the plasma boundary region. Measurements were taken at different radial positions, both in the edge (r < alimiter) and in the scrape-off layer (r > alimiter) on a shot by shot basis. The experimental results presented show that the vorticity flux divergence amplifies the shear flow in the tokamak plasma edge region. Self-similarity in the probability distribution function of several parameters, including vorticity and vorticity flux, is also observed in ISTTOK and indicate that there is no morphological change in the coherent structures in the plasma boundary region and that momentum flux is regulated by blobs.

Speaker: Bruno Soares Gonçalves

14:00 P2.1085 Parameter space of low frequency inter-ELM modes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1085.pdf Parameter space of low frequency inter-ELM modes B. Vanovac1 , E. Wolfrum2 , M. Willensdorfer2 , M. Cavedon2 , M. Griener2 , A.F. Mink2 , S.S. Denk2 , S.J. Freethy2 , M. Hoelzl2 , N.C. Luhmann Jr. 3 , the ASDEX Upgrade Team 1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands 2 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 3 Department of Applied Science, University of California at Davis, Davis, CA 95616, USA The ELM cycle of type-I ELMs consists of different phases characterized by the evolution of kinetic profiles on different time scales [1] and distinct MHD and turbulence activity. In the latest phase of the ELM cycle, the pressure gradients are clamped. During this phase low, medium and high frequency MHD modes develop simultaneously in the steep gradient region [2]. The high frequency modes are located at the minimum of the Er well, and are measured as fluctuations in the radial magnetic field on both, low and high field side [3]. In this work, the low frequency modes are studied. They are measured only at the low field side located further inwards, towards the pedestal top. They appear as fluctuations in the electron density, the electron temperature and as magnetic fluctuations [4]. These modes rotate poloidally in the electron diamagnetic direction with the velocity of the background flow at that position. The frequency of low frequency modes is inversely proportional to the input power. In order to fully characterize the low frequency modes and correlate them with the pedestal evolution pattern during an ELM cycle, this work focuses on exploration of the range of pa- rameters where these modes appear. This involves the extension of the dependence on input power and scan in the edge safety factor. Different collisionality regimes are also assessed. To identify the nature of the fluctuations, we use the newly installed He-line ratio diagnostics at ASDEX Upgrade that measures simultaneously electron density and electron temperature in the plasma edge. The phase relation between the two is compared with n-T phase measurements from reflectometer and correlation electron cyclotron emission diagnostics [5]. References [1] A Burckhart et al 2010 Plasma Phys. Control. Fusion 52 105010 [2] F Mink et al 2016 Plasma Phys. Control. Fusion 58 125013 [3] F M Laggner et al 2016 Plasma Phys. Control. Fusion 58 065005 [4] B Vanovac et al 2018 Plasma Phys. Control. Fusion 60 045002 [5] S.J. Freethy et al 2018 Phys. Plasmas, accepted

Speaker: Branka Vanovac

14:00 P2.1086 Real time capable turbulent transport modelling using neural networks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1086.pdf Real time capable turbulent transport modelling using neural networks K. van de Plassche1 , J. Citrin1 , C. Bourdelle2 , V. Dagnelie1,3 , F. Felici4 , A. Ho1 1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands 2 CEA, IRFM, F-13108, Saint-Paul-lez-Durance, France. 3 Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands. 4 EPFL-SPC, CH-1015, Lausanne, Switzerland. Quasilinear gyrokinetic models are very successful in predicting particle and heat transport in tokamaks, and in reproducing experimental profiles in wide parameter regimes. One such code is QuaLiKiz, validated on JET, ASDEX-U and Tore-Supra discharges [1, 2, 3, 4]. While an impressive six orders of magnitude faster than local nonlinear gyrokinetics, they are still too slow for efficient scenario optimization and realtime applications. A feed-forward neural network regression of QuaLiKiz was used in a successful proof-of- concept [5, 6]. Such a network can be evaluated within a few microseconds, another six orders of magnitude faster than the original model. These networks are tested and designed for the RAPTOR rapid profile evolution code [7], but can also be used in other frameworks. This current work is a major extension of the proof-of-principle from 4D to 10D. A large database of 3.108 flux calculations over a 9D input space generated with the QuaLiKiz code is used to extend the original input space of ion temperature gradient R/LTi , ion-electron temper- ature ratio Ti /Te , safety factor q and magnetic shear ŝ with the electron temperature gradient R/LTe , density gradient R/Ln , minor radius ρ, collisionality ν ∗ and effective ion charge Ze f f . The 10th dimension, ExB shear, is added in post-processing using a new turbulence quenching rule [8]. We present our methodology of training and validating these neural networks, which are ready for applications within RAPTOR [9]. The speed of the networks created in this work combined with RAPTOR allow for transport simulations at a speed that is unprecedented, and opens new avenues in the modelling of fusion experiments. References [1] J. Citrin et al. Plasma Physics and Controlled Fusion 59 12400 (2017) [2] C. Bourdelle et al., Plasma Physics and Controlled Fusion 58, 1 (2016) [3] O. Linder et al., to be submitted to Nuclear Fusion [4] M. Marin et al., this conference (EPS Prague 2018); A. Ho et al., this conference (EPS Prague 2018) [5] J. Citrin et al. Nuclear Fusion 55 092001 (2015) [6] F. Felici et al., submitted to Nuclear Fusion [7] F. Felici and O. Sauter, Plasma Physics and Controlled Fusion 54, 2 (2012) [8] V.I. Dagnelie et al. University of Utrecht MSc thesis (2017) [9] F. Felici et al., this conference (EPS Prague 2018)

Speaker: Karel Lucas van de Plassche

14:00 P2.1087 Gyrokinetic theory of turbulence-driven intrinsic rotation and intrinsic current

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1087.pdf Gyrokinetic theory of turbulence-driven intrinsic rotation and intrinsic current Lu Wang1, Shuitao Peng1, Wen He1, P. H. Diamond2 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, State Key Laboratory of Advanced Electromagnetic Engineering and Technology, SEEE, Huazhong University of Science and Technology, Wuhan, China 2 University of California at San Diego, California, USA A new mechanism for turbulent acceleration of parallel rotation in electrostatic ion temperature gradient (ITG) is discovered from electrostatic gyrokinetic theory [1]. The turbulent acceleration acts as a local source/sink, which cannot be written as a divergence of the parallel Reynolds stress. It has different physics from the residual stress, which enters the rotation equation via its divergence. Via comparison between the cases for ITG and collisionless trapped electron mode, a possible connection of our theoretical results to the experimental observations of ECH effects on toroidal core rotation is discussed [2]. Recent experimental results show that the fluid Reynolds stress cannot explain the rotation profile [3], and kinetic stress can drive parallel rotation [4]. Therefore, we extended our previous work to electromagnetic turbulence [5]. The quasilinear intrinsic parallel flow drive including parallel residual stress, kinetic stress, cross Maxwell stress and parallel turbulent acceleration by electromagnetic ITG turbulence is calculated analytically using electromagnetic gyrokinetic theory. The possible implications of our results for experimental observations are discussed [5]. To clarify that turbulent acceleration does not contradict the momentum conservation, we also present the relationship between turbulent acceleration and momentum conservation in electromagnetic turbulence [6]. Our ongoing works focus on intrinsic toroidal rotation by taking toroidal effects into account and intrinsic current drive by electromagnetic turbulence. References： [1] Wang L. and Diamond P.H. 2013 Phys. Rev. Lett. 110 265006 [2] Wang L., Peng S. and Diamond P.H. 2016 Phys. Plasmas 23 042309 [3] Müller S.H. et al 2011 Phys. Plasmas 18 072504 [4] Ding W.X. et al 2013 Phys. Rev. Lett. 110 065008 [5] Peng S., Wang L. and Pan Y. 2017 Nucl. Fusion 57 036003 [6] Peng S. and Wang L. 2017 Phys. Plasmas 24, 012304

Speaker: Lu Wang

14:00 P2.1088 Turbulent transport and their mechanisms in Wendelstein 7-X plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1088.pdf Turbulent transport and their mechanisms in Wendelstein 7-X plasmas J.A. Alcusón1† and the Wendelstein 7-X team 1 Max-Planck-Institute für Plasmaphysik, Greifswald, Germany. Traditionally, radial transport in stellarators is dominated by a high neoclassical (NC) contri- bution. In tokamaks, as this contribution is inherently minimal, thanks to the symmetry of the device, the radial losses are essentially attributed to turbulence [1]. The optimized Wendelstein 7-X (W7-X) stellarator is designed to reduce the NC transport down to tokamak levels. Results from the first experimental campaign in W7-X suggest that NC transport is not sufficient to explain the radial losses in several scenarios (specially at the edge re f f > 0.6), opening the door to the turbulent transport contribution as a plausible candidate to explain these discrepancies. The present work performs a turbulent transport analysis using linear and nonlinear gyroki- netic simulations for stellarator geometry [2] with the GENE [3] code in Wendelstein 7-X ex- perimental plasmas and direct measurements of the machine. The milestones of the study are: i) identify when the turbulent transport becomes relevant in different configurations with real plasmas, ii) characterize the turbulence according to the instabilities present in the experiment and, in addition, iii) compare the numerical results with direct measurements of the W7-X di- agnostics. Different drift-wave instabilities are studied (mainly driven by the ion temperature gradient and the trapped-electron mode [4]) using experimental profiles of density and temperature from the OP1.2a W7-X campaign (provided by Thomson scattering and XICS inversion). These pro- files are obtained from high-density discharges, with a significant temperature gradient in the core and density gradient localized in the edge. Two magnetic configurations, standard and high mirror, are used to analyse the optimization properties and their effects on the device’s trans- port such as turbulence stabilization [4]. In order to compare with diagnostics’ measurements at fixed positions (reflectometers, CECE, PCI, etc), special attention to the evolution of the insta- bilities and how they propagate is considered and studied. Power-balance analysis is also used to assess the relative role of NC and turbulent processes in the overall heat transport. References [1] P. Helander, et al., Plasma Phys. Control. Fusion 54, 124009 (2012). [2] F. Jenko, et al., Phys. Plasmas 7, 1904 (2000). [3] P. Xanthopoulos, et al., Phys. Rev. Lett. 113, 155001 (2014). [4] J. Proll, et al., Phys. Rev. Lett. 108, 245002 (2012). † jorge.alcuson@ipp.mpg.de

Speaker: Jorge Alberto Alcusón

14:00 P2.1089 Core boron transport studies using CXRS at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1089.pdf Core boron transport studies using CXRS at ASDEX Upgrade C. Bruhn1,2 , R.M. McDermott1 , C. Angioni1 , J. Ameres3,1 ,V. Bobkov1 , M. Cavedon1 , R. Dux1 , A. Kappatou1 , A. Lebschy1,2 , R. Ochoukov1 , P. Manas1 , and the ASDEX Upgrade Team 1 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany 2 Physik-Department E28, Technische Universität München, D-85748 Garching, Germany 3 Zentrum Mathematik M16, Technische Universität München, Garching, Germany Impurities in fusion plasmas arise from many different sources including the erosion and sputtering of material from plasma facing components, the intentional injection of impurities for divertor cooling and core radiation control, and the production of helium from the fusion process itself. To achieve optimum fusion performance, future fusion reactors need to control the build up of both high- and low-Z impurities in the plasma core. Therefore, it is important to develop and validate our theoretical understanding of impurity transport in fusion plasmas. At ASDEX Upgrade (AUG), a novel method of studying the core boron transport has been de- veloped and is being used to validate the theoretical understanding as well as the mechanisms behind low-Z impurity transport. This method utilizes the fact that a modulation of the power from the ion cyclotron resonance frequency (ICRF) antennae induces a modulation of the boron density, which can be measured with high spatial and temporal resolution by the charge ex- change recombination spectroscopy (CXRS) diagnostics. From a time perturbed boron density signal the transport coefficients, D and v, can be separately determined with high radial reso- lution by solving an inverse problem, and this is in contrast to what is usually being done for low-Z impurities. This method, thus, combines the advantages of a transient transport analysis performed on modulated signals over many periods, as often applied for heat transport stud- ies, with the high radial resolution enabled by the CXRS diagnostic. It has been applied to a wide variety of AUG H-mode plasmas, and from this, a database of core boron transport coeffi- cients has been assembled. This database and how the transport coefficients depend on the local plasma parameters will be presented in this contribution as well as an in-depth comparison to theory. For the bulk of the database, there is a strong scaling of the transport coefficients with the electron cyclotron resonance heating (ECRH) power and consequently with Te /Ti . Addi- tionally, there is a quantitative agreement between the measured and the predicted theoretical diffusion coefficients. However, in all cases the convection is predicted to be more inward than is measured, resulting in an over-prediction of the peaking of the impurity density profiles. These results and explanations to the discrepancy will be presented in this contribution.

Speaker: Cecilia Bruhn

14:00 P2.1090 The study of long range electric potential correlation on the GAM frequency on the T-10 tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1090.pdf The study of long range electric potential correlation on the GAM frequency on the T-10 tokamak V.N. Zenin1, 2, M.A. Drabinskij1, 2, L.G. Eliseev1, S.A. Grashin1, P.O. Khabanov1, 2, N.K. Kharchev1, A.V. Melnikov1, 3 1 NRC Kurchatov Institute, Moscow, Russia 2 Moscow Institute of Physics and Technology, Dolgoprudny, Russia 3 National Research Nuclear University MEPhI, Moscow, Russia In the recent years there has been significant interest to Geodesic Acoustic Modes (GAM). GAMs, being the high-frequency counterpart of zonal flows, can be a possible mechanism of the turbulence self-regulations. It has been shown theoretically that GAMs manifest themselves as oscillations of plasma electric potential with m = n = 0 (and can weakly be seen on density with m = 1, n = 0). GAMs have been studied with two main diagnostics: Langmuir probes and Heavy ion beam probing (HIBP), a unique method for direct measurement of the electric potential in the hot plasma core. Diagnostics are separated by half of torus of the T-10 tokamak (R= 1.5 m, a= 0.3 m, B < 2.5 T). This work is dedicated to simultaneous measurements of plasma potential oscillations at GAM frequencies in different locations and studying of their correlation properties. It was found that coherency between signals of two diagnostics is up to 0.8 that is unexpectedly high for such a large distance between them, half of torus in toroidal and about π in poloidal direction. Such coherency appears when Langmuir probes were located at about ρ = 0.95. Also, the phase shift between potentials measured with two diagnostics has been obtained. The value of coherency decreases with increasing in radial distance between HIBP sample volume and probes position. The phase shift between electric potential oscillation measured with HIBP and measured with Langmuir probes in the GAM frequency range was negative (about - 1.5 – 2.2 rad). Its value increases with increasing in radial distance between points of observation of two diagnostics. We assume that phase shift in toroidal and poloidal directions is equal to zero because m = n = 0 for GAM. Since phase shift is negative plasma potential wave propagates outwards. The magnitude of its velocity changes from ~ 2 km/s (Δr ≈ 3 cm) to 7 km/s (Δr ≈ 11 cm). This work was funded by Russian Science Foundation, Project 14-22-00193.

Speaker: Vitaly Zenin

14:00 P2.1091 Statistical analysis of SOL fluctuations on COMPASS tokamak as measured by the Li-BES diagnostic

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1091.pdf Statistical analysis of SOL fluctuations on COMPASS tokamak as measured by the Li-BES diagnostic A. Buzás1 , A. Bencze1 , J. Krbec2,3 , P. Hacek2,4 , J. Seidl2 , R. Panek2 1 Wigner Research Center for Physics, Budapest, Hungary 2 Institute of Plasma Physics of the CAS, Prague, Czech Republic 3 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic 4 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic In this paper the COMPASS Li-BES (Lithium Beam Emission Spectroscopy) system is intro- duced to demonstrate its capabilities in Scrape-off Layer (SOL) density fluctuation studies. The effect of atomic physics is examined by applying small perturbations (with different amplitudes and radial locations) to artificial density profiles. From these synthetic perturbed density pro- files, using a collisional-radiative model, Li-light profiles are calculated. It has been shown that the beam attenuation has a significant effect on the observed perturbation amplitudes and local- isation. Simple numerical simulations based on stochastic models of the SOL filaments (blobs) [1] have been performed and the effect of atomic physics on the statistical properties of the same filament events in the Li-light fluctuations such as amplitude distributions, waiting times, conditionally averaged waveforms have been studied. The results are compared to experimental data and theoretical expectations [2]. It is found that they are in good agreement with what is seen on other tokamaks and what the models suggest. Moreover the interesting problem of the so called ’hole’ emergence has also been addressed in the context of atomic physics effects. Analysing the statistics of the measured Li-BES signals, it has been shown that the PDFs are not in fact dominated by large an rare events but by the small and frequent. However the emerg- ing statistics are qualitatively still in line with model predictions albeit with different model parameters. These results can also be recreated by numerical simulations using the modified parameter set. References [1] Garcia, O. E., Physical Review Letters 108, 6 (2012) [2] Theodorsen, A. and Garcia, O. E. and Horacek, J. and Kube, R. and Pitts, R. A., Plasma Phys. Control. Fusion 58, 1 (2016)

Speaker: Attila Buzás

14:00 P2.1092 A critical edge ion heat flux for L-H transition from combined analysis using Alcator C-Mod and ASDEX Upgrade tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1092.pdf A critical edge ion heat flux for L-H transition from combined analysis using Alcator C-Mod and ASDEX Upgrade tokamaks * J.W. Hughes1, M. Schmidtmayr2, F. Ryter3, E.A. Tolman1, N. Cao1, A.J. Creely1, N. Howard1, A.E. Hubbard1, Y. Lin1, A. Mathews1, M.L. Reinke4, J.E. Rice1, E. Wolfrum3, S. Wukitch1, Alcator C-Mod Team and ASDEX Upgrade Team 1 MIT Plasma Science and Fusion Center, Cambridge MA, USA; 2 Institute of Applied Physics, TU Wien, Fusion@ÖAW, Vienna, Austria; 3 Max-Planck-Institut für Plasmaphysik, Garching, Germany; 4 Oak Ridge National Laboratory, Oak Ridge TN, USA Experimental studies of the transition from L-mode to H-mode confinement (L-H) on Alcator C-Mod and ASDEX Upgrade (AUG) strengthen the basis for projecting power requirements for future fusion devices. On C-Mod, L-H experiments at toroidal field 𝐵𝐵𝑇𝑇 of 4.0—7.8T reveal that H-mode power threshold 𝑃𝑃𝑡𝑡ℎ accords roughly with projections from a scaling law used to determine power needs for ITER. However, as on AUG, the scaling law does not capture the experimental density dependence of 𝑃𝑃𝑡𝑡ℎ at low normalized density 𝑛𝑛�⁄𝑛𝑛𝐺𝐺 . Furthermore, at higher line averaged density 𝑛𝑛� the inferred experimental 𝑃𝑃𝑡𝑡ℎ does not scale as strongly with 𝐵𝐵𝑇𝑇 as the scaling law indicates [1]. We can partially resolve these discrepancies by performing transport and power balance analysis of C-Mod plasmas just prior to L-H transitions [2]. Analysis confirms and extends a key result found on AUG: a critical value of surface-integrated ion heat flux per particle 𝑄𝑄𝑖𝑖 ⁄𝑛𝑛� is necessary to enable the transition from L-mode to H-mode [3]. The analysis of C-Mod data indicates that 𝑄𝑄𝑖𝑖 at the L-H transition not only increases linearly with 𝑛𝑛� but also with 𝐵𝐵𝑇𝑇 . The 𝑛𝑛�, 𝐵𝐵𝑇𝑇 scalings are not necessarily reflected in the experimental total L-H power because of changing balance of edge electron and ion heat fluxes, which depends in turn on the auxiliary heating scheme and the strength of electron-ion equilibration. Combining data from C-Mod and AUG yields a general expression for the edge ion heat flux at the L-H transition, 𝑄𝑄𝑖𝑖 /𝑆𝑆 ∝ 𝑛𝑛�1.07 𝐵𝐵𝑇𝑇 0.76 , where 𝑆𝑆 is the plasma surface area. This result is consistent with a critical shear in edge 𝐸𝐸 × 𝐵𝐵 being necessary for H-mode access, and can explain the 𝑛𝑛�, 𝐵𝐵𝑇𝑇 , and 𝑆𝑆 dependencies in the 𝑃𝑃𝑡𝑡ℎ scaling law, providing an additional means of extrapolating H-mode power requirements to ITER. [1] E.A. Tolman, NF 58 (2018) 046004; [2] M. Schmidtmayr NF (2018); [3] F. Ryter, NF 54 (2014) 083003. * Supported by US Department of Energy awards DE-FC02-99ER54512, DE-SC0014264 and by National Science Foundation Graduate Research Fellowship under Grant No. 1122374. This work has been partly carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training program 2014-2018 under grant agreement No 633053. M. Schmidtmayr was a fellow of the Austrian Marshall Plan Foundation.

Speaker: Jerry Hughes

14:00 P2.1093 GAM evolution in L-mode approaching the L-H transition on JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1093.pdf GAM evolution in L-mode approaching the L-H transition on JET C. Silva1, J. C. Hillesheim2, L. Gil1, C. Hidalgo3, C.F. Maggi2, L. Meneses1, E.R. Solano3, and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Lisboa, PT 2 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 3 Laboratorio Nacional de Fusión, CIEMAT, 28040 Madrid, Spain * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001 The interaction between zonal flows (ZFs) and turbulence is a self-regulating mechanism. Understanding this interaction is crucial to control plasma confinement. The shearing due to ZFs is thought to dominate in regimes when the mean shear flow is modest as before and during the L-H transition [e.g. 1]. This was corroborated by findings in different devices demonstrating the importance of both the oscillating and mean flow shear and their interaction in triggering the transitions [1-4]. While on AUG the sheared flow below the L-H threshold is dominated by Geodesic Acoustic Modes (GAMs) [1], on devices such as DIII-D [2], EAST [3] and HL-2A [4] GAMs do not appear to be important on the way to H-mode. The reported results reveal that no clear picture exists on the relevance of GAMs in the turbulence collapse required for the formation of steep pressure gradients at the transition. This contribution focuses on the characterization of GAMs in JET L-mode plasmas when approaching the L-H transition aiming at understanding its possible role in triggering the transition. Doppler backscattering has been used to investigate GAMs by measuring oscillations in the E × B flow velocity. Experiments were performed in NBI heated discharges for different values of plasma current (2.2 < Ip < 3.2 MA) and line-averaged density (1.6 < n < 3.1×1019 m-3). The dataset also includes variations in toroidal magnetic field, magnetic configuration and hydrogen isotopes. Results demonstrate that parameters such as plasma current and density have a strong effect on the GAM amplitude. By assessing the importance of critical parameters such as safety factor and collisionality, experimental evidence is found for the different mechanisms determining the GAM amplitude: turbulence drive, collisional and collisionless damping. GAMs have been studied along the power ramp used to induce the L–H transition, taking advantage of the unique JET dataset. As the heating power increases, the GAM amplitude first increases but then is reduced as the L-H transition is approached. GAMs are either suppressed or have a modest amplitude at the transition. The cause of this reduction is however unclear as the GAM damping rate is expected be reduced along the heating power ramp and density fluctuations levels and the E × B shear flow display modest changes. Experimental investigation of isotope effects in hydrogen and deuterium plasmas was also performed. Stronger GAMs were found in D than in H plasmas at low heating power (PNBI < 4 MW) associated with larger edge density fluctuations in H. However, above PNBI  4 MW, the GAM amplitude is reduced in D plasmas while increases for H plasmas. Unfortunately, the L-H transition could not be achieved in H plasma due to heating power limitations. [1] G.D. Conway et al., PRL 106, 065001 (2011) [2] Z. Yan et al, NF 53 113038 (2013) [3] G.S. Xu et al, PRL 107, 125001 (2011) [4] M. Xu et al, PRL. 108, 245001 (2012)

Speaker: Carlos Silva

14:00 P2.1094 Observations of sheared turbulence in the H-mode Er well by phase contrast imaging on DIII–D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1094.pdf Observations of sheared turbulence in the H-mode Er well by phase contrast imaging on DIII–D∗ J.C. Rost1 , A. Marinoni1 , E.M. Davis1 , M. Porkolab1 , K.H. Burrell2 1 Massachusetts Institute of Technology, Cambridge, USA 2 General Atomics, San Diego, USA Phase Contrast Imaging (PCI) has been used on DIII–D to measure turbulent density fluc- tuations in several H-mode regimes, observing highly sheared turbulence in the Er well. Two sources are identified: instabilities in the pedestal that extend into the Er well and instabilities located in the well itself. PCI has a high bandwidth 10 kHz < f < 2 MHz and wavenumber- resolved measurements over 1 < k < 25 cm−1 , with a beam geometry that results in enhanced sensitivity to turbulence distorted by velocity shear. The sheared edge turbulence resolves into two frequency ranges with well-defined lab-frame phase velocities. Studies of the medium frequency f < 800 kHz turbulence in the Quiescent H-mode regime (QH-mode) scanned the plasma edge through the PCI beam, allowing the radial structure of the sheared edge turbulence to be reconstructed, revealing turbulence with kr < 0 on the inner half of the Er well and with kr > 0 on the outer half. Varying the injected torque in QH-mode plasmas shows that the lab-frame phase velocity of this turbulence varied directly with the E×B velocity at the top of the pedestal. In combination, these observations suggest that an instability located at the top of the pedestal extends into the Er well, where the shear distorts the turbulence. The high frequency, high phase velocity turbulence is, in contrast, observed to change on sub- ms time scales with changes in the Er well, forming within 100 µs of the L-H transition, and appearing and vanishing as the Er well collapses and reforms during Limit-Cycle Oscillations (LCO) and at an ELM. The lab-frame phase velocity is seen to vary with VE×B at the center of the well. The instability is sensitive to the shape of the Er well, being absent in the very narrow well seen in QH-mode but often present in the wider well seen in ELM-free H-mode and wide-pedestal QH-mode. The research presented here characterizes highly-sheared density turbulence in the pedestal and Er well of non-ELMing H-mode regimes with the ultimate goal of understanding the role of turbulence in determining the structure in these regimes. ∗ Work supported in part by the US Department of Energy under DE-FG02-94ER54235, DE- FC02-04ER54698, and DE-FC02-99ER54512.

Speaker: Jon Christian Rost

14:00 P2.1095 Impurity induced kinetic micro-electromagnetic instabilities in toroidal plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1095.pdf Impurity induced kinetic micro-electromagnetic instabilities in toroidal plasmas J. Q. Dong1,2, Yong Shen1, W. L. Zhong 1, A. P. Sun1, M. K. Han3,1, Z. X. Wang3, H. D. He1, X. L. Zou4 1 Southwestern Institute of Physics, Chengdu, 610041, China 2 Institute of Fusion Theory and Simulation, Zhejiang University, Hangzhou, 310027, China 3 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian, 116024, China 4 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France Abstract New kinetic micro-electromagnetic instabilities are found in magnetically confined toroidal plasmas in the presence impurity ions with gyrokinetic simulations [1]. The instabilities are induced by impurity ion density gradient, which is parallel (negative) or opposite (positive) to the gradient of electrons, and finite (plasma pressure/magnetic pressure) effect even in the absence of ion temperature gradient and trapped electrons. The requirements of dual critical impurity density gradients (one positive and one negative), finite impurity charge concentration and plasma are identified for the instabilities to be exited. The instabilities are identified as kinetic shear Alfvén and kinetic ballooning types, respectively, and are unstable in the first and second stable regimes of the ideal MHD ballooning modes and may have significant influence on plasma confinement. Possible relevance with the recent experimental observation in the pedestal of H-mode plasmas on HL-2A tokamak and further experimental investigations [2-4] are discussed. References [1] Yong Shen, J. Q. Dong, A. P. Sun et al., Plasma Phys. Control. Fusion 58, 045028 (2016). [2] Z.Y. Cui, S. Morita, H.Y. Zhou et al., Nucl. Fusion 53, 093001(2013). [3] Yong Shen, J.Q. Dong, A.P. Sun, M.K. Han et al., Nucl. Fusion 58, 014004 (2018). [4] W. L. Zhong, Y. Shen, X. L. Zou et al., Phys. Rev. Lett. 117, 045001 (2016).

Speaker: Jiaqi Dong

14:00 P2.1096 On the penetration of heavy impurities in the JET ELMy H-mode plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1096.pdf On the penetration of heavy impurities in the JET ELMy H-mode plasmas M. Valisa1, L. Carraro1 F. J. Casson2, J Citrin3, L. Frassinetti4, F. Koechl2, M.Romanelli2 M. E. Puiatti1, I. Coffey5, E Delabie6, C. Giroud2, A. Loarte7, S. Menmuir2, M. O’Mullane8, M. Sertoli2 and JET contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 2 Consorzio RFX, Padova, Italy, CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK, 3 4 FOM Inst. Differ NL, KTH, Royal Institute of Technology, Sweden 5 6 Queen’s University, Belfast, UK, ORNL Oak Ridge US 7 ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France 8 Department of Physics SUPA, University of Strathclyde, Glasgow, G4 ONG, UK E-mail contact of main author: valisa@igi.cnr.it This paper reports the main outcomes of the recent modeling activities in which the way the penetration of medium and high Z impurities into the plasma core of JET evolves with ELM frequency and heating power has been investigated. The motivation was to assess and to pro- vide physics basis for the ELM-control requirements in ITER. Modeling has focused on the simulation of experiments in which traces of Ne have been puffed in ELMy H-mode plasmas with medium (12 MW) and high (32 MW) NBI power in- jection and in which the ELM frequency was varied by controlling the main gas fueling. The main experimental evidences investigated by means of the simulation are the inverse proportionality between the concentration of any impurities and the ELM frequency, and the ELM-resolved time evolution of the Ne density at the edge as provided by charge exchange measurements [1]. In addition, the effect of increasing heating power has been studied: as the heating power is increased, the edge kinetic profiles change in the direction of reducing the neoclassical inward velocity of impurities and therefore in the direction of the situation ex- pected in ITER, where heavy impurities should be repelled at the H mode barrier by a favora- ble combination of density and ion temperature profiles. Full predictive modeling includes simulations by means of JETTO-SANCO with three impu- rities (Be, Ne, W) and integrated JETTO-SANCO-Edge2D with two impurities (Ne, W), both available in the JINTRAC suite of codes [2]. Turbulent transport in the core is simulated by means of QualiKiz [3] or GLF23 [4]. In simple cases the BgB model multiplied by a suitable factor has been used. While waiting for the in- put from physics based models such as JOREK [5], for the ELM description we have assumed a heuristic model with either ad hoc enhancements of heat and particle diffusivities in the bar- rier region or an ad hoc burst of the outward radial velocity. In this way the impact of convec- tive versus diffusive transport during an ELM event has also been investigated. Analogously, transport in the barrier region outside the ELM event is also described heuristically imposing neoclassical transport and an ad hoc turbulent transport multiplier. [1] Valisa M et al Proc. 44th EPS Conf.2017 http://ocs.ciemat.es/EPS2017PAP/pdf/P4.174.pdf [2] Romanelli M et al Plasma Fusion Res. 9, 3403023 [3] Bourdelle C et al Phys Pl. 14 112501(2017) [4] Waltz RE & Miller RL Phys Plasmas 6 4265 1999 [5] Hujsmans GTA & Czarny _Nucl .Fus 47 659 (2007) __ ____________________ *See the author list of “X. Litaudon et al. Nucl. Fusion 2017 57 102001”

Speaker: Marco Valisa

14:00 P2.1097 Impact of nonuniform zonal flow on the resistive-drift eigenmode near adiabatic state

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1097.pdf Impact of nonuniform zonal flow on the resistive-drift eigenmode near adiabatic state C.-B. Kim1 , C.-Y. An1 , B. Min1 1 Soongsil University, Seoul, Korea The profile of the eigenmode of the resistive-drift plasma with large growth rate is studied with a sinusoidally forced zonal flow V . A generalized vorticy ψ, which is the difference be- tween the electron density and the vorticity, is found to be advected by the gradients of the density and the zonal vorticity. The phase difference δ between the electric potential and ψ is positive for the linearly growing mode. δ is found to be larger for larger zonal-flow amplitude whereas the growth is larger for smaller zonal-flow. Eigenmode is found to be localized with the width of less than 10ρs around the peak of V in the direction of the electron diamagnetic drift. Eigenmode is almost vanishing where V is fastest and parallel to the ion-diamagnetc drift. Extension to the turbulence with a spontaneous zonal flow and its implications to the formation of the transport barrier will be presented at the conference.

Speaker: Chang-Bae Kim

14:00 P2.1098 Reflectometry at Wendelstein 7-X: Initial results from the first island divertor campaign

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1098.pdf Reflectometry at Wendelstein 7-X: Initial results from the first island divertor campaign T Windisch1 , D Carralero2 , T Estrada2 , A Krämer-Flecken3 , GM Weir1 1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 2 Centro de Investigationes, Medioambientales y Technologicas (CIEMAT), Madrid, Spain 3 Institut für Energie- und Klimaforschung, Forschungszentrum Jülich, Germany The different reflectometry diagnostic systems at W7-X are versatile tools for investigating the coherence and poloidal propagation of density fluctuations. Doppler reflectometry systems with fixed tilt angles θ = 18 ◦ in V-band (o−mode) and W-band (x−mode) are used to derive radial electric field Er in a broad density range ne = 0.75 . . . 14 · 1019 m−3 . A poloidal correlation reflectometry (PCR) system in K/Ka -band (o−mode) operates in an radially overlapping region with the W -band Doppler system and allows for cross-calibration of the necessary assumptions in the derivation of Er . With a novel Doppler phased array antenna (W-band) the tilt angle can be modified without movable parts. This allows to measure the fluctuation spectrum in a broad wavenumber range k⊥ ≤ 15 cm−1 . The radial accessible range extends across the separatrix to the scrape-off layer (SOL) region. In contrast to the first operation phase with a limiter con- figuration [1, 2], the SOL is dominated by a m/n = 5/5 island chain which intersects with the divertor tiles. The paper introduces the capabilities of the individual reflectometry systems and presents initial results from the first W7-X island divertor campaign. Special attention is paid to the 5/5 island in the SOL where strong modifications of fluctuations characteristics and Er are typically observed. References [1] T Windisch et al. Plasma Phys. Control. Fusion 59 105002 (2017) [2] A Krämer-Flecken et al. Nucl. Fusion 57 066023 (2017)

Speaker: Thomas Windisch

14:00 P2.1099 Implementation and tests of Multiple species collision operator in Gyrokinetic code GS2

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1099.pdf Implementation and tests of Multiple species collision operator in Gyrokinetic code GS2 A. Mauriya1 , M. Barnes3 , M. F. F. Nave1,2 and F. Parra3 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, P1049-001 Lisbon, Portugal 2 Associação do Instituto Superior Técnico para a Investigação e Desenvolvimento, P1049-003, Lisbon, Portugal 3 Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford, United Kingdom Abstract It is essential to study collisional effects in tokamak plasmas, because it may alter the momentum redistribution of impurities and main ions. Thus it is required to have a robust and an accurate collision operator to treat cross-species collisions. Since collision frequency has Z 4 dependence where Z is the charge, it is essential to consider the impurities. However, Their densities are significantly less than main ion’ density. Fully linearised gyroaveraged Fokker-Plank collision operator has been implemented in Gyrokinetic code GS2. Previous collision operator was gyroaveraged, had pitch angle scattering, diffusion operator and a modeled field particle operator which conserved the particles, momentum, and energy sat- isfied the Boltzmann’s H theorem [1]. It was self-collision operator and had finite Larmor radius effects included in it. It was implicit in time and met all these properties precisely in the code. Newly implemented collision operator is the extension of previous collision oper- ator which accounts for cross-species collisions and satisfies the conservation of particles, momentum, and energy. It also increases the total entropy in time which is an outcome of Boltzmann’s H theorem. Sugama’s collision operator [2] has been adopted to include inter-species collisions in GS2. Sugama’s field particles operator is modified to retain the exact numerical conservation properties. Recursive Sherman Morrison numerical scheme is implemented to invert the matrix obtained to treat collision operator implicitly. It has been verified that it satisfies the conservation properties and H Theorem in the GS2. Effects of impurities along with the main ions has been tested for cyclone base case. References [1] M. Barnes, I. G. Abel, W. Dorland, D. R. Ernst, G. W. Hammett, P. Ricci, B. N. Rogers, A. A. Schekochihin, and T. Tatsuno. [2] H. Sugama, T.-H. Watanabe, and M. Nunami. Linearized model collision operators for multiple ion species plasmas and gyrokinetic entropy balance equations. Physics of Plasmas, 16(11):112503, 2009.

Speaker: Adwiteey Mauriya

14:00 P2.1100 Absolute versus convective instabilities in subcritical tokamak plasmas.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1100.pdf Absolute versus convective instabilities in subcritical tokamak plasmas. Ben F. McMillan1 , Chris C. T. Pringle2 , Bogdan Teaca2 1 Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry, United Kingdom 2 Applied Mathematics Research Centre, Coventry University, Coventry, CV1 5FB, United Kingdom In tokamak plasmas, sheared flows perpendicular to the driving temperature gradients can strongly stabilize linear modes. While the system is linearly stable, regimes with persistent nonlinear turbulence may develop, i.e. the system is subcritical. A perturbation with small but finite amplitude may be sufficient to push the plasma into a regime where nonlinear effects are dominant and thus allow sustained turbulence. The resulting excitation of the system spreads through the system and can progressively destabilise larger and larger regions of the device. Interestingly, for sufficiently large values of shear flow, the excition propagates only in one direction, and the turbulence is transient when viewed at a fixed spatial location. The system is thus only convectively unstable, and in a bounded physical tokamak, the plasma will eventually return to a quiscent state. This suggests a strong role for nonlocality in the system, and provides a mechanism for trigerring of the plasma edge by core turbulence, even if the edge region is locally quiescent. We numerically explore these issues using a standard tokamak testcase, the CYCLONE benchmark, by scanning the size of the background flow shear. The relationship between this phenomena is examined in light of propagating phenomena found in the edge of chaos, and the the avalanche-like bursts found in earlier work.

Speaker: Ben Fynney McMillan

14:00 P2.1101 2-D filament dynamics in high and low shear flows in the edge of the RFX-mod tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1101.pdf 2-D filament dynamics in high and low shear flows in the edge of the RFX-mod tokamak G. Grenfell, M. Spolaore, M. Agostini, L. Carraro, R. Cavazzana, L. Cordaro, G. De Masi, P. Franz, L. Marrelli, E. Martines, B. Momo, M. E. Puiatti, P. Scarin, S. Spagnolo, N. Vianello, B. Zaniol, M. Zuin and the RFX-mod Team Consorzio RFX, 35127, Padova, Italy The edge and Scrape-Off-Layer (SOL) transport is dominated by filaments [1]. They can carry turbulent energy from the edge to the SOL, impacting the local SOL fluctuation and en- hancing the interaction with plasma-facing components. In addition, they can affect the SOL decay width, by increasing the cross-field transport, which can be a critical issue for future fusion reactors [2]. On the other hand, filaments can be strongly modified by the background shear flow, as well as modify it [3]. In this work, we study the filaments dynamic in differ- ent background shear flows using a set of 2-D electrostatic and magnetic sensors array in the plasma edge of the RFX-mod device operated as a tokamak. In addition, first wall poloidally symmetric electrostatic sensors. Through advanced statistical techniques, we detect filaments in different scales and track them from the edge to the SOL, in a 2-D floating potential map. Filaments relevant parameters are computed in the proper plasma frame (in contrast to the labo- ratory frame) and compared for different scenarios, including ohmic L-mode to H-mode ELMy and ELM-free, the latter induced by edge electrode biasing technique [4]. Their measured fea- tures in the different scenarios are compared and discussed in the framework of theoretical and simulation predictions [3]. In L-mode, their radial velocity and size at near SOL region, close to separatrix, are typically vr ≈ 2 km/s, δr ≈ 10 mm and δθ ≈ 15 mm, so their convection time (δr2 /(vr δθ ) ≈ 4 µs) is shorter than the shear time (B/dEr /dr ≈ 100 µs). In contrast, during the ELM-free H-mode, the shear time is ≈ 2 µs, so only smaller and/or faster filaments survive. Whereas, in the ELMs phase, the relaxation of the transport barrier allows bigger and/or slower structures to endure the background flow shear. Finally, the role of the sheath connection for the three scenarios is addressed, highlighting the potential structure tilt angle and ellipticity as function of the radius and the measurement of the local parallel density current. References [1] D. A. D’Ippolito et al. Phys. Plasmas 18.6 (2011): 060501 [2] J. Horacek et al. Plasma Phys. Control. 58.7 (2016): 074005 [3] Myra, J. R., et al. Nucl. Fusion 53.7 (2013): 073013 [4] M. Spolaore et al. Nucl. Fusion 57.11 (2017): 116039.

Speaker: Gustavo Guedes Grenfell

14:00 P2.1102 Dependence of the Core Radial Electric Field on Ion and Electron Temperature in W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1102.pdf Dependence of the Core Radial Electric Field on Ion and Electron Temperature in W7-X N. Pablant1, A. Langenberg2, A. Alonso4, C.D. Beidler2, S. Bozhenkov2, K.J. Brunner2, D.A. Gates1, A. Dinklage2, G. Fuchert2, J. Geiger2, M. Hirsch2, U. Hoefel2, J. Knauer2, J. Kring5, M. Landreman7, S. Lazerson1, H. Massberg2, O. Marchuck3, E. Pasch2, A. Pavone2, S. Satake6, J. Svensson2, P. Traverso5, Y. Turkin2, G. Weir2, F. Warmer2, R.C. Wolf2, D. Zhang2, and the W7-X Team 1Princeton Plasma Physics Laboratory, Princeton, NJ, USA 2 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 3 Forschungszentrum Jülich, Jülich, Germany 4 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain 5 Auburn University, Auburn, AL, USA 6 National Institute for Fusion Science, Toki, Japan 7University of Maryland, College Park, MD, USA The dependence of the core radial electric field (Er) on the ion and electron temperatures in the Wendelstein 7-X stellarator is investigated. The core radial electric field plays an important role in stellarator plasmas, and is expected to have a strong effect on both the particle and heat fluxes. Because the neoclassical particle fluxes in a stellarator are not intrinsically ambipolar, the Er is strongly tied to the ion and electron temperature and density profiles. In W7-X a large positive radial electric field is expected in cases in where Te >> Ti, while a smaller negative electric field is expected when the temperatures are close to equal (Ti ~ Te). This dependence of Er on the temperature ratio is investigated experimentally in W7- X, and compared to expectations from neoclassical theory. Determination of the Er profile is made possible by utilizing the X-Ray Imaging Crystal Spectrometer (XICS). This diagnostic is able to measure perpendicular plasma flow (u⟂), which is closely related to the radial electric field through the radial force balance. Experimentally inferred Er profiles are then compared with predictions from the neoclassical code SFINCS, which are based on measured temperature and density calculations from the Thomson Scattering, XICS and Interferometer diagnostics. Finally the evolution of the Er profile during high performance plasmas with pellet injection is investigated. These discharges demonstrate a clear dynamic change in the Er profiles commensurate with the increase in density and equilibration of the ion and electron temperatures. Comparisons between measured and predicted values of Er are used to better understand the validity of neoclassical calculations during the dynamic phases of these plasmas.

Speaker: Novimir Antoniuk Pablant

14:00 P2.1103 Simulations of divertor plasma turbulence driven by the current-convective instability under DIII-D-like detached conditions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1103.pdf Simulations of divertor plasma turbulence driven by the current-convective instability under DIII-D-like detached conditions A.A. Stepanenko1, H.Q. Wang2, S.I. Krasheninnikov1,3 1 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Kashirskoe highway 31, Russia 2 Oak Ridge Associated Universities, Oak Ridge, TN, USA 3 Department of Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA Investigation of the physical processes determining dynamics of detached divertor plasmas is highly important for successful prediction of the operational limits of the present-day and future tokamaks. Recent observations at ASDEX Upgrade (AUG) [1] have demonstrated the presence of the new state of detachment, called the fluctuating state, characterized by strong fluctuations of the divertor plasma parameters in the vicinity of the machine X-point, which vanish once the transition to complete detachment occurs. One of the possible mechanisms responsible for these oscillations, recently suggested in Ref. 2, can be related to the onset of the current-convective instability (CCI). The first numerical simulations of plasma dynamics, driven by the CCI, have demonstrated the plausibility of this mechanism for formation of saturated turbulence with temporal characteristics akin to those observed at AUG [3]. In this contribution, we employ the model of Ref. 3 to simulate divertor plasma turbulence, formed by the CCI under the DIII-D-like detached conditions, characterized by the asymmetry in detachment of the tokamak inner and outer divertors. We demonstrate the frequency and spatial spectra of turbulence formed by the instability, and their dependence on the plasma and magnetic field parameters, such as the field line connection length between the target and the X-point, the magnitude of the electron temperature at the inner strike point, the magnitude of the electron temperature drop along the magnetic field line inside the inner divertor leg, etc. The simulation results are also used to reconstruct the fluctuations of the parallel current and magnetic field at the target near the inner strike point. Where possible, the results of the simulations are compared with the available experimental data. References [1] D. Carralero, G. Birkenmeier, et al., Nucl. Fusion 54, 123005 (2014). [2] S.I. Krasheninnikov and A.I. Smolyakov, Phys. Plasmas 23, 092505 (2016). [3] A.A. Stepanenko, S.I. Krasheninnikov, Physics of Plasmas 25, 012305 (2018).

Speaker: Aleksandr Stepanenko

14:00 P2.1104 STRAHL modelling of impurity transport on Wendelstein 7-X during first divertor campaign

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1104.pdf STRAHL modelling of impurity transport on Wendelstein 7-X during first divertor campaign P. J. Traverso1, N. A. Pablant2, A. Langenberg3, R. Burhenn3, Th. Wegner3, D. Zhang3, B. Buttenschön3, B. Geiger3, D. A. Maurer1, J. Kring1, J. Schmitt1, and the W7-X Team 1 Auburn University, Auburn, AL, USA 2 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 3 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany In the first divertor operational phase (OP 1.2A) of Wendelstein 7-X, impurity transport experiments were performed with non-recycling materials via laser blow-off injection (LBO) [1]. The x-ray imaging spectrometer systems, HR-XIS [2,3] and XICS [4], were used to measure He-like spectra from the injected impurities in steady-state Helium discharges at various input ECRH heating powers and plasma densities. For these particular experiments the spatial and temporal emissivities from the mid-Z materials of either Titanium or Iron were measured, allowing for the estimation of the diffusion and convective velocity parameters for the respective measured charge state [5]. Utilizing the 1D transport code STRAHL [6], the spatial and temporal evolution of each impurity ionization charge state is modelled for assumed anomalous diffusion and convective velocity profiles. To match the experimentally measured emissivities, a chi-squared minimization is done on the experimental data by varying the input anomalous diffusion and convective velocity parameters for STRAHL. In addition a Gaussian process regression (GPR) [7] is used to improve and to better propagate the uncertainty estimates from the input electron temperature and density profiles in STRAHL to the modelled output diffusion and convective velocity parameters. [1] Th. Wegner et. al. HTPD conference San Diego (2018) [2] A. Langenberg, J. Svensson, H. Thomsen et al. Fusion Sci. Technol. 69 560-567 (2016) [3] G. Bertschinger, W. Biel, H. Jaegers, and O. Marchuk, Rev. Sci. Instrum. 75 3727 (2004) [4] N.A. Pablant, M. Bitter, R. Burhenn et al. 41st EPS conference on Plasma Physics Berlin (2014) [5] A. Langenberg, N.A. Pablant, O. Marchuk et al. Nucl. Fusion 57 086013 (2017) [6] R. Dux et al. IPP report 10/30 (2006) [7] M. A. Chilenski et al., Nucl. Fusion, 55, 2, 023012 (2015)

Speaker: Peter Traverso

14:00 P2.1105 Experimental charaterization of a quasi-coherent turbulence structure in the edge plasmas in W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1105.pdf Experimental charaterization of a quasi-coherent turbulence structure in the edge plasmas in W7-X X. Han1 , A. Krämer-Flecken1 , T. Windisch2 , S. Liu1 , Y. Liang1 , M. Rack1 , P. Drews1 , J. Cosfeld1 , Y. Gao1 , G. Fuchert2 , J. Geiger2 , O. Grulke2 , and the W7-X team 1 Institute für Energie-und Klimaforschung - Plasmaphysik, Forschungszentrum Jülich, 52425 Jülich, Germany 2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany A quasi-coherent turbulence structure (QC mode) in a frequency range of 10 kHz to 25 kHz has been studied by measuring the electron density fluctuation via a hopping Poloidal Corre- lation Reflectometer (PCR) [1, 2] in W7-X. It is observed in the standard and narrow mirror configurations, and absence in the high-iota configuration, which implies a certain dependence of the QC mode on the edge rotational transform. The QC-mode appears in the edge region accompanied by a steep electron density gradient inside the last-closed flux surface (LCFS). Its initial typical frequency of 25 kHz decreases to 10 kHz when the probing position moves toward the core. By calculating the cross correlation spectrum within each of the two antennae combination, the poloidal wavenumber of the QC mode is estimated to be kθ ≈ −0.21cm−1 propagating in the electron diamagnetic drift direction. The turbulence rotation velocity in this standard configuration is vturb ≈ 8.4km/s in the laboratory frame, which is consistent with the result from the slope of the cross-phase spectrum. With the edge electron temperature and the magnetic field in the edge region, the gyroradius at the sound speed of the QC-mode is calcu- lated to be ρs ≈ 0.207, and kθ ρs ≈ 0.145. This is qualitatively demonstrates that the QC-mode is in the range expected for drift- waves. Evidence shows that the existence of the QC-mode might be influenced by the edge radiation level, also the turbulence in the low frequency range ( f < 10kHz) is suppressed when the QC-mode exists. Acknowledgment This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union’s Horizon 2020 research and innovation pro- gramme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References [1] A. Krämer-Flecken et al, Nucl. Fusion 57, 066023 (2017) [2] T. Windisch et al, Plasma Phys. Control. Fusion 59, 105002 (2017)

Speaker: Xiang Han

14:00 P2.1106 Phase contrast imaging of turbulent density fluctuations in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1106.pdf Phase contrast imaging of turbulent density fluctuations in Wendelstein 7-X A. von Stechow1 , L.-G. Böttger1,2 , E. Edlund3 , Z. Huang4 , M. Porkolab4 , O. Grulke1,2 and the Wendelstein 7-X team 1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 2 Technical University of Denmark, Kgs. Lyngby, Denmark 3 SUNY Cortland, Cortland, USA 4 MIT PSFC, Cambridge, USA The Wendelstein 7-X stellarator (W7-X) is optimized to reduce neoclassical transport. Thus, turbulent transport is expected to play a significant role in the regulation of particle and heat fluxes. Numerical simulations in the full W7-X magnetic field geometry indicate a range of in- stabilities from electron (trapped electron and electron temperature gradient modes, TEM and ETG) to ion scales (ion temperature gradient modes, ITG) that can contribute to turbulent trans- port. Their growth rates at different radii are sensitive to the local gradients in plasma parameters (electron and ion temperature, density), collisionality, ion mass as well as the specific (exter- nally imposed) magnetic configuration. Full flux surface simulations also show a localization of fluctuations both toroidally and poloidally, contrary to the toroidally symmetrical outboard localization observed in Tokamaks. W7-X has recently completed its second operation phase, the first in full divertor geometry. Throughout the campaign, a wide range of electron cyclotron heating and fueling scenarios have been tested, including pellet injection and possible divertor detachment in a range of dif- ferent magnetic configurations. Of specific interest to turbulence characterization are matched discharges across different magnetic configurations. TEMs have been shown analytically to be suppressed in quasiisodynamic configurations (which W7-X can come close to), while ITG sim- ulations show increased activity at high elongation. Turbulence diagnostics at W7-X include re- flectometers, correlation ECE systems and the recently completed phase contrast imaging (PCI) system that measures poloidally resolved electron density fluctuations along a sight line through the plasma center. The project is a collaboration between the MIT PSFC and IPP. This contribution aims to identify characteristic features of density fluctuations in W7-X across its wide range of operating scenarios in both frequency and poloidal k-space, taking advantage of the 32 poloidal measurement channels that cover a large wavenumber range from 0.5-23 cm−1 . In particular, the existence and modification of density gradient driven TEMs and ion temperature gradient driven ITGs under changes to both the magnetic configuration and plasma profiles will be investigated.

Speaker: Adrian von Stechow

14:00 P2.1107 A comparison of measurements from radial and poloidal correlation ECE diagnostics on Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1107.pdf A comparison of measurements from radial and poloidal correlation ECE diagnostics on Wendelstein 7-X G.M. Weir1 , T. Windisch1 , M. Hirsch1 , A. Card1 , O. Grulke1 , H.-J. Hartfuss1 , U. Hoefel1 , J.H.E. Proll2 , T. Schroeder1 , J. Smoniewski3 , T. Klinger1 and the W7-X Team1 1 Max-Planck Institute for Plasma Physics, Greifswald, Germany 2 Eindhoven University of Technology, Eindhoven, The Netherlands 3 HSX Plasma Laboratory, University of Wisconsin-Madison, Madison, WI. USA The stellarator Wendelstein 7-X (W7-X) is designed to produce an approximately quasi- omnigeneous magnetic configuration that is optimized to have low neoclassical transport under steady state conditions relevant for a fusion reactor [1]. Electron temperature (Te ) fluctuations driven by drift wave turbulence are below the sensitivity of a single Electron Cyclotron Emis- sion (ECE) diagnostic, but they can be measured by correlating the signal between two inde- pendent ECE measurements [2]. A two-sightline poloidal correlation ECE (CECE) diagnostic has been developed and installed on W7-X that operates through spatial decorrelation of the electron cyclotron emission. The poloidal CECE diagnostic is sensitive to long wavelength Te fluctuations that are relevant for the study of Ion Temperature Gradient and Trapped Electron Mode turbulence. Similarly, the ZOOM device [3] that is installed on W7-X functions as a ra- dial CECE diagnostic through spectral decorrelation of the electron cyclotron emission. Over a 1s long plasma discharge, both radiometers are sensitive to Te fluctuations of less than 0.3%. The poloidal CECE has 8 fixed-frequency channels per sightline covering 10 cm on the high- field side of the magnetic axis, while the radial CECE has 16 variable-frequency channels over 6 cm that can be shifted across the plasma minor radius. These correlation radiometers have been used to measure the magnitude of Te fluctuations as well as the radial correlation length in plasma with electron cyclotron resonant heating. The ECE radiation spectrum is measured to be asymmetric across the magnetic axis of W7-X, and relativistically downshifted emission affects measurements on the low-field side of the magnetic axis. In this contribution, Te fluctuation measurements from the two radiometers will be presented and compared to gyrokinetic calcu- lations of Trapped Electron Mode turbulence in W7-X, and the impact of relativistic downshift on Te fluctuation measurements will be discussed. References [1] T. Klinger et al. Plasma Phys. Control. Fusion 59 014018 (2017). [2] C. Watts, H.J. Hartfuss, and M. Häse, Rev. Sci. Instrum. 75 3177 (2004). [3] Ch. Fuchs and H.J. Hartfuss, Rev. Sci. Instrum. 72 383 (2001).

Speaker: Gavin McCabe Weir

14:00 P2.1108 First results of core and edge plasma instability simulations at Globus-M

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1108.pdf First results of core and edge plasma instability simulations at Globus-M V.V. Solokha1, G.S. Kurskiev2, V.V. Bulanin3, A.V. Petrov2, A.Yu. Yashin2, S.Yu. Tolstyakov1, E.E. Mukhin1, V.K. Gusev1, Yu.V. Petrov1, N.V. Sakharov1, V.B. Minaev1, V.A. Tokarev1, N.A. Khromov1, M.I. Patrov1, N.N. Bakharev1, A.D. Sladkomedova1, A.Yu. Telnova1, P.B. Shchegolev1, E.O. Kiselev1 1 Ioffe Institute, Saint-Petersburg, Russia 2 Peter the Great Polytechnical University, Saint-Petersburg, Russia This work represents the first results of core and edge plasma instability simulations at Globus-M. Globus-M was a compact spherical tokamak with typical parameters are as follows: ɛ = 0.24 m / 0.36 m = 0.66, BT= 0.4-0.5 T, Ip = 0.18-0.25 MA, = (1-8) •1019 m-3, PNBI ≤ 1 MW. The H-mode is a common operational regime at moderate densities both in OH and NBI heated discharges. The first part of the report is devoted to simulations of the edge plasma peeling-ballooning mode instability using BOUT++ code [1]. Simulations were performed in linear approximation with restricted high-n toroidal modes (n < 16). Instability structure with the mode toroidal number n=12 was found to be the most unstable. This statement is in agreement with DBS measurements [2] and could be an evidence of ballooning branch destabilization. The second part is concentrated on core and edge plasma microinstability simulations using GKW code [3] in linear approximation. The edge plasma of Globus-M tokamak has typical toroidal beta higher than 3% and found to be kinetic-ballooning unstable. It motivates to investigate edge plasma stability using EPED-like model [4]. The core plasma in Globus-M is characterized by the moderate collisionality, high normalized Larmor radius and beta. These conditions are unusual for plasma of present day tokamaks. Linear gyrokinetic simulations were performed for identifying electromagnetic or electrostatic origin of dominating microturbulence that may explain existing Globus-M BτE scaling. References [1] B.D. Dudson et al. Computer Physics Communications 180 (2009) [2] V.V. Bulanin et al Technical Physics Letters 37 (2011) [3] A.G. Peeters et al. Computer Physics Communications 180 (2009) [4] P.B. Snyder et al. Nucl. Fusion 51 (2011)

Speaker: Vladimir Vladimirovich Solokha

14:00 P2.1109 Experimental investigation of turbulence in the Wendelstein 7-X stellarator with phase contrast imaging

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1109.pdf Experimental Investigation of Turbulence in the Wendelstein 7-X Stellarator with Phase Contrast Imaging L.-G. Böttger1,2 , O. Grulke1,2 , A. von Stechow1 , J. Alcusón1 , P. Xanthopoulos1 , E. Edlund3 , Z. Huang4 , M. Porkolab4 and the W7-X Team1 1 Max-Planck Institute for Plasma Physics, Greifswald, Germany 2 Technical University of Denmark, Kgs. Lyngby, Denmark 3 SUNY Cortland, Cortland, USA 4 MIT Plasma Science and Fusion Center, Cambridge, MA, USA In the recent experimental campaign OP 1.2a of Wendelstein 7-X (W7-X), currently the world’s largest optimized stellarator with a plasma volume of 30 m3 , high-performance discharges with a maximum stored energy of 1MJ were achieved. As one of the optimization criteria of W7-X was the reduction of neoclassical transport, turbulent transport mechanisms are believed to play a much more important role now. Numerical gyrokinetic simulations suggest a significantly dif- ferent appearance of turbulence in stellarators than in tokamaks. However, a systematic experi- mental investigation of turbulence in optimized stellarators has not been done, yet. To address this topic the phase contrast imaging (PCI) diagnostic was installed at W7-X and successfully put into operation in the recent experimental campaign OP 1.2a. The PCI diagnostic allows for non-invasive spatiotemporal measurements of electron density fluctuations. It is sensitive to ion temperature gradient turbulence and trapped electron modes – in the hot core up to the colder edge. Gyrokinetic simulations have shown that density fluctuations depend strongly on geometrical effects. One particular aspect is the influence of the elongation or the correlated inverse safety factor iota on the development of ion temperature driven turbulence [1]. In W7-X different mag- netic field configurations were used which allow for an experimental comparison. Since W7-X uses as main heating source electron cyclotron resonance heating, the ion-temperature is influ- enced by the coupling between ions and electrons which depends on the plasma density. With this in mind ion temperature gradient driven turbulence is expected to be dependent on the ex- perimentally accessible plasma density. In order to gain insights in the underlying mechanisms, the experimental analysis is accompanied by comparisons to data obtained from GENE. This gyrokinetic code allows for investigating numerically ion temperature gradient driven instabili- ties based on actual experimental configurations and profiles. References [1] P. Xanthopoulos et al., Phys. Rev. Lett. 113, 155001 (2014)

Speaker: Lukas-Georg Böttger

14:00 P2.1110 Understanding and controlling the ITER baseline plasma response

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1110.pdf Understanding and controlling the ITER baseline plasma response J.M. Hanson1 , N. C. Logan2 , T. C. Luce3 , F. Turco1 , G. A. Navratil1 , and E. J. Strait3 1 Columbia University, New York, NY 10027-6900, USA. 2 Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451, USA. 3 General Atomics, San Diego, California 92186-5608, USA. DIII-D experiments with low-torque ITER baseline demonstration discharges show that the plasma’s magnetic response to applied low-frequency, non-axisymmetric field perturbations is correlated with the onset of plasma disruptions. Measurements of the low-frequency RWM growth rate DIII-D ITER baseline demonstration discharges plasma response have previously been Measurements Measurements -0.4 Ideal MHD (DCON) Ideal MHD (DCON) linked to proximity to the resistive wall 0.925 < ℓi < 0.975 -0.6 3.0 < q 95 < 3.4 γτw mode (RWM) stability boundary [1]. -0.8 However, understanding the response in 1.5 < βN < 1.8 -1.0 3.0 < q95 < 3.4 (a) (b) plasma regimes, such as the ITER base- 0.7 0.8 0.9 1.0 1.0 1.5 2.0 2.5 ℓi βN line, that are well below the RWM pres- sure limit and subject to resistive tear- Figure 1: Comparisons of the (a) `i and (b) βN dependen- ing instabilities remains an active area cies of the normalized RWM growth rate γτw inferred from of research. The growth rate γ of the plasma response measurements (squares) with predictions driven, stable RWM is calculated from of the linearized, ideal MHD, resistive wall dispersion re- lation (diamonds). n = 1 response measurements using a single mode model [1], normalized to the wall eddy current decay timescale τw = 2.5 ms, and compared with the linearized, ideal MHD, resistive wall dispersion relation [2]. Figure 1 shows that the dependencies of γτw on the plasma normalized internal inductance `i and normalized beta βN are consistent with ideal MHD predictions. The βN dependence was exploited to demon- strate closed-loop control of the response via feedback modulation of the neutral beam injected power in the low-torque baseline regime. Using heating power to directly control a plasma stability-related parameter, such as the response, may help facilitate the optimization of fusion output while simultaneously avoiding stability limits. This work was supported in part by the US Department of Energy under DE-FG02-04ER54761, DE-AC02-09CH11466, and DE-FC02-04ER54698. References [1] H. Reimerdes et al., Physical Review Letters 93, 135002 (2004). [2] S. W. Haney and J. P. Freidberg, Physics of Fluids B: Plasma Physics 1, 1637 (1989).

Speaker: Jeremy M. Hanson

14:00 P2.2001 Controlled Laser Wakefield Electron Acceleration Driven by Elliptically Shaped Femtosecond High Power Laser Beams

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2001.pdf Controlled Laser Wakefield Electron Acceleration Driven by Elliptically Shaped Femtosecond High Power Laser Beams B. S. Rao1, H. T. Kim1,2, J. H. Shin1, K. H. Oh1, J. H. Jeon1, and C. H. Nam1,3 1 Center for Relativistic Laser Science (CoReLS), Institute for Basic Science, Korea 2 Advanced Photonics Research Institute, Gwangju Institute of Science and Technology (GIST), Korea 3 Department of Physics and Photon Science, GIST, Korea We report on controlled laser wakefield acceleration driven by elliptically shaped ultra-short high power laser beam. For the experimental study 25-fs 150-TW laser pulses have been spatially shaped by passing them through an ellipse shaped hard aperture with ellipticity, e =1.5 (ratio of major-to-minor axis diameter) before focusing in a He gas jet target using a spherical mirror. The shaped laser beam produced elliptical focal spot and the orientation of the major radius of the focus w.r.t. to the laser polarization axis could be varied by rotating the hard aperture. The laser wakefield acceleration with the shaped laser beam produced more stable and higher energy electron beams than those without shaping, as shown in Fig. 1. We have demonstrated that the electron beam charge and beam profile could be controlled by simply rotating the orientation angle of the aperture. The observations clearly indicate that the shape of the laser focal spot affects the injection process as well as acceleration dynamics in the plasma bubble, which can be exploited to tailor electron beams for many applications. Fig. 1. Images of spectrally dispersed electron beam produced from 2.3mm long helium gas jet plasma at constant plasma density in series of consecutive shots (a) when the elliptically shaped laser beam with major axis along laser polarization was used, and (b) when a laser beam without shaping was applied with appropriately reduced energy to maintain similar laser strength parameter.

Speaker: Bobbili Sanyasi Rao

14:00 P2.2002 Detailed measurements of the time structure of a self-modulated proton bunch exiting a plasma in AWAKE

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2002.pdf Detailed measurements of the time structure of a self-modulated proton bunch exiting a plasma in AWAKE P. Muggli, for the AWAKE Collaboration Max Planck Institute for Physics, Munich, Germany and CERN, Geneva, Switzerland The self-modulation of a long (>1 cm), relativistic, charged particle bunch in a dense plasma (>1014 cm−3 ) offers the possibility to resonantly drive wakefields to large amplitude (>1 GV/m) [1]. A witness electron (or positron) bunch can then be externally injected in the wakefields and accelerated. Because long proton bunches can carry large amounts of energy, the acceleration process can be sustained over long distances and the accelerated bunch can reach very large energies along a single plasma [2]. The witness bunch must be deterministi- cally placed in the accelerating and focusing phase of the wakefields. The wakefields can be seeded, for example, by an ionization front created by a short laser pulse traveling together with the proton bunch, as in the AWAKE experiment [3]. The wakefields used for acceleration are those after the growth of the seeded modulation process has saturated, some meters into the plasma and approximately one rms bunch length behind the seed point, where they peak. It is es- sential to understand the variation of the phase of the wakefields with respect to the seed points and with respect to variations of the parameters of the incoming proton bunch. The phase of the wakefields is very difficult to measure. However, there is a one-to-one correspondence between the wakefields and the bunch structure driving the wakefields. We can therefore measure the time structure of the bunch exiting a first plasma, which is used as self-modulator of the drive bunch. We show that, despite variations in the bunch input parameters, the time structure of the bunch to be used to drive wakefields in a second plasma, the accelerator itself, is reproducible to within a fraction of a wakefields period (∼8 ps). Since a witness electron bunch would be generated on a photo-cathode or in a laser wakefield accelerator by a replica of the ionizing pulse used for seeding, these measurements show that the witness bunch can in principle be deterministically placed at the proper phase of the wakefields in the accelerator plasma, even when many periods behind the seed point (e.g., ∼100 at a plasma density of 7×1014 cm−3 and with σz =12 cm). References [1] N. Kumar et al., Phys. Rev. Lett. 104, 255003 (2010) [2] A. Caldwell et al., Phys. Plasmas 18, 103101 (2011) [3] P. Muggli et al., Plasma Physics and Controlled Fusion, 60(1) 014046 (2017)

Speaker: Patric Muggli

14:00 P2.2003 A new scenario design for enhanced magnetic vortex ion acceleration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2003.pdf A new scenario design for enhanced magnetic vortex ion acceleration W. L. Zhang1 , B. Qiao2 , X. F. Shen2 , L. O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 Center for Applied Physics and Technology, HEDPS, Peking University, Beijing, China Laser-based ion accelerator has been considered to be a compact and cost-saving alternative to the conventional radio-frequency accelerators. While relentless experiments have been per- formed based on various models, the generation of high-flux and well-defined monoenergetic ion beams is still facing formidable challenges. Magnetic vortex acceleration[1] is a model pro- posed to generate collimated energetic ion beams by the time-varying magnetic dipole vortex at the rear of near-critical/underdense plasmas. However, both the numerical studies[1, 2] and experiments[3, 4] indicate that the resultant ion beams from such acceleration have low particle number with an exponentially decaying spectrum. In our study, the magnetic vortex acceleration driven by intense laser pulses is theoretically analyzed, which reveals that both the accelerating field and the ion energy in such acceleration have strong scalings with the laser and plasma parameters. But this effective acceleration will break down and the ion beam quality will as well be degraded along with the depletion of electron density in the interaction channel[5]. A new ion acceleration scenario, in which the intense laser directly interacts with a cone-like dense hollow tube, is proposed to achieve a sustained high density plasma and realize an enhanced and stable magnetic vortex structure at the rear side. Such magnetic fields induce a strong and stable electric field which produces high- flux and more energetic ion beam with a well-defined monoenergetic spectrum. This new and robust acceleration scenario is verified by 3-dimensional particle-in-cell (PIC) simulations. References [1] S. S. Bulanov, et al., Phys. Plasmas, 17, 043105 (2010). [2] T. Nakamura, et al., Phys. Rev. Lett. 105, 135002 (2010). [3] L. Willingale, et al., Phys. Rev. Lett. 96, 245002 (2006). [4] Y. Fukuda, et al., Phys. Rev. Lett. 103, 165002 (2009). [5] W. L. Zhang, et al., Phys. Plasmas, 24, 093108 (2017).

Speaker: Wenlong Zhang

14:00 P2.2004 Advanced study of laser triggered proton acceleration from low-density target

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2004.pdf Advanced study of laser triggered proton acceleration from low-density target A.V.Brantov1,2, P. A. Ksenofontov1, V. Yu. Bychenkov1,2 1 P. N. Lebedev Physics Institute (LPI), Russian Academy of Science, Moscow, Russia 2 Center of Fundamental and Applied Research, VNIIA, ROSATOM, Moscow, Russia Here we discuss the recently proposed concept of proton synchronized acceleration by slow light (SASL) from low-density targets by powerful laser pulses [Brantov et.al, Phys.Rev.Lett. 116, 085004 (2016)]. In SASL regime ions are accelerated by laser ponderomotive electric sheath, which propagates in a plasma with the same velocity as a laser pulse. Monotonic increase of the pulse group velocity during propagation of light makes ions possible to move in sync with accelerating electrostatic sheath. We extend the general idea of SASL concepts on the low-density targets available in practice and present the 3D PIC simulations of proton acceleration from low-density carbon nanotube target with hydrocarbon contaminated edges or bulk target volume. It has been shown that maximum proton energy is rather independent on the hydrogen density inside low-density target unless it does not exceed 10% of carbon density. The pre-pulse effect on proton acceleration efficiency has been also studied by modeling the targets by given pre-plasmas or by using picosecond wings for incident laser pulse. We have demonstrated as well, that using of circular polarization allows laser pulse to enter SASL regime at considerably lower intensity, as compared to earlier reported value at the level of about 1021 W/cm2. The discussion of advances of circularly polarized laser pulses for ion acceleration is addressed in details. This work was supported by the Russian Science Foundation (grant 17-12-01283).

Speaker: Andrey Brantov

14:00 P2.2005 LWFA Electron Bunch Spatial Reconstruction through CTR Imaging

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2005.pdf LPA Electron Bunch Spatial Reconstruction Through CTR Imaging M. LaBerge1,2, O. Zarini2, A. Hannasch1,2, R. Zgadzaj1,2, J. Couperus2, A. Köhler2, A. Debus2, A. Lumpkin3, A. Irman2, M. C. Downer1,2 1 University of Texas at Austin, Austin, USA 2 Helmholtz-Zentrum Dresden Rossendorf, Rossendorf, Deutschland 3 Fermi National Accelerator Laboratory, Batavia, USA Due to their tiny accelerating cavities, laser-plasma accelerators (LPAs) can produce extremely low-emittance e-beams, but to date the smallest transverse LPA e-beam sizes have been characterized only indirectly inside the LPA by betatron x-ray spectroscopy. Here we report observations of visible coherent transition radiation (CTR) imaged from a foil placed immediately (<1mm) outside a ~300 MeV, 300 pC bubble-regime LPA. We use a double foil: the first reflects the drive laser pulse; the front edge of the second foil (0.5-1mm downstream) rejects emission from the first foil, while its back surface emits CTR from transmitted LPA e-bunches. We observe radially polarized annular distributions with a strong central minimum at many different wavelengths, which allows us to characterize the beam shape. The size and radial distribution of the CTR images, which we observe in conjunction with CTR and electron spectra, vary significantly and reproducibly as we translate the double foil over a ~1mm range along the e-beam propagation axis. We will present CTR data in conjunction with an e-beam 3D reconstruction model.

Speaker: Maxwell LaBerge

14:00 P2.2006 Enhanced betatron-radiation energy from plasma self-injection using two collinear laser pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2006.pdf Enhanced betatron-radiation energy using two collinear laser pulses Z. Chitgar, J. Böker, M. Büscher, P. Gibbon, A. Lehrach Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany A new self-injection scheme is proposed for the laser wakefield accelerator in the nonlinear (bubble) regime using a pair of matched, copropagating laser pulses which yields a pC electron bunch. By tuning their relative delay and intensity, the subsequent betatron radiation energy can be considerably (3 fold) enhanced compared to the single pulse scheme for the same total energy. A new condition for the optimal bubble size is derived and verified by particle-in-cell simulations, further demonstrating the advantages of the double-pulse scheme for self-injection. Bubble regime of electron acceleration [1] is the highly non-linear regime of laser wake field accel- eration, evolving a plasma wave following the laser pulse. The condition is that laser pulse intensity is high enough to create a cavity, free from back- ground plasma electrons, and that the pulse duration is the order of plasma wavelength. Some electrons get trapped in the cavity, are accelerated and start to wiggle around the laser pulse propagation axis. This results in betatron radiation. In this work we propose an improved, double-pulse scheme in the bubble regime with significantly improved electron beam and radiation properties, c.f . figure 1. Based on the simulation results, the optimum condition is Figure 1: 2D snapshot of the electron num- that the energy of first pulse to be high enough to ber density distribution at t=1500 fs, with the target being irradiated by a laser of a0 = 3.85, meet the bubble condition. Allocating the remain- for a) the double pulse scheme with the op- ing energy to the second pulse and positioning it at timum condition, b) the single pulse scheme. the rear of first bubble leads to increased electron The total pulse energy is 2 J and is the same beam energy and higher betatron energy yield than in both cases. The double pulse scheme yields for a single-pulse with the same total energy [2]. an improved electron beam. References [1] A. Pukhov and J. Meyer-ter Vehn, Applied Physics B - Lasers and Optics, 74 (4-5):355-361, 2002. [2] Z. Chitgar et al., Enhanced betatron-radiation energy from plasma self-injection using two collinear laser pulses, (submitted for publication, 2018).

Speaker: Zahra Chitgar

14:00 P2.2007 Enhancement of Target Normal Sheath proton acceleration through multi- pulse laser-target interaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2007.pdf Enhancement of Target Normal Sheath proton acceleration through multi- pulse laser-target interaction J.Ferri1, E. Siminos2, T. Fülöp1 1 Department of Physics, Chalmers University of Technology, SE-41296 Göteborg, Sweden 2 Department of Physics, University of Gothenburg, SE-41296 Göteborg, Sweden Target normal sheath acceleration (TNSA) has been the most commonly used accelerating method for protons in laser-matter interaction for the past decades, thanks to a relatively simple experimental implementation. However, even with the continuous increase of the available laser power, the poor scaling of the maximum energy of the accelerated protons with the laser energy still constitutes a major drawback for many interesting applications. Recent experiments proposed to split the energy of the main laser pulse in two pulses, incident on the target within a short time delay, showing that an increase of the proton energy and number was possible [1]. Further investigations with careful control of the time delay between the pulses suggested however that the conditions for such an increase could be quite specific [2]. In this paper, we describe a slightly modified TNSA scheme, consisting of splitting the main laser pulse in two pulses of equal energy incident on the target simultaneously, but with different angles of incidence. Based on 2-dimensional simulations with the EPOCH Particle-In-Cell code, we show that the multi-pulse interaction that arises leads to an increase of the peak value of the electric fields and substantial modification of the hot electron generation process, which leads to a higher hot-electron temperature. This in turn leads to a strong enhancement of the proton energy (from 8.5 to 14 MeV with a 45 degree angle and 0.8 J laser) and proton number, and this conclusion remains valid for a large range of incident angle for the laser pulses. References [1] K. Markey et al, Physical Review Letters 105, 195002 (2010) [2] J. Ferri et al, arXiv:1802.06999 (2018)

Speaker: Julien Ferri

14:00 P2.2008 Enhancing laser ion acceleration by using advanced target designs

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2008.pdf Enhancing laser ion acceleration by using advanced target designs S. S. Bulanov1, J. Park1, Q. Ji1, S. Steinke1, T. Schenkel1, C. B. Schroeder1, E. Esarey1, W. P. Leemans1 1 Lawrence Berkeley National Laboratory, Berkeley, USA The ion acceleration is considered one of the main applications of the high power laser systems that are being projected, built, and already operational around the world. The laser driven ion acceleration is not only attractive from the point of view of potential applications of high energy ion beams, but also from the point of view of investigations of fundamental aspects of laser-matter interaction and advanced concepts of particle acceleration. It is well understood that different mechanisms of the laser ion acceleration have its own limitations, connected with either some fundamental properties of the laser-matter interaction, developments of instabilities, or a finite parameter range, where they can operate. Some of these limitations can be compensated by pulse tailoring or advanced target design. In this paper we present several concepts of composite targets with the aim of enhancing the properties of Radiation Pressure Acceleration and Magnetic Vortex Acceleration mechanisms.

Speaker: Stepan Bulanov

14:00 P2.2010 Geant4 Monte Carlo simulations for the optimization of spatial dose distributions of clinical relevance with laser-driven proton beams.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2010.pdf Geant4 Monte Carlo simulations for the optimization of spatial dose distributions of clinical relevance with laser-driven proton beams. F. Romano 1,2, F. Schillaci 3, G. Milluzzo 2,4, J. Pipek 2, A. G. Amico 2, G. Cuttone 2, G. Korn 3 , G. Larosa 2, R. Leanza 2,5, D. Margarone 3, G. Petringa 2,5, A. Russo 2, V. Scuderi 2,3, G. A. P. Cirrone 2. 1 National Physical Laboratory, CMES - Medical Radiation Science, Teddington, UK 2 INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy 3 Institute of Physics ASCR, v.v.i (FZU), ELI-Beamlines project, 182 21 Prague, CZ 4 School of Mathematics and Physics, Queen’s University Belfast, Belfast, UK 5 Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania, Italy The main purpose of this work is to quantitatively study the possibility of delivering dose distributions of clinical relevance with laser-driven proton beams in order to investigate the feasibility of these beams for multidisciplinary applications, included the medical ones. In particular, a Monte Carlo application has been developed with the toolkit Geant4 aiming to simulate the ELIMED (MEDical and multidisciplinary application at ELI- Beamlines) beam line which is being installed at ELI-Beamlines in Prague (CZ) [1]. The beam line will be used to perform irradiations for multidisciplinary studies, aiming to demonstrate the possible use of optically accelerated beams for therapeutic purposes [2]. The ELIMED application, developed with the Geant4 code, accurately simulates each single element of the beam line, designed to collect the accelerated beams and to select them in energy, and it has been validated with reference transport codes [3]. The final aim of this work is to try to quantitatively answer the question if such kind of beam lines, and specifically the systems developed for ELIMED in Prague, will be actually able to transport beams not only for multidisciplinary applications but also for delivering dose patterns of clinical relevance, which are worth to explore possible medical applications. On this regard, an original approach for actively shaping, through the magnetic energy selection system, depth dose distributions to achieve clinical spread out Bragg peaks will be also presented. [1] J. Pipek et al., J. Instrum. 12 (03) (2017) C03027 [2] F. Romano et al., Nucl Instrum Methods Phys Res Sect A (2016); 829:153-158 [3] G. Milluzzo et al., Nucl Instrum Methods Phys Res Sect A (in press)

Speaker: Francesco Romano

14:00 P2.2011 Generation of low energy LWFA electron beams suitable for WDM diagnostics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2011.pdf Generation of low energy electron beams suitable for WDM diagnostics M. Šmíd1, K. Boháček2, U. Chaulagain2, Y. Gu2, M. Kozlová2 and K. Falk1 1 Helmholtzz-Zentrum Dresden-Rossendorf, Dresden, Germany 2 Institute of Physics, ELI-Beamlines project, Czech Academy of Sciences, Prague, Czech Republic One of possible approaches to the diagnostics of Warm Dense Matter is to use a low energy ( ~<1 MeV) electron beam as a backlighter. From the nature of WDM experiment it is suitable to have this beam produced by laser and to have sufcient brightness to obtain a single shot diagnostic image for, e.g., electron difraction, which could show the ionic structure of the matter. Downramp gradient laser wakefeld acceleration has the capabilities to produce such beams. This approach relies on focusing the fs laser onto a decreasing density gradient in a gas jet. We have investigated this approach on the PALS Ti:Saph laser system (Prague) with diferent types of gas nozzles producing various density profles and gradients. We present the transition between standard and downramp acceleration regimes and compare this to the result of relevant PIC simulations. We propose a scheme of magnetic beampath aimed at improving the beam quality, especially decreasing the beam bandwidth and divergence.

Speaker: Michal Smid

14:00 P2.2012 Investigating the influence of the picosecond leading pulse edge on ultra-intense laser heating of solids with 3D PIC simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2012.pdf Investigating the influence of the picosecond leading pulse edge on ultra-intense laser heating of solids with 3D PIC simulations T. Kluge1, M. Garten1,2, A. Huebl1,2, R. Widera1, I. Goethel1, H. Burau1,2, T. Cowan1, U. Schramm1, M. Bussmann1 1 Helmholtz-Zentrum Dresden – Rossendorf, Germany 2 Technische Universität Dresden, Germany With recent improvements in plasma mirror techniques [1] achieving a reproducibly high laser contrast, systematic studies of short-pulse, ultra-high intensity laser-ion acceleration from thin foil targets (~10nm) become experimentally available [2][3]. A deeper understanding of the influence of the pre-pulse phase and ps leading pulse edge of the drive laser could lead to better control and reproducibility of ion cut-off energies which are crucial for using laser-accelerated ions in medical applications. Plasma dynamics accompanying the acceleration are highly non-linear and require precise knowledge about the influence of both ab-initio electromagnetic and atomic evolution of the plasma. Consequently, modelling these processes requires a fully kinetic high resolution treatment and extensive 2D surveys, while comparisons to experiments have shown that a quantitative prediction of proton cut-off energies and evolution of plasma instabilities demand a full 3D approach [4]. We present first results from a 3D PIC simulation campaign, modelling ultra-intense (a0 = 20- 60) laser interaction with up to micrometer thick foils covering the pico-second time span prior to the arrival of the main pulse. Simulations have been performed at the Piz Daint supercomputer at Figure 1: CSCS, Switzerland, using the fully-relativistic 3D3V open-source Longitudinal current density component of particle-in-cell code PIConGPU [5] developed at HZDR. a 300nm Cu target with organic contamination layer. [1] H. B. Shaw, S. Steinke, J. Van Tilborg and W. P. Leemans, Phys. Plasmas 23 (2016) [2] P. L. Poole, L. Obst, G. Cochran et al., New J. Phys. 20 13019 (2018) [3] A. Higginson, R. J. Gray, M. King, et al., Nat. Commun. 9 724 (2018) [4] P. Hilz, T. M. Ostermayr, A. Huebl et al., Nat. Commun. 9 423 (2018) [5] M. Bussmann, A. Huebl, R. Widera et al., Proceedings of SC13, Denver CO USA, Nov 17-21th (2013)

Speaker: Thomas Kluge

14:00 P2.2013 Investigations on the seeded self-modulation in a long proton bunch using coherent transition radiation measurements

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2013.pdf Investigations on the seeded self-modulation in a long proton bunch using coherent transition radiation measurements F. Braunmueller for the AWAKE collaboration Max Planck Institut for Physics Munich, Föhringer Ring 6, 80805 München, Germany AWAKE is a proof-of-principle experiment at CERN for testing proton-driven plasma wake- field acceleration over a 10 m laser-ionized plasma [1]. This novel acceleration method promises strong acceleration (∼GeV/m) of electrons over long distances with a single drive bunch and a single, long plasma [2]. It is planned to accelerate a witness electron bunch in the plasma wake- field of a long proton bunch that is transformed into a train of microbunches by Seeded Self- Modulation (SSM) [3]. We present frequency measurements of the modulated proton bunch exiting the plasma, as well as investigations on the physics of SSM using these measurements. The self-modulated proton bunch is expected to be modulated at the plasma frequency, which can be varied in the range of 90-300 GHz, and the modulation is expected to have a duration of 300-700 ps. A waveguide-integrated heterodyne diagnostic for coherent transition radiation (CTR) was designed to precisely measure the modulation frequency of the modulated proton pulse through the frequency of its CTR-pulse [4]. In this contribution, we first describe the mea- surement principle and the experimental set-up of AWAKE, and of the diagnostic in particular. Moreover, we show how the frequency-measurement of this diagnostic can be used for investi- gating the nature of the SSM. We confirm that the modulation frequency indeed coincides with the expected plasma frequency, as predicted by theory, by measuring modulation frequency as a function of vapour density, that is ionized by a short laser pulse. In a second measurement, the modulation process in the presence of a linear density gradient is analysed. Using both the pre- cise frequency-measurement of the heterodyne CTR-diagnostic and a streak-camera capturing the Optical Transition Radiation (OTR) emitted by the protons, the modulated bunch exiting the plasma can be studied in detail. From this, one can draw conclusions about the SSM-interaction inside the plasma, and inside the changing plasma density. Using these measurements, we will try to obtain a better understanding of important processes governing the SSM, which is impor- tant for optimizing and analysing the upcoming electron acceleration experiments. References [1] P. Muggli et al., Plasma Physics and Controlled Fusion 60(1), 014046 (2017) [2] A. Caldwell et al., Phys. Plasmas 18, 103101 (2011) [3] N. Kumar, et al., Physical Review Letters 104, 255003 (2010). [4] F. Braunmueller et al., Nuclear Instruments and Methods A, DOI 10.1016/j.nima.2018.02.080 (2018)

Speaker: Falk Braunmueller

14:00 P2.2014 Ion acceleration with on-shot monitored ultra-high contrast using the DRACO Petawatt laser facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2014.pdf Ion acceleration with on-shot monitored ultra-high contrast using the DRACO Petawatt laser facility T. Ziegler1,2, C. Bernert1,2, F.-E. Brack1,2, S. Kraft1, F. Kroll1, J. Metzkes-Ng1, L. Obst1,2, M. Rehwald1,2, H.-P. Schlenvoigt1, U. Schramm1,2, K. Zeil1 1 Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany 2 TU Dresden, Dresden, Germany Laser-driven ion acceleration promises to provide a compact solution for demanding applications like particle therapy, proton radiography or inertial confinement research. Controlling the beam parameters to achieve these goals is currently pushing the frontier of laser driven particle accelerators. We present an overview of recent achievements at the high power ultra-short pulse laser source DRACO at the HZDR in Dresden (Germany). The laser system was recently upgraded by new front end components and an additional Petawatt (PW) amplifier stage, finally providing high contrast pulses of 30J within 30fs at 1 Hz pulse repetition rate. The performance of the plasma acceleration is strongly dependent on the complex pre- plasma formation process at the target front surface which is determined by the temporal intensity contrast. Plasma mirror setups have proven to be a valuable tool to significantly improve the temporal contrast by reducing pre-pulse intensity and steepening the rising edge of the main laser pulse. Re-collimating single plasma mirror devices have therefore been implemented into the Draco laser beam lines, enabling investigation of laser proton acceleration and proton energy scaling within the TNSA regime using ultra-thin foil targets. The results of the simultaneously measured proton emission energies in laser forward direction, laser backward direction and the temporal contrast, measured on a single-shot base by means of self-referenced spectral interferometry with extended time excursion (SRSI-ETE) at unprecedented dynamic and temporal range, will be presented.

Speaker: Tim Ziegler

14:00 P2.2015 Laser ion acceleration in an overdone plasma with relativistic non-Maxwellian electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2015.pdf Laser ion acceleration in an overdone plasma with relativistic non-Maxwellian electrons A. Kargarain Department of Physics and Institute for Plasma Research, Kharazmi University, Tehran, Iran The ion acceleration in a foil plasma irradiated by a high intensity laser has been studied by applying a relativistic electromagnetic Particle-In-Cell code. The considered plasma contains non- Maxwellian electrons. The presence of the initial non-Maxwellian electrons drastically affect the excited charge-separation electric field, ion velocity, and the ion expansion (see Fig. 1). Moreover, the results show that the presence of the initially non-Maxwellian electrons impress on the ion energy spectrum different from the initially Maxwellian distribution. Figure. 1: The ion density for plasma with initial Maxwellian (red plot) and non-Maxwellian (black plot) electron distribution at time τ = 120.

Speaker: Ameneh Kargarian

14:00 P2.2016 Laser ionized rubidium plasma column geometric effects on wakefields at AWAKE

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2016.pdf Laser Ionized Rubidium Plasma Column Geometric Effects on Wakefields at AWAKE J. T. Moody for the AWAKE Collaboration Max Planck Institute for Physics, Munich, Germany AWAKE is a proton driven plasma wakefield electron acceleration experiment at CERN [1]. In this experiment a proton bunch much longer than the plasma wavelength, i.e., σz >> λpe = c/fpe , undergoes seeded self-modulation through a plasma, resulting in a radially modulated proton bunch that effectively drives wakefields. The plasma column through which this process occurs is created by a laser field in the intermediate Keldysh/photoionization regime of rubidium va- por. The rubidium vapor’s density is controlled within <0.5% over its 10 m length, resulting in a plasma column of uniform density at its transverse center and sharply falling radial edges (σedge << λpe ) for the full length of the vapor. Resonances of two neutral rubidium valence elec- tronic transitions fall within the bandwidth of the ionizing laser pulse. These resonances create a region of dynamically saturated anomalous dispersion near the radial edge of the plasma col- umn where the ionizing laser field is strong but significant populations of unionized rubidium atoms exist. This dynamically dispersive region causes the ionizing laser pulse to propagate in an unusual way, changing the geometry of the radial plasma boundary. At AWAKE the opera- tional density range allows plasmas where λpe ∼ Rplasma , resulting in wakefields that can react with the radial plasma boundary. This effect is more pronounced at the lower limit of the density range and particularly if there is inexact spatial overlap between the ionizing laser pulse and the proton bunch through the rubidium vapor. In this presentation, we explore the determination of the plasma column and the effects that the column wall may have on wakefields driven by a self modulated proton bunch with and without perfectly symmetric cylindrical overlap. References [1] A. Caldwell et al., Phys. Plasmas 18, 103101 (2011)

Speaker: Joshua Timothy Moody

14:00 P2.2017 Laser-driven ion acceleration through controlled motion of electrons by standing waves

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2017.pdf Laser-driven ion acceleration through controlled motion of electrons by standing waves J. Magnusson1 , F. Mackenroth1,2 , M. Marklund1 , A. Gonoskov1,3,4 1 Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden 2 Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany 3 Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia 4 Lobachevsky State University of Nizhni Novgorod, Nizhny Novgorod 603950, Russia The generation of high-energy ions via the interaction of high-intensity femtosecond laser pulses with various targets provides a promising basis for a new kind of compact ion sources, with numerous applications in medicine, industry and science. Over the last couple of decades, extensive theoretical and experimental studies have made it possible to identify several favour- able interaction regimes and has led to the development of related acceleration schemes. Many of these schemes, however, inherently lack well-controlled acceleration stages and thus provide only limited opportunities for a controlled generation of a well-collimated, high-charge beam of ions and with a given energy. In an effort to alleviate this problem, it was recently proposed that the ions can be dragged by an electron bunch trapped in a controllably moving potential well formed by laser radia- tion. Such standing-wave acceleration (SWA) can be achieved through reflection of a chirped laser pulse from a mirror, which has been formulated as the concept of chirped-standing-wave acceleration (CSWA) [1]. In this contribution we further analyze general feasibility aspects of the SWA approach and demonstrate its reasonable robustness against field structure imperfections, such as those caused by misalignment, elliptical polarization and limited contrast. Using this we also identify prospects and limitations of the CSWA concept [2]. References [1] F. Mackenroth, A. Gonoskov, and M. Marklund, Phys. Rev. Lett. 117, 104801 (2016). [2] J. Magnusson, F. Mackenroth, M. Marklund, and A. Gonoskov, arXiv:1801.06394.

Speaker: Joel Magnusson

14:00 P2.2020 Optimization of wakefield amplitude in the AWAKE experiment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2020.pdf Optimization of wakefield amplitude in the AWAKE experiment M. Moreira1,3 , J. Vieira1 , P. Muggli2,3 1 Instituto Superior Técnico, Lisbon, Portugal 2 Max-Planck Institute for Physics, Munich, Germany 3 CERN, Geneva, Switzerland AWAKE is a proton-driven plasma wakefield experiment [1] under way at CERN that in- tends to prove one of the concepts for a plasma-based accelerator. The long length of the proton bunches used in the experiment (∼6-12 cm) causes the bunch to undergo a self-modulation process [2], through which the initial bunch is self-consistently transformed into a train of mi- crobunches with lengths of the order of the plasma wavelength. This train can resonantly excite a wakefield in the plasma, and the objective of the experiment is to ultimately accelerate an externally injected electron bunch in this wakefield. Though plasma-based accelerator concepts promise acceleration gradients a few orders of magnitude larger than with conventional technology, in the case of AWAKE numerical simula- tions indicate that the amplitude of the wakefield tends to drop significantly after saturation of the self-modulation process, thus undermining the potential energy gain for injected electrons. This work will investigate the causes of this decline using both particle-in-cell simulations and linear wakefield theory. Two possible measures to sustain a high wakefield amplitude after satu- ration are also studied: the use of an anti-proton driver, since electrons have been known to drive wakefields more effectively than their positively-charged counterparts [3], and the introduction of a plasma density step [4]. Simulation results will be presented. References [1] P. Muggli et al., Plasma Physics and Controlled Fusion, 60(1) 014046 (2017) [2] N. Kumar, A. Pukhov and K. Lotov, Phys. Rev. Lett. 104, 255003 (2010) [3] S. Lee, T. Katsouleas, R. G. Hemker, E. S. Dodd, and W. B. Mori, Phys. Rev. E 64, 045501 (2001) [4] A. Caldwell, and K. V. Lotov, Phys. Plasmas 18, 103101 (2011)

Speaker: Mariana Moreira

14:00 P2.2021 Particle-in-cell simulations of filamentation in laser wakefields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2021.pdf Particle-in-cell simulations of filamentation in laser wakefields Eva Los1,2 , Raoul Trines2 , Luis O. Silva3 , Robert Bingham2,4 1 University of Manchester, Manchester, M13 9PL, UK 2 Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom 3 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 4 SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, United Kingdom The laser filamentation instability is observed in plasma wakefields with sub-critical den- sities, and in high density inertial fusion plasmas. This leads to non-uniform acceleration or compression respectively. Here, we present simulation results on laser filamentation in plasma wakefields. Two-dimensional simulations have been carried out using the particle-in-cell code Osiris. The filament intensity was found to increase exponentially before saturating. The max- imum amplitude to which the highest intensity filament grew for a specific set of parameters was also recorded, and plotted against a corresponding parameter value. Clear, positively cor- related linear trends were established between plasma density, transverse wavenumber k, laser pulse amplitude and maximum filament amplitude. Plasma density and maximum filament am- plitude also showed a positive correlation, which saturated above a certain plasma density. Pulse duration and interaction length did not affect either filament intensity or transverse k-value in a predictable manner. There was no discernible trend between pulse amplitude and filament width.

Speaker: Raoul Trines

14:00 P2.2022 Revisit of the optimal condition for radiation pressure acceleration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2022.pdf Revisit of the Optimal Condition for Radiation Pressure Acceleration X. F. Shen1 , B. Qiao1 , H. Zhang1,2 , S. Kar3 , C. T. Zhou1,2 , S. P. Zhu2 , M. Borghesi3 , X. T. He1,2 1 Center for Applied Physics and Technology, HEDPS, State Key Laboratory of Nuclear Physics and Technology, and School of Physics, Peking University, Beijing, 100871, China 2 Institute of Applied Physics and Computational Mathematics, Beijing 100094, China 3 Center for Plasma Physics, School of Mathematics and Physics, Queenaŕs ˛ University Belfast, Belfast BT7 1NN, United Kingdom Laser-driven ion acceleration has the potential to be compact sources of energetic ions, which can be applied for proton radiography, tumor therapy, inertial fusion energy and warm dense matter [1]. Several acceleration mechanisms have been proposed, in which radiation pressure acceleration (RPA) promises higher scaling and laser-ion conversion efficiency and monoener- 1 nc getic ion beams with the optimal condition lo = π ne a0 λ , with lo , nc , ne , a0 and λ the target thickness, the critical density, the electron density, the normalized laser amplitude and the laser wavelength [2]. However, experiments and simulations show that the pulse can punch through the target during the acceleration even under the optimal condition as various instabilities set in and grow nonlinearly with time and other parameters during the laser plasma interactions, which will terminate the acceleration early and reduce the conversion efficiency and beam qual- ity [1, 3]. Through theoretical and simulation studies, we show that the optimal condition of RPA is related to the pulse duration, the ellipticity of the elliptically polarized laser pulse and the scale length of the preplasma. With the modified optimal condition, the acceleration can maintain stable until the pulse ends and the quality of ion beams is improved. Meanwhile, the conversion efficiency can be increased two times. References [1] A. Macchi, M. Borghesi, and M. Passoni, Rev. Mod. Phys. 85, 751 (2013). [2] B. Qiao, M. Zepf, M. Borghesi, and M. Geissler, Phys. Rev. Lett. 102, 145002 (2009). [3] X. F. Shen, B. Qiao, H. Zhang, S. Kar, C. T. Zhou, H. X. Chang, M. Borghesi and X. T. He, Phys. Rev. Lett. 118, 204802 (2017).

Speaker: Xiaofei Shen

14:00 P2.2023 Self-injection of multiple electron microbunches into a beam-driven plasma bubble

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2023.pdf Self-injection of multiple electron microbunches into a beam-driven plasma bubble Zs. Lécz1 , A. Andreev1,2 , A. Seryi3 , I. Konoplev3 1 ELI-ALPS, ELI-HU Nonprofit Ltd., Szeged, Hungary 2 Max-Born Institute, Berlin, Germany 3 John Adams Institute for Accelerator Science, Oxford, UK The self-injection of electrons into non-linear plasma wave is governed by the rate of change of its phase velocity. In uniform plasma the phase velocity is difficult to control in the case of laser-driven plasma wakefields, where the spatial and spectral evolution of the laser pulse causes small fluctuations in the size of the cavity [1, 2]. The expansion of the bubble can be triggered by using a non-uniform plasma with sharp density transition [3] or with continuously decreasing density [4]. In our work we study an extreme version of the scheme presented in Ref. [4], where continuous injection was observed. In our case higher beam charges and longer density down-ramps are considered leading to bunched injection of electrons. As an example, Fig. 1 shows the injected micro-bunches near the end of the density ramp. The plasma density profile in our simulations is de- scribed by the following function: 1 + cos(π x/Ln ) ne = n0 ρ + (1 − ρ ) , (1) 2 where ρ = n1 /n0 < 1, with n0 and n1 being the density before and after the ramp, respectively, and x goes from 0 to Ln . Although the density profile is smooth the injection is not continuous. The reasons of this will be discussed Figure 1: Density distribution of elec- in the presentation and a semi-analytical model will be trons from a simulation where the driv- presented, which gives an estimation for the periodicity ing beam charge is 2.4 nC and the den- and size of the injected bunches. sity down-ramp is Ln = 1.5 cm long. References [1] M. R. Islam et al., New Journal of Phys. 17, 093033 (2015) [2] S. Y. Kalmykov et al., Plasma Physics and Controlled Fusion 58, 034006 (2016) [3] H. Suk et al., Phys Rev Lett 86, 1011 (2001) [4] A. Martinez de la Ossa et al., Physical Review Accelerators and Beams 20, 091301 (2017)

Speaker: Zsolt Lécz

14:00 P2.2024 Simulation of the chromatic focusing phenomenon in laser-driven proton acceleration experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2024.pdf Simulation of the chromatic focusing phenomenon in laser-driven proton acceleration experiments M. Bardon1, L. Perrachon1, J. G. Moreau1, F. Lubrano1, O. Cessenat1 1 CEA-CESTA, Le Barp 33114, France A new scheme of the proton post-acceleration and collimation was proposed recently [1] by researchers from the Queen’s University of Belfast (QUB). A solenoid, connected at one end to a thin metallic target, and, at the other end, to the ground, is used to flow the discharge current induced by the charge ejection from the target. This system generates an ElectroMagnetic Pulse (EMP) around the proton beam produced by the Target Normal Sheath Acceleration (TNSA) mechanism. A Lorentz force is then applied to the proton beam. Finally, this device can simultaneously: accelerate, focus, and energy select the proton beam generated by the interaction of a short-pulse laser with a TNSA target. An experiment [1] was conducted, at low laser pulse energy, on the ARCTURUS laser, at Heinrich-Heine University in Dusseldorf (Germany). The results of the experiment were compared with a numerical modeling conducted this year at the CEA-CESTA (France). These simulations have allowed, for the first time, reproducing the physical phenomenon (called “chromatic focusing phenomenon”) in this new compact laser-driven accelerator concept. Figure 1 presents an example of the simulation conducted with the code SOPHIE developed at the CEA. SOPHIE is a 3D, Particle-In-Cell (PIC), Finite Difference in Time Domain (FDTD) code that solves Maxwell’s equations for the fields and Vlasov’s equations for particles in a large volume and with arbitrary boundary conditions. It is a highly parallelized code perfectly adapted to run on the new TERA-1000 cluster of the CEA/DAM. In the example presented in Figure 1, the mesh is made up of 109 cells and 107 macro-particles have been used. The calculation is run on the TERA-1000 CEA/DAM cluster with 1024 processors. Propagation of the proton beam and the current pulse can be represented simultaneously. In this particular example, the simulation was initiated by the ejection of electrons and protons from the rear side of the target. Figure 1 represents the proton beam propagation, at the time t=200 ps, with a color bar corresponding to the proton kinetic energy and also the electric field magnitude along the coil. The proton focusing observed is in agreement with the experimental results. 8.7 mm t = 200 ps Figure 1: Chromatic focusing phenomenon reproduced by numerical simulation (SOPHIE code). These simulations allow us to optimize the ion ejection and acceleration structures. New optimized devices will be tested on LULI 2000 facility in March 2019. [1] “Guided post-acceleration of laser-driven ions by a miniature modular structure”, S. Kar et al., Nature Com. 10792 (2016)

Speaker: Matthieu Bardon

14:00 P2.2025 Staging helical coil modules to enhance post-acceleration of ions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2025.pdf Staging Helical Coil Modules to Enhance Post-Acceleration of Ions S. Ferguson1, D. Doria1, H. Ahmed1, M. Cerchez2, R. Prasad2, P. Hadjisolomou1, P. Martin1, T. Hodge1, O. Willi2, M. Borghesi1 and S. Kar1 1 School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK 2 Institut für Laser und Plasmaphysik, Heinrich Heine Universität, Düsseldorf D-40225, Germany All-optical approaches to ion acceleration are attracting a significant research effort internationally. While ion beams are readily generated using high intensity lasers via the target normal sheath acceleration (TNSA) process [1], there are limitations in the ion energies that can be achieved through this process depending on the laser intensity and the characteristics of the target. Methods for boosting ion energies by capturing and reaccelerating the particles have been proposed in the past, but experimental demonstrations have been limited. A recent concept demonstrated post-acceleration of TNSA ions employing a miniature helical coil, which harnesses the extremely high electric fields of the electromagnetic pulse launched into the coil from the laser irradiated target [2]. Additional benefits of such approach is its ability to guide and post-accelerate a narrow energy band of protons within the broad spectrum produced by the TNSA process. Recent experiments have demonstrated pencil beams up to 50 MeV through deployment of the scheme at a Petawatt-class laser [3]. In a proof-of-principle experiment, we investigated the possibility of staging helical coil modules using the TITAN Laser at the Lawrence Livermore National Laboratory in California. The experiment employed the dual beam laser configuration and a two-stage geometry, where each beam interacted with a separate helix target. This arrangement allowed the second helix’s effect on the proton beam produced by the first helix to be studied through varying the time delay between the two laser beams. Results from this experiment will be presented along with particle tracing simulations. [1] M. Borghesi, 2014, Laser-driven ion acceleration: State of the art and emerging mechanisms, Nuclear Instruments and Methods in Physics Research A [2] S. Kar et al, 2016, Guided post-acceleration of laser-driven ions by a miniature modular structure, Nature Communications [3] H. Hamad, S. Kar et al, to be submitted 2018, Quasi-monoenergetic pencil beam up to 50 MeV employing laser-driven helical coil

Speaker: Simon Ferguson

14:00 P2.2026 Transient electromagnetic fields for high energy-density beam tailoring driven by ps-laser pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2026.pdf Transient Electromagnetic Fields for High Energy-Density Beam Tailoring Driven by ps-Laser Pulses M. Ehret 1,2, J. Alpiñaniz 3, V. Bagnoud 4, M. Bailly-Grandvaux 1, C. Brabetz 4, E. d’Humières 1, Ph. Korneev 5, S. Malko 3, C. Matveevskii 5, A. Morace 6, L. Volpe 3, M. Roth 2, G. Schaumann 2, V.T. Tikhonchuk 1, and J.J. Santos 1 1 Université de Bordeaux, CNRS, CEA, CELIA (Centre Lasers Intenses et Applications), UMR 5107, Talence, France 2 Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany 3 Centro de Láseres Pulsados, Salamanca, Spain 4 GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany 5 National Research Nuclear University MEPhI, Moscow, Russian Federation 6 Institute of Laser Engineering, Osaka University, Osaka, Japan We present experimental studies of an open-geometry platform for energy selective tailoring of laser-accelerated particle beams, with reference to different target geometries and optimization prospects. The presented results are supported by theoretical analysis based on PIC simulations and modelling. In the all-optical principle, a high intensity ps- laser pulse drives electromagnetic (EM) target-discharge and subsequent propagation of strong transient EM-fields guided by the target geometry. A sub-mm coil-shaped part of the target rod creates lensing effects that arise due to magnetic- and electric-contributions, in particular we imaged energy-selective proton beam focusing over cm-scale distances by proton-deflectometry and we showed the clear evidence of a some Tesla strong magnetic field component based on its polarity. The experiment was carried out at the PHELIX/GSI laser facility, using 500 fs, 50 J laser pulses focused at 5·1018 W/cm2 into a flat-disc target conductively connected to a 50 µm- thick wire shaped as a coil of 500 µm diameter. The discharge time and spatial scales were captured by proton-deflectometry (Figure 1), revealing the propagation of transient EM- fields emanating from the laser-plasma interaction. The measured phase speed through the target rod is (0.95 ± 0.05) c. The discharges stream around the coil over ≈ 25 ps, producing efficient focusing of the protons passing inside the coil: 12 MeV-protons are collimated over distances of several cm. In Fig. 1, the emittance of 6 MeV protons shrinks to 30% of the initial value. Energy-selection for the focused particles is possible by tuning the delay between the laser pulse driving the coil and the one accelerating the proton beam. Analysis with transport- and field-simulations using the PAFIN code [DOI: 10.13140 / RG.2.1.3855.7847] assuming a dynamic EM-discharge pulse streaming along the target capture the discharge dynamics with amplitudes of tens of GV/m and tens of T. Detailed PIC simulations of the laser-target interaction and the successive propagation of the EM- waves streaming along the target and propagating in the free space around the target agree in field strength and point us to different electromagnetic effects difficult to separate: the propagation of fast electrons, EMP and neutralization wave. Figure 1: Experimental data in the top row, PAFIN simulation results in the bottom row.

Speaker: Michael Ehret

14:00 P2.2027 Alternative efficient methods of dense plasma acceleration to high velocities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2027.pdf Alternative efficient methods of dense plasma acceleration to high velocities S. Borodziuk1, K. Jach2, R. Swierczynski2, T. Pisarczyk1, T. Chodukowski1, Z. Kalinowska1, R. Dudzak3,4, J. Dostal3,4, M. Krus3,4, 1 Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland 2 Institute of Optoelectronics, Military University of Technology, Warsaw, Poland 3 Institute of Physics, Czech Academy of Sciences, 182 21 Prague, Czech Republic 3 Institute of Plasma Physics, Czech Academy of Sciences, 182 21 Prague, Czech Republic Abstract Numerical modelling of dense plasma acceleration processes was performed. In these investigations a scheme called “cavity pressure acceleration” (CPA) was applied, which allows driving propelling plasma objects in arbitrary direction in relation to the laser beam incident on a target and more efficient absorption of the laser pulse energy. Two different versions of these “non-classic” CPA schemes were taken into account: “backward acceleration” and “forward acceleration”. Those calculations complement the previously performed experiments on the PALS system, in which the results of acceleration of dense plasma objects (average speed obtained for 20 m PS and 10m Al targets was ~ 6x107 cm/s) were at the level of the top global results. Numerical calculations were made for two different laser wavelengths: = 1.315 m (iodine laser) and  = 0,248 m (KrF laser). For the “classic” i.e. ablative drive scheme, the advantage of using a short laser wavelength is obvious. Velocities obtained in this variant are two- three times higher than in the case of using a laser with several times longer wavelength. This also applies to other important parameters of the acceleration experiment, such as pressures generated and the amount of neutrons produced (when using appropriate targets). Completed numerical calculations, as well as the previous experiments on the PALS system, show that the use of non-classical drive schemes enables comparable, very good results to be obtained also with lasers of longer wavelength.

Speaker: Stefan Borodziuk

14:00 P2.2028 Collisionless shock acceleration of high-flux quasimonoenergetic proton beams driven by circularly polarized laser pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2028.pdf Collisionless shock acceleration of high-flux quasimonoenergetic proton beams driven by circularly polarized laser pulses H. Zhang1, B. F. Shen1, 2, 3, a), W. P. Wang1, S. H. Zhai1, S. S. Li1, X. M. Lu1, J. F. Li1, R. J. Xu1, X. L. Wang1, X. Y. Liang1, Y. X. Leng1, R. X. Li1, 3, a), and Z. Z. Xu1, 3 1 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China 2 Department of Physics, Shanghai Normal University, Shanghai 200234, China 3 Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China Laser-driven ion accelerators have the prospects of realizing compact and affordable ion sources for many exciting applications, many of which require ion beams with narrow energy spread as well as high flux. Here, using an 800-nm circularly polarized laser pulse interacting with an overdense plasma that is produced by a laser prepulse ionizing an initially ultrathin plastic foil, we experimentally demonstrate collisionless shock acceleration of quasimonoenergetic proton beams with peak energies up to 9 MeV and extremely high fluxes of 3×1012 protons/MeV/sr [1]. Two-dimensional particle-in-cell simulations reveal that collisionless shocks are efficiently launched by circularly polarized lasers in exploded plasmas, resulting in a narrow energy spectrum. Furthermore, this novel scheme predicts the generation of quasimonoenergetic proton beams with peak energies of approximately 150 MeV using current laser technology. These results represent a major step for developing high-flux, high-energy and monoenergetic ion sources for applications such as cancer therapy. Reference [1] H. Zhang, B. F. Shen,a) W. P. Wang, S. H. Zhai, S. S. Li, X. M. Lu, J. F. Li, R. J. Xu, X. L. Wang, X. Y. Liang, Y. X. Leng, R. X. Li,b) and Z. Z. Xu， Phys. Rev. Lett. 119, 164801 (2017).

Speaker: Hui Zhang

14:00 P2.2030 Machine learning controlled laser wakefield acceleration simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2030.pdf Machine learning controlled laser wakefield acceleration simulations B. Malaca1 , J. Vieira1 , R. Fonseca1,2 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal 2 DCTI/ISCTE-Instituto Universitário de Lisboa, 1649-026 Lisbon, Portugal One of the most promising technologies to form the next generation of compact particle accel- erators is plasma acceleration. Plasmas have the ability to sustain waves with electric fields that can be 3 orders of magnitude higher than those in radio frequency (RF) cavities. The ultimate goal of plasma-based acceleration is to produce relativistic, high quality elec- tron and positron bunches for scientific and societal applications. The recent progress has been tremendous but improving beam quality still remains as a grand-challenge in the field. The fundamental aspects and properties of these accelerators are accessible through simpli- fied analytical models, but the self-consistent dynamics of the laser in the plasma can only be captured by numerical simulations. Search for optimised parameters to improve beam quality can be based on systematic parameter scans. However, because numerical calculations can be very computationally intensive, it is important to investigate more efficient techniques to scan over the entire parameter range currently available. In this work, we propose a machine learning approach to optimize this search based on genetic algorithms. Recent experiments have employed genetic algorithm to control plasma based accelerators [1]. Here, instead, we will employ this technique to control the outputs and optimise plasma- based accelerators. We implemented a genetic algorithm in ZPIC, a fully relativistic particle- in-cell educational code[2]. The algorithm is fully automated: it creates an initial set of input parameters, launches several simulations in parallel, and ends automatically once given con- vergence criteria are reached. The algorithm can thus take full advantage of large-scale super- computers. We present results from both 1D and 2D simulations. In 1D, we focus on plasmas with non-uniform density and lasers with variable longitudinal envelope profiles. In 2D we also consider the role of distorted wave-fronts in the acceleration. We present optimisation studies of laser plasma accelerators, towards bunches with high quality in terms of efficiency and phase- space properties (e.g. energy spread, divergence). Our algorithm is general, and can be readily applied to any other class of optimisation problems in plasma physics. References [1] Z.-H. He, B. Hou, V.Levailly, J. Nees, K. Krushelnick and A. Thomas, Nature communications, 6 (2015) [2] https://github.com/zambzamb/zpic/

Speaker: Bernardo Farinha Malaca

14:00 P2.2031 On high-quality electron beam generated by breaking wake wave in near-critical density plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2031.pdf On high-quality electron beam generated by breaking wake wave in near-critical density plasmas P. Valenta1,2 , O. Klimo1,2 , S.V. Bulanov1,3 , G. Korn1 1 ELI-Beamlines, Institute of Physics, 182 21 Prague, Czech Republic 2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, 115 19 Prague, Czech Republic 3 Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology, Kizugawa, Kyoto 619-0215, Japan High quality and stable sub-relativistic electron sources are of great demand for various ap- plications in industry and material science [1, 2]. The electron sources in such regime have been previously produced by downscaling a laser-wakefield accelerator or using high-repetition rate laser-plasma accelerators [3, 4, 5]. Here we present a novel method based on the breaking of non-linear Langmuir waves driven by a short intense laser pulse in the near-critical density plasmas. We observe a formation of a thin layer of electrons that are expelled from the target at the plasma-vacuum interface. High quality of the electron bunch is provided using a steep density profile on the target rear side and properly timed breaking of the wake wave. The electron beam is quasi-monoenergetic with several MeV energy range and its divergence depends on the curvature of the plasma wave. Properties of the electron beam (divergence, energy distribution, number of electrons) can be controlled by adjusting the shape of the target density distribution and the parameters of the laser pulse driver. We demonstrate this effect numerically using multi-dimensional large-scale particle-in-cell simulations and provide analytical formulas that describe the properties of the electron bunch. References [1] G. Sciaini and R.J.D. Miller, Rep. Prog. Phys. 74 (2011) [2] Z.-H. He et al., Sci. Rep. 6 (2016) [3] B. Beaurepaire, A. Lifschitz and J. Faure, New Journal of Physics 16, 2 (2014) [4] D. Guenot et al., Nature Photonics 11 (2017) [5] D. Gustas et al., Phys. Rev. Accel. Beams 21, 1 (2018)

Speaker: Petr Valenta

14:00 P2.2032 Optical probing during an experiment on proton acceleration from a cryogenic hydrogen ribbon

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2032.pdf Optical probing during an experiment on proton acceleration from a cryogenic hydrogen ribbon F. Grepl1,2 , D. Margarone1 , H. Ahmed4 , A. Alejo4 , P. Bonnay5 , D.C. Carroll6 , D. Chatain5 , D. Doria4 , D. Garcia5 , A. Girard5 , L. Giuffrida2 , P. Jones6 , P. Lutoslawski1 , P. Martin4 , S. Michaux5 , B. Odlozilik1,2 , F. Schillaci2 , V. Scuderi3 , A. Velyhan2 , F. Viargues5 , D. Neely6 , G. Korn1 and M. Borghesi4 1 Institute of Physics ASCR, ELI Beamlines Project, Prague, Czech Republic 2 Czech Technical University in Prague, FNSPE, Prague, Czech Republic 3 Istituto Nazionale di Fisica Nucleare, LNS, Catania, Italy 4 Centre for Plasma Physics, School of Mathematics and Physics, Queen’s University Belfast, Belfast, United Kingdom 5 CEA INAC-SBT, Grenoble, France 6 Central Laser Facility, Rutherford Appleton Laboratory, Didcot, United Kingdom Multidisciplinary applications of laser-driven ion beams, especially medical ones, have strict requirements for ion beam parameters. Some of them can be achieved by using a specially tailored target. In particular, pure proton beams (without contaminants) can be produced from cryogenic solid-hydrogen targets which could be capable of both refreshable and debris free operation at high repetition rate making this target ideal for laser-based protontherapy. This contribution reports acceleration of protons from relatively thin (75 and 100 µm) solid- hydrogen ribbon employing the petawatt arm of the VULCAN laser at Rutherford Appleton Laboratory with emphasis given on optical probing of the unstable ribbon target. Firstly, optical probing was used for characterizing the ribbon itself, and the laser focus position with respect to the target front surface. Obtained data are directly correlated with the energy of forward accelerated ions measured with radiochromic films and Thomson parabola ion spectrometer. In addition, the electron density distributions of hydrogen plasma are presented after being retrieved from interferometry snapshots taken with various delays with respect to the arrival of the main laser pulse. Monoenergetic features observed in the energy spectra measured with Thomson parabola ion spectrometer and radiochromic films stack will be also presented and compared with supporting PIC simulations with aim to explain the features origin.

Speaker: Filip Grepl

14:00 P2.2033 OSIRIS EM-PIC performance tests on Intel KNL systems

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2033.pdf OSIRIS EM-PIC performance tests on Intel KNL systems R. A. Fonseca 1 ISCTE - Instituto Universitário de Lisboa, Lisboa, Portugal 2 IPFN - Instituto de Plasmas e Fusão Nuclear, Lisboa, Portugal Intel Knights Landing (KNL) systems present a new computing paradigm for large scale computations, currently (November 2017) occupying 3 slots of the top 10 HPC sites list (http://top500.org). These systems present a new challenge for physics codes, and in particular for electromagnetic particle-in-cell (EM-PIC) codes such as OSIRIS [1], requiring a continuous effort in adapting the algorithm to the new hardware and computing paradigms. In this work, we report on our efforts on the use of OSIRIS code on KNL systems for production runs, focusing on the code performance on 1D, 2D and 3D geometries, in single in double precision. We will discuss on the parallelization and vectorization strategies followed, the use of specialized hardware features, as well as the parallel scalability of the code on multiple KNL nodes. This work was partially supported by Fundação para a Ciência e Tecnologia (FCT), Portugal, through grant no. PTDC/FIS-PLA/2940/2014. References [1] R. A. Fonseca et al., Lecture Notes in Computer Science 2331, 342-351 (2002)

Speaker: Ricardo Azambuja Fonseca

14:00 P2.2034 Parametric studies using reduced 3d modeling on plasma scale lengths

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2034.pdf Parametric studies using reduced 3d modeling on plasma scale lengths A. Helm1 , J. Vieira1 , R.A. Fonseca1,2 , L.O. Silva1 , P. Muggli3 1 GoLP/IPFN Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 Instituto Universitário de Lisboa (ISCTE-IUL), Lisboa, Portugal 3 Max Planck Institute for Physics, Munich, Germany Current modeling for plasma-based accelerators is often performed with the help of particle in cell (PIC) codes. While accurate, these codes require following the smallest spatial/temporal scales, and as a result, are computationally expensive. Reduced models, such as the ponderomo- tive guiding center solver (PGC) [1, 2] overcome this limitation and provide speedups in order of ∼(λ0 /λ p )2 , where λ0 is the laser wavelength and λ p the plasma skin depth. The speed up is a result of a reduced description of the laser: instead of resolving the fast laser wavelength, PGC captures the evolution of the laser envelope instead. The PGC is thus ideal to explore the effects of ionization seeding for the AWAKE project [3, 4]. AWAKE relies on the self-modu- lation instability (SMI) to bunch an initially long proton bunch into bunchlets smaller than the plasma wavelength. An ionizing laser co-propagates with the laser, creating a sharp ionization front that seeds the SMI. These simulations are ideal for PGC, because the computational gains, is in excess of (λ0 /λ p )2 > 106 . .We performed parametric studies using the massively parallel, fully relativistic PIC code OSIRIS [5] for the self modulation instability (SMI) as part of the main mechanism for the AWAKE project. The influence of the neutral gas density on the SMI and the injected electrons is discussed. Furthermore, studies on different injection schemes in the plasma scale regime, such as downramp injection and ionization injection is discussed and compared with full 3d PIC and Quasi-3D [6] simulations. This work was partially supported by Fundação para a Ciência e Tecnologia (FCT), Portugal, through grant no. PTDC/FIS-PLA/2940/2014 and PD/BD/105882/2014. References [1] D. F. Gordon et al., IEEE Trans. Plasma Sci., 28(4), 1135 (2000) [2] B. M. Cowan et al., Journal Comp. Physics, 230(1), 61 (2011) [3] A. Caldwell et al., Nat. Phys. 5, 363 (2009) [4] N. Kumar et al., PRL 104, 255003 (2010) [5] R. A. Fonseca et al., Lect. Notes Comp. Sci., 2331, 343 (2002) [6] A. Davidson et. al., Journal Comp. Physics, 281, 1063 (2015)

Speaker: Anton Helm

14:00 P2.2035 Ponderomotive and resonant effects in the acceleration of particles by electromagnetic modes in vacuum and plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2035.pdf Ponderomotive and resonant effects in the acceleration of particles by electromagnetic modes in vacuum and plasmas I. Almansa1 , F. Russman1 , E. Peter1 , S. Marini2 , G. I. de Oliveira3 , R, Pakter1 , F. B. Rizzato1 1 Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil 2 LULI, Sorbonne Université, CNRS, École Polytechnique, CEA, Université Paris-Saclay, Paris, France 3 Instituto de Física, Universidade Federal do Mato Grosso do Sul, Campo Grande, MS, Brasil In the present analysis we study the dynamics of charged particles submitted to the action of slowly modulated relativistic electromagnetic carrier waves, both in vacuum and in plasma media. Firstly, with the use of a high-frequency laser mode along with a modulated static mag- netic wiggler, we show that the ensuing total field effectively acts as a slowly modulated high- frequency beat-wave field typical of inverse free-electron laser schemes. This effective resulting field is capable to accelerate particles much in the same way as space-charge wake fields do in plasmas accelerators [1], with the advantage of being more stable than plasma related settings. Acceleration occurs precisely as particles transition from ponderomotive to resonant regimes, so we develop the proper ponderomotive formalism to examine the problem. The formalism includes terms hitherto not discussed in the usual applications of the approximation, but that are nevertheless of crucial importance in the vicinity of resonant capture. The role of these terms is then also discussed in the broader context of laser-plasma interactions [2, 3]. References [1] S. Marini, E. Peter, G. I. Oliveira, and F. B. Rizzato, Physics of Plasmas 24 093113 2017. [2] D. A. Burton, R. A. Cairns, B. Ersfeld, A. Noble, S. Yoffe, and D. A. Jaroszynski, Observations on the ponderomotive force, Proc. SPIE 10234, Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources II, 102340G doi:10.1117/12.2270542 (2017). [3] E. Peter, S. Marini, R. Pakter, and F. B. Rizzato, Physics of Plasmas 24 102124 2017.

Speaker: Felipe Barbedo Rizzato

14:00 P2.2036 Pulsed high-field magnets for laser-driven ion beam shaping and laboratory astrophysics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2036.pdf Pulsed High-Field Magnets for laser-driven Ion Beam Shaping and Laboratory Astrophysics Florian-Emanuel Brack1,2, Florian Kroll1,2, Josefine Metzkes-Ng1, Lieselotte Obst1,2, Stephan Kraft1, Martin Rehwald1,2, Hans-Peter Schlenvoigt1, Leonhard Karsch1,3, Jörg Pawelke1,3, Sergei Zherlitsyn1, Thomas Herrmansdörfer1, Karl Zeil1, Ulrich Schramm1 1 Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany 2 Technische Universität Dresden, Germany 3 OncoRay - National Center for Radiation Research in Oncology Pulsed high-field magnets have become a common, versatile research tool. We present a pulsed magnet technology platform that opens up new areas of application in the field of laser-driven plasma physics. Compact high-field magnets, generating ms-long magnetic field pulses with amplitudes ranging as high as 20 T, have been developed for operation under high vacuum and in close vicinity to the harsh laser-plasma environment. The combination of the presented magnet technology and portable pulsed power systems paves the way for novel experiments in laboratory astrophysics and enables unique studies on beam optics for laser-driven ion sources. We implemented a pulsed beamline at the Dresden laser acceleration source Draco consisting of two pulsed solenoids for shaping laser-accelerated ion beams spatially and spectrally for application. The bunches remain intense, leading to high dose rates when stopped in matter. These dose rates make special demands for dosimetry and are of major interest for radiobiological studies. We performed experiments with the PW beam of Draco to investigate the feasibility of worldwide first controlled volumetric in vivo tumour irradiations in a dedicated mouse model with laser-accelerated protons. The study shows the reliable generation of homogeneous dose distributions laterally and in depth. Practical issues, like magnet repetition rate and stability, mean dose rate and future radiobiological challenges will be discussed and an outlook on the volumetric tumour irradiation experiments will be given. Furthermore, a split-pair coil was developed that can be used for the investigation of magnetized plasma in the frame laboratory astrophysical phenomena. The magnet provides optical access to the magnetized laser-driven plasma via two bores perpendicular to the coil axis. These openings enable optical and X-ray probing as well as insertion of obstacles and/or laser targets.

Speaker: Florian-Emanuel Brack

14:00 P2.2038 Response of bounded plasma column to dense charged particle beams

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2038.pdf Response of bounded plasma column to dense charged particle beams A. A. Gorn1, K.V. Lotov1, P.V. Tuev1 1 Budker Institute of Nuclear Physics, Novosibirsk, Russia Studies of radially­bounded plasmas at setups having a direct relationship to particle beam­driven plasma wakefield acceleration (PWFA). The problem was solved in the linear approximation for uniform plasmas and beams of densities much lower than the plasma density. Later studies focus on effects of radial plasma non­uniformity, long term evolution of nonlinear plasma waves and beam instabilities. Recently, the experiment AWAKE1 at CERN have generated interest in interaction of dense proton beams with low­density plasmas. In AWAKE, three overlapping beams (laser, proton, and electron) propagate through the 10 meter long gas cell filled with the rubidium vapor. The short laser pulse creates the uniform plasma column with a sharp boundary. The proton beam self­modulates and drives a high­amplitude plasma wave that is witnessed by the electron beam. Since the laser pulse cannot penetrate foils, there are orifices between the gas cell and high­vacuum upstream and downstream beam lines. The rubidium vapor leaks through the orifices and condenses on cold walls of expansion volumes attached to both ends of the gas cell. The laser pulse ionizes the divergent vapor stream and creates the radially uniform plasma of a constant radius and density that gradually reduces away from the orifice. The wakefields excited in this plasma by the particle beams are rather weak to disturb the high­energy proton beam, but sufficient for changing trajectories of lower­ energy electrons and modifying electron trapping conditions. In our studies of the bounded plasma response to ultrarelativistic charged particle beams we used both linear analytical theory and the results of numerical simulations performed by LCODE2. This approach allowed us to investigate the response in the wide range of plasma densities and corresponding plasma regimes. Despite a variety of linear and non­linear plasma response effects, we discovered a strong defocusing region near the plasma cell inlet in the AWAKE experiment. Passing through it, the witness beam to be injected into the plasma will be totally destroyed. To avoid this effect we proposed a new injection scheme is called “oblique”. [1] E. Gschwendtner, et al., Nuclear Instr. Methods A 829, 76 (2016). [2] A.P.Sosedkin, K.V.Lotov, Nuclear Instr. Methods A 829, 350 (2016).

Speaker: Alexander Gorn

14:00 P2.2039 Suitability and robustness of triangular nanostructured targets for proton acceleration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2039.pdf Suitability and robustness of triangular nanostructured targets for proton acceleration M. Blanco1 , M.T. Flores-Arias1 , M. Vranic2 1 Photonics4Life Research group, Applied Physics Department, Faculty of Physics, Universidade de Santiago de Compostela, Santiago de Compostela, Spain 2 GoLP/IPFN, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal Proton acceleration via the target normal sheath acceleration (TNSA) mechanism has became a promising tool for future and current technologies where accelerated ions with energies in the MeV range are needed. The possibility of achieving these energies with table-top femtosec- ond laser sources and thin foils makes this technology cheaper for some applications than the traditional particle acceleration methods. A current challenge for TNSA is to improve the properties of the proton beam without in- creasing the laser peak power. To that end several proposals for target engineering have been made, such as manipulating the target thickness, growing a low density foam on top of the tar- get, nanostructuring the rear surface or the front surface of the target. The latter has proven to be a very efficient method to enhance the laser energy absorption and thus the transfer of energy from the laser to the electrons, having as a product more energetic protons in the accelerated beam. This method to increase the energy of the protons has demonstrated to be extremely ef- ficient for triangular nanostructures, where nearly a 100% of the laser energy can absorbed by the plasma if the proper conditions are met [1]. In this contribution we present the results from realistic three-dimensional particle-in-cell (PIC) simulations of triangular nanostructured targets, in order to give a realistic estimate of the outcome of such an experiment, and be able to estimate the expected number and corresponding energies of the accelerated protons. We also address the robustness of this acceleration method by analyzing how the laser energy absorption is affected by deviations of the setup from the assumed ideal situation, such as changes in the laser peak intensity, changes in the ion species, the existence of irregularities in the nanostructures, or the existence of a pre-plasma at the target front surface. Our findings demonstrate, on one hand, that the very high absorption percentages achieved are robust with respect to non-ideal target manufacturing, but on the other hand, that very high contrast laser pulses are needed to preclude the formation of a pre-plasma region. References [1] M. Blanco, M.T. Flores-Arias, C. Ruiz and M. Vranic, New J. Phys 19, 033004 (2017)

Speaker: Manuel Blanco

14:00 P2.2040 Temporally resolved diagnostics, based on probe beam, of laser produced plasma for electron acceleration to be implemented at ELI-NP

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2040.pdf Temporally resolved diagnostics, based on probe beam, of laser produced plasma for electron acceleration to be implemented at ELI-NP L. Neagu1,2, R. Ungureanu2, G. Cojocaru2, M. Serbanescu2, G. Giubega2, O. Tesileanu1 and C. Diplasu2 1 Extreme Light Infrastructure - Nuclear Physics (ELI-NP)/ Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Ilfov, Romania 2 National Institute for Laser, Plasma and Radiation Physics, Ilfov, Romania / CETAL-PW Laboratory The interaction of high power lasers with gas targets (gas cell or gas jet) is one of the main processes that will be used in the experimental program of Extreme Light Infrastructure - Nuclear Physics facility, especially in E6 and E7 interaction area. This is motivated by the fundamental problems of laser driven nuclear physics [1], high field physics and quantum electrodynamics [2]. Such kind of experiments require a deep knowledge of the transient plasma properties for understanding of the acceleration process itself or for efficiency optimization, control and monitoring of the electron beam formation from the laser generated plasma. The most important plasma parameter is the electron density and its dynamics in the sub-picosecond time scale, which determines the dephasing length, the pump depletion length, and the maximum amplitude of nonlinear plasma waves generated during the laser pulse propagation. Commonly, the electron density dynamics in laser generated plasmas is measured using nonperturbative laser interferometry [3]. In this work we intend to use a probe pulse as a fraction picked-up from the main laser pulse, which is under test at NILPRP - CETAL facility in Magurele. Similar to the method described in [4], this pulse is spectrally broadened via self-phase modulation in a hollow core fiber filled with argon or other noble gases. Then, in order to obtain a transform-limited pulse of few optical cycles the beam is temporally compressed via chirped mirrors in order to create a probe beam for plasma diagnostics with few-fs temporal resolution. The probe pulse is delayed at different time within hundreds of fs (with respect to the pump beam) in order to analyse the plasma wave evolution on subsequent shots assuming each produces a repeatable interaction. Finally the probe beam transversally propagates with respect to the pump pulse in order to illuminate the laser plasma interaction. Due to the length of the laser chain and the resulting timing jitter between shots, the probe pulse is splitted off from the main pulse as close as possible to the interaction point to ensure excellent pulse synchronization. Agnoledgemts: Research funded by Institute of Atomic Phisics (IFA) under contract #24 in the program ELI- RO 2016 [1] Roth M. et al., Laser driven nuclear physics at ELI-NP, technical design report, ELI-NP (2016) [2] Jaroszynski, D. et al., High field physics and QED experiments at ELI-NP, technical design report, ELI- NP (2016) [3] G. R. Plateau, et al., REVIEW OF SCIENTIFIC INSTRUMENTS 81, 033108 2010 [4] B. M. Welsh, B. L. Ellerbroek, M. C. Roggemann, and T. L. Pennington, Appl. Opt. 34, 4186 1995.

Speaker: Liviu Neagu

14:00 P2.2041 The role of a prepulse in laser-driven ion acceleration (PIC simulations)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2041.pdf The role of a prepulse in laser-driven ion acceleration (PIC simulations) M. Zakova1,2, J. Psikal1,2, D. Margarone1, S. V. Bulanov1, G. Korn1 1 Institute of Physics ASCR, ELI Beamlines Project, Prague, Czech Republic 2 Czech Technical University in Prague, FNSPE, Prague, Czech Republic Laser-driven ion beams have a great importance since high intensity pulsed lasers were developed. Many efforts were made in studying and manufacturing micro/nano-structured targets in order to both decrease beam divergence and/or increase beam charge and maximum ion energy and thus fulfill the requirements of foreseen applications such us laser-driven hadrontherapy, fast ignition of inertial fusion or pulsed radiolysis etc. Laser prepulse is being widely known and treated as unwanted feature in laser acceleration experiments. As a consequence of ablative pressure of blow-off plasma generated by a laser prepulse, a shockwave can penetrate into the target and thus destroy a micro/nano- structures on target front or even back side before the main pulse comes. This work introduces Particle-in-cell simulations performing physical situations when the laser prepulse is present. This includes firstly flat target(s) with generated layer of preplasma causing e.g. self-focusing and thus local increase of laser peak intensity and secondly scenario in which the laser prepulse causes an expansion of solid/cryogenic target up to near critical density and magnetic vortex field plays a role in ion acceleration. The optimal parameters for obtaining desired beam features or required scenario will be derived analytically. Part of the PIC results will be also compared to experimental data measured during laser-driven ion acceleration experiment at VULCAN laser (Rutherford Appleton Laboratory, UK) from cryogenic hydrogen ribbon.

Speaker: Martina Žáková

14:00 P2.2042 The ZPIC educational code suite

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2042.pdf The ZPIC educational code suite R. Calado1, B. Malaca1, M. Pardal1, A. Helm1, W.B. Mori2, V.K. Decyk2, J.Vieira1, L.O.Silva1, R. A. Fonseca1,3 1 IPFN - Instituto de Plasmas e Fusão Nuclear, Lisboa, Portugal 2 UCLA Plasma Simulation Group, Los Angeles, California 3 ISCTE - Instituto Universitário de Lisboa, Lisboa, Portugal Particle-in-Cell (PIC) codes are used in almost all areas of plasma physics, such as fusion energy research, plasma accelerators, space physics, ion propulsion, and plasma processing, and many other areas. In this work, we present the ZPIC educational code suite, a new initiative to foster training in plasma physics using computer simulations. Leveraging on our expertise and experience from the development and use of the OSIRIS PIC code, we have developed a suite of 1D/2D fully relativistic electromagnetic PIC codes, as well as 1D electrostatic. These codes are self-contained and require only a standard laptop/desktop computer with a C compiler to be run. The output files are written in a new file format called ZDF that can be easily read using the supplied routines in a number of languages, such as Python, and IDL. A Python wrapper for the code was also developed, allowing for the simulations to be totally controlled/analyzed from within Python. The code suite also includes a number of example problems that can be used to illustrate several textbook and advanced plasma mechanisms, including instructions for parameter space exploration. We also invite contributions to this repository of test problems that will be made freely available to the community provided the input files comply with the format defined by the ZPIC team. The code suite is freely available and hosted on GitHub at: https://github.com/zambzamb/zpic

Speaker: R. Calado

14:00 P2.3002 Development and characterization of low-temperature atmospheric pressure plasma jet

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3002.pdf Development and characterization of low-temperature atmospheric pressure plasma jet Veda Prakash, Kiran Patel, Narayan Behera, Ajai Kumar Institute for Plasma Research, Bhat, Gandhinagar, HBNI, Mumbai, India prakashgveda@gmail.com Atmospheric pressure plasma jet (APPJ) source with helium (He) as an active gas is developed. 4 kV p-p, 33 kHz sinusoidal voltage is used to produce plasma jet. He gas with flow rates of up to 11 liters per minute is used to produce plasma plume of around 6 cm in length into the ambient air. Thorough characterization of the plume has been carried out using optical diagnostics such as emission spectra measurements, ICCD imaging and electrical discharge using voltage and current probes. Plasma discharge parameters such as electron excitation temperature and gas temperature are estimated using emission spectra and are 800K and 305 K respectively. Further additional plume parameters such as velocity and plume current are also estimated using ICCD images and current transformer. By using velocity and plume current values, the density along the length of the plasma plume has been assessed and the values are in the range of 0.05-3.2 x 1012 cm3 at various positions of the plume length. Furthermore, the discharge ignition and plasma plume dynamics with flow rate will be presented. References: [1] M. Laroussi, M. G. Kong, G. Morfill, W. Stolz, Plasma Medicine: Applications of Low-Temperature Gas Plasmas in Medicine and Biology, Cambridge University Press, 2012, [2] K. Yambe, H. Saito, and K. Ogura, IEEJ Trans. Electr. Electron. Eng. 10, 614–618 (2015) [3] M. Laroussi, X. Lu, M. Keidar, J. Appl. Phys., vol. 122, no. 2, pp. 020901, 2017

Speaker: Veda Prakash

14:00 P2.3003 Cs-Ba Switching Devices for Efficient Current Management Using Plasma Instabilities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3003.pdf Cs-Ba Switching Devices for Efficient Current Management Using Plasma Instabilities A.S. Mustafaev1, B.D. Klimenkov1, A.Y. Grabovskiy1, V.I. Kuznetsov2 1 St. Petersburg Mining University, St. Petersburg, Russia 2 Ioffe Institute RAS, St. Petersburg, Russia At present, the problems of current control in the electrical circuits of space nuclear power plants are topical. Effective radiation-resistant electronic switching devices, thermionic converters, current and voltage stabilizers, transformers, generators are needed. To solve this problem it is possible to use radiation-resistant electronics based on a strongly nonequilibrium anisotropic plasma. Thus in this work, we have investigated electrokinetic parameters of diode and triode switching devices with cesium-barium filling, the following results were obtained: Diode device: - the possibility of controlling the current modulation by means of an auxiliary discharge, as well as external electric and magnetic fields has been founded; - it has been established, that full current modulation at an ignition voltage of 5…6 V and a discharge current density of ~10 A/cm2 can be implemented due to the development of Bursian-Pierce plasma instability [1] and the formation of nonlinear structures in the plasma. Triode device: - it has been established, that mechanism of discharge extinction using fine-mesh grid, as well as the mechanism of spontaneous breakage, is associated with nonlinear oscillations in the Knudsen plasma; - stable modulation at frequencies of 1-10 kHz of specific electric power of 5 kW/cm2 and an efficiency of more than 95% was obtained at the anode voltage 50 V; - the use of fine-mesh grid as a control electrode provides high power in the range of cesium vapor pressures of 10-4-10-2 Torr and low voltage losses in the open state of 0.8- 2.5 V. References [1] Ender A.Ya., Kuznetsov V.I., Schamel H., Akimov P.V. Switching of nonlinear plasma diodes. 1. Analytic theory. Phys. Plasmas, 2004, vol. 11, no. 10, pp. 3212–3223.

Speaker: A. Y. Grabovskiy

14:00 P2.3004 Surface treatment of coarse Y2O3 ceramic powders by a microwave plasma torch: Their mobility improvement and densification

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3004.pdf Surface treatment of coarse Y2O3 ceramic powders by a microwave plasma torch: Their mobility improvement and densification S. M. Chun1, Y.C. Hong1 1 Plasma Technology Research Center, National Fusion Research Institute, Gunsan, Korea In a ceramic powder coating processing, the coarse surface and the pores of small size ceramic powders (<25μm) are caused to porosity generation problems of coating layer and non-quantitative feeding rate. These issues are recovered by a thermal sintering technique. In this regard, a microwave plasma torch is applied to improve mobility and densification of ceramic powders. The microwave plasma treatment is carried out by suitable reaction conditions, showing both high density and mobility of ceramic powders. The Y2O3 ceramic powders (Shin-Etsu chemical) were treated by the microwave plasma torch. The ceramic powders were modified by active species in high temperature plasma flame of 6000K at atmospheric pressure. Eventually, the coarse surface on the ceramic powder was modified instantaneously by high chemical reactivity in the plasma, revealing a smooth surface, functionalization on surface. The treated small ceramic powders lubricate between coarse powders to improve mobility. In addition, the ceramic powder is polarized on the surface due to the high chemical reactivity of the plasma, so that the ceramic powders have a high repulsive force. In this test, the densification and the mobility strongly depend on the applied plasma power and feeding gas ratio of N2/O2 at a fixed powder feeding rate. The experimental results show that the microwave torch plasma will be attractive for a sintering process, which is necessary for short treatment time and high heat flux. Figure 1. The Y2O3 powder images of before and after treated by microwave plasma torch. References: 1. Rachman, C., Amit, S., Claude, E. (2009) Densification of nanocrystalline Y2O3 ceramic powder by spark plasma sintering, Journal of the European Ceramic Society., 29, 91-98.

Speaker: Semin Chun

14:00 P2.3005 The studies of diffusion mechanism and simulation model for hypersonic plasma with heterogeneous and un-magnetized characteristics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3005.pdf The Studies of Diffusion Mechanism and Simulation Model for Hypersonic Plasma with Heterogeneous and Un-magnetized Characteristics WU Runhui, LIU Jiaq, LIU Xin, MENG Gang, REN Aimin, Chai Song National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics, Beijing 100076, China The plasma diffusion mechanism and simulation model are studied for the plasma generator which the diffusion velocity is hypersonic, and the electron density and collision frequency are heterogeneous, the maximum electron density can be controlled near the nozzle and the plasma dimension could attain 100 meters or even several kilometers. The mathematical and simulation diffusion model of the ejected plasma is given in the paper, it is assumed that the supersonic plasma diffusion could be considered as the tiny jet flow expanded on the basis of the free molecular flow theory and supersonic engine theory in thin gas space. The calculation results are compared with the numerical and experimental results, the simulation model and the results are validated respectively. All results are demonstrated that: 1) The ionization degree and mass flux are the two important parameters that can decide to the results of electron density, collision frequency, whereas the shape of the transonic effuse is the essential factor that effects the diffusion angle. 2) The simulation model of the paper is compared with the numerical algorithm and experimentation, and the results are twice as great as the experimental results, but twice less than the numerical results. The errors among these results are acceptable in the study, so it is indicated that the model of this paper is the feasible way to compute the plasma diffusion, and the model has two features: its calculation is simple, and it is computationally efficient. 3) In order to accommodate more applications, the necessary plasma would be acquired by controlling the parameters of the hypersonic nozzle composition, ionization degree and mass flux. In conclusion, the authors of the paper could offer the plasma diffusion model for correlative researchers, and it is valuable for analyzing microwave propagating in the man- made plasma.

Speaker: Runhui Wu

14:00 P2.3006 Acceleration of mm-sized bodies in an electromagnetic rail accelerator with a plasma armature

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3006.pdf Acceleration of mm-sized bodies in an electromagnetic rail accelerator with a plasma armature S.A. Poniaev1, B.I. Reznikov1, R.O. Kurakin1, P.A. Popov1, M.V. Petrenko1, B.G. Zhukov1 1 Ioffe Institute, St.Petersburg, Russia At present, electromagnetic rail accelerators find a wide use in various fields of science and technology [1-3] for accelerating bodies to hyper-speeds (for high-speed collision research or for injecting fuel into a thermonuclear reaction zone, etc.), generating high-speed plasma jets with various chemical compositions (for coating sputtering). This report presents the results of experimental and theoretical studies aimed at determining the limiting characteristics of the acceleration of a plasma armature with a solid body in front of it or a free plasma armature in an electromagnetic rail accelerator with an external magnetic field. The investigations were carried out for the railgun channel filled with different gases (air, helium, argon, xenon) under different pressures. The goal was to study the influence of external factors on the acceleration characteristics. It was found that, starting from a certain speed, the free (without a solid body in front of it) plasma armature in the channel was no longer accelerated and its speed became constant. This can be explained by the fact that the gas behind the shock wave in the channel became conductive, and some of the electric current that had previously been spend on the acceleration of the plasma armature began to flow in front of it, which had a significant effect on the acceleration efficiency. The dependence of the achievable velocity on the pressure, gas type in the channel of the railgun accelerator, and the mass of the accelerated body for the case of solid impactor acceleration was obtained. 1. Hogan J.D., Spray J.G., Rogers R.J., Vincent G., Schneider M., (2013), Dynamic fragmentation of planetary materials: ejecta length quantification and semi-analytical modelling, International Journal of Impact Engineering, 62, 219–228. 2. Poniaev S.A., Bobashev S.V., Zhukov R.O., Sedov A.I., Izotov S.N., Kulakov S.L., Smirnova M.N., (2015), Small-size railgun of mm-size solid bodies for hypervelocity material testing, Acta Astronautica, 109, 162-165. 3. Chr. Day, B. Butler, T. Giegerich, P.T. Lang, R. Lawless, B. Meszaros, (2016), Consequences of the technology survey and gap analysis on the EU DEMO R&D programme in tritium, matter injection and vacuum, Fusion Engineering and Design, 109–111, 299-308,

Speaker: Sergey Poniaev

14:00 P2.3007 Modification of aluminium-titan and nickel-titan thin layers by plasma flow

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3007.pdf Modification of aluminium-titan and nickel-titan thin layers by plasma flow action N. Trklja1, B. Salatic2, I. Krstić1, B.M. Obradović1, M.M. Kuraica1 1 Faculty of Physics, University of Belgrade, Belgrade, Serbia 2 Institute of Physics, Belgrade, Serbia The main focus of this study is to investigate morphological changes occurring on aluminum-titanium (Al-Ti) and nickel-titanium (Ni-Ti) thin films when treated with a compressed plasma flow which was formed in the magnetoplasma accelerator and comparation of these changes with those obtained during the treatment with laser pulses. Al-Ti and Ni-Ti multilayer systems have been created by alternate deposition of nanometer-thick layers (of Al or Ni on Ti) on a single silicon substrate, by sputter deposition method. The thickness of each individual layer is roughly 20 nm. The total number of layers varying from 10 to 20 per target. We have compared two different types of interactions - one being an interaction between Er:glass and Nd:YAG laser beam and target, while the second was an interaction between the plasma flow and target. Relatively high values of plasma parameters of the compressed plasma flows (electron density in the order of 10^23 m^-3, and plasma temperature of 2 eV) together with large plasma flow velocity (of 100 km/s in hydrogen plasmas) and discharge duration (of up to 50 µs) makes them suitable and efficient for studies of surface modifications under high thermal loads. In addition, we are able to investigate the formation of specific micro- and nanostructures, the occurrence of morphological characteristics arising from the movement of the molten material pieces, and the formation of craters caused by ablation of the target. When a target is irradiated with a laser beam, most of the absorbed energy of the laser radiation is transformed into heat, causing the formation of intermetallic compounds. Modifications are similar as to those formed by plasma flow-target interaction. We present here a comparison of the periodic formations of previously stated modifications in these two types of interactions. Present study is of interest for investigations related with material of interest for fusion experiments. B.Salatić et al., Applied Surface Science, 360, 559-565 (2016) I.P.Dojčinović et al., Vauum, 80, 1381-1385 (2006) I Garkusha et al., J. Phys.: Conf. Ser. 959 012004 (2018)

Speaker: Nora Trklja

14:00 P2.3008 Effect of the Voltage Waveform on the Characteristics of a Dielectric Barrier Microdischarge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3008.pdf Effect of the Voltage Waveform on the Characteristics of a Dielectric Barrier Microdischarge A.A. Saifutdinova1, A. I. Saifutdinov2,3 1 Kazan National Research Technical University named after A.N Tupolev, Kazan. Russia 2 Kazan Federal University, Kazan. Russia 3 Saint Petersburg State University, St. Petersburg. Russia Dielectric barrier discharges (DBD) have been known for a rather long time. The renewed interest in this type of discharge stems from the fact that dielectric barrier discharges at pressures close to atmospheric one have a wide range of applications—from plasma aerodynamics to plasma medicine and plasma decomposition of gaseous substances. The possibility to control the DBD parameters is of great practical importance. In addition to the influence of the frequency and amplitude of the feeding voltage, experimental studies of the effect of the shape of the feeding voltage on the discharge characteristics are very challenging. As for publications devoted to numerical analysis of the effect of the shape of the feeding voltage on the spatiotemporal characteristics on the DBD, they are very scarce in number. The aim of the present work was to numerically analyze the effect of the shape of the feeding voltage on the spatial and temporal characteristics of a DBD in argon. Two waveforms of the feeding voltage were considered: sinusoidal and square ones. In this work, an extended fluid model describing the spatiotemporal characteristics of an atmospheric pressure dielectric barrier microdischarge in argon has been formulated. Numerical simulations have been carried out for sinusoidal and square feeding voltages in a wide range of external conditions. In particular, the spatiotemporal behavior of the charged particle densities; the strength and potential of the electric field; and the time dependences of the discharge current, the voltage drop across the discharge gap, and the charge accumulated on the right and left dielectric barriers have been calculated. It is shown that the spatiotemporal characteristics of an atmospheric-pressure dielectric barrier microdischarge in argon depend on the shape of the applied voltage. For a square feeding voltage, two current pulses are always observed during one period, regardless of the voltage amplitude. For a sinusoidal feeding voltage, the number of current pulses per period increases with increasing voltage amplitude. This indicates that the spatiotemporal characteristics of the DBD plasma differ significantly for different shapes of the feeding voltage, the other conditions being the same. The work was supported by Russian Science Foundation (RSF, grant № 17-79-20032) and Russian Federation Presidential Grant (grant № MK-539.2017.1)

Speaker: Aliia Saifutdinova

14:00 P2.3009 Porous silicon and graphene-based structures for novel plasma energetic systems

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3009.pdf Porous silicon and graphene-based structures for novel plasma energetic systems R.S. Smerdov1, A.S. Mustafaev1, Yu.M. Spivak2, V.A. Moshnikov2 1 Saint Petersburg Mining University, Saint Petersburg, Russia 2 Saint Petersburg Electrotechnical University “LETI”, Saint Petersburg, Russia Applying the effect of photon-enhanced thermionic emission (PETE) for solar concentrator systems makes it possible to utilize both photovoltaic and thermionic effects for energy conversion, leading to a significant increase in its efficiency [1, 2]. The possibility of synthesizing PETE-based systems with semiconductor (GaN) electrodes was demonstrated in [1], however, the number of incident photons with energies exceeding the band gap of GaN (E g = 3.3 eV) is less than 1 % of their total amount. That is why further investigation of porous silicon (PS), as well as PS-based composite structures for subsequent electrode manufacture is promising, since band gap modification of such materials is possible in the wide range from 1 to 3 eV due to the presence of the quantum confinement effect [3] and significant capabilities for surface functionalization [4]. The synthesis of anodes for thermionic plasma energy systems requires the creation of highly specific materials with low electron work function (a). The problem of a reduction is traditionally solved by the use of alkaline and alkaline-earth metal coatings, in particular, cesium (Cs) [5]. Anodes based on cesium-coated tungsten are traditionally used due to their high thermal stability and relatively low work function (1.7 eV). The use of a nickel anode coated with graphene layers intercalated by cesium atoms made it possible to obtain an unprecedented decrease in the electron work function (a<1 eV) from the surface of the material and, as a consequence, a threefold increase in energy conversion efficiency (up to 25%) [5]. References 1. Schwede J W, Bargatin I, Riley D C, Hardin B E, Rosenthal S J 2010 Photon-enhanced thermionic emission for solar concentrator systems Nature Mater. 9 762 2. Mustafaev A, Smerdov R, Klimenkov B 2017 Semiconductor nanostructures for plasma energetic systems BAPS 62 3. Nolan M, O’Callaghan S, Fagas G, Greer J C 2007 Silicon nanowire band gap modification Nano Lett. 7 34 4. Spivak Yu M, Mjakin S V, Moshnikov V A et al. 2016 Surface Functionality Features of Porous Silicon Prepared and Treated in Different Conditions J. of Nanomaterials 8 5. Mustafaev A S, Polishchuk V A, Tsyganov A B, Yarygin V I, Petrov P A 2017 Russian Journal of Physical Chemistry B 11 118

Speaker: Rostislav Smerdov

14:00 P2.3010 Laser-driven synthesis of nanoparticles for therapeutic applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3010.pdf Laser-Driven Synthesis of Nanoparticles for Therapeutic Applications Rafferty, C.1, Nersisyan, G.1, Sun, Daye.2, Sun, Dan.2, Chan, CW.2, Sarri, G.1 1 Centre for Plasma Physics, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, United Kingdom 2 School of Mechanical and Aerospace Engineering, Queen’s University Belfast, Belfast BT9 5AG, United Kingdom Nanoparticles are used in a wide range of applications in medicine, technology, energy and industry. Recent interest in gold nanoparticles suspended in a solution, is due to their applications as a radiosensitiser in radiotherapy[1], and as contrast agents in MRI and CT imaging, along with many other applications in the field of medicine [2]. The most challenging aspect in production of nanoparticles is controlling the size distribution and impurities in the solution, which arise from the chemical synthesis and ball milling [3]. Recent advancements of ultra-fast lasers have enabled a new method of synthesising nanoparticles from Laser Ablation in Liquids (LAL). Femtosecond pulsed lasers can deliver sufficient energy to a target for vaporisation within the thermal timescale, allowing the generation of cold plasmas that expand adiabatically, where nanoparticle formation has been observed. As a result a pure colloidal solution possessing a narrow size distribution, and more spherical shapes compared with other methods of synthesis[4][5] can be produced. In this investigation, a gold target will be vaporised in DI water by a 550fs pulsed laser at 1.053µm. The average size and subsequently the size distribution is controlled by varying the laser fluence from 1 J/cm 2 to 100 J/cm2. A secondary experiment involving the nanoparticle synthesis under a CW laser will be performed for comparing results, to help understand the relatively unknown physics of laser ablation and nanoparticle formation from lasers. [1] Kim (et al.), American Journal Society 129 (24):7661–7665, 2017. [2] Hainfeld (et al.), Physics in Medicine & Biology 49 (18):N30 2004. [3] Maximova (et al.), Nanotechnology 26 (6):065601 2015 [4] Gamaly (et al.), Physics Reports 508 (4-5):91-243 2011 [5] Kabashin (et al.), Journal of Applied Physics 94 (12):7941 2003

Speaker: Cormac Rafferty

14:00 P2.3011 Electric potential profile created by end electrodes in a magnetized rf discharge plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3011.pdf Electric potential profile created by end electrodes in a magnetized rf discharge plasma G. Liziakin, A. Gavrikov, R. Usmanov, R. Timirkhanov, V Smirnov Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russian Federation The reprocessing of spent nuclear fuel (SNF) is one of the ke y challenges facing the nuclear industry. Among other technologies the plasma based methods for reprocessing SNF are actively developed [1]. To separate ions in space, it is necessary to create a configuration of crossed ExH fields immersed into plasma. In a cylindrical chamber filled with plasma and placed in a magnetic field parallel to its axis, an electric field of a specified configuration must be produced. Electrodes placed at the ends of the cylindrical vacuum chamber are used for this purpose. The problem of generating a stationary electric field in a magnetized radio-frequency discharge (rf) plasma is studied experimentally. Helmholtz coils produce magnetic field in a cylindrical vacuum chamber with diameter of 85.6 cm and length of 220 cm. RF discharge is generated at a frequency of ∼ 5 MHz. The rf power absorbed by plasma lies in the range 0.5-1.5 kW. Electrodes defining a negative potential are placed at the ends of the chamber. Two pairs of circular flat electrodes with diameter of 5.5 and 45 cm are investigated. The working gas is argon. Radial profiles of electron density and temperature are obtained. Radial profile of the plasma potential is investigated, as well as the dependence of plasma potential on the voltage applied to the end-electrodes. [1] V. P. Smirnov, A. A. Samokhin, N. A. Vorona, and A. V Gavrikov, “Study of charged particle motion in fields of different configurations for developing the concept of plasma separation of spent nuclear fuel,” Plasma Phys. Reports, vol. 39, no. 6, pp. 456–466, 2013.

Speaker: Gennadii Liziakin

14:00 P2.3012 Destruction of PFCs gas using microwave plasma operating at a low pressure

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3012.pdf Destruction of PFCs gas using microwave plasma operating at a low pressure D. H. Shin1, S. M. Chun1, Y. C. Hong1 1 Plasma Technology Research Centre, National Fusion Research Institute (NFRI), Gunsan, Korea The perfluorocompounds (PFCs) gases are used mainly in industrial processes for production of display, semiconductor, metal, and etc. The PFCs are greenhouse gases with atmospheric lifetimes of more than 1000 years. They are powerful greenhouse gases and today’s emissions will still be affecting earth’s climate in the next millennium. The microwave plasma operated in a low pressure chamber for destruction of PFCs gases in this study. The microwave plasma was operated in a closed and isolated environment may provide an opportunity for the mass production of chemically active radicals for various chemical and biological processes. The operation at a low pressure of microwave plasma would be economical cost of capital, maintenance, and operational compared to other plasma devices. The electric field induced in a quartz discharge tube by microwave radiation break down the gas at a sufficiently low pressure, igniting the plasma, which is continuously sustained by the microwave radiation. The plasma profile at a low pressure was asymmetric with higher density on the incoming side of the microwaves. This behavior of the plasma inhibits high-power operation of microwave plasma at a low pressure. However, the asymmetry of the plasma profile disappears under a high gas flow rate. Destruction of PFCs gas indicates that the microwave plasma used at a low pressure can efficiently produce an abundance of chemical radicals. REFERENCES: [1] Y. C. Hong, et al, “Microwave plasma torch operating at a low pressure for material processing”, Thin Solid Films, 517, 4226, 2009.

Speaker: Dong Hun Shin

14:00 P2.3013 Plasma separation for rare earth elements recycling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3013.pdf Plasma separation for rare earth elements recycling R. Gueroult1 , J.-M. Rax2 , N. J. Fisch3 1 LAPLACE, Université de Toulouse, CNRS, 31062 Toulouse, France 2 Université de Paris XI - Ecole Polytechnique, LOA-ENSTA-CNRS, 91128 Palaiseau, France 3 Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 USA Owing to the great upside potential of plasma separation for nuclear waste cleanup [1] and nuclear spent fuel reprocessing [2], the last decade has seen a renewed interest in plasmas for the purpose of separating elements (see, e. g., Refs. [3, 4] and references therein). For these applications, the mass difference between elements to be separated is typically tens of atomic mass or more, and large throughput processing is highly desirable. This is in contrast with plasma isotope separation techniques developed since the 1970s’ [5], which aim at separating elements separated by at most a few atomic mass and typically have a limited throughput. New plasma separation mechanisms are thus called for. In an effort to address this new need, a suite of plasma configurations offering mass differ- ential confinement properties has been identified in recent years [3, 4]. These concepts rely on a variety of separation mechanisms (e. g. gyro-orbit, ion drift, mobility) which are each ef- fective for a particular range of plasma parameters such as magnetization, collisionality and ionization fraction. It is therefore anticipated that these different concepts will display different performances with respect to purification and throughput for a given input stream composition. Yet another promising application for plasma separation is rare earth elements (REEs) re- cycling [6]. Indeed, it has recently been shown that separating in a plasma the various atoms found in neodymium - iron - boron (NdFeB) magnets with respect to a threshold atomic mass mc = 100 amu could in principle allow recovering REEs at a cost comparable to the current market price of these elements (Nd, Dy). In this talk, we evaluate how different plasma mass separation concepts proposed to date perform relatively to one another for the particular case of NdFeB magnets recycling and discuss possible pathways for optimization. References [1] R. Gueroult, D. T. Hobbs and N. J. Fisch, J. Hazard. Mater. 297, 153 (2015) [2] (a) A. V. Timofeev, Sov. Phys. Usp. 57, 990 (2014) (b) R. Gueroult and N. J. Fisch, Plasma Sources Sci. Technol. 23, 035002 (2014) (c) V. B. Yuferov et al., Prob. Atom. Sci. Tech. 23, 223 (2017) [3] D. A. Dolgolenko and Yu. A. Muromkin, Phys.-Usp 60, 994 (2017) [4] R. Gueroult, J.-M. Rax, S. J. Zweben and N. J. Fisch, Plasma Phys. Controlled Fusion 60, 014018 (2018) [5] M. W. Grossman and T. A. Shepp, IEEE Trans. Plasma. Sci. 19, 1114 (1991) [6] R. Gueroult, J.-M. Rax and N. J. Fisch, J. Clean. Prod. 181, 1060 (2018)

Speaker: Renaud Gueroult

14:00 P2.3014 Nonlinear charge dynamics effects in a Hall thruster device

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3014.pdf Nonlinear charge dynamics effects in a Hall thruster device S. Marini1 , R. Pakter2 1 LULI, Sorbonne Université, CNRS, École Polytechnique, CEA, Université Paris-Saclay, France. 2 Instituto de Física - UFRGS, Porto Alegre, Brazil Plasma thrusters have been identified as a promising technology for primary propulsion in deep-space scientific missions. Among different types of plasma propulsion devices, Hall effect thrusters stand out by its current state of the art [1]. Most of the basic analyses of particle dynamics on Hall thrusters are based on models that consider a one dimensional flow that lead to integrable charge dynamics. In practice, however, the dynamics is fully three dimensional, allowing for the onset of more complex dynamical behavior [2]. In this paper, we investigate the charge dynamics in a simplified three dimensional model for the Hall thruster which presents chaotic behavior. A detailed discussion on the validity of the model is presented. It is shown that electron chaotic dynamics is intimately connected with an increased background gas ionization probability and plasma formation, which is of utmost importance for the device operation [3]. It is also shown that despite the chaotic dynamics, charge confinement can be preserved with a proper choice of the electromagnetic field profile. References [1] J. Vaudolon, S. Mazouffre, C. Hénaux, D. Harribey, and A. Rossi, Appl. Phys. Lett. 107, 174103 (2015). [2] S. Marini and R. Pakter, Phys. Plasmas 24, 053507 (2017). [3] S. Mazouffre, G. Bourgeois, K. Dannenmayer, and A. Lejeune, J. Phys. D: Appl. Phys. 45, 185203 (2012).

Speaker: Renato Pakter

14:00 P2.3015 Understanding of effect of negative ions on the sheath formation by emissive probe and laser induced fluorescence methods

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3015.pdf Understanding of effect of negative ions on the sheath formation by emissive probe and laser induced fluorescence methods M.-K. Bae1, I.J Kang1, H.T Oh1, I.S. Park1, S.J Jeong1, S.H Lee1, K.-S. Chung1 1 Department of Electrical Engineering, Hanyang University, Seoul, South of Korea To understand the effect of negative ions on the sheath formation, emissive probe (EP) and laser induced fluorescence (LIF) method were used. EP has been used to directly measure the plasma potential profile and the sheath/presheath boundary is identified from the steep slop change of the emission current. LIF determines ion flow velocities and ion temperatures from the broadening of fluorescence lines [1,2]. Basic plasma parameters such as plasma density and electron temperature are also measured by a single electric probe. Negative ion plasma is generated by the discharge of Ar+O2 gas in a cubical chamber (24 x 24 x 24 cm3) with DC filament source with the following conditions: ne ~ 108 cm-3, Te ~ 2 eV, Ti ~ 0.1 eV. O2 gas ratio have been changed 0 ~ 10 % to investigate the effect of negative ion to sheath formation. Change of sheath width, plasma potential, ion velocity due to ratio of negative ion concentration will be presented. References: [1] In. Je. Kang et al, JINST. 10 (2015) C12019. [2] G. D. Severn et al, Phys. Rev. Lett. 90 (2003) 145001-1.

Speaker: Min-Keun Bae

14:00 P2.3016 New plasma arc furnace for brown coal combustion

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3016.pdf ! " # ! " # ## ! ## $ ! ! # % % & ! # # ## # # ! ' ! ( # # ! % $ & % % # # ' ! # ! ! ( ! # # ! #$ ! % # # ! # ! ) # # ! ! & # * # ! # # # ( ! # + # # ! # ! * ! ! # ! # ) # ' % $ # ! ! # # ## ! # # ) $ # # ! # # ,$ # ## ! # ! # # !

Speaker: Irakli Nanobashvili

14:00 P2.3017 Pilot experiment on laser-plasma ion generation at HiLASE

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3017.pdf Pilot experiment on laser-plasma ion generation at HiLASE L. Giuffrida1*, H. Zulic1, A. Velyhan1, A. Picciotto2, M. Barozzi2, P. Bellutti2, R. Dell`Anna2, M. Divoky3, A. Fajstavr1, D. Giubertoni2, M. Hanus3, C. Lazzarini1, A. Lucianetti3, P. Navratil3, G. Pepponi2, J. Pilar3, D. Rostohar3 F. Schillaci1, T. Mocek3, G. Korn and D. Margarone1 1 Institute of Physics ASCR, v.v.i (FZU), ELI-Beamlines project, Prague, Czech Republic 2 Micro-Nano Facility, Fondazione Bruno Kessler, Trento, Italy 3 Institute of Physics ASCR, v.v.i (FZU), HILASE centre, Prague, Czech Republic * Corresponding author: Lorenzo.Giuffrida@eli-beams.eu Abstract An experimental campaign on ion generation was recently performed in HiLASE (Czech Rep.) by using the Bivoj laser system with a laser energy on target of 6 J, pulse duration between 5 and 10 ns, and repetition rates up to 10Hz. This laser system, focused on a solid target, was used to generate an ion beam propagating mainly along the target-normal (backward direction), aiming at its further use for applications. The laser was tightly focused on a solid target (around 5 m FWHM), thus a maximum intensity of 2*1015 W/cm2 was achieved, allowing to obtain up to 20 keV protons and 150 keV Al ions. The ion beam was characterized by using various Ion Collectors (IC), and an ion energy spectrometer, Thomson Parabola (TP). These diagnostics allowed to determine the delivered ion dose and corresponding energy. Moreover, a detailed investigation of ion/proton energy vs laser energy was carried out using various targets (semiconductors and metals). The generated ion beams have been explored for potential applications in various fields, such as material science and nuclear Physics. So far, a first attempt to demonstrate the feasibility of the produced ion beam for implantations was carried out. At this aim, Si substrates were irradiated with Al laser-plasma ions, integrating over few hundreds of laser shots. The implanted Si sample revealed the presence of Al atoms at a depth of a few hundred nanometers. This preliminary result might be promising for applications in microelectronics. A detailed description of the experimental setup will be provided, together with an analysis and interpretation of the achieved results. Finally, a perspective of future steps for possible applications in various applicative fields is given.

Speaker: Lorenzo Giuffrida

14:00 P2.3018 Numerical and feasibility study of MHD power extraction on supersonic vehicle

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3018.pdf Numerical and Feasibility Study of MHD Power Extraction on Supersonic Vehicle Song Chai, Gang Meng, Runhui Wu, Jiaqi Liu, Xin Liu and Ruiqi Sun National Key Laboratory of Science and Technology on Test Physics and Numerical Mathematics, China Academy of Launch Vehicle Technology, Beijing 100076, China The previous studies [1-2] have shown that there is sufficient ionized plasma surrounding the vehicle with a flight Mach number equal or greater than 10 which could sustain the plasma power extraction process via current collection electrodes and proper magnetic field methods. Thus, it is suitable to equip hypersonic vehicles with onboard thermal plasma energy extraction system, i.e. MHD power supply system. In this paper, a reduced model containing main features of on-board MHD generators has been constructed and problems have been solved numerically for the purpose of providing preliminary guidelines for the design of external MHD generators on board hypersonic vehicles. As it shows, the power extracted from the plasma flow field was related to profiles of magnetic field and fluid velocity, fundamental plasma characteristic, geometry parameter of electrodes, spacing and load voltage between electrodes. Based on the numerical results, an onboard MHD power extraction scenario was proposed accordingly, and systematic feasibility studies were performed. The results revealed that the power output of the MHD generator is capable of providing substantial energy output up to several hundred kilowatts or tens of kilowatts per square meter from the alkali-seeded/non-seeded boundary layer for typical flight condition, separately. [1] Macheret, S. O., et al, AIAA Paper 2004-2560 (2004) [2] Sheikin, E. G., et al, AIAA Paper 2005-1335 (2005).

Speaker: Song Chai

14:00 P2.3019 Effect of low-plasma treatment for GABA content and germination of barley

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3019.pdf Effect of low-plasma treatment for GABA content and germination of barley M.J. Lee1, H.S. Kim2, H.Y. Kim1, S.W. Choi1, W.D. Seo1, H.M. Ham, K.C. Jang1, H.J. Kang1, K.D. Park1 1 Crop Foundation Division, National Institute of Crop Science, 181 Hyeoksin-ro, Iseo-myeon, Wanju-Gun, Jeollabuk-do, 565-851, Republic of Korea 2 Department of Biomolecular and Chemical Engineering, Seonam University, Asan-city Chungnam-do, 31556, Republic of Korea Low-plasma has been recently investigated in the field of agricultural science as an alternative to the traditional pre-sowing seed treatment such as physical scratching, heat treatment and chemical treatment. The influence of low-plasma treatment on barley seeds(Hordeum vulgare L.) has been investigated by using a surface dielectric barrier discharge at atmospheric pressure and room temperature. Naked barley cultivars were Saessal and Saechal, covered barley cultivars were Hyeyang and Quenal1. We investigated the seed germination, surface morphology and functional material changes. Plasma treatment induced significant changes in the seed surface which was related to water permeability into the seeds. Seed surface was cracked and eroded after plasma treatment. Germination ratio was not significantly different according to plasma treatment. Hypocotyl and root length of barley that was treated for 3 minute with plasma increased. But they did not show the any tendency. GABA content of Saessal and Heyang did not show a big difference by plasma treatment, while in Saechal and Quenal showed an increasing tendency. After 3 germination days, GABA content increased approximately five times. DPPH was slightly decreased as plasma treatment time increased in seed and germination. However, the amount was different according to crops. [1] D. Dorbin, M. Magureanu, N. B. Mandache and M. D. Ionita, Ino. F. Sci. and Ener. Tech., 39, 255-260 (2015). [2] T. Stolarik, M. Hencelovia, M. Martinka, O. Novak, A. Zahoranova and M. Cernak, Plasma Chem. Plasma Process, 35, 659-676 (2015). [3] R. Montiel, I. M. Cabrejas. A. Peiroten and M. Medina, Ino. F. Sci. and Ener. Tech., 35, 111-118 (2016).

Speaker: Mi Ja Lee

14:00 P2.3020 Purification of water-soluble cutting fluid using an air DBD plasma and its characteristic analysis

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3020.pdf Purification of water-soluble cutting fluid using an air DBD plasma and its characteristic analysis S.H. Ma1, 2, K.I. Kim2, Y.C. Hong2,* 1 Department of Applied Plasma Engineering, Chonbuk National University, Jeonju, Korea 2 Plasma Technology Research Center, National Fusion Research Institute, Gunsan, Korea E-mail: ychong@nfri.re.kr Cutting fluids are essential for cutting performance and rust prevention in metalworking processes. Among cutting oils, the usage of water-soluble cutting fluids is increasing rapidly because they afford excellent cooling performance and ensure fire safety. However, water-soluble cutting fluids also offer a favorable environment for the growth of a wide variety of microorganisms. The growth of microorganisms can lead to various problems such as deterioration of the cutting fluids and odor generation. Thus, technologies for purifying the waste of water-soluble cutting fluids are required. In this study, we developed an ozone treatment technology that uses an air DBD plasma system. Furthermore, sterilization experiments were performed with K. pneumoniae, P. aeruginosa, E. coli, and P. vulgaris as representative microorganisms. The system offers the advantages of low power consumption and simple structure. Approximately 1000 ppm of ozone could be stably generated under optimized conditions, and the ozone was injected into the reactor as micro-bubbles for improving reactivity and inactivation rate. The sterilization experiments confirmed that the water-soluble cutting fluid was sterilized by 99.99%. As a result, the turbidity, pH, and odor of water-soluble cutting fluid have been improved. (a) Fig. 1. Schematic drawing of the developed (b) DBD system grounded with (a) coiled copper or (b) surrounded water for purifying Fig. 2. Photographs showing the stable DBD waste water-soluble cutting fluids plasma from air gas grounded with (a) coiled electrode and (b) surrounded with water. References [1] Y.C. Hong and H.S. Uhm, Appl. Phys. Lett., 89, 221504 (2006). [2] S.H. Ma, K.I. Kim, J.Y. Huh and Y.C. Hong, Sep. Purif. Technol. 188, 147 (2017)

Speaker: Sukhwal Ma

14:00 P2.3021 Source of extreme ultraviolet light based on expanding jet of dense plasma supported by microwaves: theory and modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.3021.pdf Source of extreme ultraviolet light based on expanding jet of dense plasma supported by microwaves: theory and modelling I. S. Abramov, A. G. Shalashov, E. D. Gospodchikov, A. V. Sidorov, A. V. Vodopyanov Institute of Applied Physics RAS, Nizhny Novgorod, Russia Transition to exposure using the extreme ultraviolet (EUV) radiation is vital for the development of next-generation projection lithography for the semiconductor industry [1]. The only practical method of EUV light generation is based on a line radiation of multiply charged ions considering that stripping causes a shift of the ion emission spectrum towards the shorter wavelengths for highly ionized charge-states. The most successful projects use evaporation of Sn droplets in a focused laser beam [2]. In this paper, inspired by the success of recent experiments in the Institute of Applied Physics [3, 4], we discuss a new advantageous concept of EUV light sources, based on the expanding jet of dense plasma of heavy noble gases (Xe, Ar) supported by high-power microwaves. Basing on a quasi-one- dimensional theory of plasma flows with varying charge-state composition [5, 6], we develop a numerical model of the EUV radiating jet [7]. The results of modelling are used for the analysis of recent experimental data and exploration of physical constraints for next generation devices. The work is supported by Russian Foundation for Basic Research (grant No. 17-02-00173). References [1] V. Bakshi, EUV Sources for lithography (SPIE press, 2006). [2] H. Mizoguchi et al., Proc. of SPIE 10143, 101431J-1 (2017). [3] M. Y. Glyavin et al., Applied Physics Letters 105(17), 174101 (2014). [4] A. V. Vodopyanov, EPJ Web of Conferences 149, 02009 (2017). [5] I. S. Abramov et al., Radiophysics and Quantum Electronics 58, 914 (2016). [6] A. G. Shalashov et al., JETP 123, 219 (2016). [7] I. S. Abramov et al., arXiv:1712.10026 (2018).

Speaker: Ilya Abramov

14:00 P2.4001 Ion velocity distributions in front of a ceramic surface: an inverse sheath ?

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4001.pdf Ion velocity distributions in front of a ceramic surface: an inverse sheath ? V. Pigeon1 , N. Claire1 , C. Arnas1 1 Aix-Marseille University, CNRS, PIIM, Marseille, France Plasma-wall interaction is a fundamental field of research in plasma physics for numerous applications. In Hall thrusters, it is known that the wall properties may influence the discharge, mainly through electron emission and sputtering. The sheath and pre-sheath in front of an in- sulator ceramic sample (BNSi02, used in the aforementioned thruster), immersed in the low temperature Argon plasma of a multipolar device are studied experimentally using an emissive probe and the laser-induced fluorescence diagnostic. Firstly obtained ion velocity distribution functions exhibited an unexpected flow of ions directed away from the wall toward the bulk plasma, and an other one toward the wall. But later experiments involving the laser beam prop- agation through a 0.8mm drilled hole (slightly smaller than the Debye length λD ' 1cm), see Fig.1, discarded the wall-directed ion flow. Despite the diffuse laser beam reflection at the ce- ramic surface, and small detection solid angle of sight, fluorescence transition saturation may explain the presence of the wall-directed flow in the first measurements. It seems that the BNSi02 secondary electron emission[1] and/or electrons reflected from an insulator surface [2] could be the cause of this phenomenon, which would correspond to an inverse sheath [3]. The ionizing energetic electrons present in the multipolar discharge are sus- pected to play a major role. Emissive probe measurements did not show this probable inverse sheath but a monotonic poten- tial drop. It seems that emissive probes could be too intrusive to measure potential in this thin high gradient region, especially if electron emission/reflection at the wall is present, leading biased measurements. Experimental artifacts removal and theoretical modeling (involving the Campanell’s model [3]) are currently performed in order to confirm the formation of an inverse sheath in front of the ceramic. 19 25 18 References 17 20 Position(cm) [1] T. Tondu, M. Belhaj and V. Inguimbert , J. Appl. 16 15 15 Phys. 110, 093301 (2011) 14 10 13 [2] F.X. Bronold and H. Fehske, Phys. Rev. Lett., 115, 5 12 225001 (2015) 11 -5 -4 -3 -2 -1 0 1 2 3 4 5 0 Velocity (km/s) [3] M.D. Campanell and M.V. Umansky, Phys. Plas- mas, 24, 057101 (2017) Figure 1: 2D ion velocity distributions in front of the drilled ceramic. Wall is at 23cm. Negative velocities are oriented toward the bulk plasma.

Speaker: Nicolas Claire

14:00 P2.4002 Ray tracing in weakly turbulent, randomly fluctuating media: A quasilinear approach

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4002.pdf Ray tracing in weakly turbulent, randomly fluctuating media: A quasilinear approach H. Hugon, J. P. S. Bizarro, R. Jorge Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal Ray propagation of electromagnetic and sound waves in turbulent media is important in a wide range of research areas, which can vary from astronomy and free-space communications to the scattering of rf waves in plasmas. y We describe the ray propagation in weakly tur- 600 bulent media using a quasilinear (QL) approach, 500 which relies on the Hamiltonian form of the ray equations and makes use of a second-order expan- 400 sion (in the medium and ray fluctuations) of the dis- 300 persion relation and ray equations, in order to inte- 200 grate the ensemble-averaged ray and its root-mean- 100 square (rms) spreading. Due to the second-order x terms, the averaged ray may exhibit a drift when -100 0 100 200 300 400 500 compared with the zero-order, unperturbed one. Figure 1: Average ray trajectories and their The QL formalism is validated against Monte rms spreadings from the QL formalism (red) Carlo (MC) calculations and, when possible, veri- vs. a MC calculation using 100 rays (black) fied using analytical predictions. For this, a single random mode and a multimode isotropic turbulent spectrum (see Fig. 1) was used as practical examples. The level of turbulence fluctuations and its maximum wavenumber are chosen to be not too small, yet small enough such that the second order expansion and the geometrical optics approximation remain valid. Overall, the agreement between the QL and MC results is fair, particularly for the distance travelled by the average ray, its perpendicular rms spread and the averages of the wave-vector components. This approach comes as an efficient alternative to MC calculations and, while similar to the so-called statistical ray tracing [1], it appears to be much easier to implement in the case of more complex geometries or dispersion relations (as when tracing rays in tokamaks). References [1] R. Epstein and R. S. Craxton, Phys. Rev. A 33, 1892 (1986)

Speaker: Hugo Pereira Hugon

14:00 P2.4003 The effect of advected magnetic fields in jet propagation experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4003.pdf The effect of advected magnetic fields in jet propagation experiments D. R. Russell1, S. V. Lebedev1, G. C. Burdiak2, J. W. D. Halliday1, J. D. Hare1, L. G. Suttle1, F. Suzuki-Vidal1, E. Tubman1, T. A. Clayson1 1 Imperial College London, UK 2 First Light Fusion Ltd, Oxford, UK Astrophysical jets are a common feature during star formation. It is believed that magnetic fields play a key role in the formation of these jets, however the interaction of the jet with the ambient medium far from the source is dominated by purely hydrodynamical processes [1]. Appropriately scaled laboratory experiments, in which the amount of advected magnetic field can be controlled, can aid our understanding of the observed complex structure of these jets. The use of pulsed power-driven ablation of conical wire arrays [2] has allowed the production of supersonic, radiatively cooled jets scalable to astrophysical systems. In some of these experiments, the advected magnetic field was dynamically significant, which was most evident in the interaction of the jet with an ambient medium [3]. To enable the full range of jet dynamics to be studied, it is desirable to be able to modify the jet magnetisation within the same experimental setup. Here we present experimental results from a new conical wire array jet-launching platform, in which the magnetic field advected by the jet is expected to be significantly reduced in comparison with previous experiments. This is achieved by preconditioning the wires with a pre-pulse current [4], allowing the formation of a supersonic jet driven by a fast plasma implosion. These experiments are carried out on the Magpie (~1 MA, 250ns) pulsed power generator, using a suite of high temporal and spatial resolution diagnostics. Faraday rotation polarimetry, Thomson scattering and laser interferometry, allow direct measurement of the magnetic field, electron and ion temperatures, flow velocities and electron density distributions. This work was supported in part by First Light Fusion Ltd, the Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/N013379/1, and by the NNSA under DOE agreements DE-F03-02NA00057, DE-SC-0001063 and DE-NA-0003764 [1] P. Hartigan et al (2001). ApJ, 559, L157 [2] D. J. Ampleford et al (2008). PRL, 100, 035001 [3] D. J. Ampleford et al (2005). Astrophys. Space Sci, 298 (1–2), 241 [4] G. C. Burdiak et al (2015). PoP, 22, 112710

Speaker: Daniel Russell

14:00 P2.4004 Hybrid Simulation of KH Instability in the Presence of Flow

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4004.pdf Hybrid Simulation of K-H Turbulence in the Presence of Flow D. LIN, Virginia Tech, VA, S. SEN, William & Mary, VA; National Institute of Aerospace, VA; and Bowie State University, MD, W. SCALE, Virginia Tech, VA, N. PETULANTE, Bowie State University, MD, and M. L. GOLDSTEIN, NASA-GSFC, MD, University of Maryland at Baltimore County, MD and University of Colorado, CO, USA We study the effect of inhomogeneous flow on the Kelvin-Helmholz instability and turbulence. The inhomogeneous flow includes both flow shear and flow curvature. The effect of flow curvature (second radial derivative of flow) is shown to have significant effect in controlling the turbulence level contrary to the usual prediction that flow shear (first radial derivative of flow) alone controls the turbulence level. The detail result of this simulation will be reported. In this study of flow curvature effects, a two-dimensional hybrid model is used to simulate the Kelvin-Helmholtz instability (KHI). The hybrid model treats the ions as particles, and electrons as massless fluid. Pressure and resistivity are assumed as isotropic. A classical configuration for the study of KHI is investigated, i.e. transverse shear flow to uniform background magnetic field. This is thought as the most unstable situation in magnetohydrodynamic (MHD) theory. There are 50 super particles per cell in the current simulations, which number could be increased to as much as 200 in the future. The boundary is periodic along the flow direction and reflective in the perpendicular direction. The code was originally developed by the Los Alamos National Laboratory and has been successfully applied to the study of Kelvin-Helmholtz instability on the Earth's magnetopause. In this study, the code has been running on the Advanced Research Computing (ARC) platforms of Virginia Tech. Four distinct shear profiles are simulated to investigate the effects of flow curvature on the growth of the KH instability: uniform flow, linear shear without curvature, quadratic profile with positive curvature, and quadratic profile with negative curvature. By comparing plasma flows from the four simulations with the same amount of time of evolvement, it is visible that the KH vortex is most nonlinearly developed in the case of negative curvature. In the case of linear shear, the vortex is less developed, but coalesce of two adjacent vortices is about to occur. Two vortices can also be seen in the case of positive curvature. The uniform flow basically keeps stable. This work is supported by the DOE grant DE-SC0016397

Speaker: Sudip Sen

14:00 P2.4005 Whistler wave instabilities of runaway electrons in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4005.pdf Whistler wave instabilities of runaway electrons in tokamaks Chang Liu1 , Eero Hirvijoki1 , Dylan Brennan2 , Guo-yong Fu1,3 , Amitava Bhattacharjee1,2 1 Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA 2 Princeton University, Princeton, New Jersey 08544, USA 3 Zhejiang University, Hangzhou, Zhejiang, 310027, China Highly energetic runaway electron beam can be generated in tokamak disruptions, which can be destructive to the device. The runaway electron beam has a bump-on-tail and anisotropic distribution due to parallel acceleration and radiation reaction, thus can be susceptible to kinetic instabilities. In this work the whistler wave instabilities associated with runaway electron beam is investigated using a newly-developed simulation model, and the anomalous dissipation and the fast pitch angle scattering of runaway electrons in low energy are explained[1]. The interaction of runaway electron avalanche (a) 10.0 7.5 and the kinetic instabilities are studied self- (mc) 5.0 consistently using quasilinear model. Results show p 2.5 0.0 that excited whistler waves can cause electrons to 0 5 10 15 20 (b) 25 10.0 be scattered to large pitch angle (Fig. 1) and form 7.5 (mc) 5.0 vortices in momentum space, creating a new en- p 2.5 0.0 ergy loss channel, and enhance the radiations. This 0 5 10 15 20 25 p (mc) explains the higher-than-expected critical electric Figure 1: Compared to the case without kinetic in- field and the loss of runaway electron population stabilities (a), the electrons scattered by whistler in low energy regime identified experimentally[2]. waves has broader distribution in pitch angle (b). The whistler waves excited in runaway electron ex- periments have recently been measured in both flattop phases[3] and post-disruption stages, which is consistent with the simulation results. The fast growth of electron cyclotron emission (ECE) signals observed in experiments is reproduced by a synthetic diagnostic tool. In addition, the oscillations of the ECE signals is explained through the nonlinear interactions between the excitation of whistler waves and the scattering of electron distribution function. References [1] C. Liu, E. Hirvijoki, G. Y. Fu, D. P. Brennan, A. Bhattacharjee, and C. Paz-Soldan, arXiv:1801.01827 (2018). [2] C. Paz-Soldan, C. M. Cooper, P. Aleynikov, D. C. Pace, N. W. Eidietis, D. P. Brennan, R. S. Granetz, E. M. Hollmann, C. Liu, A. Lvovskiy, R. A. Moyer, and D. Shiraki, Phys. Rev. Lett. 118, 255002 (2017). [3] D. A. Spong, W. W. Heidbrink, C. Paz-Soldan, X. D. Du, K. E. Thome, M. A. V. Zeeland, C. Collins, A. Lvovskiy, R. A. Moyer, D. P. Brennan, C. Liu, E. F. Jaeger, and C. Lau, submitted to Phys. Rev. Lett.

Speaker: Chang Liu

14:00 P2.4006 Global modes of gradient drift instability in Hall plasma thruster

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4006.pdf Global modes of gradient drift instability in Hall plasma thruster N.A. Marusov1−3 , E.A. Sorokina1,2 , V.P. Lakhin1,2 , V.I. Ilgisonis2,4 , A.I. Smolyakov2,5 1 NRC "Kurchatov Institute", Moscow, Russia 2 Peoples’ Friendship University of Russia (RUDN University), Moscow, Russia 3 Moscow Institute of Physics and Technology, Moscow region, Russia 4 State Atomic Energy Corporation ROSATOM, Moscow, Russia 5 University of Saskatchewan, Saskatoon, Canada Plasma in coaxial Hall thrusters is subject to a lot of instabilities driven by azimuthal E × B electron flow [1, 2]. Such instabilities directly affect the operational capabilities of plasma thrusters due to their impact on anomalous electron mobility across the external magnetic field [1, 3, 4]. In this paper the instability analysis of global electrostatic modes in inhomogeneous partially magnetized plasmas (unmagnetized ions and magnetized electrons) is performed in the framework of two fluid model. The eigenvalue equation, including the effects of electron inertia, gradients of plasma density and magnetic field, along with the shear of equilibrium electron flow, is derived and numerically solved for the Hall thrusters specific values and axial profiles of external magnetic field and plasma parameters [5]. The obtained solutions are compared with the results of local stability analysis, predicting the existence of the long-wavelength instability in the near-anode region of thruster channel [6]. It is shown that the characteristics and the structure of unstable eigenmodes strongly depend on the geometry of the thruster. For some ratios of the acceleration channel length to its radius the instability can be fully stabilized. References [1] E.Y. Choueiri, Phys. Plasmas 8, 1411 (2001) [2] J.P. Boeuf, Front. Phys. 2, 74 (2014) [3] A.I. Morozov, Yu.V. Esipchuk, A.M. Kapulkin, V.A. Nevrovskii, and V.A. Smirnov, Sov. Phys. Tech. Phys. 17, 482 (1972) [4] Yu.V. Esipchuk and G.N. Tilinin, Sov. Phys. Tech. Phys. 21, 417 (1976) [5] R. Hofer, I. Mikellides, I. Katz, and D. Goebel, in Proc. of 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, AIAA 2007-5267, 2007 [6] N.A. Marusov, E.A. Sorokina, V.P. Lakhin, V.I. Ilgisonis, in Proc. of 44th EPS Conference on Plasma Physics, P4.416, 2017

Speaker: Nikita Marusov

14:00 P2.4007 Influence of electrode area asymmetry on harmonics generated in a direct coupled radio frequency discharge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4007.pdf Influence of electrode area asymmetry on harmonics generated in a direct coupled radio frequency discharge A. Rawat, A. Ganguli, R. Narayanan, R.D. Tarey Indian Institute of Technology Delhi, New Delhi, India Radio frequency (RF) discharges have been serving modern plasma processing technologies for several decades [1]. In this context, an important issue that arises is the mechanism of power coupling in RF discharges. For instance, while at high pressures, collisions are responsible for the net power transferred to plasma (ohmic heating), it is conjectured that at low pressures nonlinear RF sheath oscillations may be responsible (stochastic heating) for sustaining the discharge [2]. However, the latter mechanism is unable to explain fully power absorption at low pressures. A key feature of low pressure (few mTorr) RF discharges is the presence of harmonics of the fundamental RF frequency. It is well known that the non-linearity of sheaths can generate multiple harmonics and so it may be expected that detailed characterization of the harmonics may provide important signatures of absorption mechanisms. Although numerous theories and simulations have been proposed so far, experimental studies on nonlinear characterization of RF discharges are very rare. In this work, a novel non-invasive plasma diagnostic technique using a Dual Directional Coupler (DDC) was used to investigate these nonlinear phenomena in RF discharges. Different electrode geometries were used (AP/AG = 1, 0.91, 0.51, where AP and AG are the area of powered and grounded electrodes respectively). The technique not only determines the harmonics present in plasma, but also yields accurately the power in the forward and reflected waves of the fundamental and each harmonic generated in the plasma. Plasma is ignited using 13.56 MHz RF generator with argon pressure ranging from 5 mTorr to 200 mTorr. The experiments were performed in a directly coupled capacitive RF discharge (without a blocking capacitor) since a blocking capacitor induces a large, negative DC self-bias on the powered electrode, that damages the coupler. Experimental results show the presence of even and odd harmonics for symmetric geometry (AP/AG = 1) along with a high plasma potential. Both these facts contradict the theoretical models [3] for AP/AG = 1. Also, the power content of these harmonics increases with increasing geometrical asymmetry and decreasing pressures. Some of the results from the ongoing experiments will be presented in the conference. References [1] P. Chebert et al, Physics of radio-frequency plasmas, Cambridge University Press (2011). [2] J. Schulze et al, Plasma Sources Sci. Technol.18, 034011 (2009). [3] M. A. Lieberman, IEEE Trams. Plasma Sci. 16, 6 (1988).

Speaker: Arti Rawat

14:00 P2.4008 Demonstration of loss cone induced quasi-longitudinal (QL) whistlers in large laboratory plasma of LVPD

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4008.pdf Demonstration of Loss Cone Induced Quasi-Longitudinal (QL) Whistlers in Large Laboratory Plasma of LVPD A. K. Sanyasi1, L. M. Awasthi1, Prabhakar Srivastav1, P. K. Srivastava1, R. Sugandhi1, S. K. Mattoo1, D. Sharma1, R. Singh2, R. Paikaray3 and P. K. Kaw 1 Institute for Plasma Research, Gandhinagar 382428, India 2 Advance Technology Centre, NFRI, Daejeon, South Korea 3 Ravenshaw University, Cuttack – 753001, India E-mail: amulya@ipr.res.in Abstract Whistler turbulence observed in earth’s magnetosphere has free energy source lies in energetic electrons, electron beams, anisotropies in temperature and electron distribution function, density gradients, loss cone etc. and is responsible for the precipitation of energetic electrons into the ionosphere. This has been observed that when pole bound electrons get trapped in the earth’s magnetic field and suffers loss cone instability, which results in the excitation of Quasi-Longitudinal (QL) whistlers at large oblique angles. We report experimental observation of loss cone driven Quasi-Longitudinal (QL) whistlers in a laboratory plasma excited by the reflected electrons from a magnetic mirror. The QL whistler propagate highly obliquely ( θ = tan −1 (k ⊥ / k || ) ≈ 87 0 ) in a broad band of 40kHz < f ≤ 80 kHz with k ⊥ ~ 1.4 cm −1 and k || ~ 0.06cm −1 respectively. It exhibits strong correlation between density and magnetic field fluctuations ( , = −0.9), and interestingly it shows a continuous variation of wave polarization with frequency. We have compared experimental observations with numerical results obtained from the theoretical models of Sharma et al. [1], Olga et al. [2] and Quasi Longitudinal (QL) whistlers by Henry G. Booker et al., [3] and found a good agreement between them. This is probably first laboratory demonstration of QL whistlers and detailed results on it will be presented in the conference [4]. References [1] R. R. Sharma and Loukas Vlahos, The Astrophysical Journal 280, 405(1984). [2] O. P. Verkhoglyadova et. al., J. Geophys. Res. 115, A00F19 (2010). [3] Henry G. Booker and Rolf B. Dyce, Radio Science Journal of Research NBS/ USNC-URSI, Vol. 69D, No. 4, April 1965. [4] A. K. Sanyasi, L. M. Awasthi, P. K. Srivastava, S. K. Mattoo, D. Sharma, R. Singh, R. Paikaray and P. K. Kaw, Phys. Plasmas 24, 102188 (2017).

Speaker: Amulya Kumar Sanyasi

14:00 P2.4009 Shock propagation through cepheid envelopes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4009.pdf Shock propagation through cepheid envelopes O. Saincir1,2 , C. Michaut2 , L. Di Menza1,2 , S. Bouquet3,2 , M. Mancini2 1 Laboratoire de Mathématiques, Université de Reims, Moulin de la Housse, 51687 Reims, France 2 LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, 92190 Meudon, France 3 CEA, DAM, DIF, 91297 Arpajon, France A cepheid is a supergiant variable star which is positioned in the instability band of the HR diagram. Spectroscopic and interferometric observations [1] show that long-period cepheids exhibit asymmetries in the P Cygni-type profiles around the Hα line [2]: an absorption compo- nent with an emission component redshifted or blueshifted depending on the pulsation phase. Astronomers assume that these asymmetries are caused by the presence of strong shocks [3] propagating in the envelope due to the pulsation of the photosphere [4]. The HADES code [5] is a numerical tool which is developed since several years to perform numerical simulations of radiative hydrodynamics models for the study of hypersonic flows in stellar physics (jets of young stars, accretion shocks, supernova remnants, etc.). The interest of our work is to use HADES to carry out simulations of shock in the envelope of cepheids accord- ing to the scenarios proposed by astronomers. In order to compare our numerical results with observations, an observable around the Hα line is reconstructed from hydrodynamic quantities resulting from numerical simulations (density, velocity and temperature of the fluid). References [1] P. Kervella, A. Mérand, A. Gallenne, Astron. & Astrophys. 498, 425 (2009) [2] N. Nardetto, J.H. Groh, S. Kraus, et al., Astron. & Astrophys. 489, 1263 (2008) [3] D. Gillet, A. B. Fokin, Astron. & Astrophys. 68, A72 (2014) [4] A. Mérand, P. Kervella, V. Coudé du Foresto et al., Astron. & Astrophys. 453, 155 (2006) [5] C. Michaut, L. Di Menza, H.C. Nguyen et al., High Energy Density Physics 22, 77 (2017)

Speaker: Claire Michaut

14:00 P2.4010 Multi-diagnostics investigation of an ECR plasma confined in a simple mirror trap

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4010.pdf Time-characterization of RF/X-ray bursts during a Cyclotron Instability in Simple Mirror and B-minimum Traps D. Mascali1, J. Angot2, G. Castro1, A. Galatà,3 S. Gammino1, M. Giarrusso1, F. Leone4,5,1, M. Mazzaglia1, R. Miracoli6, E. Naselli4,1, G. Torrisi1 1 Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, 95123 - ITALY 2 Univ. Grenoble Alpes, CNRS, Grenoble INP*, LPSC-IN2P3, 38000 Grenoble, France * Institute of Engineering Univ. Grenoble Alpes 3 Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro (PD) - Italy 4 Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, I-95123 Catania, Italy 5 INAF—Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy 6 ESS - Bilbao, Bilbao, Spain A Cyclotron-type instability has been observed at INFN-LNS on an axis-symmetric plasma trap based on a Simple Mirror configuration, where the plasma is sustained via 4 and 7 GHz Electron Cyclotron Resonance heating, and at the LPSC in Grenoble, in a B-minimum trap operating at 14 GHz. The Radio and X-ray bursts produced by the unstable plasma have been characterized in a time resolved way: a) Radio-signals detected along and across the magnetic axis have been measured in a timescale <100 ns via 80 Gs/s, 20 GHz band scope; a dedicated wavelet analysis shows the inner-plasma self-generation of waves far from the pumping frequency; b) fast Germanium detectors provide the evolution of the X-rays emitted axially and radially, allowing time-resolved spectroscopy; typical observed X-ray bursts lie in the timescales of ms or tens of ms, depending on the mirror ratio, and are emitted by the plasma few ms after the RF ones. Both RF and X-ray signals can be ranked on a temporal sequence which provides the whole characterization of the instability. Implications on laboratory plasma physics and astrophysical plasmas will be discussed.

Speaker: Giuseppe Castro

14:00 P2.4011 Apparatus for investigating non-linear microwave interactions in magnetised plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4011.pdf Apparatus for investigating non-linear microwave interactions in magnetised plasma K. Ronald1, A.D.R. Phelps1, R.A. Cairns2,1, R. Bingham3,1, B Eliasson1, M.E. Koepke4,1, A.W. Cross1, D.C. Speirs1, C.W. Robertson1, and C.G. Whyte1 1 Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, Scotland, UK 2 School of Mathematics and Statistics, University of St Andrews, KY16 9SS, Scotland 3 STFC Rutherford Appleton Laboratory, Harwell, Oxford, Didcot, OX11 0QX, England 4 Department of Physics, West Virginia University, Morgantown, WV 26506-6315, USA Electromagnetic wave injection plays a dominant role in the introduction of energy in laser plasma interactions and in the heating of magnetically confined fusion reactors. Nonlinear coupling enables energy to be transferred between one or more EM waves interacting in plasma. Coupling of injected EM waves to Langmuir and ion acoustic waves is of interest for a number of laser plasma interactions and in ionospheric physics experiments. Long (and short) pulse signals with normalised intensities approaching those used in some recent laser plasma interactions can be generated using flexible microwave amplifiers. Multi-wave microwave interactions can be directly relevant to the delivery of heating and current drive in future magnetic confinement fusion (MCF) reactors coupling to cyclotron motion of ions and electrons and to lower hybrid waves. Understanding of the nonlinear electrodynamics will benefit from employing microwave sources and amplifiers to precisely launch and electronically control multiple EM signals. The relatively long lived, benign and accessible plasma relevant to coupling of microwave frequency signals will enable the use of insertion diagnostics in addition to analysing the EM signals. A linear plasma experiment is being designed, which will be magnetised at up to 0.8T. The plasma will be created by an RF helicon source, using a whistler wave injected from a high-field region to generate a dense, large, cool plasma with high ionisation fraction (an electron number density up to 1019m-3 has been reported in other helicon experiments). A range of frequency-flexible microwave sources will provide beams to enable multi-wave coupling experiments. The paper will present the proposed apparatus and will outline the envisioned research programme. The authors gratefully acknowledge support from the EPSRC, MBDA UK Ltd and TMD Technologies Ltd.

Speaker: Kevin Ronald

14:00 P2.4012 Flow control and its impact on avalanche dynamics in a basic transport experiment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4012.pdf Flow control and its impact on avalanche dynamics in a basic transport experiment S. Jin1, B. Van Compernolle1, M. J. Poulos1, G. J. Morales1 1 Department of Physics and Astronomy, University of California, Los Angeles, United States Results of a basic heat transport experiment1,2 involving an offaxis heat source are presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A ringfshaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic feld into a prefexisting, large and cold plasma. The injected electrons provide an offaxis heat source that results in a long, hollow, cylindrical region of elevated plasma pressure embedded in a colder plasma, and far from the machine walls. The offaxis source is active for a period long compared to the density decay time, i.e. as time progresses the power per particle increases. Two distinct regimes are observed to take place, an initial regime dominated by avalanches, identifed as sudden intermittent rearrangements of the pressure profle, and a second regime dominated by sustained driftfAlfven wave activity following a global collapse of the density profle. The avalanches are triggered by the rapid growth of driftfAlfven waves. The data suggest that fows play a critical role in the dynamics, in particular in the onset of the avalanches through the interplay of the stabilizing fow shear and the destabilizing pressure gradient. The fows are imposed by the boundary condition at the ringfsource. This source has now been modifed from previous experiments to gain active control of the fows by controlling the bias between the emitting ring and surrounding carbon masks. A regime was found in which avalanches are absent. The new source also provides some control over the size and frequency of avalanches when present. Supported by the NSF grant PHY1619505, and performed at the Basic Plasma Science Facility, sponsored jointly by DOE and NSF. 1 B. Van Compernolle et al. Phys Rev. E 91, 031102 (2015) 2 B. Van Compernolle et al, Phys. Plasmas 24, 112302 (2017)

Speaker: Suying Jin

14:00 P2.4013 Current sheets in kinetic simulations of plasma turbulence between ion and electron scales

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4013.pdf Current sheets in kinetic simulations of plasma turbulence between ion and electron scales Kirit Makwana1 1 Center for mathematical Plasma Astrophysics, Dept. of Mathematics, KU Leuven, Belgium We present 3D PIC simulations of plasma turbulence relevant for turbulence in the solar wind. These are performed by initializing an ensemble of shear Alfven waves with wavelengths moderately larger than the ion skin depth scale. In earlier work such simulations were performed with ion-positron pair plasmas [1, 2]. Now we use a reduced but non-unity mass ratio between ions and electrons. This allows us to investigate the range of scales between ion and electron skin depth. We present the turbulent spectrum between the ion and electron scales and an analysis of the current sheets that form in this range. This is relevant for observations of current sheets in solar wind turbulence. References [1] K. D. Makwana, V. Zhdankin, H. Li, W. Daughton and F. Cattaneo, Physics of Plasmas 22, 042902 (2015) [2] Kirit Makwana, Hui Li, Fan Guo, and Xiaocan Li, Journal of Physics: Conference Series 831, 012004 (2017)

Speaker: Kirit Makwana

14:00 P2.4014 Electron acceleration and maser radiation from collisionless shocks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4014.pdf Electron acceleration and maser radiation from collisionless shocks R. Bingham1,2, D.C. Speirs1, K. Ronald1, A. Rigby3, R. Bamford2,3, R. A. Cairns4, A.D.R. Phelps1, M. E. Koepke5, B. J. Kellett2, L. O. Silva6, S. Lebedev7, G. Gregori3 1Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, U.K. 2Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England, OX11 0QX, U.K. 3Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, U.K. 4School of Mathematics and Statistics, University of St. Andrews, Fife, Scotland, KY16 9SS, U.K. 5Department of Physics, West Virginia University, Morgantown, WV 26506-6315, U.S.A. 6GoLP/Instituto de Plasmas e Fusau Nuclear, Instituto Superior Tecnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 7Imperial College London, London, SW72AZ, U.K. In this paper we describe a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetised collisionless shocks. It is inspired by the work of Begelman, Ergun and Rees [1] who argued that the cyclotron maser instability occurs in localised magnetised collisionless shocks such as those expected in Blazar jets. We report on two recent laboratory experiments and numerical simulations carried out to investigate electron acceleration at collisionless shocks and the maser radiation mechanism [2][3][4]. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. Magnetic compression and conservation of magnetic moment lead to the formation of an electron velocity distribution having a horseshoe shape as the electrons are accelerated along the magnetic field. Under certain conditions the horseshoe electron velocity distribution is unstable to the cyclotron maser instability. Electron ring distributions are also unstable to cyclotron maser emission and we show that such distributions can also be generated at collisionless magnetised shocks. [1] M. C. Begelman, R. E. Ergun, and M. J. Rees, Astrophys. J. 625, 51 (2005). [2] F. Cruz et al., Physics of Plasmas 24, 022901 (2017). [3] D. C. Speirs et al., Phys. Rev. Lett. 113, 155002 (2014). [4] K. Ronald et al., Physics of Plasmas 15, 056503 (2008).

Speaker: R. Bingham

14:00 P2.4015 Particle acceleration in high energy density magnetic reconnection experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4015.pdf Particle acceleration in high energy density magnetic reconnection experiments J. W. D. Halliday1 , J. D. Hare1 , L. G. Suttle1 , S. V. Lebedev1 , S. N. Bland1 , T. A. Clayson1 , E. Tubman1 , D. R. Russell1 , S. Pikuz2,3 , and T. Shelkovenko2,3 1 Blackett Laboratory, Imperial College, London, SW7 2AZ, United Kingdom 2 Cornell University, Ithaca, USA 3 Lebedev Institute of Physics, Moscow, Russia Magnetic reconnection is important in astrophysical and space plasmas, from the strongly driven and collisionless interaction of planetary magnetospheres with the solar wind; to the more weakly driven and collisional flows found in the solar convective zone. In these plasmas, fast particles are a key signature of reconnection. In this presentation, we describe experimental results from a novel reconnection platform [1, 2] which are consistent with the direct accel- eration of electrons by the reconnecting electric field. The platform uses the MAGPIE pulsed power generator to produce plasma inflows (uin ∼ 50 km/s) that carry a strong azimuthal mag- netic field (Bin ∼ 3T ) and persist for many hydrodynamic timescales ( Ttotal ∼ 500 ns Thydro 10 ns). These experiments are typically diagnosed using laser interferometry, Faraday rotation, and Thomson scattering. For the results presented here thermal, magnetic, and ram pressure are all dynamically sig- nificant (βdyn ∼ βth ∼ 1); the Lundquist number is S ∼ 120; and the ratio of the ion skin depth to the layer width is di /δ ∼ 1. This regime is distinct and complimentary to laser driven and gas discharge reconnection experiments. In this work we enhanced our diagnostic capability to study non-thermal electron acceleration by the reconnecting electric field. Metal foils were placed in the path of the accelerated electrons, which collisionally excited atomic transitions, producing characteristic X-Ray spectra. These were diagnosed using spherically bent crystal X-Ray spectroscopy and filtered pinhole imaging. Time resolved measurements were obtained using fast silicon diode detectors. We observed spectra consistent with a significant population of super thermal particles, exceeding the thermal velocity of the plasma by over an order of magnitude. By combining these fast particle diagnostics with our existing diagnostic suite, we can enhance our growing understanding of the link between astrophysical observations and lab- oratory experiments. [1] Suttle, L. G., Hare, J. D., Lebedev, S. V. et. al. (2016). PRL, 116, 225001 [2] Hare, J. D., Suttle, L. G., Lebedev, S. V. et. al. (2017). PRL, 118, 85001

Speaker: Jack Davies Hare

14:00 P2.4016 Megajoule designs relevant to study radiative accretion shocks in magnetic accreting white dwarfs

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4016.pdf Megajoule designs relevant to study radiative accretion shocks in magnetic accreting white dwarfs L. Van Box Som1,2,3 , É. Falize1,3 , J.-M. Bonnet-Bidaud3 , C. Busschaert1 , A. Ciardi2 , M. Koenig4 , M. Mouchet5 1 CEA, DAM, DIF, F-91297 Arpajon, France 2 LERMA, Sorbonne Université, Observatoire de Paris, Université PSL, Paris, France 3 CEA Saclay, DSM/Irfu/Service d’Astrophysique, F-91191 Gif-sur-Yvette, France 4 LULI - CNRS, École Polytechnique, CEA : Université Paris-Saclay ; UPMC Univ. Paris 06 : Sorbonne Université, Palaiseau, France 5 LUTH, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, F-92195 Meudon, France Magnetic accreting white dwarfs are perfect laboratory objects to study the high-energy pro- cesses in extreme astrophysical regimes. These objects are part of complex binary systems and they accrete matter from a low-mass companion star [1]. The radiation observed from these sys- tems comes mainly from an unresolved area where the accretion flow impacts the white dwarf surface creating an accretion column [2, 3]. Based on the similarity properties of this high- energy environment [4], millimetre-sized models of accretion columns can be produced with powerful lasers and can give us new opportunities to study the radiative accretion processes in laboratory. For the first time, we will introduce a new target design to produce similar astro- physical regime which are only achievable on megajoule facilities (LMJ, NIF) [5]. The data ob- tained from such laboratory experiments will provide new insights and help clarify outstanding questions related to radiative transfer in accretion column models. By gathering astronomical observations, theoretical, numerical and experimental studies, we will improve our understand- ing of the radiative effects on both the post-shock structure and the accretion shock dynamics which are fundamental for the characterization of magnetic accreting white dwarfs systems. References [1] Warner, B. Cambridge Astrophysics Series, 28 (1995) [2] Mouchet, M., Bonnet-Bidaud, J.-M., Van Box Som, L., et al. Astron. & Astrophys., 600, A53 (2017) [3] Van Box Som, L., Falize, É., Bonnet-Bidaud, J.-M., et al. Mont. Not. R. astr. Soc. 444, 420-428 (2018) [4] Falize, É., Michaut, C., & Bouquet, S., Astrophys. J., 730, 96 (2011) [5] Casner, A., Caillaud, T., Darbon, S., et al. 2015, High Energy Density Physics, 17, 2

Speaker: Lucile Van Box Som

14:00 P2.4017 Experimental study of laser plasma expansion in presence of the strong external magnetic field

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4017.pdf Experimental study of laser plasma expansion in presence of the strong external magnetic field A. Soloviev1, K. Burdonov1, S. N. Chen1,2, G. Revet2, S. Pikuz3, E. Filippov3, M. Cerchez4, T. Gangly2, A. Sladkov1, A. Korzhimanov1, V. Ginzburg1, E. Khazanov1, A. Kochetkov1, A. Kuzmin1, I. Shaykin1, A. Shaykin1, I. Yakovlev1, M. Starodubtsev1, and J. Fuchs1,2 1 Institute of Applied Physics, Russian Academy of Science, Nizhny Novgorod, Russia 2 LULI, CNRS UMLR7605, Ecole Polytechnique, Palaiseau, France 3 Joint Institute for High Temperatures, Russian Academy of Science, Moscow, Russia 4 HHU, Dusseldorf, Germany We present recent experiments, performed at PEARL laser facility (Institute of Applied Physics), aimed at investigating the dynamic of plasma flows expending into the ambient magnetic field. The main attention has been paid to the case when the plasma flow penetrates across the magnetic field. Such geometry of the experiment is related to laboratory modeling of accretion of matter into compact stars and, especially, to the processes developing at the inner edge of the accretion disks in the region where the pressure of the magnetic field of the star is of the order of the dynamic pressure of the accreting plasma. Using two femtosecond interferometers, 2D snapshots of plasma flow expanding into the ambient magnetic field have been obtained in two geometries (perpendicular and parallel to the direction of the magnetic field lines) and in different times after the plasma flow formation. It has been found that the plasma flow exhibits strong Rayleigh–Taylor instability in the region where the pressure of the magnetic field is of the order of the plasma flow dynamic pressure. As a result of this instability, the plasma flow deeply penetrates into the magnetic field forming a narrow (‘pancake-like’) tongs of supersonic plasma streams (in practice, a thin plasma layer penetrates between the magnetic field lines). This result, confirmed also by numerical modeling, calls into question the generally accepted astrophysical model of matter accretion in form of ‘accretion columns’, when the matter falls onto the star from the inner edge of the accretion disc (which is formed at the magnetic/plasma dynamic pressures balance region) along the magnetic field lines to the polar regions of the star. On the contrary, the results of the present experiment make it possible to propose an alternative model for the fall of matter onto the equator of the star.

Speaker: Alexander A. Soloviev

14:00 P2.4018 Experimental studies of electron emission properties under magnetic field for copper samples: effect of the surface morphology

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4018.pdf Experimental studies of electron emission properties under magnetic field for copper samples: effect of the surface morphology. N. Fil 1,2,3, J. Hillairet1, M. Belhaj2, J. Puech3, R. Mathevet4 1 CEA, IRFM, Saint Paul-lez-Durance, France 2 ONERA-The French Aerospace Lab, Toulouse, France 3 CNES-The French National Centre for Space Studies, Toulouse, France 4 LNCMI-Intense Magnetic Fields Laboratory, Toulouse, France Magnetic confinement fusion devices [1], particle accelerators [2] and space communication payload [3], among other applications, are concerned by multipactor effect. This undesirable phenomenon is a resonant process which can lead to power handling limitation of RF components [4]. To determine the multipactor power threshold, experimental tests or/and simulations are commonly used. The power threshold is closely related to the electron emission properties of the RF component materials. Accurate power threshold predictions by simulations should be based on the use of accurate electron emission propriety data [5]. In some situations [1]–[3], the RF components are submitted to DC magnetic fields which might affect the electron emission properties and hence the multipactor power threshold. In a collaborative effort between French research centres CEA, CNES and ONERA, a new experimental setup specially designed to investigate the effect of DC magnetic field on the electron emission properties was developed. In this paper, we first describe the development of the experimental setup and the optimisation of the associated measurement methodology. Then we show and analyse the total electron emission yield (TEEY) measurements made on copper samples under magnetic field perpendicular to the sample surface. We have studied various surface morphologies such as laminated and polished and have observed TEEY increase as well as decrease depending on the magnetic field amplitude and the surface morphology. With incident electron at first cross-over energy (EC1), DC magnetic field has a greater influence on the laminate surface than the polished one (respectively TEEY decreased to 45% and 5%). Such impact of the magnetic field must be considered on multipactor effect simulations codes. [1] J. de Lara, et al. Garcia-Baquero, IEEE Trans. Plasma Sci., vol. 34, no. 2, pp. 476–484, 2006. [2] G. Rumolo, et al., Phys. Rev. Spec. Top. - Accel. Beams, vol. 4, no. 1, pp. 25–36, 2001. [3] M. Goniche, et al., Nucl. Fusion, vol. 54, no. 1, p. 13003, 2014. [4] J. R. M. Vaughan, Electron Devices, IEEE Trans., vol. 35, no. 7, pp. 1172–1180, 1988. [5] N. Fil, M. Belhaj, J. Hillairet, and J. Puech, Phys. Plasmas, vol. 23, no. 12, p. 8, 2016.

Speaker: N. Fil

14:00 P2.4020 The electric field of an electron in a electron-hole plasma with degenerate electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4020.pdf The electric field of an electron in a electron-hole plasma with degenerate electrons S. P. Sadykova1 , A. A. Rukhadze2 1 Forschungszentrum Julich (Jlm.), Jülich, Germany 2 Prokhorov General Physics Institute, RAS, Vavilov Str. 38., Moscow, 119991, Russia We consider the conditions for formation of a superconductivity state either in a semicon- ductor or in a electron-hole plasma with the degenerate electrons due to the attractive forces between the electrons as a result of the exchange effects through the electron-hole sound wave by analogy to the phonon waves in a solid state. One of the major unsolved problems of the superconductivity theory is determination of the static potential of a point electron. We have determined the view of an interaction potential between two electrons in a degenerate electron- hole plasma (1) with non-degenerate holes. The potential appears to be attractive at distances large than the Debye radius and decreases as 1/r3 , See Fig.1. We discuss the conditions at which the bound electron state - Cooper Pair in a such field can be formed. The interaction potential of two electrons α and β in a electron-hole plasma can be described by the following equation [1]: Z ~ eα eβ 1 U(r) = eık~rU(~k)d~k, U(k) = , (1) 2π 2 k2 ε l (kVα , k) where [2] 3ωL− 2 ωL+ 2 3π Vα ωL− 2 k ε (kVα , k) = k + 2 − 2 + ıβ , β = 2 l 2 3 , (2) VF− Vα VF− here Vα is the speed of a test electron with the charge eα producing the potential φα at a point r = 0 where the charge eβ is located; VF− - the speed of a weakly damped electron-hole sound wave, ωL+,L− - the hole and electron Langmuir frequencies. References [1] E. M. Livshits , L.P. Pitaevsky , Physical Kinetics (Pergamon Press, London, 1982). [2] A.F. Alexandrov, L.S. Bogdankevich, A.A. Rukhadze, Principles of Plasma Electrodynamics (Springer, Heidelberg, 1984), pp. 167- 170. Figure 1: The potential (1) where 1 the integration till the k ≤ rDi was r performed, here R = rDe

Speaker: S. P. Sadykova

16:00 → 16:30 COFFEE

16:30 → 18:30 BPIF

Chair: O. Klimo

Convener: O. Klimo

16:30 I2.205 Measuring quantum radiation reaction and electron—positron cascades in laser-matter interactions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.205.pdf Measuring quantum radiation reaction and electron—positron cascades in laser-matter interactions C.P. Ridgers1, D. Del Sorbo1, C. Slade-Lowther1, C.D. Murphy1, S.P.D Mangles2, T.G. Blackburn3, M. Marklund3, P. McKenna4, R. Capdessus4 1 York Plasma Institute, Department of Physics, University of York, UK 2 Blackett Laboratory, Department of Physics, Imperial College London, London, UK 3 Department of Physics, Chalmers University of Technology, Gothenberg, Sweden 4 Department of Physics SUPA, University of Strathclyde, Glasgow, UK Strong-field quantum electrodynamics (QED) processes are predicted to play a role in the interaction of next-generation high-intensity (> 10^23W/cm^2) laser pulses with matter. In particular quantum radiation reaction will play a major role in the motion of the electrons and positrons in the plasma created in the laser focus. The emitted hard-photons resulting in this radiation reaction can also generate pairs, resulting in a cascade and so the creation of dense pair plasmas. We will discuss laser absorption caused by quantum radiation reaction and electron-positron cascade development in next-generation (intensity > 10^23W/cm^2) laser-matter interactions, comparing the predictions using quantum and classical radiation reaction models. We will also investigate experiments possible with current high-intensity (10^21W/cm^2) lasers. Signatures of quantum radiation reaction on a counter-propagating energetic (1GeV) electron beam will be discussed. In particular we will quantify the degree of broadening of the energy spectrum of the beam due to quantum stochasticity.

Speaker: Christopher Paul Ridgers

17:00 I2.206 Flying Focus and its Application to Plasma-Based Laser Amplifiers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.206.pdf Flying Focus and its Application to Plasma-Based Laser Amplifiers D. Turnbull1 , S.-W. Bahk1 , I. A. Begishev1 , R. Boni1 , J. Bromage1 , S. Bucht1 , A. Davies1 , P. Franke1 , D. Haberberger1 , J. Katz1 , T. J. Kessler1 , A. L. Milder1 , J. P. Palastro1 , J. L. Shaw1 , and D. H. Froula1 1 University of Rochester Laboratory for Laser Energetics, Rochester, USA An advanced focusing scheme called a “flying focus” has been demonstrated, in which a diffractive lens combined with a chirped laser pulse enables a small-diameter laser focus to propagate nearly 100× its Rayleigh length [1]. Furthermore, the speed at which the focus— and therefore the peak intensity—moves is decoupled from the group velocity of the laser; it was demonstrated to co- or counter-propagate along the laser axis at any velocity. Experiments validating the concept measured subluminal (−0.09c) to superluminal (39c) focal-spot veloci- ties, generating a nearly constant peak intensity over 4.5 mm. We propose a new laser amplifier scheme utilizing stimulated Raman scattering in plasma in conjunction with such a flying focus [2]. Pump-intensity isosurfaces are made to propagate at v ≈ −c so as to be in sync with the injected counter-propagating seed pulse. By setting the pump intensity in the interaction region to be just above the ionization threshold of the background gas, an ionization wave is produced that travels a fixed distance ahead of the seed. Simulations show that this will make it possible to optimize the plasma temperature and mitigate many of the issues that are known to have impacted previous Raman amplification experiments, in particular, the growth of precursors. In addition to plasma-based laser amplifiers, the spatiotemporal control of laser intensity provided by the flying focus could mitigate dephasing in other plasma devices that produce, for example, tunable radiation and/or fast particles. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, the University of Rochester, and the New York State Energy Research and Development Authority. References [1] D. H. Froula et al., “Spatiotemporal Control of Laser Intensity,” to be published in Nature Photonics. [2] D. Turnbull et al., Phys. Rev. Lett. 120, 024801 (2018).

Speaker: David Turnbull

17:30 O2.201 QED cascade in a tightly focused standing wave

QED cascade in a tightly focused standing wave M. Jirka1,2,3 , O. Klimo1,2 , M. Vranic3 , S. Weber1 , G. Korn1 1 Institute of Physics of the CAS, ELI-Beamlines project, Prague, Czech Republic 2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic 3 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal The advent of laser technology is opening exciting opportunities for testing new physical regimes. A possibility to generate an electron-positron cascade via the Breit-Wheeler process in the field of an ultra-intense laser beam has attracted considerable attention. One possible interaction scenario leading to a prolific pair production is the interaction of seed particles with an intense standing wave formed by two colliding laser pulses [1]. To efficiently generate electronpositron pairs in this configuration, the intensities of the order of 1023−24 W/cm2 are required [2]. To achieve such intense laser fields with the upcoming generation of 10 PW laser beams, the laser pulse has to be focused to a λ scale spot size. However, as the laser pulse is focused more tightly, the ponderomotive force becomes stronger and seed particles are expelled more rapidly from the interaction region, so the focusing acts against an efficient cascade seeding. That prevents cascade development even at very high laser intensities in case of low-density targets [3]. Nevertheless, here we show that using a target with an appropriate density can help balance the effect of expelling seed particles from the high-intensity region [4]. We also show how tight focusing affects the cascade development for a wide set of initial conditions. Optimising the target density lowers the threshold power required for cascade pair production, which is favourable for experiments at upcoming 10 PW-class laser facilities that are now under construction and will become accessible soon. References [1] A. R. Bell and J. G. Kirk, Phys. Rev. Lett. 101 , 200403 (2008) [2] J. P. Zou et al., High Power Laser Science and Engineering 3, e2 (2015) [3] M. Tamburini, A. Di Piazza and C. H. Keitel, Scientific Reports 7, 5694 (2017) [4] M. Jirka, O. Klimo, M. Vranic, S. Weber and G. Korn, Scientific Reports 7, 15302 (2017)

Speaker: Martin Jirka

17:45 O2.202 Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.202.pdf Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam J.R. Warwick1 , T. Dzelzainis1 , M. Yeung1 , D.J. Corvan1 , M.E. Dieckmann2 , D. Doria1 , L. Romagnani3 , W. Schumaker4 , A. Alejo1 , J.M. Cole5 , K. Krushelnick6 , S.P.D. Mangles5 , Z. Najmudin5 , K. Poder7 , B. Reville1 , G.M. Samarin1 , D.R. Symes8 , A.G.R. Thomas6 , M. Zepf1,9, M. Borghesi1 and G. Sarri1 1 Queen’s University Belfast, Belfast, UK 2 Linköping University, Norrköping, Sweden 3 LULI, École Polytechnique, CNRS, CEA, UPMC, Paris, France 4 SLAC National Accelerator Laboratory, Menlo Park, USA 5 Imperial College London, London, UK 6 University of Michigan, Ann Arbor, USA 7 Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany 8 Rutherford Appleton Laboratory, Didcot, UK 9 Helmholtz Institute Jena, Jena, Germany The first experimental observation of a current-driven instability developing within a quasi-neutral matter-antimatter beam is reported herein. Using the proton radiography technique, strong remnant magnetic fields (≥ 1 T) are measured after the propagation of a quasi-neutral electron-positron beam through a background electron-ion plasma [1, 2]. The data, along with supporting particle-in-cell simulations and analytical estimations, implies that the generated magnetic fields persist for thousands of inverse plasma frequencies. The relation of this work with the dynamics of pair-dominated astrophysical jets will be discussed [1, 2]. References [1] Warwick, J., et al. “Experimental observation of a current-driven instability in a neutral electron-positron beam.” Physical Review Letters, 119, 185002 (2017). [2] Warwick, J. R., et al. “General features of experiments on the dynamics of laser-driven electron-positron beams.” Nucl. Instrum. Meth. Phys. Res. A, in press, (2018). arXiv:1802.01394v1 [physics.plasm-ph]

Speaker: M. Dieckmann

18:00 O2.203 Enhanced relativistic electron beam collimation using two consecutive laser pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.203.pdf Enhanced relativistic electron beam collimation using two consecutive laser pulses Sophia Malko1 , Xavier Vaisseau1 , Michael Ehret2, 3 , Dimitri Batani2 , Alessandro Curcio4 , J.J. Honrubia5 , Katarzyna Jakubowska2 , Alessio Morace6 , Frédéric Perez7 , Joao Santos2 , and Luca Volpe1, 8 1 CLPU (Centro de Láseres Pulsados), Spain 2 Univ. Bordeaux, CNRS, CEA, CELIA (Centre Lasers Intenses et Applications), France 3 Institut für Kernephysik, Technical University of Darmstadt, Germany 4 INFN, Laboratori Nazionali di Frascati, Italy 5 ETSI Aeronauticos, Universidad Politecnica de Madrid, Madrid, Spain 6 LULI (Laboratoire pour l’Utilisation des Lasers Intenses), Ecole Polytechnique, France 7 Institute of Laser Engineering, Osaka University, Japan 8University of Salamanca, Spain Here we report an experimental investigation of a scheme based on using of two consecutive intense laser pulses in order to optimize electron transport and collimation in dense matter. The two laser pulses, of different intensities, are focalized in a solid target at a given delay to generate two successive co-axial electron populations, where the azimuthal magnetic field generated by the first electron beam can guide the second one [1]. Previous experimental results have confirmed the general validity of the scheme: optimum delay time and intensity ratio yielding the best guiding effect [2]. It was shown that the ratio between the pre-formed magnetic field extension and the diameter of the second electron beam plays a major role in determining the guiding efficiency [3]. A systematic investigation of the scheme, exploring the role played by the radial extension of the seed magnetic field and the delay time between seed and main laser pulses, was recently carried out on the LULI-ELFIE facility. The experimental results showed a reduction of the electron beam size in the optimum conditions of both focal spot ratio and delay time between the first and the second laser pulses, yielding in factor of 2. In addition, we present the numerical simulations using hybrid PIC code and kinetic transport code that reproduce performed experimental parametrical study and benchmark the scheme efficiency. References [1] A.P.L. Robinson, et al., Phys. Rev. Lett. 100, 025002 (2008) [2] R.H.H. Scott, et al. Phys. Rev. Lett. 109, 015001 (2012) [3] L. Volpe, et al., Phys. Rev. E. 90, 063108 (2014)

Speaker: Sophia Malko

18:15 O2.204 High order harmonic beams emitted from plasma gratings

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.204.pdf High order harmonic beams emitted from plasma gratings A. Leblanc1, S. Monchocé1, H. Vincenti1, S. Kahaly1, J-L. Vay2, and F.Quéré1 1 LIDYL, CEA Saclay, Université Paris-Saclay, 91 191 Gif-sur-Yvette, France 2 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA When focusing an ultra-intense femtosecond laser pulse (I>1016W/cm2) onto a solid target, it is ionized at the very beginning of the laser pulse. The resulting dense plasma specularly reflects the laser: this is a plasma mirror. The nonlinear response of the plasma to the ultra-intense laser field results in the generation of trains of attosecond pulses associated, in the frequency domain, to high-order harmonics of the laser frequency. Two main HHG processes on plasma mirrors have been observed for different interaction conditions. At moderate laser intensities (I<1018W/cm2), Brunel electrons, accelerated into the target, excites plasma oscillations in the high density plasma gradient, which radiate at the local plasma frequency. It is the Coherent Wake Emission (CWE) process. At ultra-high intensity (I>1018W/cm2), the electron density oscillates normally to the target with a relativistic velocity. It periodically distorts the reflected field by a Doppler effect: this is the Relativistic Oscillating Mirror (ROM) process. These two processes carry rich information on the laser-plasma interaction. For instance, the spatial curvature of each emitted attosecond pulse directly results from the interaction properties: the spatial curvature either of the plasma oscillations or of the plasma surface under radiation pressure. However, measuring the spatial curvature of the harmonic source is very challenging as the detection occurs at macroscopic distances from target. To circumvent this issue, a coherent diffraction imaging technique, named ptychography, was adapted to this system. It consists in measuring the angular profile of a probe beam diffracted out on an object for different relative positions of one to the other. This technique was transposed to HHG on plasma mirrors by spatially microstructuring the target with an ionizing pre-pulse, typically a few picoseconds before the main pulse which drives HHG [1]. Harmonic fields in the target plane are then reconstructed spatially in amplitude and phase [2]. This new method is used to study of the harmonic spatial properties in different interaction conditions. Thanks to a parametric study, previously developed analytical models of the interaction in the non-relativistic and relativistic regimes are experimentally validated [3]. Its accuracy is also used to test different numerical schemes of Maxwell’s equations solvers in PIC simulations. [1] Optically controlled solid-density transient plasma gratings, Monchocé et al, Phys. Rev. Lett. 112 (2014). [2] Ptychographic measurements of ultrahigh-intensity laser-plasma interactions, Leblanc et al, Nat. Phys. 12 301 (2016). [3] Spatial properties of high-order harmonic beams from plasma mirrors: a ptychographic study, Leblanc et al, Phys. Rev. Lett. 119 (2017).

Speaker: Adrien Leblanc

16:30 → 18:30 BSAP/ESPD

Chair: T. Carter

Convener: T. Carter

16:30 I2.J301 Particle heating and acceleration inside the turbulent Solar Corona

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J301.pdf Particle heating and acceleration inside the turbulent Solar Corona Loukas Vlahos Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece The links between turbulence, reconnection and shocks in unstable plasmas will be discussed briefly. All three processes co-exist in explosively unstable plasmas, forming a new electromag- netic environment which we will call here turbulent reconnection, where spontaneous forma- tion of current sheets inside turbulence appear. The heating and the acceleration of particles will be the result of the synergy of the stochastic (second order Fermi) and the systematic acceler- ation (first order Fermi). The solar atmosphere is magnetically coupled with a turbulent driver (the convection zone) therefore the formation of turbulent reconnection in the solar atmosphere is externally driven. The magnetic topologies observed in the solar atmosphere are generated and driven by the convective motions bellow the solar surface and leading to spontaneous gen- eration of reconnecting current sheets and small and large scale eruptions which reinforce the turbulent reconnection state. It is shown that long term heating and impulsive heating of the plasma up to 10’s of million degrees and generation of Solar Energetic Particles is a natural consequence of the turbulent state of the solar atmosphere. The observed small or large scale eruptions are the signatures of the turbulent solar atmosphere. For the purpose of this review we can split the solar atmosphere in two broad classes of magnetic topologies (1) the quiet sun, where the magnetic field is weak and chaotic and (2) the active regions, where the magnetic fields are stronger and complex but we can have a rough estimate of their topology from the Non-Linear Force Free Extrapolations. The large eruptions which are related with large scale magnetic reconstructions (Flares, Coronal Mass Ejection) appear in active regions were heat- ing (stochastic) and particle acceleration (systematic) of the high energy tail of the distribution function co-exist almost in equal footing. In the quite sun or the active regions during the non- eruptive phase, the small scale explosions (microflares, nanoflares) dominate and the stochastic heating overpower particle acceleration. Turbulent reconnection, once it is established in the so- lar corona, drives corona heating and particle acceleration in all explosions in the solar surface from nanoflares to CMEs.

Speaker: Loukas Vlahos

17:00 I2.J302 Understanding the energy release in solar flares and stellar superflares by quasi-periodic pulsations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J302.pdf Understanding the energy release in solar flares and stellar superflares by quasi-periodic pulsations Valery M Nakariakov (University of Warwick, UK) Flaring energy releases observed in atmospheres of the Sun and stars in all bands of the electromagnetic radiation and particle fluxes, are produced by the conversion of the magnetic energy stored in the plasma into heat and kinetic energies of nonthermal particles and bulk flows. Magnetic reconnection is commonly accepted as the mechanism for the energy release in flares. However a number of important details, such as the unexpected speed of the reconnection, partition and amount of the released energy, triggering, and so on, remain to be revealed. Moreover, those questions are connected with the flare forecasting in the context of space weather, and also with the question whether the Sun is capable to produce a devastating superflare, similar to those observed on sun-like stars. Often the EM radiation generated in solar and stellar flares shows a pronounced (quasi)-oscillatory pattern - quasi-periodic pulsations (QPPs), with characteristic periods ranging from a fraction of a second to several tens of minutes. We review the current understanding of QPP in solar and stellar flares, focussing on possible physical mechanisms generating them, address the similarity of QPP in flares and superflares and its implications for space weather, and discuss future directions and key unanswered questions of this emerging research field. ile:///vboxsrv/Linux/crpp/papers/eps18/programme_committee/final_invited_abstracts/nakariakov_abstract.txt[04/03/2018 00:42:16]

Speaker: Valery M. Nakariakov

17:30 I2.J303 Multi-scale photospheric plasma motions and energy transfer to the solar corona

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.J303.pdf Multi-scale photospheric plasma motions and energy transfer to the solar corona V. Fedun The University of Sheffield, Sheffield, UK Recent ground- and space-based observations reveal the presence of multi-scale motions, such as vortex motions, swirling in the complex intergranular lanes. In these regions, magnetic flux tubes are generated via the interaction of granulation motion and the background magnetic field. Vortex motions are particularly important in understanding the dynamics of the solar at- mosphere since they stress the magnetic field, increase the available magnetic energy, drive the upper atmosphere and contribute towards heating of the solar corona. They are also important from a hydrodynamic perspective, redistributing momentum and mass in turbulent flows. In this talk, I will present a statistical analysis of the properties of photospheric vortices and the results of numerical simulations in order to answer the following research question: Can photospheric flow patterns reorganise the magnetic field emanating from inter-granular lanes sufficiently to create efficient conduits for transporting mass and energy from the lower solar atmosphere into the upper atmosphere, solar corona and solar wind?

Speaker: Viktor Fedun

18:00 O2.J301 Cumulative instabilities of the solar wind electron core and halo temperature anisotropies, and their drift velocities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.J301.pdf Cumulative instabilities of the solar wind electron core and halo temperature anisotropies, and their drift velocities S.M.Shaaban1,2 , M. Lazar1,3 , S. Poedts1 1 Centre for Mathematical Plasma Astrophysics, KU Leuven, Leuven, Belgium 2 Theoretical Physics Research Group, Faculty of Sci., Mansoura University, Mansoura, Egypt 3 ITP IV, Weltraum- und Astrophysik, Ruhr-Universität Bochum, Bochum, Germany In-situ measurements reveal two central components, i.e. thermal bi-Maxwellian core and a bi-Kappa suprathermal halo, forming the electron velocity distribution in the solar wind. These components may exhibit temperature anisotropies, which destabilize the electron anisotropy- driven instabilities and core-halo relative velocity, which destabilize heat flux instabilities. In the existing studies these two sources of free energy and the resulting instabilities are investi- gated independent of each other. Here we present the results of an advanced study of the inter- play of kinetic instabilities driven by the cumulative effect of relative drifting components and their intrinsic temperature anisotropies. Such complex analysis leads to an important number of various regimes of instability, and distinguishing between them becomes highly demanding.

Speaker: Shaaban Mohammed Shaaban

18:15 O2.J302 On the Formation and Properties of Fluid Shocks and Collisionless Shock in Astrophysical Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.J302.pdf Generation of Laser-Driven, High-Mach-Number Magnetized Collisionless Shocks D.B. Schaeffer1 , W. Fox1,2 , D. Haberberger3 , G. Fiksel4 , A. Bhattacharjee1,2 , D.H. Barnak3 , S.X. Hu3 , K. Germaschewski5 , R.K. Follett3 1 Princeton University, Princeton, USA 2 Princeton Plasma Physics Laboratory, Princeton, USA 3 Laboratory for Laser Energetics, Rochester, USA 4 University of Michigan, Ann Arbor, USA 5 University of New Hampshire, Durham, USA Collisionless shocks are ubiquitous in space and astrophysical systems, and the class of su- percritical shocks is of particular importance due to their role in accelerating particles to high energies. While these shocks have been traditionally studied by spacecraft and remote sensing observations, laboratory experiments can provide reproducible and multi-dimensional datasets that provide complementary understanding of the underlying microphysics. We present exper- iments undertaken on the OMEGA and OMEGA EP laser facilities that show the formation and evolution of high-Mach number collisionless shocks created through the interaction of a laser-driven magnetic piston and magnetized ambient plasma [1, 2]. Through time-resolved, 2- D imaging we observe large density and magnetic compressions that propagate at an Alfvénic Mach number MA ∼ 15 and that occur over ion kinetic length scales. Additional shock structure and electron and ion heating are observed with optical Thomson scattering, which is also used to characterize the initial ambient plasma. Particle-in-cell simulations constrained by experimental data further detail the shock formation and separate dynamics of the multi-ion-species ambient plasma. The results show that the shocks form on timescales as fast as one gyroperiod, aided by the efficient coupling of energy, and the generation of a magnetic barrier, between the piston and ambient ions. The development of this experimental platform opens the way for controlled laboratory investigations of high-Mach-number collisionless shocks, including mechanisms of shock heating and particle acceleration. References [1] D.B. Schaeffer, W. Fox, D. Haberberger, et al., Phys. Rev. Lett. 119, 025001 (2017) [2] D.B. Schaeffer, W. Fox, D. Haberberger, et al., Phys. Plasmas 24, 122702 (2017)

Speaker: Antoine Bret

16:30 → 18:30 LTDP

Chair: A. Granier

Convener: A. Granier

16:30 I2.307 Fundamental Study of Synthesis of Carbon and Boron Nitride Nanostructures in Atmospheric Pressure Arc Discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.307.pdf Fundamental Study of Synthesis of Carbon and Boron Nitride Nanostructures in Atmospheric Pressure Arc Discharges Y. Raitses1, I. D. Kaganovich1, A. Khrabryi1, A. Khodak1, V. Vekselman1, S. Yatom1, V. Nemchinsky5, L. Han6, P. Krstic6, B. Santra8, A. Gerakis1, Y-W. Yeh1,2, M. Shneider3, B. Stratton7, X. Fang4, M. Keidar4, B. Koel7, and R. Car8 1 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 2 Department of Electrical Engineering, Princeton University, Princeton, NJ, USA 3 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA 4 Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC, USA 5 Keiser University, Fort Lauderdale, FL, USA 6 Institute for Advanced Computational Science and Department of Material Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY, USA 7 Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, USA 8 Department of Chemistry, Princeton University, Princeton, NJ, USA Plasma synthesis of nanomaterials offers potentially higher throughput, lower cost, and better control of material properties than conventional chemical methods. Over the past few years we have conducted comprehensive fundamental studies of nanomaterials synthesis by atmospheric pressure arc discharges. This work has led to significant advancements in the understanding of the synergistic roles of plasma and materials processes in the arc synthesis of carbon and boron-nitride nanomaterials. In order to understand nanostructure formation we needed to determine the plasma and gas composition conditions in the nucleation and growth region. This data was not available and well-known before, because it is difficult to measure plasma parameters inside the arc. We determined plasma parameters in the growth region using various in-situ plasma diagnostics and fluid modelling. Additionally, atomistic simulations helped to analyse crucial processes in nanomaterial synthesis. The dominance of diatomic carbon molecules in the arc periphery, a probable pre-cursor species for synthesis of carbon nanostructures, and the dominance of C atoms in the arc core are important new findings of these studies. For boron nitride nanotubes two possible mechanisms of synthesis root-growth from boron clusters and volumetric growth from boron-nitride nanocages are being investigated. Papers are available at nano.pppl.gov

Speaker: Igor D. Kaganovich

17:00 I2.308 Plasma deposition of nanocomposite films with polymeric matrix

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.308.pdf Plasma deposition of nanocomposite films with polymeric matrix A. Choukourov1, O. Kylian1, A. Shelemin1, P. Solar1, H. Biederman1 1 Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic In the past decades most of the attention has been paid to the nanocomposite metal/plasma polymer films. These have been studied since 70ties of the last century and have usually been prepared by simultaneous plasma polymerization and RF or later even DC sputtering of a metal target. In recent years gas aggregation cluster sources (GAS) employing a planar magnetron sputtering at high pressure ( ~ 100 Pa) have been used. Nanoparticles of various metals such as Ag, Cu, Al, Ti and etc. in the form of beams were produced by these sources. Ag and Al NPs were embedded into C:H plasma polymer. Cu and Ag NPs were incorporated into a-C:H(amorphous hydrogenated carbon) matrix. This material originates on RF driven DC negatively biased substrate at elevated values (usually more than -200 V). Below this value the matrix material is a hard plasma polymer (C:H). Soft plasma etching in O2 enhanced Ag exposition and therefore short term release of Ag in antibacterial applications. RF magnetron sputtering of Nylon 6,6 and/or PTFE targets in the GAS at pressures 40 – 100 Pa of Ar was used to prepare nanoparticles of corresponding plasma polymer. In addition, a planar magnetron with the graphite target in the GAS operated in the vapours of n-hexane or HMDSO mixed with Ar allowed to prepared C:H and SixOyCz plasma polymer nanoparticles. Preparation and properties of nanocomposite and nanoparticle - nanostructured films (e.g. Ag, Ti or plasma polymer nanoparticles overcoated by plasma polymer or Ti) are described as well as GLAD (glancing angle deposition) over seed nanoparticles. Lately, core@shell nanoparticles composed of Ag core or even Ag multicore embedded in a plasma polymer shell are presented. These are prepared in a GAS using RF or even DC magnetron sputtering in a working gas mixture Ar + HMDSO (or n-hexane). Basic physical properties of nanocomposites metal/plasma polymer films deposited from the above heterogeneous NPs are described. In conclusion further development and potential applications are discussed. Acknowledgement This work was supported by the grant GACR 17-22016S from the Czech Science Foundation.

Speaker: Hynek Biederman

17:30 O2.305 Laser induced fluorescence spectroscopy in a nanoparticle forming plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.305.pdf Laser induced fluorescence spectroscopy in a nanoparticle forming plasma E. von Wahl1, S. Iséni1, T. Lecas1, T. Gibert1, S. Tsikata2, S. Mazouffre2, M. Mikikian1 1 GREMI, UMR7344 / CNRS-Univ. Orléans, F-45067 Orléans, France 2 ICARE, UPR3021 / CNRS, F-45067 Orléans, France The presence of huge quantities of nanoparticles strongly modifies plasma properties [1, 2]. Collecting free electrons from the discharge [3], an increase of the electron temperature is provoked [4] and, thus, the entire chemistry is changed. Not seldom even plasma instabilities are created, some of them on time scales visible to the human eye [5, 6]. Because instabilities are a tempo-spatial phenomenon, adequate techniques have to be applied in order to understand their nature. In this study laser induced fluorescence [7] and absorption [8] spectroscopy were used to monitor the evolution of argon metastable atoms during the growth of dense nanoparticle clouds from sputtering melamine-formaldehyde in a sealed RF plasma chamber. The spectroscopic data are correlated with the pressure evolution and discharge current [9] to comprehend the impact of localized effects, like void formation, on the entire process. Acknowledgements: This work was supported by Region Centre Val de Loire, project DYSCO n°201500104004. [1] A. M. Hinz et al., J. Phys. D: Appl. Phys. 48 (2015) 055203 [2] M. Mikikian et al., Pure Appl. Chem., 83 (2010) pp. 1273-7282 [3] T. Wegner et al., Appl. Phys. Lett. 108 (2016) 063108 [4] V. Masserau-Guilbaud et al., IEEE Transactions on Plasma Science 41 (2013) pp. 816 [5] M. Mikikian, H. Tawidian and T. Lecas, Phys. Rev. Lett. 109 (2012) 245007 [6] L. Couëdel et al., Phys. Plasmas. 17 (2010) 083705 [7] I. Stefanović et al., Plasma Sources Sci. Technol. 26 (2017) 065014 (15pp) [8] V. Sushkov, A-P. Herrendorf and R. Hippler, J. Phys. D: 49 (2016) 425201 (11pp) [9] H. Tawidian, T. Lecas and M. Mikikian, Plasma Sources Sci. Technol. 23 (2014) 065009 (9pp)

Speaker: Erik von Wahl

17:45 O2.306 Pushing charged dust with an electron beam in a plasma crystal

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.306.pdf Pushing charged dust with an electron beam in a plasma crystal C.M. Ticoş1, D. Ticoş1, J.D. Williams2 1 National Institute for Laser, Plasma and Radiation Physics, Bucharest 077125, Romania 2 Wittenberg University, Physics Department, Springfield, OH 45501, USA We demonstrate transport of charged microscopic matter by a 13 keV collimated electron beam (EB) over tens of millimetres in a dusty plasma. Hundreds of electrically charged microspheres levitated inside a weakly ionized plasma and forming a plasma crystal are locally irradiated. When the EB is turned on a dust flow moving with a peak speed ~10 mm/s in the direction of the EB is produced. Far from the irradiation zone the plasma crystal preserves its spatial structure. The peak kinetic energy of the dust flow is ~630 eV resulting in an energy transfer factor of 0.048 from the EB to the microparticles. The flow is laminar in the first 300 ms and becomes turbulent as its speed and width increase. During this transition vortices formed initially at the entrance of the EB in the plasma crystal give rise to subsequent eddies which propagate downstream the flow. The particle image velocimetry (PIV) technique is employed to monitor the evolution of the dust flow in time. Spatio-temporal maps of the dust flow speed, kinetic energy and vorticity give insights into the flow dynamic regime.

Speaker: Catalin Mihai Ticos

18:00 O2.307 Low-temperature plasma removal of deposits from fusion first mirrors

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.307.pdf Low-temperature plasma removal of deposits from fusion first mirrors D. Shaw1 , A. Gibson1 , M. Kushner2 , E. Wagenaars1 1 York Plasma Institute, York, UK 2 University of Michigan, Ann Arbor, USA Within a fusion device the optical component closest to the plasma is called the first mirror. With the device in operation the high energy atoms within the plasma erode the plasma facing material and redeposit it around the reactor. Mirrors suffer this erosion and re-deposition process and it causes degradation in the quality of the signal reaching the diagnostics. Erosion is easily overcome with single crystal or small scale crystal structures but the deposition is substantial and with no easy solution [1]. The proposed method of removal of these deposits is using a low-temperature plasma in-situ in order to maintain reflectivity. This involves creating a capacitively coupled plasma using the mirror itself as the powered electrode. Experiments have been carried out to test this method and they have yielded good results [2]. Due to the toxicity of the beryllium used in the con- struction of the first wall the majority of experiments have used aluminium oxide as a proxy. It is only recently that experiments using beryllium deposits have been conducted, and in lim- ited numbers. In order to improve the removal process it has become prudent to use computer simulations. The Hybrid Plasma Equipment Model has been used in order to investigate and optimise the deposition removal process through simulating conditions and chemistry as close to the working environment as possible. This has been done in comparison with experimental results conducted in York and gathered from literature. In order to conduct this work a plasma chemistry for beryllium has also been created so that both the aluminium oxide experiments and beryllium experiments can be investigated. References [1] A. Costley, T. Sugie, G. Vayakis, et al., Fusion Engineering and Design 74, 74 (2005) [2] L. Moser, R. Steiner, F Leipold, et al., Journal of Nuclear Materials 463, 463 (2015)

Speaker: David Shaw

18:15 O2.308 Emission properties of a point-like discharge in an inhomogeneous gas flow supported by sub-THz radiation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.308.pdf Emission properties of a point-like discharge in an inhomogeneous gas flow supported by sub-THz radiation A. Vodopyanov, A. Sidorov, S. Razin, D. Sidorov, M. Morozkin, A. Tsvetkov, A. Fokin, A. Veselov, V. Malygin, A. Kuftin, M. Glyavin, S. Golubev Institute of Applied Physics of Russian Academy of Sciences, Nizhny Novgorod, Russia The latest developments of the powerful and reliable gyrotrons of the sub-terahertz range opens up new opportunities in research. In particular, detailed studies of the gas discharge in a focused beam of terahertz frequency range electromagnetic waves in an inhomogeneous gas flow were carried out recently [1–3]. This paper presents the results of experimental studies of point-like plasma emission in three spectral ranges: 112 - 180 nm, 20-40 nm, and 12 - 17 nm. The discharge was induced in a nonuniform gas flow (Ar, Kr, Xe) under the action of a focused beam of sub-terahertz waves. Two gyrotron complexes were used as the radiation source. They were 40 kW at 670 GHz and 250 kW at 250 GHz. An absolutely calibrated photomultiplier and an absolutely calibrated solid state detector with a set of filters were used to measure light properties. Promising results were obtained - a point-like discharge with a size of not more than 1 mm and a plasma density of more than 3×1016 cm-3 with valuable emission in extreme ultraviolet band was demonstrated. For instance, the light emission power of the point-like discharge sustained by the THz waves with frequency of 250 GHz in the wavelength range of 20-40 nm reached 300 W. Such a plasma object can be a promising source of extreme ultraviolet light for high-resolution projection lithography. The report contains the results of measurements of the light power for the above spectral ranges with temporal resolution. Prospects to increase the conversion degree of plasma heating power to extreme ultraviolet light are discussed in the paper. The work was supported by the Russian Science Foundation, project No. 14-12-00609. References [1] M. Glyavin et al., “A point-like source of extreme ultraviolet radiation based on a discharge in a non-uniform gas flow, sustained by powerful gyrotron radiation of terahertz frequency band,” Appl. Phys. Lett., vol. 105, no. 17, 2014. [2] A. V. Sidorov et al., “Measurement of plasma density in the discharge maintained in a nonuniform gas flow by a high-power terahertz-wave gyrotron,” Phys. Plasmas, vol. 23, no. 4, p. 43511, 2016. [3] A. V. Vodopyanov, “Sources of ultraviolet light based on microwave discharges,” EPJ Web Conf., vol. 149, p. 2009, Aug. 2017.

Speaker: Alexander Vodopyanov

16:30 → 18:30 MCF

Chair: G. Huijsmans

Convener: G. Huijsmans

16:30 I2.108 Closing the gap between experiment and modelling to understand the stability of the edge transport barrier at JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.108.pdf Closing the gap between experiment and modelling to understand the stability of the edge transport barrier at JET C. Perez von Thun1 , L. Frassinetti2 , L. Horvath3 , S. Saarelma4 , E. de la Luna5 , M. Beurskens6 , J. Flanagan4 , C.F. Maggi4, S.J.P. Pamela4 , and JET Contributors∗ 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung — Plasmaphysik, 52425 Jülich, Germany. 2 Royal Institute of Technology KTH, Stockholm, Sweden. 3 York Plasma Institute, University of York, Heslington, York, YO10 5DD, UK. 4 Culham Centre for Fusion Energy, Abingdon, OX14 3DB, UK. 5 Laboratorio Nacional de Fusión, CIEMAT, E-28040, Madrid, Spain. 6 Max-Planck-Institut für Plasmaphysik, Wendelsteinstr. 1, D-17491 Greifswald, Germany. The most widely accepted physics model to explain the occurrence of Edge Localised Modes (ELMs) in tokamaks is the peeling-ballooning (PB) model, in which ELMs are triggered by the excitation of coupled PB modes. The validity of the model has been investigated experimentally mainly with detailed pedestal profile measurements, and theoretically with help of MHD stabil- ity codes. However, the non-ambiguous experimental identification of the PB modes themselves has so far been missing. The work presented here closes this gap by characterising of macro- scopic pre-ELM fluctuation measurements of the pedestal on JET for a wide operational range, making use of a combination of improved edge profile and fluctuation diagnostics, and by car- rying out a systematic comparison of the results with stability modelling predictions. We have characterised the existence domain of modes, the measured toroidal mode numbers up to n = 16 and the dependency on the pedestal pressure gradient and current density, and the mode num- bers are consistent with stability calculations. Together with earlier findings, the properties of these fluctuations allow their identification as coupled PB modes. Effectively, this extends and generalises to higher toroidal mode numbers (up to n ≤ 16) the identification [G.T.A. Huysmans et al Nucl. Fusion 38 179 (1998)] of the lowest n = 1 modes (also termed ‘outer modes ’) as pure external kink (peeling) modes. The observation of these modes opens up a new avenue to test existing ELM models. We will show how these modes can be used to diagnose what regions of plasma boundary stability space are being accessed in the various operating scenarios on JET, and explore in how far the differences in pedestal behaviour between the previous CFC-based wall and the current Be/W-based first wall can be explained in terms of PB stability. ∗ See the author list of ”X. Litaudon et al 2017 Nucl. Fusion 57 102001”

Speaker: Christian Perez von Thun

17:00 I2.109 An in depth look into the physics of ELM triggering via vertical kicks through non-linear MHD simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.109.pdf An in depth look into the physics of ELM triggering via vertical kicks through non-linear MHD simulations F.J. Artola1,2, G. Huijsmans3,4, M. Hoelzl5, P. Beyer1, A. Loarte2, Y. Gribov2 & JET Contributors* 1 Aix-Marseille Université, CNRS, PIIM UMR 7345, 13397 Marseille, France 2 ITER Organization, 13067 St Paul Lez Durance Cedex, France 3 CEA, IRFM, F-13108 St. Paul-lez-Durance Cedex, France 4 Eindhoven University of Technology, Eindhoven, The Netherlands 5 Max Planck Institute for plasma physics, Boltzmannstr. 2, 85748 Garching, Germany Triggering of ELMs via vertical plasma position oscillations was first reported in the TCV tokamak. These vertical oscillations often called "vertical kicks" were used for ELM frequency control in the type-I ELM regime in ASDEX Upgrade and are routinely used for ELM control at JET [1]. The conjectured mechanism destabilizing ELMs during the vertical motion was an increase in the edge current pushing the pedestal to the peeling-ballooning unstable region. In order to clarify the physics basis behind this ELM control approach and its potential for application in ITER, we make use of the non-linear MHD code suite JOREK-STARWALL. We have simulated for the first time the processes of vertical plasma movement and ELM destabilization in an integrated and self-consistent form. Our simulations show that initially stable plasmas are destabilized by the application of a vertical motion, where the unstable modes present a peeling-ballooning structure in the linear phase. Plasmas with lower pedestal currents require larger vertical displacements to trigger ELMs, which confirms the hypothesis of the increased edge current as the ELM triggering mechanism. The origin of the current induced during the vertical motion is also analysed, revealing that it arises from the compression of the plasma cross section due to its motion through an up/down asymmetric magnetic field. In the case of single null plasmas compression occurs when the plasma moves vertically towards the X-point, with the velocity of the movement playing only a minor role. The presentation will describe modelling of JOREK-STARWALL of ELM triggering with vertical “kicks” for JET-C plasmas [1], comparing quantitatively code predictions with experimental results, and its application to triggering of ELMs in ITER 7.5MA/2.65T plasmas. [1] De la Luna, E., et al. "Understanding the physics of ELM pacing via vertical kicks in JET in view of ITER." Nuclear Fusion 56.2 (2015): 026001. *See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″

Speaker: Francisco Javier Artola

17:30 I2.110 Pedestal structure and energy confinement studies on TCV

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I2.110.pdf Pedestal Structure and Energy Confinement Studies on TCV U. A Sheikh1 , L. Frassinetti2, M. Dunne3 , P. Blanchard1 , B. P. Duval1, B. Labit1 , A. Merle1 , C. Theiler1 , C. K. Tsui1 , the TCV Team1 and the EUROfusion MST1 Team4 1 Swiss Plasma Center, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 2 KTH Royal Institute of Technology, Stockholm, Sweden 3 Max Planck Institute für Plasmaphysik, Garching, Germany 4 Author list of H. Meyer et al., Nucl. Fusion 57 (2017) 102014 The high confinement plasma mode is characterised by an edge transport barrier leading to strong Te and ne gradients at the plasma edge, termed the pedestal. The pedestal can be tailored through fuelling and seeding to improve core confinement, enhance fusion yield and reduce divertor power loads. Recent studies have focussed on the role of the pedestal position, partic- ularly the location of the density gradient relative to the separatrix. In AUG, an outward shift of pedestal position was correlated to a high density front in the high field side scrape-off layer (HFSHD), resulting in reduced pedestal top pressure and global confinement[1]. Similarly, a relative shift between the locations of the peak Te and ne gradients was observed in low triangu- larity discharges at JET-ILW, although it has not been conclusively linked with the HFSHD[2]. TCV is an ideal machine to address these uncertainties as a HFSHD is not expected due to the open geometry and carbon walls. Pedestal behaviour can therefore be investigated in conditions that are not attainable in standard operation in AUG or JET. Furthermore, due to the TCV’s present engineering characteristics and flexible shaping capabilities, experiments can shed light on the effect of combinations of impurity seeding, fuelling and plasma shape. A database consisting of 36 shots scanning plasma triangularity, fuelling and nitrogen seeding rates in NBH heated ELM-y H-mode plasmas was constructed. Increases in pedestal top Pe and stored energy of approximately 30% and 10% respectively were measured with increasing triangularity. These were accompanied by a reduction in the relative shift between the locations of the peak Te and ne gradients. Increased seeding at high triangularity led to an outward shift in pedestal position and decreasing pedestal top Pe , but with increased total stored energy by up to 5% and core Pe by up to 15%. These observations suggest that the outward shift of the pedestal and the relative shift between the locations of the peak Te and ne gradients are not necessarily correlated with the HFSHD, but may include changes in pedestal transport. The relevance of these results in relation to results from AUG and JET, will be discussed in comparison with interpretive modelling carried out with an EPED-like code. References [1] Dunne, M. G., et al., Plasma Phys. Control Fusion, 59, 025010, (2017). [2] Frassinetti, L., et al., Plasma Physics and Controlled Fusion, 59, 014014, (2017).

Speaker: Umar Ahmed Sheikh

18:00 O2.111 Scientific results of the collaboration on tokamak pedestal physics between Europe and the Asia-Pacific region (2018 PPCF Dendy Award)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.111.pdf Scientific results of the collaboration on tokamak pedestal physics between Europe and the Asia-Pacific region (2018 PPCF Dendy Award) Hajime Urano1, Costanza Maggi2, Ohjin Kwon3, Samuli Saarelma2 1 National Institutes for Quantum Radiological Science and Technology, Naka Fusion Institute, Naka, 311-0193 Japan 2 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 3 Daegu University, 201 Daegudaero,Gyeongsan, Gyeongbuk, 38453 Republic of Korea The collaboration has expanded the understanding of tokamak pedestal physics through multimachine experiments, in particular JET and JT-60U, and theoretical analysis. The issues considered were plasma shape (including X-point location), neutrals, global plasma beta, TF ripple and edge rotation. The work has led to more accurate models for predicting ITER and DEMO pedestals. In both JET and JT-60U a robust correlation was found between total and pedestal thermal stored energy and improved edge stability was correlated with increasing total poloidal normalized pressure [1]. Despite their similar plasma size, the plasma performance of the two tokamaks can be different, which arises from machine-related aspects, such as shape, aspect ratio, TF ripple. The effects of TF ripple and edge rotation on the pedestal structure were investigated by the collaboration between the two tokamaks [2]. The effect of plasma shape on the pedestal width was examined focusing on the different operational areas of JET and JT-60U [3]. The effects of plasma triangularity, global beta and neutrals on pedestal confinement and stability were investigated in JET with the Be/W ITER-like wall [4]. On the theoretical side, the collaboration initially focussed on the effect of the X-point on pedestal stability. The X-point, depending on its poloidal location, can have opposite effects on peeling and ballooning modes, the two instabilities that govern linear MHD pedestal stability [5]. Analysis of simulated ITER plasmas has shown that, unlike most currently operating tokamaks that are limited by coupled peeling-ballooning modes, ITER pedestals are likely to be limited by low-n peeling modes due to very low collisionality and, consequently, high bootstrap current [6]. Pedestal predictions for the European DEMO have indicated that the beneficial effect of triangularity on pedestal stability saturates at a certain triangularity value, giving an upper limit for system studies for the maximum pedestal that can be achieved by plasma shaping alone. The Award recipients feel privileged that their collaborative work was highly recognized. [1] CF Maggi et al., Nucl. Fusion 47 (2007) 535; [2] H Urano et al., Nucl. Fusion 51 (2011) 113004; [3] H Urano, S Saarelma et al., Proc. IAEA FEC 2016, Kyoto, EX/3-4.; [4] CF Maggi et al., Nucl. Fusion 55 (2015) 113031; [5] S Saarelma, OJ Kwon et al., Plasma Phys. Control. Fusion 53 (2011) 025011; [6] S Saarelma et al., Nucl. Fusion 52 (2012) 103020.

Speaker: Costanza Maggi

18:15 O2.112 Wide pedestal quiescent H-mode plasmas in DIII-D tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O2.112.pdf Wide Pedestal Quiescent H-mode Plasmas in DIII-D Tokamak Xi Chen1, K.H. Burrell1, T.H. Osborne1, K. Barada2, D. R. Ernst3, C. Chrystal1, B.A. Grierson4, G.R. McKee5, T. Odstrcil3, C.P. Paz-Soldan1, C.C. Petty1, T.L. Rhodes2, J.C. Rost3, W.M. Solomon1, T.M. Wilks3, Z. Yan5 and L. Zeng2 1 General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, USA 2 University of California Los Angeles, P.O. Box 957099, Los Angeles, CA 90095 USA 4 3 Massachusetts Institute of Technology, Cambridge, MA 02139, USA Princeton 5 Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451, USA University of Wisconsin-Madison, 1500 Engineering Dr., Madison, WI 53706, USA A new quiescent H-mode (QH-mode) regime with enhanced pedestal without ELMs has been discovered in the DIII-D tokamak in ITER relevant low torque and collisionality [1, 2]. The regime was originally discovered in conventional QH-mode when the counter-Ip neutral beam torque drops to ~2Nm in balanced double null shape. Across the transition, the pedestal electron pressure increases by 60% and widens by 50% and the plasma confinement rises by 40%. It is referred to as ‘wide-pedestal QH-mode’ because the pedestal width exceeds the EPED-KBM limit. The onset of edge broadband MHD modes and micro-turbulence accompanied with a lower ExB shear in this region is a common feature of the wide-pedestal QH, instead of the edge harmonic oscillations (EHO). It is conjectured that the increased transport provided by these edge modes reduces the pedestal gradients resulting in an enhanced pedestal while still remaining below the ELM-limit. The wide-pedestal QH-mode has been created and sustained in a range of shapes from slightly upper single null to lower single null, including the ITER similar shape and for a range of torques spanning the ITER equivalent range. Wide-pedestal QH has been initiated and sustained with net zero NBI torque throughout the discharge with good confinement and terminated only due to hardware constraints. Surprisingly, confinement improvement has been observed with core electron heating using ECH. Impurity transport is studied with Silicon and Aluminum injection using laser blow-off diagnostics. The role of edge magnetic and density fluctuations in forming the wide pedestal is being studied. The broadband MHD is composed of two counter-propagating low-k branches while the intermediate-k density turbulence propagates in the electron-direction (lab frame) and oscillates periodically [3]. A flat spot is observed in the pedestal profiles of wide- pedestal QH-mode, especially that of the electron temperature. The location of the flat spot is close to the location of the peaking of the amplitudes of some of these edge modes. [1] K.H. Burrell et al, Phys. Plasmas 23, 056103 (2016). [2] Xi Chen, et al, Nucl. Fusion 57, 086008 (2017). [3] K. Barada, et al, accepted by Phys. Rev. Lett. This work was supported in part by the US Department of Energy under DE-FC02-04ER546981, DE-FG02-08ER549842, DE-FG02-94ER542353, DE-AC02-09CH114664, DE-FG02-08ER549995.

Speaker: Xi Chen

Wednesday, 4 July

09:00 → 10:45 PLENARY SESSION

Chair: C. Michaut

Convener: C. Michaut

09:00 I3.007 Laser driven electron acceleration with high repetition rate lasers: from plasma physics to condensed matter applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.007.pdf Laser driven electron acceleration with high repetition rate lasers: from plasma physics to condensed matter applications Jérôme Faure LOA, ENSTA-CNRS-Ecole Polytechnique, Palaiseau, France Laser wakefield acceleration is an emerging technique for accelerating electron bunches to relativistic energies in very short distances using ultra-intense laser pulses. It relies on the excitation of an intense plasma wave, or wakefield, that is able to trap and accelerate electrons in a single arch of the wakefield, thereby generating femtosecond relativistic electron bunches. Because of their extremely short duration and natural synchronization with the laser pulse, these electron bunches are of great interest for probing matter on femtosecond time scales via pump-probe experiments, possibly offering unprecedented temporal resolutions for studies in structural dynamics in condensed matter [1]. Such applications require high stability, massive data averaging and would therefore benefit greatly from a high repetition rate electron source. In this context, our group has started the further miniaturization of laser-plasma accelerators by using small-scale and high-repetition rate lasers. In this talk, we will review the recent development of these kilohertz laser-plasma source [2]. In initial experiments, electrons reached 100 keV energy. The enhanced stability and high repetition rate allowed us to perform ultrafast electron diffraction experiments in which the dynamics of a Silicon lattice could be revealed on the picosecond time scale [3]. In more recent experiments, we have used laser pulses composed of a single optical cycle (3.5-fs duration) in order to drive the plasma wakefield resonantly. This led to an increase of the energy and the charge by two orders of magnitude, and the electron beams now reach 5 MeV energy with >10 pC charge [4]. We will discuss the physics of the laser plasma interaction, the potential of this new source for applications as well as future foreseen developments. [1] J. Faure et al., Phys. Rev. Acc. & Beams 19, 021302 (2016) [2] B. Beaurepaire et al., Phys. Rev. X 5 031012 (2015). He et al., New. J. Phys. 15, 053016 (2013) [3] He et al., Appl. Phys. Lett. vol. 102, 064104 (2013). He et al., Scientific Report 6, 36224 (2016). [4] D. Guénot et al., Nature Photonics 11, 293 (2017). D. Gustas et al., accepted to Phys. Rev. Acc. & Beams

Speaker: Jerome Faure

09:35 I3.008 Plasma-nano-interface: from plasma-for-nano to nano-plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.008.pdf Plasma-nano-interface: from plasma-for-nano to nano-plasmas K. Ostrikov1,2,3 1 Queensland University of Technology (QUT), Brisbane, Australia 2 CSIRO-QUT Sustainable Processes and Devices Laboratory, Sydney – Brisbane, Australia 3 College of Chemistry and Molecular Engineering, Peking University, China This presentation reviews and highlights the key aspects of progress achieved in plasma nanoscience research over the last dozen years. The advances made and the knowledge base created is critically examined through the prism of the fundamental framework structured along the key fundamental questions: (1) what happens when low-temperature plasmas face a solid object of nanoscale dimensions [1] and (2) is it possible to reduce the plasma size to the nanoscales, similar to other (solid, liquid, and gas) states of matter [2]? These fundamental questions are at the foundations of plasma nanoscience. The answers lead to better understanding of many unique and interesting physical and chemical effects that could be generated through such nanoscale localizations of multi-phase interactions at plasma-solid interfaces under extreme non-equilibrium conditions. Many synergistic (1 + 1 >2) effects appear through these interactions at the plasma interface. These effects enable several advanced applications of low-temperature plasmas in micro- and nanofabrication, nanoscale materials synthesis and processing, industrial catalysis, new sustainable industrial processes based on green-chemistry approaches. Many exotic effects appear when plasma size is reduced into nanometre domain. The examples are: plasma-nano catalysis [3], sustainable nanotechnology [4], nanoscale plasma-surface interactions [5], and nano-plasmas generated by intense radiation [2]. The presentation will conclude with some examples of using plasma, thermal, ionic and other processes to control macroscopic properties of materials by precise manipulations of atomic bonds, atoms and defects at nanoscales and the opportunities for industrial applications and entrepreneurship [6], and the challenges and cross-disciplinary platforms such as plasma-materials informatics on the way materialize these ambitious goals. [1] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2005) [2] K. Ostrikov, F. Beg, and A. Ng, Rev. Mod. Phys. 88, 011001 (2016) [3] E. C. Neyts, K. Ostrikov, et al. Chem. Rev. 115 (24), 13408–13446 (2015). [4] K. Bazaka, J. Mohan, and K. Ostrikov, Chem. Rev. 116 (1), 163–214 (2016). [5] K. Ostrikov, E. C. Neyts, and M. Meyyappan, Adv. Phys. 62, 113 (2013) [6] D. H. Seo,…, and K. Ostrikov, Nature Comm. 8, 14217 (2017); Nature Comm. 9, 683 (2018).

Speaker: K. Ostrikov

10:10 I3.009 First results from divertor operation in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.009.pdf First results from divertor operation in Wendelstein 7-X Thomas Sunn Pedersen , for the W7-X Team. 1 1 Max Planck Institute for Plasma Physics, Greifswald, Germany Stellarators provide a potentially attractive concept for fusion power production, owing to their intrinsic steady-state capabilities, and their lack of current-driven disruptions, but high confinement at high ion temperatures has in the past been an elusive goal, primarily owing to prompt orbit losses. This issue is addressed in the new generation of optimized stellarators. Wendelstein 7-X (W7-X) is a highly optimized stellarator experiment that went into operation in 2015 [1-4]. With a 30 cubic meter volume, a superconducting coil system operating at 2.5 T, and steady-state heating capability of eventually up to 10 MW, it was built to demonstrate the benefits of optimized stellarators at parameters approaching those of a fusion power plant. Operation phase 1.2, which was performed in the second half of 2017, featured the full complement of 10 divertor units, ECRH heating with up to 10 gyrotrons, more than 30 diagnostic systems, and a pellet fueling system. This talk will give a general overview of the W7-X goals and capabilities, and describe results from the first divertor operation, including measurements and corrections of error fields, symmetrization of divertor heat loads, evidence of detachment, and operation at significantly higher densities (n >10 m ), ion temperatures (T =4 keV), pulse lengths (up to 26 seconds), e 20 -3 i and stored energies (E>1 MJ) than in operation phase 1.1. Various tests of the W7-X optimization will also be reported, and the results will be put into a broader fusion perspective. Finally, an outlook towards the future operation phases OP1.2b and OP2 will be given. References [1] T. Klinger et al. Plasma Phys. Controlled Fusion 59(1) 014018 (2017) [2] H.-S. Bosch et al., Nuclear Fusion 57, 116015 (2017) [3] R. C. Wolf et al., Nuclear Fusion 57 102020 (2017) [4] T. Sunn Pedersen et al., Physics of Plasmas 24 055503 (2017)

Speaker: Thomas Sunn Pedersen

10:45 → 11:15 COFFEE

11:15 → 13:15 BPIF

Chair: J. Faure

Convener: J. Faure

11:15 I3.207 Optical control of the topology of plasma accelerators

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.207.pdf Optical control of the topology of plasma accelerators J. Vieira1, J.T. Mendonça1, F. Quéré2 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal 2 LIDYL, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91 191 Gif-sur-Yvette, France Exploring advanced plasma based accelerators is important research issue, as they can lead to more compact particle accelerators and light source for scientific and societal applications. One of the most advanced schemes is the laser wakefield accelerator, which employs laser pulses to excite the plasma. A twisted laser pulse driver with orbital angular momentum can change the spatial structure of the plasma wave dramatically, in comparison to Gaussian drivers. Plasma waves driven by intense twisted light acquire a doughnut shape, which are useful to accelerate ring shaped electron beams, which could be used as a lens, being also suited for high gradient positron acceleration, providing a solution to an ongoing outstanding challenge. These results point towards a remarkable property, specific of plasma accelerators, which is the topological flexibility of plasma wakefields, which may provide unprecedented control over the internal degrees of freedom of relativistic beams. We illustrate the concept with lasers characterized by helical intensity profiles, also known as light springs. This approach is motived by the recent advances on ultra-fast beam shaping, which provide new paths to produce ultra-intense lasers with unusual spatiotemporal properties. We show that light springs can drive relativistic twisted plasma wakefields, which carry orbital angular momentum themselves. In the nonlinear regime, these twisted wakes can generate and accelerate relativistic vortex electron beams, which have quantized orbital angular momentum levels, although they are of a purely classical origin. These beams are challenging to produce by other means, and could be already of interest to the communities exploiting particle beams to probe matter. We confirm our theoretical results with 3D particle-in-cell simulations in Osiris. [1] J. Vieira, J.T. Mendonça, Phys. Rev. Lett. 112 215001 (2014). [2] G. Pariente, F. Quéré, Optics Lett. 40, 2037-2040 (2015).

Speaker: Jorge Vieira

11:45 I3.208 Laser wakefield accelerators as tools for studying extreme conditions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.208.pdf Laser wakefield accelerators as tools for studying extreme conditions S.P.D. Mangles1 John Adams Institute for Accelerator Science, The Blackett Laboratory, Imperial College London, London SW7 2AZ, UK Wakefield accelerators driven by intense laser pulses can now produce GeV electron bunches and broadband multi-keV X-rays with femtosecond durations. By using the multiple-beam capabilities available at typical high-intensity laser facilities, these beams are potentially useful tools for exploring extreme conditions that are found in astrophysical environments and can be created in highly transient experiments in the laboratory. Conditions that can be studied the high temperatures and pressures in planetary and stellar interiors, the high X-ray flux found in the vicinity of accretion disks around black holes, and even the intense electromagnetic fields on the surface of quasars. This talk will describe some recent and planned experiments that use laser wakefield accelerators to probe a diverse range of physics including: radiation reaction physics at high intensity, electron-positron pair production in high-flux X-ray fields, time resolved X-ray imaging of high-density shocks and time resolved X-ray absorption spectroscopy of warm dense matter.

Speaker: Stuart Mangles

12:15 O3.201 Plasma channel based new laser wakefield staging scheme and radiation source

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.201.pdf Plasma channel based new laser wakefield staging scheme and radiation source J. Luo1,7, M. Chen1,7, W. Y. Wu1,7, S. M. Weng1,7, Z. M. Sheng1,2,5,6,7, C. B. Schroeder3, D. A. Jaroszynski2,6, E. Esarey3, W. P. Leemans3, W. B. Mori4, and J. Zhang1,7 1 Key Laboratory for Laser Plasmas (MOE), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China 2 SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK 3 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 4 University of California, Los Angeles, CA 90095, USA 5 Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai 200240, China 6 Cockcroft Institute, Sci-Tech Daresbury, Cheshire WA4 4AD, UK 7 Collaborative Innovation Centre of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China Multistage coupling of laser-wakefield accelerators with independent driving laser pulses is essential to overcome laser energy depletion for high energy applications such as the TeV level electron-positron collider. Currently a staging scheme is achieved by feeding a second laser pulse via a plasma mirror and by controlling the electron beam focusing via active plasma lenses. Here a more compact and efficient scheme is proposed to realize simultaneous coupling of the electron beam and the laser pulse to the second stage with plasma channels [1]. A special designed bending channel is used to guide a fresh laser into a following straight channel, while the electron beam always propagate in the straight channel. Benefiting from the shorter coupling distance and continuous guiding of the electron beam in plasma, its transverse dispersion is suppressed. With moderate laser parameters, our particle-in-cell simulations demonstrate that the electron beam from the previous acceleration stage can be efficiently injected into the following stage for further acceleration, where the re-injection ratio, stability, and beam quality can be kept at a high level. At the same time, based on plasma channel, we propose a new scheme of controlled X-ray radiation [2,3]. The laser centroid motion in a plasma channel can be well controlled by tuning the channel depth and width. Wakefield behind the driver laser makes similar transverse oscillation, which makes the electrons inside the wake structure do transverse betatron motion and radiate. Three-dimensional PIC simulation and VDSR radiation calculation codes are used to study plasma channel based Helical plasma undulator radiation. It shows both the radiation spectrum and polarization can be well controlled. [1] J. Luo, et al., submitted. [2] M. Chen, et al., Light: Science & Applications 5, e16015 (2016). [3] J. Luo, et al., Sci. Rep. 6, 29101 (2016)

Speaker: Min Chen

12:30 O3.202 Inverse Compton scattered gamma-rays from an MeV laser plasma electron accelerator and plasma mirror

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.202.pdf Extremely intense laser-based electron acceleration in a plasma channel M. Vranic1 , R.A. Fonseca1,2 , L. O. Silva 1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 2 DCTI/ISCTE - Instituto Universitário de Lisboa, 1649-026 Lisboa, Portugal Plasma channels represent a well-suited environment for particle acceleration using lasers. The reasons for this are twofold. On one hand, the laser can be self-guided within the channel, which allows for long propagation distances. In fact, the highest electron energy to-date from laser wakefield acceleration (∼4 GeV) was obtained in a capillary discharge waveguide [1]. On the other hand, the channel can affect the particles directly. For example, self-generated elec- tromagnetic fields can assist direct laser acceleration within the channel and allow energy gain beyond the vacuum acceleration limit [2]. As fluctuations of the longitudinal electric field affect the dephasing between the electrons and the laser, it becomes possible to generate "superpon- deromotive" electrons [3] within the channel. Laser pulses of extreme intensities (I > 1022 W/cm2 ) are about to become available in the laboratory. The prepulse of such a laser can induce a plasma expansion that generates a low- density channel in near-critical gas jets. Here we present a study of channel formation and subsequent direct laser acceleration of electrons within the pre-formed plasma channel [4]. We show that the radiation reaction is important for the global plasma dynamics and affects the electron acceleration in two ways. It first interferes with the motion of the return current on the channel walls, which changes the dynamics of the channel-splitting. In addition, it reduces the radial expelling efficiency of the transverse ponderomotive force, leading to radiative trapping of particles near the channel axis. Both effects are favourable for placing particles in the region of space where they interact with the peak laser intensity and can attain multi-GeV energies. References [1] W. Leemans et al, Physical Review Letters 113, 245002 (2014) [2] G. D. Tsakiris, C. Gahn and V. K. Tripathi, Physics of Plasmas 7, 3017-3030 (2000) [3] A. P. L. Robinson, A. V. Arefiev and D. Neely, Physical Review Letters 111, 065002 (2013) [4] M. Vranic, R. A. Fonseca and L. O. Silva, Plasma Physics and Controlled Fusion 60, 034002 (2018)

Speaker: Andrea Hannasch

12:45 O3.203 Extremely intense laser-based electron acceleration in a plasma channel

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.203.pdf Enhanced relativistic electron beam collimation using two consecutive laser pulses Sophia Malko1, Xavier Vaisseau1, Michael Ehret2, 3, Dimitri Batani2, Alessandro Curcio4, J.J. Honrubia5, Katarzyna Jakubowska2, Alessio Morace6, Frédéric Perez7, Joao Santos2, and Luca Volpe1, 8 1 CLPU (Centro de Láseres Pulsados), Spain 2 Univ. Bordeaux, CNRS, CEA, CELIA (Centre Lasers Intenses et Applications), France 3 Institut für Kernephysik, Technical University of Darmstadt, Germany 4 INFN, Laboratori Nazionali di Frascati, Italy 5 ETSI Aeronauticos, Universidad Politecnica de Madrid, Madrid, Spain 6 LULI (Laboratoire pour l’Utilisation des Lasers Intenses), Ecole Polytechnique, France 7 Institute of Laser Engineering, Osaka University, Japan 8 University of Salamanca, Spain Here we report an experimental investigation of a scheme based on using of two consecutive intense laser pulses in order to optimize electron transport and collimation in dense matter. The two laser pulses, of different intensities, are focalized in a solid target at a given delay to generate two successive co-axial electron populations, where the azimuthal magnetic field generated by the first electron beam can guide the second one [1]. Previous experimental results have confirmed the general validity of the scheme: optimum delay time and intensity ratio yielding the best guiding effect [2]. It was shown that the ratio between the pre-formed magnetic field extension and the diameter of the second electron beam plays a major role in determining the guiding efficiency [3]. A systematic investigation of the scheme, exploring the role played by the radial extension of the seed magnetic field and the delay time between seed and main laser pulses, was recently carried out on the LULI-ELFIE facility. The experimental results showed a reduction of the electron beam size in the optimum conditions of both focal spot ratio and delay time between the first and the second laser pulses, yielding in factor of 2. In addition, we present the numerical simulations using hybrid PIC code and kinetic transport code that reproduce performed experimental parametrical study and benchmark the scheme efficiency. References [1] A.P.L. Robinson, et al., Phys. Rev. Lett. 100, 025002 (2008) [2] R.H.H. Scott, et al. Phys. Rev. Lett. 109, 015001 (2012) [3] L. Volpe, et al., Phys. Rev. E. 90, 063108 (2014)

Speaker: Marija Vranic

13:00 O3.204 Enhanced laser-energy absorption in laser-foil interactions driven by recirculating electron currents

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.204.pdf Enhanced laser-energy absorption in laser-foil interactions driven by recirculating electron currents R. Wilson1, R. J. Gray1, M. King1, S. D. R. Williamson1, R. J. Dance1, C. Armstrong1,2, C. Brabetz3, F. Wagner3, B. Zielbauer3, V. Bagnoud3, D. Neely2,1, P. McKenna1 1 SUPA Department of Physics, University of Strathclyde. Glasgow, UK 2 Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire, UK 3 Plasma Physics Department, GSI GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, D-64291 Darmstadt, Germany Laser energy absorption in dense plasma is fundamental to a range of intense laser-driven particle and radiation generation mechanisms. The coupling of energy to plasma electrons defines the properties of the radiation beams produced and strongly influences the optical properties of the plasma. Using the high power PHELIX laser at the GSI laboratory, we measure the total reflected and scattered laser energy as a function of intensity, by using an integrating (Ulbricht) sphere. We distinguish between the influence of pulse energy and focal spot size on total energy absorption, in the interaction of intense laser pulses with thin foils. We confirm the scaling of absorption with intensity by variation of laser pulse energy as previously reported in reference [1], but find a slower scaling when changing the focal spot size. The results were recently published in reference [2]. Using 2D particle-in-cell simulations, we show that the measured differences arise due to energetic electrons recirculating within the target. These electrons undergo multiple interactions with the laser pulse, enhancing absorption in the case of a large focal spot. This effect is found to be dependent on the laser pulse duration, the target thickness and the divergence of the fast electron beam. The parameter space over which this occurs is explored via an analytical model. The experimental, simulation and model results will be presented, and the impact of the results on our understanding of the fundamental physics of laser energy absorption in solids will be discussed. [1] Y. Ping et al, Phys. Rev. Lett., 100, 085004 (2008). [2] R. J. Gray et al, New J. Phys., At press (2018): DOI:10.1088/1367-2630/aab089

Speaker: Robbie Wilson

11:15 → 13:15 BSAP/SNPD

Chair: M. Koepke

Convener: M. Koepke

11:15 I3.J401 Characterizing nonlinear processes in simulations of turbulent space plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.J401.pdf Characterizing nonlinear processes in simulations of turbulent space plasmas D. Burgess, L. Franci, D. Trotta School of Physics and Astronomy, Queen Mary University of London, London UK Natural collisionless plasmas, such as the solar wind, can be characterized in terms of their turbulence properties, which are often taken from a framework focused on universal properties, such as power spectra with power law slopes. Improving data analysis (higher resolution and multi-spacecraft) has led to a refined picture in which characteristic plasma scales play a role. For example, recent observational work has concentrated on the transition from inertial, fluid- like scales to scales where particle kinetic processes (either ion or electron) become relevant. At the same time, this transition has been much studied with kinetic simulations which can cap- ture important kinetic effects but which are large enough to cover some of the inertial range. These simulations remind us that turbulence in a collisionless plasma has a complex network of processes involving particle energization and magnetic field topology, such as magnetic re- connection, kinetic instabilities and wave-particle interactions, as well as nonlinear wave-wave processes. We present results from a number of hybrid PIC simulations (kinetic ions with elec- tron fluid) of solar wind turbulence that illustrate various aspects of this complex system. Sim- ulations of the relaxation of a system of multiple current sheets show turbulent-like behaviour with forward and inverse cascade. However, detailed characterization of the intermittency and topological evolution using cancellation analysis shows that the system does not attain a state of fully developed turbulence. Simulations initialised with long wavelength Alfvénic fluctua- tions develop many of the power law spectral features observed in the solar wind, and we show examples of comparisons between such simulations and data. We also use the simulations to understand the role of magnetic reconnection in the evolution of the turbulence, and its connec- tion to intermittency. Finally, we discuss how the particle distribution can be characterised in the turbulence in terms of diffusion (both classical and anomalous), and the fragmented energy release sites associated with reconnection.

Speaker: David Burgess

11:45 I3.J402 Recent progress in compressible plasma turbulence: theory and in situ observations in the near-Earth space

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.J402.pdf Recent progress in compressible plasma turbulence: theory and in-situ observations in the near-Earth space 1 2 3 4 3 S. Banerjee , L.Z. Hadid , S. Galtier , S.Y. Huang , F. Sahraoui 1 Department of Physics, Indian Institute of Technology, Kanpur, India 2 Swedish Institute of Space Physics, Uppsala, Sweden 3 Laboratoire de Physique des Plasmas, Ecole Polytechnique, Univ. Paris-Sud, France 4 School of Electronic Information, Wuhan University, Wuhan, China In situ measurements show that the solar wind temperature T exhibits a decrease with the -a heliocentric distance R in R , with a < 1 and 0.3AU < R < 50AU, which is significantly -4/3 slower than an adiabatic cooling in R . What is the source of heating? During the last decade, several studies have been devoted to this question by assuming that the main source of local heating is turbulence. The main idea is that the turbulent cascade provides a natural channel to transport the energy furnished by the Sun at the largest scales, down to the sub-ion scales where it is dissipated by some kinetic effects. No need to know precisely the kinetic mechanisms because we have to our disposal an inertial range at the MHD scales where exact statistical laws of turbulence can be used to extract the heating rate which identifies to the rate of energy transfer. To better understand this problem, the exact laws of turbulence have been generalized to compressible fluids. The new universal law for compressible isothermal MHD turbulence has been used as a model to evaluate the local heating in the fast and slow solar winds. Based on data collected by ESA’s Cluster and NASA’s THEMIS missions, the analysis reveals that the heating rates found are much greater than the values obtained previously when incompressible MHD was used. This new result gives a convincing explanation for the law T(R) reported above. Recently – and for the first time – this question of the local heating has been investigated for the Earth’s magnetosheath which is highly compressible. The measures reveal that the heating rate is much greater (by a factor 100) than the one found in the compressible solar wind. New empirical power-laws are evidenced and relate the heating rate to the turbulent Mach number. These new findings have potential applications in distant astrophysical plasmas that are not accessible to in situ measurements.

Speaker: Sebastien Galtier

12:15 O3.J401 Observation of CW to pulsed mode transition of cyclotron maser emission from magnetic mirror

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.J401.pdf Observation of CW to pulsed mode transition of cyclotron maser emission from magnetic mirror D. A. Mansfeld1, A. G. Shalashov1, E. D. Gospodchikov1, I. V. Izotov1, V. A. Skalyga1, O. Tarvainen2 1 Institute of Applied Physics Russian Academy of Sciences, Nizhny Novgorod, Russia 2 Department of Physics, University of Jyvaskyla, Jyvaskyla, Finland The first experimental evidence of the controlled transition from the generation of periodic bursts of electromagnetic emission into continuous wave (CW) regime of a cyclotron maser formed in magnetically confined non-equilibrium plasmas is reported. The approach to the transition to CW regime, which requires fine tuning of the magnetic field, was found experimentally. From a theoretic point of view [1], the observed transition is related to the Poincare–Andronov–Hopf bifurcation: a stationary point attributed to CW generation becomes unstable through the birth of a stable limit cycle. The kinetic cyclotron instability of the extraordinary wave of weakly inhomogeneous magnetized plasma is driven by the anisotropic electron population resulting from electron cyclotron plasma heating in MHD-stable minimum-B open magnetic trap. Except being of fundamental interest in the context of space cyclotron masers in planet magnetospheres and other astrophysical objects, our results are important for applications, in particular for the development of ECR ion sources. [1] http://arxiv.org/abs/1712.06700

Speaker: Dmitry Mansfeld

12:30 O3.J402 Frequency sweeping events in cyclotron emission of energetic electrons in ECR discharge plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.J402.pdf Frequency sweeping events in cyclotron emission of energetic electrons in ECR discharge plasmas M.E. Viktorov1 , A.G. Shalashov1 , E.D. Gospodchikov1 , D.A. Mansfeld1 , I.S. Abramov1 , S.V. Golubev1 1 Institute of Applied Physics of Russian Academy of Sciences, Nizhny Novgorod, Russia The complex dynamics have been observed in the spectra of the electron cyclotron emission of a nonequilibrium plasma created by powerful microwave radiation of gyrotron (37.5 GHz, 80 kW) under electron cyclotron resonance (ECR) conditions and confined in a tabletop mirror trap [1, 2]. The dynamic spectrum of the emission is a set of highly chirped radiation bursts with both increasing and decreasing frequencies which are repeated periodically. Such patterns are not described in the frame of a quasilinear approach which is standard for the description of a broadband plasma emission. From the other hand, the simultaneous observation of several chirping bursts in the same frequency range is typical for the formation of nonlinear phase-space structures in a proximity of the wave-particle resonances of a kinetically unstable plasma, also known as the “holes and clumps” mechanism [3]. Our data provide the experimental evidence for the spontaneous formation of self-consistent structures in the new frequency domain (a few GHz) linked to the electron cyclotron frequency in a laboratory mirror-confined plasma. The work is done in the frame of the RSF grant (project 17-72-10288). References [1] M.E. Viktorov, A.G. Shalashov, D.A. Mansfeld and S.V. Golubev, EPL 116, 55001 (2016) [2] A.G. Shalashov, M.E. Viktorov, D.A. Mansfeld and S.V. Golubev, Phys. Plasmas 24, 032111 (2017) [3] H.L. Berk, B.N. Breizman, N.V. Petviashvili, Phys. Lett. A 234, 213 (1997)

Speaker: Mikhail Viktorov

12:45 O3.J403 Electron-positron plasma turbulence driven by pressure gradients

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.J403.pdf Electron-Positron Plasma Turbulence Driven by Pressure Gradients M.J. Pueschel1,2 , P.W. Terry2 , F. Jenko1,3 , and B. Tyburska-Pueschel2,4 1 University of Texas at Austin, Austin, Texas 78712, USA 2 University of Wisconsin-Madison, Madison, Wisconsin 53706, USA 3 Max Planck Institute for Plasma Physics, 85748 Garching, Germany 4 German Aerospace Center, 51147 Cologne, Germany The stability and turbulence properties of pair plasmas are of significant consequence in many, disparate physical systems. Fluctuations may appear in laser-induced or magnetically confined pair plasmas, and electron-positron plasma turbulence may affect the radiation signa- ture of objects such as Gamma Ray Bursts (GRBs). Here, the focus lies on electron-positron plasmas in a strong, homogeneous magnetic guide field, subject to a background density or temperature gradient. It is shown that this setup allows the E×B and ∇Bk drifts to couple, causing instability. This process is referred to as the Gradient- driven Drift Coupling (GDC) mode [1], which is also able to drive turbulence in helium plasma experiments [2]. Unlike standard fluid models, which do not include a succinct description of the ∇Bk drift, a new fluid model is presented that recovers gyrokinetic analytical and numerical mode prop- erties. Furthermore, nonlinear gyrokinetic simulation results are shown, demonstrating that the GDC instability may indeed drive quasi-stationary turbulence in pair plasmas. Consequences are discussed for specific physical systems: in addition to GRBs, the focus lies on high-density, laser-induced pair plasma experiments [3] – assuming the addition, presently under discussion, of a magnetic guide field – and low-density, zero-shear magnetic-confinement experiments [4]. References [1] M.J. Pueschel, P.W. Terry, D. Told, and F. Jenko, Phys. Plasmas 22, 062105 (2015) [2] M.J. Pueschel et al., Plasma Phys. Control. Fusion 59, 024006 (2017) [3] G. Sarri et al., Nat. Commun. 6, 6747 (2015) [4] H. Saitoh et al., J. Phys. Conf. Ser. 505, 012045 (2014)

Speaker: M. J. Pueschel

13:00 O3.J404 Average flows and stochastic islands in the magnetic field line random walk

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.J404.pdf Average flows and stochastic islands in the magnetic field line random walk M. Vlad, F. Spineanu National Institute of Laser, Plasma and Radiation Physics, Magurele-Bucharest, Romania The nonlinear effects that appear in the field line random walk (FLRW) in magnetic turbulence are discussed. The magnetic lines show both random and quasi-coherent aspects. The random motion leads to diffusive transport while the coherent motion is associated with trapping or eddying in the structure of the stochastic field. The strength of each of these aspects depends on the parameters of the turbulence reflected in the magnetic Kubo number 𝑅 = 𝐿𝐼𝐼 𝛽/𝐿⊥ 𝐵0 , where 𝛽 is the amplitude of the stochastic magnetic field b, B0 is the average magnetic field, 𝐿𝐼𝐼 , 𝐿⊥ are the correlation lengths of b along and perpendicular to B0, respectively. Trapping is negligible for R < 1, and it is statistically relevant for R > 1, with effects that become stronger as R increases. At large R the field line statistics is a mixture of random and quasi-coherent behaviour, with diffusive spreading combined with the generation of stochastic islands. In the limit R →∞, the transport is subdiffusive. In special conditions, orientated steps of the field lines can appear even if the average of b is zero. They lead to quasi-coherent flows of the magnetic lines. We identify and analyse two sources of flows in FLRW, the large scale variation of the amplitude 𝛽 and of B0. We have shown that the gradient of 𝛽 determines a quasi-coherent flow along its direction. The average velocity Vf is an increasing function of R at R<1, it reaches a maximum around R=1 and eventually decreases. The decrease is determined by the stochastic magnetic islands, which yield an average velocity in the opposite direction. This process determines the tendency of field line accumulation on the maxima of the amplitude 𝛽. The gradient of B0 also determines a flow, but with different properties and physical reasons. It is similar to a process found in confined plasmas [3]. The transport coefficients, the average size of the stochastic magnetic islands and the average flows of the magnetic lines are determined. Our instrument, the decorrelation trajectory method [4] is essentially analytical. [1] Vlad M and Spineanu F 2014 Astrophys. J. 791 56 [2] Vlad M, Spineanu F and Croitoru A 2015 Astrophys. J. 815 11 [3] Vlad M, Spineanu F and Benkadda S 2006 Phys. Rev. Lett. 96 085001 [4] Vlad M, Spineanu F, Misguich J H and Balescu R 1998 Phys. Rev. E 58 7359

Speaker: Madalina Vlad

11:15 → 13:15 MCF

Chair: A. Dinklage

Convener: A. Dinklage

11:15 I3.111 Plasma-Surface Interaction and Plasma-Edge Studies in Wendelstein 7-X Operating with Passively Cooled Graphite Divertor

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.111.pdf Plasma-Surface Interaction and Plasma-Edge Studies in Wendelstein 7-X Operating with Passively Cooled Graphite Divertor S. Brezinsek1, M. Jakubowski2 and the Wendelstein 7-X team 1 Forschungszentrum Jülich, Institut für Energie und Klimaforschung – Plasmaphysik, 52545 Jülich, Germany 2 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany The stellarator Wendelstein 7-X (W7-X) restarted operation in 2017 with ten divertor modules made of inertially cooled graphite plasma-facing components PFCs [1]. The plasma exhaust concept and first wall properties are substantially different from those in the initial campaign which had limiters and explicitly avoided edge magnetic islands. The ten divertors now intercept an edge island chain. Additionally the inner vessel has been complemented by adding graphite PFCs to the already installed CuCrZr heat shields. Before the initial divertor operation started, the vessel was baked up to 150°C, and glow discharges in helium (He) and hydrogen (H) were performed to condition the device. ECRH discharges were conducted in He in order to reduce the impurity and H content to acceptable values for steady and long pulse operation. The main impurities have been identified spectro- scopically to be carbon and oxygen in the plasma-edge layer (~10%) whereas the post- plasma outgassing also includes methane, water, and carbon monoxide. H outgassing from the first wall components, operated at room temperature, largely determined the fueling, but much less prominently than in the initial limiter phase [2]. Conditions improved with increased deposition of plasma flux and heat to plasma-facing sides during plasma operation. A major part of the initial studies was devoted to symmetrisation of the power and particle load to the divertor modules with the aid of a small external field in order to correct 1/1 error fields and target module misalignment [3]. Indeed the footprint of particle and heat load was successfully measured with a multitude of edge diagnostics including interference filtered cameras, infrared cameras, divertor spectroscopy, and sets of Langmuir probes embedded in the divertor PFCs. Typical heat fluxes achieved so far are up to 5 MWm-2 and particle fluxes in the range of a few 1023H+s-1m-2 at the strike line distributed on the horizontal or vertical target. The edge topology at W7-X depends strongly on the selected magnetic configuration, i.e. due to different island chains responsible for the divertor function. Indeed divertor detachment associated with low electron temperature and high density has been observed. The reduction in the emission of CII and CIII light in the divertor suggests a strong reduction of the carbon source with higher fueling which is consistent with a reduction of the physical sputtering, whereas the chemical sputtering still remains. Detailed analysis of the recycling and radiation distribution in the divertor and associated modelling with EMC3-EIRENE is progressing [4] and results will be presented, The global material migration from main chamber locations such as graphite tiles will be studied by dedicated post-mortem analysis of extracted plasma-facing components with markers after the initial campaign, i.e. in early 2018, and will be compared with modelling predictions. In addition dedicated plasmas with tracer injection are foreseen to describe and quantify the transport from the outer midplane to the divertor target plates. Indicating also the remote areas where layers will be build-up in time. These studies will aid in predicting the behavior in longer pulses in W7-X and the expected fuel retention levels by implanted and co-deposited fuel as well as point to areas where cleaning activities might be required. [1] T. Sunn Pedersen et al. (2017) presented at the ISHW conference Kyoto [2] T. Wauters et al. (2017) private communication [3] P. Drewelow et al. (2018) to be presented as inv. oral at the PSI conference Princeton [4] F. Effenberg et al. (2018) to be presented as contr. oral at the PSI conference Princeton

Speaker: Sebastijan Brezinsek

11:45 I3.112 Pellet Injection in the Stellarator TJ-II

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.112.pdf Pellet Injection in the Stellarator TJ-II K. J. McCarthy1, N. Panadero1, S. K. Combs2, N. Tamura3, J. L. Velasco1, E. Ascasíbar1, J. Baldzuhn4, E. de la Cal1, T. Estrada1, J.M. Fontdecaba1, R. García1, J. Hernández1, F. Koechl5, M. Liners1, A. López-Fraguas1, A. V. Melnikov6, M. Navarro1, D. Silvagni7, J. L. de Pablos1, I. Pastor1, A. Soleto1, A. Zhezhera8, TJ-II team1, LHD experimental group3, and W7-X team4 1 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain 2 Fusion & Materials for Nuclear Systems Division, ORNL, Tennessee, USA 3 National Institute for Fusion Science, Toki, Japan 4 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 5 Atominstitut, Technische Universität Wien, Vienna, Austria 6 National Research Centre ‘Kurchatov Institute’, Moscow, Russia 7 Max-Planck-Institut für Plasmaphysik, Garching, Germany 8 Institute of Plasma Physics, NSC KIPT, Kharkov, Ukraine Cryogenic pellet injection (PI) is a standard tool on most medium- and large-sized magnetically confined plasma devices. Technologies are well developed and PI systems are earmarked as critical items in future reactors. Despite significant progress, a complete comprehension of ablation, enhanced ablation, and particle drift/diffusion remains to be achieved. Indeed, understanding these is essential to improve codes and to optimize fuelling. In contrast, in some devices, other pellet types are also often injected, e.g. impurities. Given the similar ablation physics, etc., comparative studies may help extend current knowledge. A cryogenic PI system is used for low-field side injections into the TJ-II, a highly flexible, medium-sized, stellarator. TJ-II is fitted with a wide range of diagnostics, making it a powerful tool for pellet physics studies [1, 2]. Good agreement is found between experimental and predicted profiles (ablation/deposition) when using a new stellarator version of the HPI2 code [3]. For instance, fast-frame imaging of the ablation process finds outward plasmoid drifts that concur with simulations. This has permitted benchmarking HPI2 for W7-X and has provided input for related studies [3]. Moreover, comparative studies, using a TESPEL (C8H8) system piggybacked to the up-stream end of the TJ-II PI, substantiate the influence of pellet particle mass on plasmoid drift, deposition profile peaking and deposition efficiency [4]. Finally, TJ-II studies reveal a strong penetration depth/fuelling efficiency relationship, and show that Er changes are consistent with effective ion charge variations and that density fluctuations are strongly reduced over a short time scale immediately after an injection. [1] J. L. Velasco et al., Plasma Phys. Control. Fusion 58 (2016) 084004. [2] K. J. McCarthy et al., Nucl. Fusion 57 (2017) 056039. [3] N. Panadero et al., Nucl. Fusion 58 (2017) 026025. [4] K. J. McCarthy et al., Europhys. Lett. 120 (2017) 25001.

Speaker: Kieran Joseph McCarthy

12:15 O3.101 Effect of pumped closed helical divertor on edge plasma behavior in LHD

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.101.pdf Effect of pumped closed helical divertor on edge plasma behavior in LHD T. Morisaki1,2, G. Motojima11,2, T. Murase1, H. Tanaka3, S. Masuzaki1,2, M. Shoji1, S. Oliver4, and LHD Experiment Group 1 National Institute for Fusion Science, Toki 509-5292, Japan 2 SOKENDAI, The Graduate University for Advanced Studies, Toki 509-5292, Japan 3 Nagoya University, Nagoya 464-8603, Japan 3 University of Wisconsin, Madison, WI, USA The closed helical divertor (CHD) with cryogenic pump was installed in LHD, aiming for the confinement improvement through the effective edge plasma control [1]. Due to the strong nonuniformity of helical divertor flux distribution, quite large pumping capability is available only with partial installation of CHD modules along the divertor striking trails. The measured pumping speed was 675 m3/s which is identical to ~ 20 % of the LHD main evacuation system, and the pumping capacity was 58,000 Pa m3, which is equivalent to 20,000 deuterium pellets or 20 days of gas amounts of high density experiments [2]. The CHD experiment has started since the last experimental campaign which was the first deuterium experiment in LHD, and initial results to demonstrate the CHD performance were obtained. In the experiment, the plasma was produced and maintained by NBI with moderate power of 10 – 20 MW. Fuelling was performed with pellet injection and/or gas puffing. It was found that about half of the fuelled gas was efficiently evacuated with pumped CHD, thus quite low recycling state was obtained, where effective particle confinement time is one order smaller than that without CHD pumping. This strong controllability for neutral particles also affects the formation of electron density and temperature profiles. In the repetitive pellet fuelled plasma, a peaked temperature profile was realized, and higher central temperature was obtained, compared to the reference discharge without pumping in the same fuelling condition. However, a hollow profile of electron density was formed, although continuous pellet fuelling was performed. This result was brought about by the combination of some physical processes, e.g., heat and particle transport, particle recycling, energy balance, pellet ablation, etc. At the conference, effects of the pumped CHD on profile formation are discussed, taking those process into consideration. [1] T. Murase et al., Plasma. Fusion Research 11, (2016) 1205030. [2] G. Motojima et al., 2018 Nucl. Fusion 58 014005.

Speaker: Tomohiro Morisaki

12:30 O3.102 Scalings for the energy confinement time and radiative density limit in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.102.pdf Scalings for the energy confinement time and radiative density limit in Wendelstein 7-X G. Fuchert1 , A. Alonso2 , C.D. Beidler1 , S. Bozhenkov1 , A. Dinklage1 , Y. Feng1 , M. Hirsch1 , A. Langenberg1 , Y. Turkin1 , N. Pablant3 , E. Pasch1 , F. Warmer1 , D. Zhang1 , R.C. Wolf1 , and the W7-X team 1 Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 14791 Greifswald, Germany; 2 CIEMAT, Madrid, Spain; 3 Princeton Plasma Physics Laboratory, Princeton, NJ, USA In the first two experimental campaigns of the new stellarator Wendelstein 7-X (W7-X), a positive density scaling of the energy confinement time has been observed. The density de- pendence is comparable to the empirical energy confinement time scaling for stellarators, the ISS04 [1]. It is not only found by scaling analyses of different experiments, but also during density ramps in individual experiments. Since the low-density hydrogen plasmas achieved so far are, however, far away from the high-performance plasmas W7-X was designed for, it re- mains to be shown that this trend can be extrapolated to reactor-relevant conditions. Such an investigation is hampered by the occurrence of radiative collapses at relatively low densities. Similar collapses are observed in most stellarators at a critical density depending on the heating power and the impurity concentration. Under given machine conditions this can be considered as a type of (radiative) density limit often referred to as the Sudo (density) limit [2]. The density and power scaling of the energy confinement time is investigated for the limiter and first test divertor campaigns of W7-X and the scaling obtained is then employed to evaluate a simplified model for the radiative density limit [3]. A critical density has been calculated and a reasonable agreement with experimental data is found. However, comparing hydrogen and helium plasmas in different magnetic field configurations it is shown that the radiative density limit in W7-X is an operational limit where the critical density varies between different scenarios, probably due to differences in the plasma wall interaction, island geometry and main edge radiators (presumably C, O and H in hydrogen and additionally He in helium plasmas). This opens an interesting perspective where the critical density can not only be influenced by improving the machine conditions (e. g. by boronization), but also by scenario development. References [1] H. Yamada et al., Nuclear Fusion 45 1684 (2005) [2] S. Sudo et al., Nuclear Fusion 30 11 (1990) [3] P. Zanca et al., Nuclear Fusion 57 056010 (2017)

Speaker: Golo Fuchert

12:45 O3.103 First observation of a stable highly-radiative divertor regime at stellarator W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.103.pdf First observation of a stable highly-radiative divertor regime at stellarator W7-X D. Zhang1, R. König1, Y. Feng1, S. Brezinsek2, M. Jakubowski1, R. Burhenn1, B. Buttenschön1, H. Niemann1, M. Krychowiak1, A. Alonso3, J. Baldzuhn1, S. Bozhenkov1, M. Hirsch1, L. Giannone4, S. Kwak1, F. Penzel4, K. Rahbarnia1, J. Svensson1, H. Thomsen1, V. Winters5 and the W7-X team 1 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany 2 Forschungszentrum Jülich GmbH, IEK-4, D-52425 Jülich, Germany 3 Laboratorio Nacional de Fusión – CIEMAT, 28040 Madrid, Spain 4 Max-Planck-Institut für Plasmaphysik, Garching, Germany 5 University of Wisconsin – Madison, Wisconsin 53706, USA Shortly after the first successful operation with five inboard limiters, the stellarator Wendelstein 7-X (W7-X) was upgraded by installing ten up/down-symmetrically-paired test divertor units (inertially cooled) and already conducted divertor experiments late last year. The first divertor experiments have shown significant differences in radiation behavior of impurities (carbon and oxygen as major intrinsic impurities) in comparison with the previous limiter plasmas. First, the region of intensive radiation, which was typically several cm inside the LCFS of the limiter configuration, shifted outwards towards the separatrix of the divertor configuration or even into the Scrape-Off layer (SOL) depending on the radiation strength. Secondly, for certain plasma scenarios the radiated-power fraction is significantly increased without serious degradation of energy confinement. Most importantly, a stable highly-dissipative divertor regime was discovered for an ECR- heated hydrogen discharge in which the total radiation power (measured by the bolometer) approached 95% of the total 3MW input power and the edge bolometer channel signals remained almost unchanged over several energy confinement times. Despite this high radiation, there was no remarkable loss of the diamagnetic energy. In consistence with the bolometer measurement, the IR-cameras monitoring the divertor targets revealed reduced heat load on all ten divertor units down to a remaining fraction which might be assigned to contributions from photons and CX-neutrals. This experimental finding motivated a careful survey of all relevant divertor plasmas as well as a dedicated divertor program in the last two weeks of the past campaign for its reproducibility. This plasma state turned out to be well repeatable. Based on bolometer measurements, this paper presents a systematic analysis of this regime, including the radiation strength and location in the island divertor as well as their dependences on divertor configuration and plasma parameters.

Speaker: Daihong Zhang

13:00 O3.104 Effects of toroidal plasma currents on the strike-line movements on W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.104.pdf Effects of toroidal plasma currents on the strike-line movements on W7-X Y. Gao1 , M. Jakubowski2 , J. Geiger2 , M. Endler2 , P. Drewelow2 , S. Bozhenkov2 , K. Hammond2 , K. Rahbarnia2 , A. Puig Sitjes2 , F. Pisano3 , H. Niemann2 , A. Ali2 , H. Thomsen2 , T. Andreeva2 , U. Neuner2 , J. Schilling2 , M. Rack1 , Y. Liang1 , and the W7-X Team 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Max-Planck-Institut für Plasmaphysik, Wendelsteinstraße 1, 17491 Greifswald, Germany 3 Department of Electrical and Electronic Engineering, University of Cagliari, Piazza d’Armi, Cagliari 09123, Italy Wendelstein 7-X (W7-X) stellarator has been optimized amongst other criteria for small boot- strap current. However, even small plasma currents can change the rotational transform and displace the magnetic island chains at the plasma edge, due to its low shear characteristic. Be- sides possible changes to the plasma core confinement, the power loads to the plasma facing components are affected, which is most important for divertor operation. Thus scenarios with a small bootstrap current are crucial for W7-X [1]. The evolution of toroidal plasma currents has been measured by a set of Rogowski coils [2, 3], during the first divertor operation phase on W7-X. In the case of freely evolving bootstrap currents (without electron cyclotron current drive), strike lines on the divertor targets monitored by means of infra-red cameras are observed to move in accordance with the measured toroidal current. The net positive toroidal current shifts the strike lines on the vertical and horizontal targets away from the pumping gap in the standard magnetic configuration. Heat flux profiles have been calculated and compared with diffusive field line tracing mod- elling [4] considering also the effective plasma current. As a preliminary result we see qualita- tive consistency between experimental results and modelling suggesting a strike-line movement of ∼ 3 cm along the target surface caused by a net toroidal current of ∼ 5 kA. This current is developed in the order of 10 s. This movement of the strike line corresponds to approximately one third of the strike-line width. References [1] J. Geiger et al. Plasma Physics and Controlled Fusion, 57 (1), 014004 (2015). [2] M. Endler et al. Fusion Engineering and Design, 100, 468 (2015). [3] K. Rahbarnia et al. Nuclear Fusion, submitted. [4] S. Bozhenkov et al. Fusion Engineering and Design, 88 (11), 2997 (2013).

Speaker: Yu Gao

11:15 → 13:15 MCF

Chair: G. Pautasso

Convener: G. Pautasso

11:15 I3.113 Runaway Electron Beam Control

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I3.113.pdf Runaway Electron Beam Control D. Carnevale1 for the FTU team2 , the EUROfusion MST1 team3 and JET Contributors4 1 Dip. di Ing. Civile ed Informatica, Università di Roma Tor Vergata, Italy 2 See the author list of “ G. Pucella et al., Proc. 25th IAEA FEC 2014” 3 See the author list of “Meyer et al. 2017, Nucl. Fusion 57 102014” 4 See the author list of “ X. Litaudon et al 2017 Nucl. Fusion 57 102001” Post-disruption runaway electrons (RE) beam mitigation is one of the main concerns for ITER operations. RE beam control algorithms (Tore-Supra [1], DIII-D [2], FTU [3] and TCV [4]) for stabilization and current reduction can be combined with SPI/MGI and provide redundancy and backup in case of SPI/MGI failure. DINA simulations have shown that RE beam control could be effective for Current Quenches (CQ) below 4 MA in ITER. In the first part of the work the RE Control (REC) architecture to stabilize the RE beam position and ramp down its current is presented and experimental results on FTU and TCV are discussed. REC effective- ness is demonstrated by analyzing Hard X-ray (HXR) monitors and the Runaway Electrons Imaging and Spectroscopy (REIS) system. An estimation technique to retrieve the RE energy distribution function from REIS is proposed. RE beam instabilities and their correlation with toroidal electric field and density are discussed. Further, experimental results will be presented from FTU on deuterium pellet and heavy particle injection into steady-state flat-top discharges with runaway electrons and on RE beams. Analyzed data from the fast scanning CO2 -CO in- terferometer and spectroscopy diagnostics are also reported to help understanding the particle interaction with the RE beam to possibly extrapolate information for ITER predictions. Finally, the REC installation at JET to improve the RE beam stabilization will be introduced. Acknowledgement: This work has been carried out within the framework of the EUROfusion Con- sortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. References [1] Saint-Laurent F. et al., Proc. 38th EPS Conf. Plasma Physics O3 118, 2011 [2] Hollmann E. M. et al., NF 53 083004, 2013 [3] Esposito B. et al, PPCF, ISSN: 0741-3335, Vol 59, 2016 [4] Carnevale D. et al., 44th EPS, P 1.152, 2017

Speaker: Daniele Carnevale

11:45 O3.105 Asymmetric wall force reduction in ITER and JET disruptions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.105.pdf Asymmetric wall force reduction in ITER and JET disruptions H. Strauss1 , S. Jachmich2 , E. Joffrin3 V. Riccardo4 ,R. Paccagnella5 ,J. Breslau4 and JET Contributors ∗ 1 HRS Fusion, West Orange NJ, USA 07052 2 EURATOM/UKAEA Fusion Association, Culham Science Centre, OX14 3DB, UK 3 IRFM, CEA centre de Cadarache, 13108 Saint-Paul-lez-Durance, France 4 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 08570 5 Consorzio RFX and Istituto Gas Ionizzati del C.N.R., Padua, Italy Asymmetric vertical displacement event (AVDE) ∆Fx, πB∆MIZ, vs. τCQ/τwall disruptions in ITER should produce a relatively 1.4 1.2 small electromechanical force on the conducting 1 structures surrounding the plasma, in contrast to 0.8 MN previous predictions based on JET data. This is 0.6 ∆ Fx 71985 85858 shown in simulations [1, 2] with the M3D 3D MHD 0.4 90386 code [3] and confirmed in JET experiments [4] in 0.2 which the current was quenched with massive gas 0 1 10 τCQ/τwall injection (MGI). In ITER the current quench (CQ) time τCQ is less than or equal to the resistive wall Figure 1: simulated asymmetric wall force penetration time τwall . JET is in a different param- ∆Fx , and wall force estimated from MGI eter regime, with τCQ /τwall > 1. JET simulations shots, labeled with JET shot number. were validated by comparison [1] to JET shot 71985 data and were in good agreement. The wall time τwall was then artificially increased, keeping τCQ fixed, and it was found that the wall force decreased. The reduction of the asymmetric wall force was also found in analysis of experimental data of JET MGI mitigated disruption shots, although the published data only concerned the symmetric wall force [4]. Further simulations [2] were carried out of ITER AVDEs. For τCQ /τwall ≤ 1, the force was 4MN, comparable to the force in JET. A fast CQ may cause production of runaway electrons (REs). Simulations using a modified version of M3D with a fluid RE model [5] will be presented. Acknowledgment Work supported by USDOE and Euratom research and training programme 2014- 2018 under grant agreement No 633053, within the EUROfusion Consortium. Views and opinions herein do not necessarily reflect those of the European Commission. References [1] H. Strauss, E. Joffrin, V. Riccardo, J. Breslau, R. Paccagnella, Phys. Plasmas 24 102512 (2017). [2] H. Strauss, Physics of Plasmas 25 020702 (2018). [3] W. Park, E. Belova, G. Y. Fu, et al., Phys. Plasmas 6 1796 (1999). [4] S. Jachmich, P. Drewelow, et al., 43rd EPS Conf. Plasma Physics (2016) [5] Huishan Cai and Guoyong Fu, Nucl. Fusion 55 022001 (2015). ∗ see author list of X. Litaudon et al 2017 Nucl. Fusion 57 102001

Speaker: Henry Strauss

12:00 O3.106 Magnetic fluctuations during the Thermal and current quench of mitigated disruptions and comparison with 3D non-linear MHD predictions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.106.pdf Magnetic fluctuations during the Thermal and current quench of mitigated disruptions and comparison with 3D non-linear MHD predictions C. Fougere1, E. Joffrin2, E. Nardon2, E. Alessi3, M, Baruzzo4, P. Buratti5, A. Ficker6, S. Gerasimov7, G. Szepesi7, and JET contributors. 1ESPCI, 10 Rue Vauquelin, 75005 Paris, France 2CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 3IFP-CNR, Via R Cozzi, 5, 20152 Milan, Italy 4Consorzio RFX, Corso Stati Uniti, 4 – 35127 Padova, Italy 5ENEA, 00044 Frascati (Roma), Italy. 6IPPCR of the CAS, 182 00 Prague 8, Czech Republic 7 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK Plasma disruptions are considered as the main risk for the operation of ITER. In JET, the magnetic fluctuations structures taking place prior to and during the thermal and the current quench of disruption mitigated by massive gas injection (MGI) have been analysed in details and compared with the predictions of the 3D non-linear MHD code JOREK. This experimental analysis makes use of the JET full poloidal (18 coils) and toroidal (8) arrays of pick-up coils sampled at 50kHz for rotating mode up to ~10kHz, the 14 saddle loops for low frequency (<1kHz cut-off frequency) modes and uses the singular value decomposition (SVD) technique to identify the mode structure. The analysis has also made use of the JET soft X-ray arrays to confirm the internal structures of the modes in correlation with the magnetics. Before the current quench of a discharge with massive deuterium gas injection (86887), it is found that a dominant n=1/m=2 mode and an n=2/m=3 modes are destabilized and their amplitude is growing rapidly (by typically 5 folds) in the window 5ms before the thermal quench and 6ms after the gas is launched by the mitigation valve. The analysis has been repeated for a discharge with massive deuterium + 10%Ar gas injection (89795) and consistent result have been found with in addition the presence of an n=3/m=4 structure growing in the last 2ms before the thermal quench occurs. These analyses support the picture predicted by the JOREK code [1], that the MGI gas destabilizes the n=1/m=2 tearing mode which flattens the current profile, destabilizing a n=2/m=3 mode, which in turn destabilizes higher n modes such as the n=3/m=4. This mode activity is observed to peak at the thermal quench with frequency of a few kHz and then is replaced in about 1 to 2ms by a low frequency activity (300 to 500 Hz) when the n=1/m=2 mode locks and the plasma stops rotating. Just after the thermal quench, the chain of mode activity disappears but there is a persistent 6kHz mode identified as a core n=1 mode using the fast magnetic pick-up coils and the soft X-ray. Comparing two different massive gas injections with different pressures in the valve (90%D+10%Ar), it appears that this n=1 structure is observed in the low valve pressure case, i.e. when the disruption is imperfectly mitigated (i.e. the total radiation at the end of the current quench lower than in the high valve pressure case). In this case, this indicates that the plasma inside q=1 still exists and survives the massive gas injection for some time. In the high valve pressure case, this core n=1 mode is not observed to persist, indicating that the core has collapsed. JOREK simulations predict an n=1/m=1 kink mode in the core at the time of the thermal quench and this behaviour is also found in NIMROD simulations for other tokamaks [2]. These results suggest that the q=1 surface could prevent the gas penetration until a sawtooth occurs in the mitigation process and provide an explanation why massive gas injection has not been found efficient enough for radiating the plasma energy. [1] : Nardon E et al 2017 Plasma Phys. Control. Fusion 59 014006 [2] : Izzo V A et al 2008 Phys. Plasmas 15 056109

Speaker: Emmanuel Henri Joffrin

12:15 O3.107 DIII-D research in support of the ITER disruption mitigation system

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.107.pdf DIII-D Research in Support of the ITER Disruption Mitigation System N.W. Eidietis1, P. Aleynikov2, J. Herfindal3, E.M. Hollman4, A. Lvovskiy5, R.A. Moyer4, C. Paz-Soldan1, D. Shiraki3 1 General Atomics, San Diego, USA 2 Max-Planck Institute for Plasma Physics, Greifswald, Germany 3 Oak Ridge National Laboratory, Oak Ridge, USA 4 University of California - San Diego, San Diego, USA 5 Oak Ridge Associated Universities, Oak Ridge, USA Pioneering studies on DIII-D directly support the development and operation of the ITER disruption mitigation system. Recent experiments examined the effects of SPI trajectory orientation and the superposition of multiple SPIs upon mitigation metrics. In experiments, the tangential SPI trajectory increases the current quench duration and halo current impulse compared to a core-directed SPI trajectory. The degraded SPI performance due to the change in injection trajectory implies ballistic transport, in addition to MHD mixing, is an important aspect of SPI mitigation. The superposition of dual toroidally separated SPI is also examined. It is found that when two differently sized pellets (10 torr-L and 400 torr-L) are injected into the plasma simultaneously, the radiation fraction measured near the injector ports is reduced, the current quench duration increases, and the plasma cooling duration decreases relative to injection of the single 400 torr-L pellet, indicating a degradation in the effectiveness of mitigation. Examination of the runaway electron (RE) energy distribution function evolution in the flattop of low-density, Ohmically driven discharges using MeV-scale bremsstrahlung emission provides direct comparison to theoretical models of RE evolution. The observed energy spectra display the predicted energy “bump” indicating the energy attractor predicted by theory, as well as the motion of the bump in energy space as the collisionality (density) is varied. Measured spectra also exhibit a strong dependence of the high-energy tail upon the synchrotron force (varied using Bt) in qualitative agreement with theory. A novel shell pellet technology has been installed on DIII-D to study the deposition of impurities in the core without significantly cooling the edge, and recent experimental results are discussed. * This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award DE-FC02-04ER54698.

Speaker: Nicholas Eidietis

12:30 O3.108 High-field side error field effects on H-mode plasma performance and their correction in ITER-like experiments on COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.108.pdf High-field side error field effects on H-mode plasma performance and their correction in ITER-like experiments on COMPASS T. Markovic1,2, M. Peterka1,2, A. Loarte3, J. K. Park4, Y. Gribov3, J. Havlicek1, R. Panek1, P. Hacek1,2, M. Hron1, M. Imrisek1,2, K. Kovarik1, L. Kripner1,2, K. Mitosinkova1,2, M. Sos1, M. Tomes1,2, J. Varju1, P. Vondracek1,2, V. Weinzettl1 and the COMPASS team1 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 3 ITER Organization, 13067 St Paul-lez-Durance, France 4 Princeton Plasma Physics Laboratory, Princeton University, Princeton, USA Plasma performance in magnetic confinement fusion (MCF) devices is degraded by the presence of error fields (EF) e.g. due to misalignments of magnetic coils during assembly process. By utilizing error field correction (EFC) coils, detrimental effects of EF can be annulled or, alternatively, artificially induced. Typically, EFC coil-induced EF couples equally well to both the core and the edge plasma resonant surfaces due to their location on the low-field side (LFS) of the device. However, coupling of the intrinsic EF originating at the high-field side (HFS) of a tokamak (e.g. due to a tilt of the toroidal field coils (TF) or of the central solenoid (CS)) is different. The effects of such EF on the plasma or the need for their correction have not been sufficiently characterized yet (mainly due to lack of capabilities of the present MCF devices to generate controlled HFS EF). However, they are highly important for ITER since the magnitude and correction of such effects have direct implications on the accuracy of installation and alignment of the TF/CS coil sets. In the COMPASS tokamak we have used EFC coils at the HFS to generate controlled EF in ITER-like (q95=3) plasmas, mimicking the effects of tilt and displacement of the CS on H-mode plasma confinement and on the L-H transition/H-mode access. We report that these effects prevent H-mode access (due to disruptions), and if EF are applied to a pre-existing H-mode, they lower the energy confinement by 20%. We show that while n=1 EFC by LFS coils can fully recover the H-mode energy confinement, H-mode accessibility is only partially restored – 50% of the discharges in which this EF correction scheme is applied disrupt. Initial experiments show that an addition of the top and bottom coils (as available in ITER) to the correction of the HFS EF decreases significantly this disruption rate. The experimental observations are interpreted using IPEC and MARS-F modelling and the implications for ITER are discussed.

Speaker: Tomas Markovic

12:45 O3.109 Size matters: ITER breakdown and plasma initiation revisited

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.109.pdf Size matters: ITER breakdown and plasma initiation revisited P.C. de Vries and Y. Gribov ITER Organization, Route de Vinon sur Verdon, 13067 St Paul Lez Durance, France. Breakdown and plasma initiation are a well-established part of operations of present day tokamaks and hence, usually gain little interest. As a result, some misconceptions about this first and important stage in a Tokamak discharge exist. This paper revisits a number of key aspects of plasma initiation, aiming to clarify concepts and improve understanding, in view of ITER first plasma operation. The paper will show that size matters and that breakdown and plasma initiation differs in larger devices. Firstly, breakdown is only a small and short part of the total plasma initiation phase, which also includes the preparation, plasma formation burn through phase and finally the initiation of control. The breakdown phase is usually described by Townsend avalanche discharge physics and its typical characteristics can be used to determine its duration and the level of ionization or plasma current that can be achieved by it [1]. This 0D description neglects the finite size and therefore the self- inductance of the system (initial plasma torus). This paper will show that for a Townsend discharge in a toroidal system of finite size, the system inductances, reduces the internal electric field and slows down the avalanche at high levels of ionization. This effect scales with the system L/R-time and it can be shown that this parameter scales with the size of the torus cross-section. Thus, it is more relevant in larger devices, such as ITER, and should be included in the breakdown study. Secondly, it is a misconception that breakdown ionises the prefill gas and that burn-through only relates to impurity radiation. The Townsend avalanche only achieves ionization fractions of about 3%. Thereafter, Coulomb collisions dominate and further ionization is achieved by consumption of Ohmic heating. Low-Z impurity line-radiation can indeed, affect this process, but even without it the plasma has to burn-through the ionization of the main species [2]. The paper will show why the main species burn-through will limit the range of possible prefill pressures for Ohmic breakdown, being especially relevant for plasma initiation in a large vessel, such as for ITER first plasma operation. Thirdly, tokamak plasma initiation at low prefill pressure is thought to increase the chance that the electron energy runs away, forming a highly energetic runaway-electron discharge. The paper will show that the traditional criterion derived from the establishment of a constant electron drift during the Townsend avalanche phase [1] is insufficient to predict the formation of a runaway discharge. The importance to first establish closed-magnetic flux surfaces is stressed, allowing the electrons to be better confined. At this stage, a high current should have been established and Coulomb collisions and plasma physics prevail. Hence, a criterion for the runaway formation during plasma initiation based on the classical critical-electric field balancing generation and losses against the development of the thermal plasma is derived. This criterion depends on the electric field and density at this stage during the plasma initiation, and these are not necessarily the same as the pre- breakdown electric field and prefill pressure. All these aspects are discussed in view of ITER first plasma operations, which will make use of a toroidal electrical field of only 0.3V/m, aiming to breakdown in a vacuum vessel of 1700m2, to achieve a minimum 100kA of plasma current. The paper clarifies typical parameters expected for ITER first plasma operations such as the duration of the avalanche and burn-through phase, lasting roughly ~20ms and several 100ms, respectively, and the narrow pre-fill pressure range for Ohmic plasma initiation, between 0.5 and 1mPa. [1] B. Lloyd, et al., Nucl. Fusion 31 (1991) 2031. [2] H.T. Kim and A.C.C. Sips, Nuclear Fusion 53 (2013) 083024.

Speaker: Peter de Vries

13:00 O3.110 Plasma breakdown in the WEST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O3.110.pdf Plasma breakdown in the WEST tokamak E. Nardon1, H. Heumann2, J.F. Artaud1, N. Fedorczak1 and the WEST team 1 CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France 2 CASTOR, INRIA SAM, 06902 Valbonne, France & LJAD, Université de Nice Sophia Antipolis, 06108 Nice Cedex 02, France The WEST project involved important changes from Tore Supra in terms of magnetic configuration, the main ones being two new in-vessel divertor coils surrounded by stainless steel casings and two new copper stabilizing plates. These additional components had major consequences on the magnetic field map at breakdown. In the initial WEST configuration, breakdown could be achieved but the plasma current would not go above a few tens of kA. This was attributed to induced currents in the stabilizing plates. It was therefore decided to remove the lower stabilizing plate and, when this proved not sufficient, to also cut the upper one (which was hard to remove). This finally allowed successful plasma breakdown and Ip ramp-up, using a high electric field (~1V/m) and low D2 prefill pressure (~3mPa). Due to these parameters, plasma breakdown is however often accompanied by runaway electron (RE) formation but, counter intuitively, it has been found that reducing the prefill pressure can help avoid RE. Extensive vacuum magnetic field modelling has been performed, for both preparation and analysis of the experiments. For the preparation, inverse time evolutive simulations with the FEEQS.M code have been used to calculate optimal premagnetization poloidal field coils currents and voltages to be applied in the breakdown phase. For the analysis, magnetic field maps have been reconstructed with two different approaches: direct time evolution simulations with FEEQS.M (starting from measured coils currents and applying measured voltages) and extrapolation from magnetic measurements with the FREEBIE_ID code. FEEQS.M- and FREEBIE_ID-reconstructed field maps are consistent with each other and with fast visible camera images, which allows for a precise assessment of the necessary conditions in terms of magnetic field for plasma breakdown in WEST.

Speaker: Eric Nardon

13:15 → 14:00 LUNCH

14:00 → 17:00 EXCURSIONS

Thursday, 5 July

09:00 → 10:10 PLENARY SESSION

Chair: M. Mantsinen

Convener: M. Mantsinen

09:00 I4.010 Heating and Current Drive systems in the ITER research plan

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.010.pdf Heating and Current Drive systems in the ITER research plan M. Schneider, D. Boilson, M. Henderson, S.-H. Kim, P. Lamalle, A. Loarte, A. Polevoi ITER Organization, Route de Vinon / Verdon, CS 90 046, 13067 St Paul-lez-Durance, France Reaching ITER’s mission goals of exploring burning plasma physics and achieving high fusion gain will depend on the efficiency and robustness of its ancillary heating and current drive (H&CD) systems for a routine access to high performance plasmas. In view of the many roles foreseen for the H&CD systems, ITER's baseline capability consists of neutral beam injection (NBI), electron cyclotron heating (ECH) and ion cyclotron resonance heating (ICRH). Their complementary capabilities will address the challenges anticipated in establishing and sustaining burning plasmas with high fusion power for various operating scenarios. This flexibility will also be key to the development of scenarios in hydrogen and helium plasmas during the pre-fusion power operation phase. High power heating is essential to ensure H-mode access for high fusion gain, relying on the most advanced built to date systems, utilizing several aspects of novel technology. They must ensure routine stationary or modulated operation for 3600 s to support the development of long-pulse plasmas, particularly in predominantly non-inductive operation. NBI will deliver 33 MW through vertically steerable beamlines to provide radial variation of H&CD profiles. It is the main source of bulk current drive in ITER. As in most fusion devices, the main operational constraint is the plasma density, which must be sufficiently high to prevent excessive ‘shinethrough’ heat loads on in-vessel components. ECH system can launch 20 MW via a single equatorial launcher combining co- and counter-current injection, or through 4 upper ports, enabling plasma breakdown EC-assist, MHD control, current profile shaping and core tungsten control. Its local H&CD deposition over a substantial radial range provides high flexibility for both inductive and non-inductive scenarios. ICRH antennas will deliver 20 MW providing high flexibility ion and electron heating, through the appropriate choice of frequency and heating scheme to support scenarios over a significant range in toroidal field, current, density and fuel species. They also provide sawtooth and core tungsten control capabilities. Outstanding issues are related to ITER edge plasma profiles that influence coupling efficiency and RF sheath effects. This paper will discuss recent developments of the ITER project and specific roles of ITER H&CD systems in meeting the challenges associated with the successful implementation of the ITER Research Plan, making use of physics modelling and supporting experiments to evaluate their expected performance in ITER. Options available to the ITER project for longer term upgrades of the H&CD systems will also be discussed.

Speaker: Mireille Schneider

09:35 I4.011 Using radioastronomy techniques and cold plasmas to study transient and stable molecular species of astrophysical interest: a proof of concept

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.011.pdf USING RADIOASTRONOMY TECHNIQUES AND COLD PLASMAS TO STUDY TRANSIENT AND STABLE MOLECULAR SPECIES OF ASTROPHYSICAL INTEREST: A PROOF OF CONCEPT I. Tanarro1, B. Alemán2, E. Moreno2, R. J. Peláez1, J. L. Doménech1, V. J. Herrero1, P. de Vicente3, J. D. Gallego3, K. Lauwaet2, G. Santoro2, J. A. Martín-Gago2, J. R. Pardo2, J. Cernicharo2 1 IEM-CSIC. C/Serrano 123, 28006 Madrid, Spain. 2 ICMM-CSIC. C/ Sor Juana Inés de la Cruz 3. Cantoblanco,28049 Madrid. Spain 3 CNTRAG-IGN, Observatorio Astronómico de Yebes, Spain The development of new powerful radiotelescopes is enhancing tremendously the detection of stable and transient species in the interstellar space at mm and sub-mm wave wavelengths, and is improving the understanding of the kinetic processes involved. Evaluation of these data can take great advantage of the information obtained in laboratory cold plasmas. In this work we describe the proof of concept of the joint use of standard radio astronomical receivers and low pressure cold plasmas for emission spectroscopic studies of different precursors and products. The goal is to obtain in the laboratory valuable information on rotational emissions of molecular species of astrophysical interest at high spectral resolution. An inductively coupled RF discharge has been used to generate the plasma. Gas pressures 10-30 Pa allow stable plasma operation and produce column densities similar to those of interstellar clouds. The experiment is performed in the 40 m radio-telescope of the Observatory of Yebes (Spain), using its 41-49 GHz band receiver. The beam of the antenna pointing towards the zenith is used as cold emission background. The RF discharge doesn’t induce any electromagnetic spurious signals in the receiver, and astronomical detection of a SiO maser in the AGB star TX Cam is unaffected by the presence of the plasma. OCS is selected for preliminary gas detection in this emission band. OCS and CS2 are chosen as plasma precursors of the CS radical, which emits also in this region. O2 discharges applied after sulphur deposition on the reactor walls by the previous OCS and CS2 plasmas lead to the detection of SO2 produced by surface reactions. In conclusion, these experiments confirm the viability of using standard radioastronomy receivers to detect molecular and short lived species in gas simulation chambers based on plasma reactors.

Speaker: Isabel Tanarro

10:10 → 10:40 COFFEE

10:40 → 12:55 BPIF

Chair: S. Kar

Convener: S. Kar

10:40 I4.209 Ion acceleration mechanism in deuterium z-pinches

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.209.pdf Ion acceleration mechanism in deuterium z-pinches D. Klir1, A.V. Shishlov2,3, V.A. Kokshenev2, P. Kubes1, K. Rezac1, R.K. Cherdizov2, J. Cikhardt1, B. Cikhardtova1, G.N. Dudkin3, F.I. Fursov2, J. Kaufman4, J. Krasa4, J. Kravarik1, N.E. Kurmaev2, V. Munzar1, H. Orcikova5, V.N. Padalko3, N.A. Ratakhin2,3, O. Sila1, K. Turek5, V.A. Varlachev3 and R. Wagner5 1 Czech Technical University in Prague, Prague, Czech Republic 2 Institute of High Current Electronics SB RAS, Tomsk, Russia 3 National Research Tomsk Polytechnic University, Tomsk, Russia 4 Institute of Physics, AS CR, Prague, Czech Republic 5 Nuclear Physics Institute, AS CR, Prague, Czech Republic Acceleration of high energy ions was observed in z-pinches as early as in the 1950s. Even though many theories have been suggested, the ion acceleration mechanism remains a source of controversy. Recently, the experiments on the GIT-12 generator demonstrated acceleration of hydrogen ions up to 30 MeV from a deuterium gas-puff z-pinch [1,2]. High deuteron energies enable us to obtain unique information about ions and to discuss various hypotheses of ion acceleration. The acceleration of 30 MeV deuterons can be explained by the fast increase of a z-pinch impedance with a sub-nanosecond e-folding time. The high impedance of >10 Ω and the generation of >GV/m electric fields could result from a breakdown of quasi-neutrality and a gap formation after the ejection of plasmas from m=0 constrictions. Detailed knowledge of the ion acceleration mechanism is used with a neutron-producing catcher to increase neutron yields above 1013 at a current of 2.7 MA. [1] D. Klir, P. Kubes, K. Rezac, J. Cikhardt, J. Kravarik, O. Sila, A.V. Shishlov, B.M. Kovalchuk, N.A. Ratakhin, V.A. Kokshenev, A.Yu. Labetsky, R.K. Cherdizov, F.I. Fursov, N.E. Kurmaev, G.N. Dudkin, B.A. Nechaev, V.N. Padalko, H. Orcikova, and K. Turek, Physical Review Letters 112, 095001 (2014). [2] D. Klir, A.V. Shishlov, V.A. Kokshenev, P. Kubes, A.Yu. Labetsky, K. Rezac, R.K. Cherdizov, J. Cikhardt, B.Cikhardtova, G.N. Dudkin, F.I. Fursov, A.A. Garapatsky, B.M. Kovalchuk, J. Krasa, J. Kravarik, N.E. Kurmaev, H. Orcikova, V.N. Padalko, N.A. Ratakhin, O. Sila, K. Turek, V.A. Varlachev, A. Velyhan, and R. Wagner, Phys. Plasmas 23, 032702 (2016).

Speaker: Daniel Klir

11:10 I4.210 Advances in laser driven ion acceleration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.210.pdf Advances in Laser Driven Ion Acceleration B. Qiao Center for Applied Physics and Technology & School of Physics, Peking University, Beijing, China Laser-driven ion acceleration is conceived to be one of the main applications of many pow- erful laser facilities that are being projected, built, or already in operation around the world. It opens a way for a future new generation of compact accelerators providing high-quality ion beams for many applications in medicine, industry, science and others. Several acceleration methods, including target normal sheath acceleration (TNSA), shock wave acceleration (SWA), and radiation pressure acceleration (RPA), have been proposed and identified in experiments. However, so far, the obtained ion beams have not achieved the required high qualities yet, such as high energy, narrow energy spread, large particle number, etc. RPA is in principle regarded as the most promising scheme, nevertheless, it currently meets the great challenge: the dramatic growth of the multi-dimensional instabilities that lead to premature break of the effective accel- eration and destruction of the beam quality [1]. In this talk, I shall give an overview of recent advances in study of laser-driven ion acceleration at Peking University (PKU) [2, 3, 4, 5]. In particular, I shall report our recent progresses in theoretical and numerical studies on stabiliza- tion of laser-driven ion RPA [2, 3]. A novel dynamic stabilization scheme to achieve stable RPA of ions from laser-irradiated ultrathin foils is proposed, where a high-Z material coating in front is used. The coated high-Z material, acting as a moving electron repository, continuously replenishes the accelerating foil with comoving electrons in the light-sail stage due to its suc- cessive ionization under laser fields with Gaussian temporal profile. As a result, the detrimental effects such as foil deformation and electron loss induced by the Rayleigh-Taylor-like and other instabilities are significantly offset and suppressed so that stable RPA of ions are maintained. Three-dimensional PIC simulations show that a monoenergetic Al13+ beam with peak energy 3.8GeV and particle number 1010 (charge > 20nC) can be obtained at intensity 1022 W/cm2 . Experimental verification of this novel scheme is planned on Petawatt laser facilities in China. References [1] B. Qiao et al., Phys. Rev. Lett. 108, 115002 (2012). [2] X. F. Shen, B. Qiao* et al., Phys. Rev. Lett. 118, 204802 (2017). [3] X. F. Shen, B. Qiao* et al., New. J. Phys. 19, 033034 (2017). [4] W. L. Zhang, B. Qiao* et al., New. J. Phys. 18, 093029 (2016); [5] J. Kim, B. Qiao* et al., Phys. Rev. Lett. 115, 054801 (2015).

Speaker: Bin Qiao

11:40 O4.201 Coherent proton acceleration from isolated micro-plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.201.pdf Coherent proton acceleration from isolated micro-plasmas J. Gebhard1 , T.M. Ostermayr1,2 , D. Haffa1 , E. Sperling1 , P. Hilz1 , J. Schreiber1,2 1 Ludwig-Maximilians-Universität,Am Coulombwall 1,85748 Garching, Germany 2 Max-Planck-Institut für Quantenoptik, Hans-Kopfermannstr 1, 85748 Garching, Germany We present a unique target system to position micrometer sized targets freely levitating in the focus of a PW laser. The system is based on an electrodynamic trap [1], enabling the use of targets of different form and material. First experiments at the Texas-PW laser [2] allowed for studying the transition from Coulomb explosion towards plasma expansion for increasing target diameters. Experiments at the PHELIX PW laser resulted in a coherent proton acceleration with a narrow energy spectrum around 30 MeV [3]. The novel acceleration mechanism is based on a plasma density slightly below the critical density and features a very good reproducibilty. The density is reduced due to pre-expansion in the rising edge of the laser pulse, which at the same time limits the acceleration process that stops long before the main pulse arrival. As a result only a small fraction of the overall laser energy is effectively used for particle acceleration. Future experimental plans are targeted to shape a fs laser pulse to control the plasma con- ditions at the main pulse and thus increase the conversion efficiency from laser into particle energy. We plan plasma expansion studies of isolated micro-plasmas at intensities up to 1018 W/cm2 using the ZEUS laser, which also has a separate probe beam path, at the ’Centre for Ad- vanced Laser Applications’ (CALA) in Garching. In this scope we are currently atomizing the operation of the target positioning system for a faster trapping process and (sub-minute) target replacement. This is also a necessary requirement for future experiments at higher repetition rate of the 3 PW ATLAS 3000 laser. References 1. T. M. Ostermayr et al., Review of Scientific Instruments 89, 013302 (2018). 2. T. M. Ostermayr et al., Phys. Rev. E 94, 033208 (2016). 3. P. Hilz et al., Nature Communications 9, 423 (2018).

Speaker: Johannes Thomas Gebhard

11:55 O4.202 Staged ion acceleration from ultrathin foils with sub-ps, near-PW pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.202.pdf Staged ion acceleration from ultrathin foils with sub-ps, near-PW pulses P. Martin1, H. Ahmed1, D. Doria1, A. McIlvenny1, S. Ferguson1, S. Zhai1, J. Jarrett2, J. Green3, P. McKenna2, M. Borghesi1 and S. Kar1 1 Centre for Plasma Physics, Queen’s University Belfast, Belfast, United Kingdom 2 SUPA, Department of Physics, University of Strathclyde, Glasgow, United Kingdom 3 Central Laser Facility, Rutherford Appleton Laboratory, Oxfordshire, United Kingdom Acceleration of ions using ultrashort intense laser pulses is an ongoing area of research with a wealth of possible applications. Ions are typically accelerated via the target normal sheath acceleration (TNSA) mechanism [1], whereby the laser generates a hot electron sheath on the rear surface of the target, creating a very large electric field, which accelerates protons and heavier ions present on the target rear surface to MeV energies over much shorter distances compared to conventional RF accelerators. Beyond TNSA, as the laser ramps up in intensity, radiation pressure acceleration (RPA) progressively acquires more importance. If the target is sufficiently thin, the bulk of the target is accelerated as a whole, in the so-called light sail (LS) mechanism. However, in order for LS to work, the plasma must remain opaque to the laser radiation, meaning that effects such as relativistic transparency must be suppressed. This has been achieved previously by using circularly polarized laser pulses, as opposed to linearly polarized, to minimize the J×B heating of electrons [2]. Another method to delay the onset of transparency and enhance the effect of RPA is to split the main pulse into multiple pulses at lower intensities in a staged acceleration scenario – subsequent pulses will irradiate the target at later times and focussed deeper into the target. This scheme works because in the LS regime, the ion energy scales with the laser fluence, rather than the intensity [3]. Presented here are the latest results from an experimental campaign undertaken on the Vulcan Petawatt laser system at the Central laser facility in the UK. In this experiment ultrathin gold, plastic, and deuterated plastic foils were irradiated with picosecond pulses in both single and double stage scenarios. Deuterated foils were chosen because, during the LS acceleration phase, D-D reactions in the compressed target produces a beam of high energy neutrons, allowing the ability to diagnose the efficiency of the LS mechanism without the influence of any TNSA field post-RPA. Examining the proton, ion and neutron spectra together allows to identify the optimal conditions under which the LS regime is most dominant. [1] A. Macchi, M.Borghesi, M.Passoni, Rev. Mod. Phys., 85, 751 (2013) [2] C. Scullion et al., Phys. Rev. Lett. 119, 054801 (2017) [3] S. Kar et al., Phys. Rev. Lett., 109, 185006 (2012)

Speaker: Philip Martin

12:10 O4.203 Proton acceleration from a solid hydrogen cryogenic target

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.203.pdf Proton acceleration from a solid hydrogen cryogenic target D. Margarone1, H. Ahmed2, A. Alejo2, P. Bonnay3, D.C. Carroll4, D. Chatain3, D. Doria2, D. Garcia3, A. Girard3, L. Giuffrida1, P. Jones4, P. Lutoslawski1, P. Martin2, S. Michaux3, D. Neely4, B. Odložilík1, F. Schillaci1, V. Scuderi1, A. Velyhan1, F. Viargues3, G. Korn1, M. Borghesi2 1 Institute of Physics of the ASCR, ELI Beamlines Project, Prague, Czech Republic 2 Centre for Plasma Physics, School of Mathematics and Physics, Queen’s University Belfast, UK 3 CEA INAC-SBT, Grenoble, France 4 Central Laser Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK The interaction of a high power laser and a pure hydrogen target has advantages from the experimental point of view in terms of plasma characterization, as well as for a potentially use at high repetition rates since such target is essentially debris free. A cryogenic hydrogen ribbon (75-100 µm thick) was irradiated with the VULCAN-PW laser (0.6 kJ/1 ps) at the RAL facility. High current proton beams with energies exceeding 50 MeV were accelerated into both directions (forward and backward with respect to the incoming laser beam). The energy coupling into energetic protons was higher than standard plastic foils. This is linked to the laser absorption along the overall target thickness, which is strongly enhanced as confirmed by particle-in-cell simulations. Furthermore, quasi-monoenergetic features in the proton beam energy distribution (around 55 MeV) was shown experimentally. Such results are very promising for future multidisciplinary applications of laser driven proton beams, e.g. hadrontherapy, both due to high energy and high charge of the proton beam, as well as technological advantages coming from the debris free nature of the used target.

Speaker: Daniele Margarone

12:25 O4.204 Plasma density limits of laser hole boring and superthermal electron generation by relativistic picosecond lasers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.204.pdf Plasma density limits of laser hole boring and superthermal electron generation by relativistic picosecond lasers N. Iwata , Y. Sentoku , S. Kojima , M. Hata and K. Mima 1 1 2 1 1,3 1 Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, Japan 2 Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Japan 3 The Graduate School for the Creation of New Photon Industries, 1955-1 Kurematsu, Nishiku, Hamamatsu, Shizuoka, Japan Intense lasers can penetrate into overdense plasmas by the laser hole boring (HB) where giga-bar-level radiation pressure pushes the critical plasma surface forward. The HB proceeds with making a sharp laser-plasma interface which plays an important role in energy transfer from laser to electrons. Hence, the HB is a fundamental concern in applications such as ion acceleration and fast ignition-based laser fusion. Conventionally, the HB had been considered to proceed as long as the laser pulse continues [1]. However, recent studies have found that during over-picosecond (ps) laser irradiation, surface plasma starts to expand towards the laser resulting the superthermal electron production [2]. In this study, we find that under the continuous laser heating in ps time scale, the pressure balance between plasma and laser light is established being assisted by the sheath electric field, which acts as the surface tension, and the HB stops consequently. Based on the pressure balance equation, we theoretically derive the limit density for the HB, i.e., the maximum density laser light can reach, as 8a02nc where a0 is the normalized laser amplitude and nc is the critical density [3]. The time scale for the laser front to reach the limit density is found to be in the ps regime. After the laser front reaches the limit density, the hot plasma starts to blowout back towards the laser. In the blowout plasma, electrons interact with the intense laser multiple times and stochastic electron heating can be enhanced. This results in generating copious superthermal electrons and affects the subsequent phenomena in the laser-plasma interaction, such as ion acceleration [4]. [1] S. C. Wilks et al., Phys. Rev. Lett. 69, 1383 (1992) ; Y. Sentoku et al., Fusion Sci. Technol. 49, 278 (2006) [2] S. Kojima et al., J. Phys. Conf. Ser. 717 (2016) 012102; A. J. Kemp and L. Divol, Phys. Rev. Lett. 109, 195005 (2012); N. Iwata et al, Phys. Plasmas 24 (2017) 073111; A. Yogo et al., Sci. Rep. 7 (2017) 42451 [3] N. Iwata et al., Nat. Commun. 9:623 doi: 10.1038/s41467-018-02829-5 (2018) [4] N. Iwata et al, Phys. Plasmas 24 (2017) 073111

Speaker: Natsumi Iwata

12:40 O4.209 Near-100 MeV protons via hybrid acceleration scheme in an ultrathin foil

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.209.pdf NEAR-100 MEV PROTONS VIA A HYBRID ACCELERATION SCHEME IN AN ULTRATHIN FOIL N. M. H. Butler1, A. Higginson1, R. J. Gray1, R. J. Dance1, S. D. R. Williamson1, R. Wilson1, R. Capdessus1, C. Armstrong1,2, J. S. Green2, S. J. Hawkes2, P. Martin3, W. Q. Wei4, S. R. Mirfayzi3, X. H. Yuan4, S. Kar1, M. Borghesi2, R. J. Clarke3, D. Neely2,1, P. McKenna1 1 SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK 2 STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX, UK 3 Centre for Plasma Physics, Queens University Belfast, Belfast BT7 1NN, UK 4 Key Laboratory for Laser Plasmas and CICIFSA, Shanghai Jiao Tong University, Shanghai 200240, China The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes, such as those involving ultrathin foils, to increase achievable ion energies and to control the spectral and divergence properties of the ion beam. The fast evolving nature of the interaction means that typically more than one acceleration mechanism occurs during the interaction with a thin foil target. Here, experimental and numerical results on the interaction of linearly polarized, picosecond-duration, ultra-intense laser pulse interactions with ultrathin foils, in which proton energies close to 100 MeV are achieved [1], are presented. It is shown that record high energies are produced via a hybrid scheme involving both radiation pressure and sheath acceleration, and that the acceleration field is boosted by the onset of relativistic self-induced transparency in the expanding foil. This takes place due to the formation of a relativistic plasma jet [2,3], supported by a self-generated, azimuthal magnetic field. Electrons within this jet experience direct acceleration to super-thermal energies by the portion of the laser pulse transmitted through the target. The resultant streaming of electrons into the layers of expanded sheath-accelerated ions enhances their energy in the vicinity of the jet, leading to the acceleration of protons to high energies [4]. New experimental measurements of the properties of these jets, including measurements the self-generated, azimuthal magnetic field supporting the jet, and the range of laser and target parameters over which the hybrid acceleration scheme works are presented. [1] A. Higginson et al., Nature Communications, 9, 724 (2018) [2] H. W. Powell et al., New Journal of Physics, 17, 103003 (2015) [3] S. Palaniyappan et al., Nature Communications, 6,10170 (2015) [4] M. King et al., Nuclear Instruments and Methods in Physics Research A, 829, 163-166 (2016)

Speaker: N. M. H. Butler

10:40 → 13:00 BSAP

Chair: E. Falize

Convener: E. Falize

10:40 I4.403 Observing Interstellar and Intergalactic Magnetic Fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.403.pdf Observing Interstellar and Intergalactic Magnetic Fields J. L. Han1,2 1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China 2 School of Astronomy and Space Sciences, University of the Chinese Ac ademy of Sciences, Beijing 100049, China email: hjl@nao.cas.cn A variety of approaches are used to investigate interstellar and intergalactic magnetic fields these fields. Observational results of these magnetic fields are reviewed: The large-scale mag- netic fields in the Milky Way have been best probed by Faraday rotation measures of a large number of pulsars and extragalactic radio sources. The coherent Galactic magnetic fields are found to follow the spiral arms and have their direction reversals in arms and interarm regions in the disk. The azimuthal fields in the halo reverse their directions below and above the Galac- tic plane; The orientations of organized magnetic fields in nearby galaxies have been observed through polarized synchrotron emission. Magnetic fields in the intracluster medium have been indicated by diffuse radio halos, polarized radio relics, and Faraday rotations of embedded radio galaxies and background sources. Future observational perspectives are given to reveal the 3D tomography of the large-scale coherent magnetic fields in our Galaxy and nearby galaxies, a better description of intracluster field properties, and firm detections of intergalactic magnetic fields in the cosmic web. See Han (2017) for a review and Han et al. (2018) for a most recent paper. References [1] J. L. Han, Annual Review of Astronomy and Astrophysics 55, 111 (2017) [2] J. L. Han, R. N. Manchester, W. van Straten, P. Demorest, ApJS in press, (2018). arXiv: 171201997

Speaker: JinLin Han

11:10 I4.404 Multiple manifestations of whistler-mode wave-particle interactions in Earth’s Outer Radiation Belt

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.404.pdf Multiple manifestations of whistler-mode wave-particle interactions in Earth’s Outer Radiation Belt C. E. J. Watt1, H. Ratcliffe2, O. Allanson1, D. Verscharen3, R. B. Horne4, N. Meredith4, S. Glauert4 1 University of Reading, Reading, UK, 2University of Warwick, Coventry, UK, 3Mullard Space Science Laboratory, UCL, Holmbury St Mary, UK, 4British Antarctic Survey, Cambridge, UK The Earth’s Outer Radiation Belt is a highly-variable region of high-energy electrons that forms a torus spanning 2.5-7 Earth radii from our planet. In this region, the number flux of electrons of energies between 100keV to a few MeV can vary by an order of magnitude in a matter of hours. It is now widely understood that a large contribution to the variability in the Outer Radiation Belt is wave-particle interactions in the collisionless natural plasma environment of the Earth’s magnetosphere. Many different wave modes, across a large frequency range, are important for the dynamics of the Outer Radiation Belt, but here we focus on the physics of the whistler-mode interaction with electrons in all its different manifestations. The whistler-mode wave is a right-hand polarised electromagnetic wave mode with frequency between the proton and electron gyrofrequency that displays different characteristics in different parts of the magnetosphere. Evidence of temperature anisotropy and beam-driven instabilities both exist, but some magnetospheric whistler-mode waves are generated in the terrestrial atmosphere during lightning strikes (true “whistlers”), and some from man-made transmitters on Earth’s surface. Additionally there is evidence that waves are naturally generated in one part of the magnetosphere and propagate through the inner magnetosphere to other locations where the wave-particle interaction changes due to different ambient plasma conditions [e.g. Bortnik et al., 2008]. We use linear and quasilinear theory and fully nonlinear numerical experiments to study both acceleration and loss of electrons in the Outer Radiation Belt of Earth as a result of all the different manifestations of whistler-mode waves. We compare and contrast the observational evidence for different types of whistler-mode waves in the magnetosphere and discuss the theoretical approaches suitable to study the wave-particle interactions that result. Bortnik, J., R. M. Thorne and N. P. Meredith (2008), The Unexpected origin of plasmaspheric hiss from discrete chorus emissions, Nature, 452, 62-66, doi:10.1038/nature06741

Speaker: Clare Emily Jane Watt

11:40 O4.401 Energetic particle production and magnetic field amplification in protostellar jets

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.401.pdf Energetic particle production and magnetic field amplification in protostellar jets A. Araudo1 , M. Padovani2 , A. Marcowith3 1 Astronomical Institute of the Academy of Sciences, Prague, Czech Republic 2 INAF-Osservatorio Astrofisico di Arcetri, Firenze, Italy 3 Laboratoire Univers et Particules de Montpellier (LUPM) Université Montpellier, Montpellier, France Supersonic and collimated bipolar jets are launched from the inner regions of accretion discs in forming stars. Jets from young stellar objects are well known thermal emitters due to the pres- ence of radiative shocks. However, non-thermal radio emission from a handful of protostellar jets has been reported in the last years thanks to the improved sensitivity of radio interferometers [1]. The detection of synchrotron radiation indicates the presence of relativistic electrons and magnetic fields of ∼0.1 mG. We study diffusive shock acceleration and magnetic field amplifi- cation in protostellar jets with velocities ∼500 km s−1 . We show that the jet magnetic field can be amplified by non-resonant hybrid instabilities excited by the streaming of cosmic rays [2]. The maximum energy that electrons and protons can achieve is constrained by radiative losses and damping of scattering waves, where the ionization of the plasma plays an important role. In the case that particles being accelerated can circumvent these limits and achieve energies greater than a GeV, they can emit gamma rays in their interaction with photon and matter fields. The detection of this radiation by the Fermi satellite and the forthcoming Cherenkov Telescope Array will open a new window to study the stellar formation, as well as diffusive acceleration and magnetic field amplification in astrophysical shocks with velocities of about 500 km s−1 . References [1] A. Rodríguez-Kamenetzky, C. Carrasco-González, A. Araudo, G.E. Romero, J.M. Torrelles, L.F. Rodríguez, G. Anglada, J. Martí, M. Perucho, C. Valotto, The Astrophysical Journal 851, 16 (2016) [2] A. R. Bell, Monthly Notices of the Royal Astronomical Society 353, 550 (2004)

Speaker: Anabella Araudo

11:55 O4.402 Experimental studies of bow shocks formed in supersonic plasma flows with varying advected magnetic fields.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.402.pdf Experimental studies of bow shocks formed in supersonic plasma flows with varying advected magnetic fields. E. R. Tubman1, S. V. Lebedev1, G. C. Burdiak1, S. N. Bland1, T. Clayson1, J. W. D. Halliday1, J. Hare1, D. Russell1, L. Suttle1, F. Suzuki-Vidal1 1 Imperial College, London, UK Bow shocks are ubiquitous within astrophysics, formed when supersonic, magnetised material interacts with an obstacle and disruptions occur in the flow. In this presentation we discuss novel results collected from using from a pulsed power platform to control the magnetic fields carried within the plasma and influence the bow shocks created. The supersonic, super-Alfvenic plasma flows (vflow ~ 70 km/s, MA >2.5) were produced using the MAGPIE facility at Imperial College driving a ~1 MA, 500 ns current pulse through either wire arrays [1] or planar foils [2]. The plasma flow carries a frozen-in magnetic field (B~ 1-2 T) which influences the bow shock structure formed at obstacle interfaces [3]. Obstacles of various dimensions are placed into the plasma flow and designed to mimic various scenarios including the understanding of bow shocks formed at the interface with projectiles sent through Earth’s atmosphere. Further investigations have been performed to reduce the magnetic fields carried by the plasma using parallel bar grids orientated such that the bars are perpendicular to the frozen-in magnetic field direction. We also discuss an instability developing at the obstacle in the layer of the stagnated plasma. The k-vector of the instability is oriented along the obstacle surface and is in the direction normal to the magnetic field. Faraday rotation measurements indicate that the instability leads to the modulation of the magnetic field strength in the plasma. Various diagnostics including Thomson scattering, two-colour laser interferometry, shadowgraphy and magnetic probes are used to characterize the flow velocity, temperature, density and magnetic field. By controlling the initial magnetic field magnitude, the density of the plasma and recording the temporal evolution of this feature a better understanding of the underlying seed of the instability can be gained. [1] A. J. Harvey-Thompson et al., PoP 16, (2009) [2] F. Suzuki-Vidal et al., Astrophys. J. 815, 2 (2015) [3] G. C. Burdiak et al., PoP 24, 2017

Speaker: Eleanor Tubman

12:10 O4.403 Fully kinetic large scale simulations of the collisionless magnetorotational instability

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.403.pdf Fully kinetic large scale simulations of the collisionless Magnetorotational Instability G. Inchingolo1,2 , T. Grismayer1 , N. F. Loureiro2 , R. A. Fonseca1,3 , L. O. Silva1 1 GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Universidade de Lisboa, Lisbon, Portugal 2 Plasma Science and Fusion Center, MIT, Cambridge, USA 3 Instituto Universitário de Lisboa (ISCTE-IUL), Lisbon, Portugal The magnetorotational instability (MRI) is a crucial mechanism of angular momentum trans- port in a variety of astrophysical scenarios, as accretion disks nearness neutron stars and black holes. The MRI has been widely studied using MHD models and simulations, in order to un- derstand the behaviour of astrophysical fluids in a state of differential rotation. In radiatively inefficient accretion flow models for accretion onto compact objects, the accretion proceeds via a hot, low-density plasma with the proton temperature larger than the electron temperature. In order to maintain such a two-temperature flow, the typical collision rate must be much smaller than the accretion rate. This suggests that the standard MHD approach for the description of the dynamics of such accretion disks may be insufficient, and a kinetic description is required instead. Leveraging on the recent result obtained in 2D pair plasma configuration [1], we intend to present our recent results of the analysis of collisionless MRI in electron-ion plasma. Increasing the mass ratio of our simulations, we will show the differences between electron-ion plasma and pair plasma in 2D turbulence, induced consistently during the saturation regime of the MRI. In particular, we will show the influence of micro-scale (both electron and ion scales) instabilities in the evolution of collisionless MRI and how these instabilities affect the activation of a turbulent motion during the saturation of the MRI. References [1] G. Inchingolo, et al., Submitted to The Astrophys. Jour. [2] S. A. Balbus, J. F. Hawley, The Astrophys. Jour., 376, 214 (1991) [3] S. J. Squire, et al., Jour. of Plasma Phys., 83, 6 (2017) [4] M. W. Kunz, et al., Phys. Rev. Lett., 117, 235101 (2016) [5] M. Hoshino, The Astrophys. Jour., 733, 118 (2013) [6] M. A. Riquelme, et al., The Astrophys. Jour. 755, 50 (2012) [7] M. A. Riquelme, et al., The Astrophys. Jour. 800, 1 (2015)

Speaker: Giannandrea Inchingolo

12:25 O4.404 An experimental platform for pulsed-power driven magnetic reconnection

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.404.pdf An Experimental Platform for Pulsed-Power Driven Magnetic Reconnection J. D. Hare1 , L. G. Suttle1 , S. V. Lebedev1 , N. F. Loureiro2 , A. Ciardi3 , J. P. Chittenden1 , T. Clayson1 , S. J. Eardley1 , C. Garcia1 , J. W. D. Halliday1 , R. A. Smith1 , N. Stuart1 , F. Suzuki-Vidal1 , E. R. Tubman1 1 Blackett Laboratory, Imperial College, London, SW7 2AZ, United Kingdom 2 Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge MA 02139, USA 3 Sorbonne Universités, UPMC Univ Paris 06, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, LERMA, F-75005, Paris, France We describe a versatile pulsed-power driven platform for magnetic reconnection experiments, based on exploding wire arrays driven in parallel [1-4]. This platform produces inherently mag- netised plasma flows for the duration of the MAGPIE generator current pulse (1.4 MA, 500 ns), resulting in the formation of a long-lasting reconnection layer. The layer exists for long enough to allow for the evolution of complex processes, such as plasmoid formation and movement, to be diagnosed by a suite of high spatial and temporal resolution laser-based diagnostics. These diagnostics include interferometry, Thomson scattering and Faraday rotation imaging. We can access a wide range of magnetic reconnection regimes by changing the wire material or moving the electrodes inside the wire arrays. We present results with aluminium [1] and carbon wires [2,3], in which the parameters of the inflows, and of the layer which forms, are significantly different. For aluminium plasmas, the ram pressure dominates over the magnetic and thermal pressures in the flows, and for carbon the magnetic, thermal and ram pressures are approximately equal. By moving the electrodes inside the wire arrays, we change how strongly the inflows are driven [4], which enables us to study both symmetric reconnection in a range of different regimes, and asymmetric reconnection. [1] Suttle, L. G., Hare, J. D., Lebedev, S. V. et. al. (2016). PRL, 116, 225001 [2] Hare, J. D., Suttle, L. G., Lebedev, S. V. et. al. (2017). PRL, 118, 85001 [3] Hare, J. D., Lebedev, S. V., Suttle, L. G. et. al. (2017). PoP, 24, 102703 [4] Hare, J. D., Suttle, L. G., Lebedev, S. V. et. al. (2018). Accepted by PoP. arxiv:1711.06534

Speaker: Jack Davies Hare

12:40 O4.405 Triggering QED processes by reconnection in near critical magnetic fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.405.pdf Triggering QED processes by reconnection in near critical magnetic fields K. M. Schoeffler1 , T. Grismayer1 , D. A. Uzdensky2 , R. A. Fonseca1,3 ,L O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal, 2 Center for Integrated Plasma Studies, Physics Department, University of Colorado, Boulder CO 80309, USA 3 DCTI/ISCTE Instituto Universitário de Lisboa, 1649-026 Lisboa, Portugal Magnetic reconnection is a process that is known to violently release energy from magnetic fields in events such as solar flares, geomagnetic storms, and flares found in various astrophysi- cal objects. In the most extreme magnetic fields found in magnetars, and pulsar magnetospheres, the magnetic fields reach the critical quantum (Schwinger) field BQ ≡ m2e c3 /eh̄ ≃ 4.4 × 1013 G, where various QED processes play an important role [2]. We investigate the effects of QED radiation and pair-creation in the presence of strong mag- netic fields on magnetic reconnection starting with a relativistic pair plasma using both 2D and 3D particle-in-cell simulations. The simulations are performed with the QED module [1] of the OSIRIS framework that includes single photon emission by electrons and positrons (non-linear Compton scattering) and single photon decay into pairs (non-linear Breit-Wheeler). We show that even when the magnetic fields initially do not exhibit QED effects, the reconnection leads to both energetic particles, and enhanced magnetic fields, such that radiative cooling and pair- production processes begin to play an important role. We highlight that the radiation spectra that may be observable from such events differs strongly from the classical cases with much steeper spectra. This study is a first concrete step towards better understanding of magnetic re- connection as a possible mechanism powering gamma-ray flares in magnetar magnetospheres. References [1] T. Grismayer et al., Physics of Plasmas 23, 056706 (2016) [2] D.A. Uzdensky, Space Science Reviews 160, 45-71 (2011)

Speaker: Kevin Michael Schoeffler

10:40 → 12:40 LTDP/BSAP

Chair: A. Laricchiuta

Convener: A. Laricchiuta

10:40 I4.J501 Modelling of argon-acetylene dusty plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.J501.pdf Modelling of argon-acetylene dusty plasma I. B. Denysenko1, E. von Wahl2, S. Labidi3, M. Mikikian3, H. Kersten2, T. Gibert3, N. A. Azarenkov1 1 School of Physics and Technology, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine 2 Institut für Experimentelle und Angewandte Physik, Universität Kiel, Kiel, Germany 3 GREMI, UMR 7344 CNRS/Université d’Orléans, F-45067 Orléans, France The properties of an Ar/C2H2 dusty plasma (the ion, electron and neutral particle densities, the effective electron temperature and the dust charge) in glow and afterglow regimes are studied using a volume-averaged model. The model accounts for different loss and production processes of neutral species and ions in the plasma, including the losses on the dusts, dissociation and ionization of acetylene molecules in collisions with argon atoms in excited states as well as the loss of anions in collisions with hydrogen atoms. The most important processes are determined. The numerical calculations are carried for Maxwellian and Druyvesteyn electron energy distribution functions (EEDFs). The calculated mass- distributions of neutral species and positive ions are compared with the mass spectra obtained in our experiment and found to be in a good qualitative agreement. Effects of variations of the input power, EEDF and dust particle densities and radii on the plasma properties are investigated. It is shown that the densities of most hydrocarbon ions are smaller in the plasma with large dust charge density comparing with the dust-free case, while the argon ion density is larger in the former case. The ion density differences are found to be due to larger electron temperature and smaller electron density in the dusty plasma. It is also found that the acetylene density is larger in the dust-free case as compared with that in the dusty plasma. It is obtained that dust particles affect essentially the ion densities in the plasma as well as the density of atomic hydrogen. Numerical calculations also showed that argon atoms in excited states affect the production of C2H2+, C4H2+, C2H and H as well as the loss of C2H2, C4H2 and H2. The loss of C2H – anions in the plasma is found to be mainly due to the anions’ collisions with positive ions and atomic hydrogen. It is also discussed how dust particles affect the EEDF.

Speaker: Igor Denysenko

11:10 I4.J502 Optical diagnostics of complex plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.J502.pdf Optical diagnostics of complex plasmas A. Melzer1 , M. Himpel1 , H. Krüger1 , M. Mulsow1 , S. Schütt1 1 Institute of Physics, Ernst-Moritz-Arndt-University Greifswald, Germany Particle-containing (dusty) plasmas offer and require the development of sophisticated diag- nostic techniques to measure particle motion, particle density, particle size and even particle charge. The determination of the three-dimensional trajectory of particle on the individual kinetic level can be achieved by stereoscopy using multiple cameras. This can be used to study, e.g., vortex flows in dust clusters with more than 1000 particles or wave motion in a restricted volume of of extended dust clouds. Optical tomography reveals the spatially resolved particle density in dense dust systems from angle-resolved absorption measurements. Further, Mie scattering allows to measure the size and size distribution of particles trapped in the plasma. Here, the long-time evolution of the confinement of the dust clouds as well as dust particle sputtering processes can be investigated. Finally, in the infrared spectral regime the light-scattering properties of particles can reveal the charge state of the particles from the blue-shift of the optical phonon resonance in certain types of materials. The talk will give an overview over the diagnostics and some recent applications.

Speaker: Andre Melzer

11:40 O4.J501 Emissive cathode biasing controls drift velocities in a plasma column

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.J501.pdf Emissive cathode biasing controls drift velocities in a plasma column V. Désangles1 , G. Bousselin1 , A. Poyé1 , M. Moulin1 , V. Dolique1 , L. de Poucques2 , N. Plihon1 1 Univ Lyon, Ens de Lyon, Univ Claude Bernard, CNRS, Laboratoire de Physique UMR 5672, F-69342, Lyon, France 2 Université de Lorraine, CNRS, Institut Jean Lamour UMR 7198, F-54506, Vandoeuvre-lès-Nancy, France Controlling drift velocities in a plasma column is essential for various applications: to de- velop plasma centrifuges [1], to master drift waves and electrostatic turbulence and to miti- gate anomalous transport [2] , to study astrophysical mechanisms [3] and to study flow re- lated instabilities in ionospheric like plasmas [4]. So far, only cold conductive biased electrodes 2500 Cath. ON meas. such as concentric rings, end plates 2000 Cath. ON fit (a) Cath. OFF fit (b) or grids have been used to try 1500 Cath.OFF meas. B 1000 Velocity (m.s-1 ) 500 to control plasma flows in linear 0 -500 plasma experiments. These setups -1000 to be efficient in controlling the -1500 -2000 Emissive plasma parameters profiles, how- -2500 Cathode 4 3 2 1 0 -1 -2 -3 -4 Radial Location (cm) ever they are limited by the strong Debye shielding in plasmas. Figure 1: (a.) Measured ion velocity for two cases: cathode We report here a new tool to con- floating at plasma potential (blue) and biased and emitting trol drift velocities. Using a nega- electrons (orange); (b.) Schematic drawing of the stirring setup tively biased hot emissive cathode (fig1.b.), we show the ability to control Vp and ne profiles by injecting locally strong elec- tron currents into the plasma. Direction, shear and amplitude of the plasma flow profile can also be controlled changing the cathode location and the intensity of the injected current (fig1.a.). These modifications of the plasma equilibrium have been studied extensively using Langmuir probes, emissive probes, mach probes and LIF measurements. We show that the rotation pro- files may be explained by electric and diamagnetic drifts and are directly related to the amount of current emitted by the cathode. References [1] Gueroult, R. et al., Plasma Sources Sci. Technol., 25, 35024 (2016). [2] Gilmore, M. et al., J. Plasma Phys., 81, 345810104 (2015). Thakur, S. C. et al. Phys. Plasmas, 23, 082112 (2016). Dubois, A. et al., Phys. Plasmas, 21, 062117 (2014) [3] Terasaka, K. et al., J. Plasma Phys., 81, 345810101 (2015). [4] Eadon, A. C. et al., Rev. Sci. Instrum., 82, 63511 (2011).

Speaker: Victor Désangles

11:55 O4.J502 EUV induced plasmas created in atomic and molecular gases

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.J502.pdf EUV induced plasmas created in atomic and molecular gases A. Bartnik, W. Skrzeczanowski, H. Fiedorowicz, P. Wachulak, T.Fok Institute of Optoelectronics, Military University of Technology, Warsaw, Poland Photoionized plasmas induced by irradiation of gases with X-ray or extreme ultraviolet (EUV) radiation are present in Space, where such ionizing radiation is produced by various astrophysical objects and can propagate over long distances. Photoionized plasmas can be also produced in laboratory conditions using intense EUV or X-ray radiation sources. Basic studies of these plasmas concern laboratory astrophysics, astrochemistry, inner-shell processes, X-ray lasers or matter in extreme states. Such plasmas can be also considered for some technological processes like reactive etching or surface treatment. In the latter case simultaneous plasma and radiation treatment of materials is possible. In this work investigations of EUV induced low temperature plasmas with relatively high electron density were performed. Various laser-produced plasma (LPP) EUV or soft X-ray (SXR) sources were employed for creation of such plasmas. The sources were based on two different laser systems with pulse energies ranging from 0.8 J to 10J and pulse duration 4 ÷ 10 ns. The experimental arrangements were equipped with the EUV/SXR collectors for focusing of the radiation onto the gas to be ionized or the gas was injected in the vicinity of the LPP. Ellipsoidal or paraboloidal collectors were also used in detection systems employed for measurements of weak EUV emission from the low temperature PP. Different gases, used for creation of the EUV induced plasmas, were injected into the interaction region, employing an auxilary gas puff valve. Irradiation of the gases resulted in ionization and excitation of atoms and molecules forming low temperature plasmas. Spectral investigations were performed in EUV range using a grazing incidence, flat-field spectrograph (McPherson Model 251), equipped with a 450 lines/mm toroidal grating. The UV/VIS spectra were measured using an Echelle Spectra Analyzer ESA 4000. The spectra contained spectral lines corresponding to radiative transitions in atoms, molecules, atomic or molecular ions. For analysis of the EUV spectra numerical simulations were performed, using a collisional-radiative PrismSPECT code. For computer simulations of the molecular spectra measured in the UV/VIS range a LIFBASE and Specair codes were employed. Apart from that, the electron temperatures of plasmas created in different gases were estimated employing a Boltzmann plot method. The electron density was estimated based on Stark broadening of selected spectral lines.

Speaker: Andrzej Bartnik

12:10 O4.J503 Dynamics and stability in RF-generated nonneutral plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.J503.pdf Dynamics and stability in RF-generated nonneutral plasmas G. Maero1,2 , N. Panzeri1,2 , R. Pozzoli1 , M. Romé1,2 1 Dipartimento di Fisica, Università degli Studi di Milano, Italy 2 INFN Sezione di Milano, Italy Born and used for a long time as a tool to confine a single-species nonneutral plasma, Penning-Malmberg traps have been exploited in a wider range of applications than originally imagined [1]. Deviations from ideal conditions, like the presence of several charged-particle species and the application of radio-frequency (RF) excitations, represent a challenge both in terms of physical modelling and of accurate control and manipulation. At the same time, they have led to important results (e.g., antimatter synthesis) and offer new opportunities of physics investigations in collective systems. We present here several important features arising from the in-trap generation of a non-neutral plasma by means of low-amplitude RF fields, whose continuous application plays a dramatic role in the dynamics of the confined sample [2, 3, 4]. An analysis of basic collective properties is performed by means of a series of experiments, highlighting analogies and differences between ’conventional’ trapped nonneutral plasmas (i.e., injected from a source and let to evolve) and their RF-generated and continuously excited coun- terpart. The observations on RF-excited plasmas produce a wealth of non-trivial features in terms of: Evolution towards stable configurations (single and multiple vortex structures); Man- ifestation of nonlinear diocotron modes; Accumulation of positive ions; New opportunities for plasma manipulation, e.g., by means of multipolar RF fields combined with the generation drive, which result in the possible use of the RF-drive technique as a valid alternative to conventional sources for the study of turbulent fluid flows [5]. References [1] J. R. Danielson, D. H. E. Dubin, R. G. Greaves and C. M. Surko, Rev. Mod. Phys. 87 247 (2016) [2] B. Paroli, G. Maero, R. Pozzoli and M. Romé, Phys. Plasmas 21, 122102 (2014) [3] G. Maero, R. Pozzoli, M. Romé, S. Chen and M. Ikram, JINST 11, C09007 (2016) [4] G. Maero, Il Nuovo Cimento C 40, 90 (2017) [5] N.C. Hurst, J.R. Danielson and C.M. Surko, AIP Conf. Proc. 1928, 020007 (2018)

Speaker: Giancarlo Maero

12:25 O4.J504 Mode coupling in two-dimensional complex plasma crystals

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.J504.pdf Mode Coupling in Two-Dimensional Complex Plasma Crystals V. Nosenko, J. K. Meyer, I. Laut, S. K. Zhdanov, H. M. Thomas Deutsches Zentrum für Luft- und Raumfahrt (DLR), D-82234 Weßling, Germany Wave modes of many physical systems can become coupled to each other. Mode coupling can lead to new interesting effects such as the mode-coupling instability (MCI) which was predicted theoretically [1] and observed experimentally in two-dimensional (2D) complex plasma crystals [2]. MCI occurs when the dispersion relations of the two dust-lattice wave modes, longitudinal in-plane (L) mode and transverse vertical (TV) mode intersect. In the vicinity of their intersection, a new hybrid mode appears which is unstable. If not suppressed by the neutral gas friction, it will grow exponentially with time and can result in the crystal melting. A prominent characteristic feature of MCI is mixed polarization, where traces of the L mode can be measured in the transverse vertical spectra and vice versa [2]. It was previously believed that the mixed polarization could only occur when the modes cross. In this contribution, we report on the experimental observation of mode coupling and mixed polarization of the longitudinal in-plane and transverse vertical wave modes in a 2D complex plasma crystal in the absence of mode crossing [3]. The coupling manifests itself in traces of the TV mode appearing in the measured longitudinal spectra. The observations are corroborated in molecular dynamics simulations. A theoretical analysis of the modes in a plasma crystal with finite temperature predicts the ratio of the trace to the principal mode which is in a good agreement with the experiment and simulations. 1. A. V. Ivlev and G. Morfill, Phys. Rev. E 63, 016409 (2001). 2. L. Couëdel, S. K. Zhdanov, A. V. Ivlev, V. Nosenko, H. M. Thomas, and G. E. Morfill, Phys. Plasmas 18, 083707 (2011). 3. J. K. Meyer, I. Laut, S. K. Zhdanov, V. Nosenko, and H. M. Thomas, Phys. Rev. Lett. 119, 255001 (2017).

Speaker: Vladimir Nosenko

10:40 → 12:40 MCF

Chair: J. Mailloux

Convener: J. Mailloux

10:40 I4.114 Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.114.pdf Electron-cyclotron-resonance heating in Wendelstein 7-X: A versatile heating and current-drive method and a tool for in-depth physics studies R. C. Wolf1, C. D. Beidler1, K. J. Brunner1, A. Dinklage1, G. Fuchert1, G. Gantenbein2, M. Hirsch1, U. Höfel1, J. Jelonnek2, W. Kasparek3, H. Laqua1, C. Lechte3, S. Marsen1, N. B. Marushchenko 1, B. Plaum3, T. Stange1, M. Thumm2, Y. Turkin1, M. Zanini1, and the W7-X Team 1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 2 IHM, Karlsruhe Institute of Technology (KIT), Germany 3 IGVP, University of Stuttgart, Germany Important criteria for the optimum heating mix of magnetic confinement fusion experiments are heating efficiency, power deposition profiles or the ability to also drive plasma currents. In particular, for stellarators, which need no or only small amounts of current drive, ECRH is a promising heating method even for the envisaged application in a fusion power plant. Wendelstein 7-X (W7-X) is equipped with a steady-state ECRH system consisting of ten gyrotrons which operate at 140 GHz corresponding to the 2nd cyclotron harmonic at a magnetic field of 2.5 T. The heating power available ranges from 7 to 9 MW which today is the largest ECRH facility in operation. W7-X uses ECRH for plasma start-up, heating and current drive and also plasma vessel conditioning. All ten gyrotrons are operational and already have delivered 7 MW to W7-X plasmas. With the heating power available in the first campaign, energy confinement times were achieved which were lying on the international scaling for stellarator confinement (ISS04). First studies indicate the existence of a radiative density limit with a Sudo-like power scaling. The power of the ten gyrotrons is transmitted through air to the W7-X plasma vessel using a quasi-optical mirror system. The overall transmission efficiency was experimentally estimated to be 94%, which is close to the theoretical value. Front steering launchers direct the gyrotron beams individually to the plasma. First current drive experiments revealed periodic internal plasma-crash events, which can be explained by the appearance of low order rationals of the rotational transform, ι, due to current drive close to the plasma center leading to an ι-change, ∆ι ∼ I/r2. In the current operation campaign of W7-X remote steering launchers (RSLs) were tested for the first time. Without movable parts near the plasma, the remote steering technology may be a possible solution for a power plant. Since the RSLs are located near the minimum of the magnetic field, they also allow probing of the electron distribution function by changing the amount of trapped and passing electrons. The paper addresses plasma confinement properties specific to the application of strong electron heating by ECRH, the heating of plasmas at high densities which requires a change from 2 nd harmonic X-mode to 2nd harmonic O-mode, the possibility to test our understanding of electron- cyclotron current drive, and heat-wave experiments delivering insight into the characteristics of plasma transport.

Speaker: Robert Wolf

11:10 I4.115 Waveguide to Core: A New Approach to RF Modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.115.pdf Waveguide to Core: A New Approach to RF Modelling*. J. C. Wright1, S. Shiraiwa1, J. Myra2 1 Plasma Science and Fusion, Massachusetts Institute of Technology, Cambridge, MA, USA 2 Lodestar Research Corporation, Boulder, CO, USA Modelling of coupling, propagation and absorption of RF waves in plasmas is known to be a complex task and is typically modelled in separate stages. We present a novel technique for the calculation of RF waves in toroidal geometry that enables, for the first time, the simultaneous incorporation of antenna geometry, plasma facing components (PFCs), the scrape off-layer (SOL), and core Figure 1: Rotated C-Mod Antenna propagation [Shiraiwa, Wright et al, Nucl. Fusion 57 086048 (2017)]. Calculations with this technique naturally capture wave propagation in the SOL, reflection from the core plasma or walls, and wave interactions with non-conforming PFCs as shown in Fig. 1. The technique combines the finite element approach for the SOL and antenna structure and the spectral method for the hot core using a domain decomposition technique with impedance matching to construct the full solution. Using open source software on leadership class computer permits solutions in excess of 30 Million degrees of freedom enabling the resolution of the slow and fast waves together in 3D geometries. Applications of this model to ICRF minority heating in strong and weak absorption regimes in Alcator C-Mod predict heating loss of 10% and 50% respectively, in the SOL due to collisional processes, in-line with experimental measurements of heating efficiency. Sheaths are an additional loss mechanism in the SOL that can cause localized sputtering. To address the effect of RF rectified sheaths on PFCs we use a post-processing technique that uses the finite element method SOL solution [Myra and Kohno, EPJ Web of Conferences 157 03037 (2017)] to model sheath rectification. To resolve short wavelength structures at the lower hybrid resonance in front of ICRF antennas, the edge SOL plasma model keeps finite Larmor radius effects to resolve the slow wave to ion Bernstein wave mode conversion that occurs at this layer. Simulations applying these models to the LAPD long cylindrical device, JET, and the Alcator C-Mod field aligned antenna in three dimensions will be presented. *Work supported by US DoE Contracts DE-FC02-01ER54648 and DE-FC02-99ER54512.

Speaker: John Christopher Wright

11:40 O4.101 2D mappings of ICRF-induced SOL density modifications on JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.101.pdf 2D mappings of ICRF-induced SOL density modifications on JET L. Colas1, P. Jacquet2, V. Bobkov3, M. Brix2, L. Meneses4, K. Kirov2, E. Lerche2,5, C.C. Klepper6, M. Goniche1, A. Křivská5, P. Dumortier2,5, A. Czarnecka7 and JET contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CEA, IRFM, F-13108 Saint Paul Lez Durance, France. 2 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK. 3 Max-Planck-Institut für Plasmaphysik, Garching, Germany. 4 Instituto de Plasmas e Fusão Nuclear, IST, Universidade de Lisboa, Lisboa, Portugal. 5 LPP-ERM-KMS, TEC partner, Brussels, Belgium. 6 Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, USA. 7 IPPLM, Hery 23 Str., 01-497 Warsaw, Poland. Localized Scrape-Off Layer (SOL) modifications have for long been evidenced on open magnetic field lines near active Ion Cyclotron (IC) wave launchers. These changes were shown to influence the reflection coefficient of Lower Hybrid grills, the first wall sputtering and heat loads. However, resolving their complex 3D spatial structure remains challenging. This contribution investigates SOL density distributions, measured on JET by Lithium beam emission spectroscopy and X-mode reflectometry. Assuming a parallel homogeneity of the IC-induced SOL patterns, the ratio of density with or without IC waves was plotted versus the location of observation points along the diagnostic lines of sight, mapped in front of each IC antenna. This technique was applied to L-mode pulses where the JET A2 and ITER-like antennas were toggled over a scan of the edge safety factor. 2D (radial/poloidal) maps were thus produced for each diagnostic/antenna pair, for current-drive strap phasing. The IC-induced relative density changes, reproducible from pulse to pulse, are most pronounced when the diagnostics magnetically connect in front of active IC launcher mouths. They are radially localized near antenna side limiters and extend a few cm in front of them, remaining 2-3cm outside the separatrix. They are poloidally inhomogeneous: density depletion is generally observed, but the density also increased locally above one A2 antenna. Reproducing the parallel extent, the radial width and poloidal asymmetry of the observed SOL patterns puts constraints on RF-sheath modelling. Assuming that IC-specific sputtering occurs on wall elements connecting to the flux tubes with modified density, the maps outline possible locations for IC-induced W sources that could not yet be evidenced directly on JET. * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″

Speaker: Laurent Colas

11:55 O4.102 Plasma edge modelling with ICRF coupling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.102.pdf Plasma edge modelling with ICRF coupling W. Zhang , D. Aguiam3, R. Bilato1, V. Bobkov1, D. Coster1, Y. Feng4, P. Jacquet5, T. Lunt1, 1,2 J.-M. Noterdaeme1,2, W. Tierens1, the ASDEX Upgrade team1, the EUROfusion MST1 Team6 1 Max-Planck-Institut für Plasmaphysik, Garching, Germany 2 Applied Physics Department, University of Ghent, Ghent, Belgium 3 Instituto de Plasmas e Fusão Nuclear, IST, Universidade de Lisboa, Lisboa, Portugal 4 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 5 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 6 see http://www.euro-fusionscipub.org/mst1 wei.zhang@ipp.mpg.de This contribution mainly addresses two important issues of plasma heating with waves in the Ion Cyclotron Range of Frequencies (ICRF): i) improving the ICRF power coupling; ii) understanding the ICRF – edge plasma interactions. The coupling of ICRF power to the plasmas depends sensitively on the scrape-off layer (SOL) density in front of the antennas because the fast wave is evanescent below the cut-off density. Previous experiments on ASDEX Upgrade and JET indicate that by shifting the fuelling gas source from the divertor to the main chamber, the density in front of the antennas and thus the ICRF coupling can be greatly increased. To understand this, the 3D edge plasma fluid and neutral particle transport code EMC3-EIRENE was used to calculate 3D SOL density, and the FELICE and RAPLICASOL codes were used to calculate the antenna coupling resistances. Good qualitative agreements are found between simulations and experiments. They indicate that midplane gas puffing close to the antennas increases the ICRF coupling most significantly (by ~120%) and top gas puffing increases the coupling only to a moderate level (by 20%-40%). Calculations for ITER also show that midplane gas valves close to the antennas are most effective in increasing ICRF coupling in ITER. There is a mutual influence between ICRF waves and plasma density at the edge, and in particular the measured density convection at the plasma edge is likely influenced by ICRF waves. This density convection is simulated with EMC3-EIRENE code by supplying the sheath potential as input in two different modalities: i) measured (forced problem); ii) calculated by running in an iterative loop - RAPLICASOL code for E||, SSWICH code for the sheath potential, and EMC3-EIRENE itself for the plasma density (consistency loop). The calculated density convection is in qualitative agreement with the measurements from reflectometers embedded in the antenna or reciprocating probe. The results indicate that large convective cells develop in the top and bottom of the antennas when operated with unfavorable phasing and power ratio between the straps. In comparison to the conventional 2-strap antenna, the novel 3-strap antennas installed in ASDEX Upgrade decrease the sheath potential and the associated E×B convection when operated with the proper phasing and power ratio.

Speaker: W. Zhang

12:10 O4.103 Effects of the ICRH resonance position on the profile shape of the W density in JET-ILW H-mode discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.103.pdf Effects of the ICRH resonance position on the profile shape of the W density in JET-ILW H-mode discharges M. Sertoli1,2, F. J. Casson2, R. Bilato1, J. Flanagan2, J. Boom1, A. Shaw2, E. Delabie3 and JET Contributors* 1 Max-Planck-Institut für Plasmaphysik, Boltzmannstrasse 2, D-85748 Garching, Germany 2 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 3 Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA Ion cyclotron resonance heating (ICRH) with the power deposited close to the plasma centre is necessary in JET-ILW to avoid tungsten (W) accumulation and its optimization can lead to longer, more stable plasma operation. In this contribution, the effect of the location of the ICRH resonance layer on the profile shape of the intrinsic W density has been studied in JET-ILW H-mode discharge 85377. With a scan in toroidal magnetic field from 2.5 to 2.85 (T) the resonance layer is moved from the high-field-side (HFS) to the low-field-side (LFS), but still staying within the sawtooth inversion radius. While the main plasma parameters show only slight changes and the sawtooth period remains unaffected, moving the resonance layer towards the LFS leads to a 25% decrease in central W density and in a reduction of the LFS asymmetry close to the resonance layer. The experimental W density profile has been determined using the soft X-ray (SXR) diagnostic and vacuum-ultra-violet (VUV) spectroscopy coupled together as explained in [1]. This method has been recently upgraded to account for the strong poloidal asymmetries typically present in the SXR emission profiles at JET. Contributions from low-Z impurity and deuterium have been included using the visible Bremmstrahlung Zeff measurement [2] with the assumption that their contributions are poloidally symmetric and that the only other impurity contaminating the plasma (apart from W) is Be. The method has been found to be robust for W concentrations above a few 10-5 and in cases where the contributions from medium-Z impurities such as Ni is negligible. The results are compared with modelling using the code NEO [3, 4] accounting for centrifugal effects as well as temperature anisotropy of the ICRF heated H-minority ions (modelled using TORIC-SSFPQL [5]). [1] M. Sertoli et al 2015 Plasma Phys. Controlled Fusion 57, 075004. [2] K.H. Behringer et al 1986 Nucl. Fusion 26, 751 [3] E. A. Belli et al 2008 Plasma Phys. Controlled Fusion 50, 095010. [4] E.A. Belli et al 2012 Plasma Phys. Controlled Fusion 54, 015015. [5] Brambilla M. et al 2009 Nucl. Fusion 49, 085004 * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 10200”

Speaker: Marco Sertoli

12:25 O4.104 Performance predictions for the COMPASS upgrade tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.104.pdf Study progress of challenge in LHCD capability at high density regime in EAST B. J. Ding1, M. H. Li1, R. Cesario2, A. A. Tuccillo2, A. Cardinali2, Y. C. Li1, M. Wang1, P. Bonoli3, R. Parker3, S. G. Baek3, A. Ekedahl4, M. Goniche4, J. Hillairet4, Y. Peysson4, X. L. Zou4, Y. Yang1, H. Q. Liu1, L. Wang1, S. Y. Lin1, Y. F. Wang1, C. B. Wu1, L. Liu1, L. M. Zhao1, H. C. Hu1, H. Lian1, J. C. Xu1, Q. Q. Yang1, F. Napoli2, C Castaldo2, J F Shan1, F K Liu1, X Z Gong1, J G Li1, B N Wan1, and the EAST Team 1 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China 2 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati , Italy 3 MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139, USA 4 CEA, IRFM, 13108 St. Paul-lez-Durance, France Aiming at fusion reactor, two issues must be solved for lower hybrid current drive (LHCD), namely good lower hybrid wave (LHW)-plasma coupling and effective current drive at high density. For this goal, effort has been done continuously in EAST. Investigation indicates that gas puffing from electron-side of the LH antenna is more efficient for LHW-plasma coupling [1]. Studies of high density experiments suggest that low recycling and high LH frequency are preferred for LHCD at high density, mainly due to the reduction of parasitic effects in edge region [2-4]. Recently, it is observed for the first time that LHCD characteristics are in agreement with the edge current profile and strike-point splitting behaviour, demonstrating the role and mitigation of parasitic effects in LHCD at higher frequency wave. With the combination of 2.45GHz and 4.6GHz LH wave, repeatable H-mode plasma with the maximum density up to .4.5×1019m-3 was obtained [5]. By means of LHCD, ECRH, and ICRH, fully non-inductive H-mode discharges over 100s have been achieved. [1] B J Ding et al., Phys. Plasma 20, 102504 (2013). [2] B J Ding et al., Nucl. Fusion 53, 113027 (2013). [3] B J Ding et al., Nucl. Fusion 55, 093030 (2015). [4] M H Li, B J Ding et al., Phys. Plasma 23, 102512 (2016) [5] B J Ding et al., Nucl. Fusion 57, 022022 (2017). 1

Speaker: A. Casolari

12:40 → 14:00 LUNCH

14:00 → 16:00 POSTER SESSION

Mánes Exhibition Hall: MCF P4.1x, BSAP P4.4x
Mánes Multifunctional Hall: BPIF P4.2x, LTDP P4.3x

14:00 P4.1001 Understanding the mechanism of alpha channelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1001.pdf Understanding the mechanism of alpha channelling F. Cianfrani1, S. Briguglio2, A. Cardianli2, F. Romanelli1 1 University of Rome “Tor Vergata”, Rome, Italy 2 ENEA, Frascati, Italy Alpha channelling is a mechanism to transfer the power associated with the fusion- generated alpha particles to the thermal ions through the interaction with an externally excited wave, rather than relying on classical electron slowing down. In its simplest form, the mechanism relies on the interaction between fusion alphas and a high-frequency wave (typically a mode-converted Ion Bernstein Wave). The high-frequency wave extracts the kinetic energy associated with perpendicular motion through a resonant interaction that breaks the magnetic moment invariance. The extraction of energy is associated with a radial diffusion towards the plasma edge. A low-frequency wave (typically belonging to the Alfvén spectrum) can in turn displace the particles to the plasma edge. The mechanism has been proposed about 20 years ago [1] but little evidence exists both from experimental data and numerical simulations. The aim of this work is to provide a solid theoretical basis to this mechanism. In the model considered here the effect of the high frequency wave is modeled via a quasi-linear diffusion operator whereas the low frequency wave is modeled via a boundary condition of outward particle flux Q at the boundary in phase space where the high-frequency wave induced diffusion vanishes. The associated Fokker-Planck equation (for simultaneous diffusion in space and energy) has been analytically solved in different ranges of the parameter space in order to understand the transition from wave damping to wave amplification (alpha channelling). It is shown that alpha channelling can take place only if the region in which the fusion alpha particles are generated is connected with the plasma boundary. Explicit expressions for the fraction of power transferred to the high- frequency wave have been derived and their dependence on Q analyzed. The conditions for the validity of the quasilinear approach (i.e. the transition to stochastic behavior for the alpha particle orbits in phase space) will be also discussed. In parallel, the problem of extracting kinetic energy associated to the parallel motion of alpha particles by means of a low-frequency Alfvénic wave has been addressed in the frame of hybrid MHD-particle simulations performed by the XHMGC code. The effect of injecting an Alfvén wave has been modeled by introducing a forcing term in the MHD equations solved by XHMGC. This term allows for establishing an Alfvén mode in the plasma, whose amplitude and radial structure depends both by input parameters and the interaction with bulk plasma and alpha particles. Initial studies have investigated under which conditions the Alfvén wave can extract a large fraction of kinetic energy from the alpha particle distribution and displace the exhausted alphas by a large fraction of the minor radius. The case of a large aspect ratio magnetic equilibrium was considered (a/ R=10). A wave characterized by toroidal number n=2 and frequency located in the toroidal gap was forced by the antenna term. The possibility of extracting a fraction of the energy from the alpha population was shown, along with the capability of the wave to displace alphas by a relevant fraction of the minor radius. [1] N.J. Fisch \& J.M. Rax, Phys. Rev. Lett. 69, 4, 612 (1992)

Speaker: Francesco Romanelli

14:00 P4.1002 Recent simulations of Toroidal Alfven Eigenmodes on JET with the Gyrokinetic Toroidal Code

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1002.pdf Recent simulations of Toroidal Alfvén Eigenmodes on JET with the Gyrokinetic Toroidal Code V. Aslanyan1 , M. Porkolab1 , S. Taimourzadeh2 , L. Shi2 , Z. Lin2 , G. Dong3 , P. Puglia4 , S. E. Sharapov5 , J. Mailloux5 , M. Tsalas5 , M. Maslov5 , A. Whitehead5 , R. Scannell5 , S. Gerasimov5 , S. Dorling5 , S. Dowson5 , H. K. Sheikh5 , T. Blackman5 , G. Jones5 , A. Goodyear5 , K. K. Kirov5 , R. Dumont6 , P. Blanchard4 , A. Fasoli4 , D. Testa4 and JET Contributors∗ EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 MIT PSFC, 175 Albany Street, Cambridge, Massachusetts 02139, USA 2 Department of Physics and Astronomy, UCI, California 92697, USA 3 PPPL, Princeton University, Princeton, New Jersey 08543, USA 4 Ecole Polytechnique Fédérale de Lausanne (EPFL), SPC, CH-1015 Lausanne, Switzerland 5 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 6 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France Recent experiments on the Joint European Torus have succeeded in destabilizing weakly- damped Toroidal Alfvén Eigenmodes (TAEs) by Neutral Beam Injection and ICRH-generated energetic ions. Concurrently, TAEs with insufficient drive to overcome several damping mech- anisms (including continuum damping, radiative damping, ion and electron Landau damping) have been resonantly probed with external antennas[1]. In both cases, the mode structure and the drive and damping mechanisms have been computed self-consistently by Gyrokinetic Toroidal Code (GTC)[2] and matched to measurements by magnetic probes. Energetic particle drive is compared to a synthetic antenna in linear simulations. This work is in support of efforts to observe alpha particle-driven in future JET DT experiments. References [1] P. Puglia, W. Pires de Sa, P. Blanchard, et al., “The upgraded JET toroidal Alfvén eigenmode diagnostic system” Nucl. Fusion 56, 112020 (2016). [2] Z. Wang, Z. Lin, I. Holod, W. W. Heidbrink, B. Tobias, M. Van Zeeland, and M. E. Austin, “Radial Local- ization of Toroidicity-Induced Alfvén Eigenmodes” Phys. Rev. Lett. 111, 145003 (2013). ∗ See the author list of X. Litaudon et al., Nucl. Fusion 57, 102001 (2017).

Speaker: Miklos Porkolab

14:00 P4.1003 Kinetic Electromagnetic Instabilities in an ITB Plasma withWeak Magnetic Shear

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1003.pdf Kinetic Electromagnetic Instabilities in an ITB Plasma with Weak Magnetic Shear W. Chen1 , D.L. Yu1 , R.R. Ma1 , P.W. Shi1 , Y.Y. Li2 , Z.B. Shi1 , H.R. Du3 , X.Q. Ji1 , M. Jiang1 , L.M. Yu1 , B.S. Yuan1 , Y.G. Li1 , Z.C. Yang1 , W.L. Zhong1 , Z.Y. Qiu1 , X.T. Ding1 ,J.Q. Dong1 , Z.X. Wang3 , J.Y. Cao1 , S.D. Song1 , Yi. Liu1 ,Q.W. Yang1 , M. Xu1 , and X.R. Duan1 , 1 Southwestern Institute of Physics, P.O. Box 432 Chengdu 610041, China 2 Institute for Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027, China 3 Southwest Jiaotong University, Chengdu 610031, China Internal transport barriers (ITBs) had been observed on almost fusion devices including HL- 2A. ITBs are favored by weak or reversed magnetic shear. As predicted by MHD theory, the high-n ballooning modes seem to be stabilized in ITB region, but low-n MHD instabilities re- main a problem. In this talk, we will report experimental results in HL-2A NBI ITB plasmas with weak magnetic shears (s ∼ 0)and low pressure gradients (α < 0.3). The low-n Alfvenic IT- G (AITG) instabilities with fBAE < f < fTAE and n = 2 − 8 are found to be unstable in the NBI plasmas with weak shears and low pressure gradients. The measured results are also consistent with the extended generalized fishbone-like dispersion relation (GFLDR-E) and KBM equation, and the modes are more unstable |s| is smaller in low pressure gradient regions. These modes have possibly opposite effects on the ITB formation. The interaction between AITG/KBM ac- tivities and EPs should also be investigated with greater attention in fusion plasmas, such as ITER, since weak magnetic shear amplifies the role of and possible excitation by EP of these fluctuations. It is worth emphasizing that the study of AITG/KBM should be paid more atten- tion because they link to the ITB and H-mode pedestal physics for weak magnetic shears. These results also pave the road to more in depth analysis of similar phenomena in fusion plasmas with non-perturbative EP populations, with suggestive possibility of controlling plasma performance by a careful choice of plasma profiles in the weak shear core region typical of burning fusion plasmas.

Speaker: Wei Chen

14:00 P4.1004 Modelling of Alfvén cascades in NBI heated stellarator plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1004.pdf Modelling of Alfvén cascades in NBI heated stellarator plasmas Allah Rakha1, M.J. Mantsinen1, 2, A.V.Melnikov3, 4, S.E. Sharapov5, D.A.Spong6, A. López-Fraguas7, F. Castejón7 1 Barcelona Supercomputing Center (BSC), 08034, Barcelona, Spain, 2ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain, 3National Research Center 'Kurchatov Institute', 123182, Moscow, Russia, 4National Research Nuclear University MEPhI, 115409, Moscow, Russia, 5CCFE, Culham Science Centre, OX14 3DB, UK, 6Oak Ridge National Laboratory, TN,37831,USA, 7Fusion National Laboratory, CIEMAT, 28040, Madrid, Spain In magnetic fusion, machines with a Reversed magnetic shear (RS) with an off-axis local minimum in the rotational transform are associated with internal transport barriers [1, 2]. In a RS configuration, Alfvén eigenmodes (AEs) called reverse shear Alfvén eigenmodes (RSAE) or Alfvén cascades (ACs) [2] can be excited by energetic ions enhancing fast-ion re-distribution and losses, which are of major concern for plasma scenarios with low or reversed magnetic shear [3]. In this paper, we study ACs observed [4] in the NBI heated discharge 27804 in the TJ-II stellarator (B0 = 0.95 T, R = 1.5 m, a = 0.22 m, Nfp = 4, PNBI ≤ 1.0 MW, ENBI ≤ 32 keV, PECRH ≤ 0.6 MW) using numerical calculations. In this plasma with an increasing rotational transform ι in time, an AC with fast frequency sweeping was observed, with the range of the frequency Figure: Frequency sweeping Alfvén Eigenmodes (AE) in discharge 27804 in TJ-II stellarator. We sweeping in excess of 100 kHz and a minimum focus on the AC observed at t = 1170 ms with fast frequency in the range of ̴ 25 kHz as shown in frequency sweeping and a large frequency range. Figure [4]. We have modelled discharge 27804 based on a reduced MHD model [5, 6] using the experimental density profile and the reversed ι profile reconstructed with VMEC [7]. Our modelling shows a wide spectrum of modes covering a frequency range from ̴ 50 to ̴ 200 kHz and located at a normalised minor radius of 0.3-0.7, roughly consistent with the position of the iota extremum point and the experimental findings. If we use a monotonic ι profile instead, our simulations show a smaller number of modes located at larger minor radii with frequencies covering a narrower range than that observed in the experiment. References [1] Austin M. E. et al., 2006 Phys. Plasmas 13 082502. [5] Spong D. A.,et al., 2003 Phys. Plasmas 10 3217. [2] Sharapov S.E. et al., 2002 Phys. Plasmas 9, 2027. [6] Spong D. A. et al., 2010 Phys. Plasmas 17 022106 [3] Fasoli, A. et al., 2007 Nucl. Fusion 47 S264. [7] Hirshman, S. P. and Whitson, J. C. 1983 Phys. [4] Melnikov A.V., et. al. 2014 Nucl. Fusion 54 Fluids 26, 3553. 123002

Speaker: Allah Rakha

14:00 P4.1005 Regularization extraction for real-time plasma tomography at JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1005.pdf Regularization extraction for real-time plasma tomography at JET D. R. Ferreira1 , D. D. Carvalho1 , P. J. Carvalho1 , H. Fernandes1 , and JET Contributors∗ EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Lisbon, Portugal Plasma tomography [1] consists in reconstructing the 2D radiation profile on a poloidal cross section of the fusion device. Such reconstruction is based on measurements of the line- integrated radiation along multiple lines of sight. However, since these lines are sparse, the prob- lem is under-determined, and a solution must be found by employing regularization methods [2]. Typically, such regularization is implemented by enforcing smoothness along the magnetic flux surfaces [3] or by using prior knowledge from other diagnostics [4]. In addition, an iterative procedure is needed to find the optimal regularization parameters [5]. As a result, tomographic reconstructions are computationally expensive and have extensive knowledge embedded. In this work, we describe an approach to extract the reg- KB5V line 4 ularization from existing reconstructions. Based on a set of 2.0 about 500 reconstructions that have been carefully curated at 1.5 JET, we use a machine learning framework to extract a reg- ularization matrix that can be used to generate new recon- 1.0 structions directly from measurement data. Figure 1 shows 0.5 one of the regularization patterns that can be found in such Z (m) 0.0 matrix, where a measurement taken along a line of sight con- tributes to pixels along a curvature that resembles a magnetic 0.5 flux surface. Once the regularization matrix has been found, 1.0 new reconstructions can be computed in a single matrix mul- 1.5 tiplication step, thus enabling the use of plasma tomography as a real-time diagnostic. 2.0 2.5 3.0 3.5 4.0 R (m) References [1] L. C. Ingesson et al., Fusion Sci. Technol. 53, 2 (2008) Figure 1: Regularization pattern [2] J. Mlynar et al., Fusion Sci. Technol. 58, 3 (2010) for line 4 of the vertical camera [3] M. Odstrcil et al., Nucl. Instr. Meth. Phys. Res. A 686 (2012) [4] J. Bielecki et al., Rev. Sci. Instrum. 86, 9 (2015) [5] V. Loffelmann et al., Fusion Sci. Technol. 69, 2 (2016) ∗ See the author list of X. Litaudon et al., Nuclear Fusion 57, 10 (2017) This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. IPFN activities received financial support from Fundação para a Ciência e a Tecnologia (FCT) through project UID/FIS/50010/2013.

Speaker: D. D. Carvalho

14:00 P4.1006 EEDF in the COMPASS divertor region during an impurity-seeding experiment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1006.pdf EEDF in the COMPASS divertor region during an impurity-seeding experiment M. Dimitrova1,2, Tsv. K. Popov3, M. Komm1, R. Dejarnac1, J. Stöckel1, V. Weinzettl1, P. Vondracek1,4, P. Hacek1,4, M. Hron1, R. Panek1, the COMPASS team and the EUROfusion MST1 Team5 1 Institute of Plasma Physics, The Czech Academy of Sciences, Prague, Czech Republic 2 Emil Djakov Institute of Electronics, Bulgarian Academy of Sciences, Sofia, Bulgaria 3 Faculty of Physics, St. Kl. Ohridski University of Sofia, Sofia, Bulgaria 4 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 5 See author list in H. Meyer et al., Nuclear Fusion 57 102014 (2017) This work presents results from swept Langmuir probe measurements in the divertor region of the COMPASS tokamak [1] in D-shaped, L-mode deuterium discharges, with toroidal magnetic field BT = -1.38 T, plasma current, Ipl = 210 kA and line-average electron density 4×1019 m-3. The electron energy distribution function (EEDF) was studied during a detachment experiment with nitrogen injected into the divertor region. The measured current-voltage probe characteristics were processed using the first-derivative probe technique [2]. This technique allows to evaluate the plasma potential and the real electron energy distribution function (respectively, the electron temperature and density). In the divertor region of the COMPASS tokamak, the EEDF of the attached plasma usually deviates from Maxwellian [3], but it can be approximate by a sum of two Maxwellian distributions (bi-Maxwellian EEDF) with a low-energy electron population with temperatures 3.5-5 eV and a high-energy electron group with temperatures 10-25 eV. During the nitrogen seeding, the EEDF changes to Maxwellian with temperatures 3.5-7 eV. The hypothesis that the fast electrons relax via inelastic collisions with N2 and a Maxwellian EEDF is formed will be discussed during the presentation. The poloidal profiles of the plasma potential, electron temperatures and densities are presented and used for calculation of the parallel power-flux density distribution in the divertor region of the COMPASS tokamak before and during the nitrogen seeding. References: [1] R. Panek R et al.: Plasma Phys. Control. Fusion, Vol. 58 (2016), 014015. [2] Tsv. K. Popov et al.: Plasma Phys. Control. Fusion, Vol. 51 (2009), 065014. [3] M. Dimitrova et al.: Contrib. Plasma Phys., Vol. 54, No. 3 (2014), 255 – 260.

Speaker: Miglena Dimitrova

14:00 P4.1007 Simulation of electron density measurement in Taban tokamak via reflectometry system

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1007.pdf Simulation of electron density measurement in Taban tokamak via reflectometry system S. Koohestani1 1 Department of Physics, Njafabad Branch, Islamic Azad University, Najafabad, Iran Since some tokamaks such as Taban are currently working with low density plasma, a fixed frequency reflectometer system was designed and constructed to monitor plasma production within the vacuum vessel. The system consists of a circular waveguide-antenna, a phase detector, bi-directional coupler and an RF signal generator. The waveguide antenna is working as both transmitter and receiver to measure the phase difference of transmitted and received signals. In order to evaluate performance of the antenna and also to predict the experimental results of electron density measurement in Taban tokamak, the process of electromagnetic wave transmitting from and receiving to an antenna model were simulated via CST software. The simulation were conducted within the reflectometer frequency range (1.7-2.5 GHz), which the plasma area was modelled so that to have the frequency of 2.4 GHz. In this paper, the simulations and their results will be presented in detail. Based on the simulation results, the reflectometer antenna performed appropriately all over the working frequency, since it could properly transmit and receive electromagnetic wave to and from the cut-off layer of the plasma.

Speaker: Saeideh Koohestani

14:00 P4.1008 Diagnostics of optical characteristics of gas- discharge plasma in a mixture of mercury diiodide аnd mercury dibromide vapor, xenon and helium

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1008.pdf DIAGNOSTICS OF OPTICAL CHARACTERISTICS OF GAS- DISCHARGE PLASMA IN A MIXTURE OF MERCURY DIIODIDE АND MERCURY DIBROMIDE VAPOR, XENON AND HELIUM A. A. Malinina Uzhgorod National University, Uzhgorod, Ukraine, Gas- discharge atmospheric plasma in mixtures of mercury diiodide vapor аnd mercury dibromide vapor (HgI2 and HgBr2), xenon and helium is a working medium of exciplex sources of coherent and spontaneous radiation in the visible spectral range of the spectral bands with a maximum intensity at wavelengths () 444nm and 502 nm. Interest in the study and creation of exciplex sources of spontaneous radiation of visible light source is more effective than the existing ones, which would emit in the range of photosynthetic active radiation (PAR). The aim of studies was to make a diagnosics of spectral, energy and temporal characteristics of radiation and parameters of gas-discharge plasma in mixtures of mercury diiodide аnd mercury dibromide vapor, xenon and helium, to identify regularities in these characteristics and to determine the partial pressures of the mixture components at which the maximum power of the radiation in the violet- blue -green spectral range is reached. Plasma was created by barrier discharge in the device with the construction similar to that used in studies [1]. In this device the inter-electrode distance (was 0.015 m), the length of the electrodes (0.2 m) and working volume (was equal to 111 cm3). Diagnostics of spectral, temporal and energy characteristics of the radiation of gas-discharge plasma was carried out on the experimental setup description of which is presented in our article [1]. It was established that the spectrum of the radiation source consists mainly of overlapping spectral emission bands with a maximum intensity at a wavelengths () 444nm and 502 nm (with close intensities) of mercury monoiodide and monobromide molecules in the range 370-510 nm and the mercury line at 546 nm, and the xenon line at 823 nm (Fig.1). The pulses of the discharge current had different polarities, amplitude of 265 A and a duration of 150 ns. The radiation pulses of the HgBr * and HgI * molecules have a two-humped time dependence. The amplitudes of the pulses of current and radiation coincide in time. The amplitude of the second pulse is higher than the first. Specific average power of the radiation from the working volume reaches 54 mW/cm3 and a pulse 70 W / cm3 at a pump pulse repetition rate 18 kHz. Over 90% of the radiation power is in the violet- blue-green spectral region. [1]. A A Malinina, A N Malinin, A K Shuaibov, "Optical characteristics of a HgBr excilamp", Quantum Electronics, 2013, 43 (8), 757–761.

Speaker: Antonina Malinina

14:00 P4.1009 Fast simulation of local radiation fields for synthetic diagnostics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1009.pdf Fast Simulation of Local Radiation Fields for Synthetic Diagnostics A.R. Polevoi1, A.O. Kovalev2, R.N. Rodionov2, E.I. Polunovskiy1, L. Bertalot1, Yu.A. Kashchuk2, D.V. Portnov2, A. Loarte1, M. Loughlin1, S.D. Pinches1, M. De Bock1, E. Veshchev1 1 ITER Organization Headquarters, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul-lez-Durance Cedex, France 2 Project Center ITER, Moscow, Russia We describe a technique based on the concept of Green’s functions, which enables fast simulations of the local radiation fields and diagnostic signals for arbitrarily distributed volumetric sources. The technique is applicable to simulations of diagnostic signals for a range of neutron and optical diagnostics in tokamak plasmas. The development and validation of control algorithms for plasma scenarios in tokamaks require fast techniques for the simulation of the signals from plasma diagnostics. The signals should be realistic, i.e. correctly describe the source dynamics, geometry of detectors, and take into account reflection, scattering and dissipation of radiation in the real design geometry. Typically, accurate simulation of the signals requires the use of time consuming Monte-Carlo or ray-tracing codes using detailed 3D models of the reflecting, scattering, and absorbing elements affecting the diagnostic signals from the sources of radiation distributed in the plasma volume. Thus, computation of a realistic signal from evolving distributed volumetric sources of radiation becomes too time-consuming and expensive an exercise. For cases with additive impact of the sources on the diagnostic signal it is possible to use an approach based upon Green’s functions, considering the function which transfers the source of radiation to the registered signal as a generalized operator. The matrix Gij of the signals measured by a diagnostic from a set of unit ring sources on a chosen grid (Ri,Zj) is calculated by comprehensive time consuming codes just once. This is then used for interpolation of the Green’s function, g(R,Z), to simulate a signal from an arbitrarily distributed evolving volumetric source, S(R,Z;t): F(t) = ∫S(R,Z;t)g(R,Z)dV. This analytic approximation enables simulations of the signals from sources computed on the grid of different complexity adapted to a specific source to keep the required accuracy and resolution. As an example, we discuss the application of proposed technique to simulations of the signals from the neutron diagnostics in ITER. Applications of this technique have enabled a reduction in the computational time needed for a signal from dozens of hours of parallel computations by the MCNP code to less than a second of CPU time. The Green’s function matrix Gij and base grid (Ri,Zj) approach are recommended for the creation of synthetic diagnostics for ITER in the frame of IMAS.

Speaker: Andrei Olegovich Kovalev

14:00 P4.1010 New Diagnostics Developments on IShTAR

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1010.pdf New Diagnostics Developments on IShTAR K. Crombé1, 2, A. Kostic1, 3, A. Nikiforov1, R. Ochoukov3, I. Shesterikov3, M. Usoltceva1, 2, 3, T. Verstrynge1, H. Faugel3, H. Fünfgelder3, S. Heuraux4, J-M. Noterdaeme1, 3 and the IShTAR team 1 Department of Applied Physics, Ghent University, 9000 Ghent, Belgium 2 LPP-ERM-KMS, TEC partner, 1000 Brussels, Belgium 3 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 4 Université de Lorraine, 54506 Vandœuvre-lès-Nancy, France The diagnostics developed for IShTAR (Ion Cyclotron Sheath Test ARrangement) are oriented towards measurements of plasma parameters and electric fields in the vicinity of a Radio Frequency (RF) antenna in order to provide input for sheath modelling codes [1, 2]. In IShTAR the plasmas are created with a helicon antenna operated at a frequency of 11.76 MHz and with a power up to 3kW (the maximum power coupled to the plasma is around 2.7 kW). Recent improvements have been made for the density measurements in the helicon source and the main vessel. An optimised performance regime was found; by adjusting the magnetic topology the plasmas density can be increased by a factor 3 to 5, which is beneficial to the sheath studies. An additional array of RF compensated probes (Langmuir, B-dot…) has been installed to allow for a better characterization of the plasma parameters at different locations. The first results of an interferometer, installed to benchmark the electron density estimates of the Langmuir probes, will be presented. Two approaches are followed to measure the electric fields in the plasma caused by the RF antenna sheaths. Passive optical emission spectroscopy monitors Stark effects on spectral lines with a high-resolution spectrometer [3], provided that the local electric fields are strong enough to overcome the broadening of the lines. Doppler-free saturation spectroscopy is more powerful: a laser beam depletes the ground state, eliminates the line broadening effects and makes smaller electric fields visible. However, the more complicated set-up, with a careful alignment of laser beams, makes the measurements much more challenging. After a first test on a glow discharge plasma [4], the design of the optical path and the installation of the laser at IShTAR have started; the progress will be reported. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The work received support from the Research Foundation Flanders (G0B3115N). [1] K. Crombé et al., “IShTAR: a helicon plasma source to characterize the interactions between ICRF and plasma”, 26th IAEA Fusion Energy Conference (2016), EXP6_48 [2] L. Lu et al., “Modelling of radio frequency sheath and fast wave coupling on the realistic ion cyclotron resonant antenna surroundings and the outer wall”, Plasma Phys. Control. Fusion, Vol. 60, No. 3, 035003 (2018) [3] A. Kostic et al.: "Feasibility study of Passive Optical Emission Spectroscopy for the electric field measurements in IShTAR”, EPJ Web of Conferences 157, 03025 (2017) [4] K. Crombé et al.: “Helium operation of IShTAR in preparation of E-field measurements”, ECA Vol. 41F, P5- 144 (2017)

Speaker: Kristel Crombe

14:00 P4.1011 Calculation of optical depth based on electron cyclotron emission in IR-T1 Tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1011.pdf Calculation of optical depth based on electron cyclotron emission in the IR-T1 Tokamak plasmas Mona Ahmadi, Pejman Khorshid Department of Physics, Faculty of Science, Mashhad Branch, Islamic Azad University, Mashhad, Iran The electron cyclotron emission (ECE) was investigated in IR-T1 tokomak. According to the electron temperature plasma and its direct relationship with the absorption coefficient, the absorption conditions were discussed for both first and second harmonic ordinary and extraordinary modes and electron cyclotron radiation was calculated. The theory of electron cyclotron emission and absorption coefficient were considered as non-relativistic effects in low plasma temperature. By examining the area of absorption in condition pc, the profile of optical depth in perpendicular emission =/2 and the equatorial plane torus were calculated and the maximum value of optical depth =1.38 was obtained for IR-T1 tokamak. These results show that the values of optical depth have a direct relationship with electron density and electron temperature plasma mostly in second harmonic extraordinary mode.

Speaker: Mona Ahmadi

14:00 P4.1012 ITER plasma spectra modelling for charge exchange recombination spectroscopy

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1012.pdf ITER plasma spectra modelling for charge exchange recombination spectroscopy S.V. Serov1 , S.N. Tugarinov1 , M. von Hellermann2 1 Institution "Project Center ITER", Moscow, Russia 2 ITER Organization, St. Paul-lez-Durance, France One of the primary methods of fusion plasma diagnostics is charge exchange recombination spectroscopy [1]. The CXRS diagnostics is widely used at many modern tokamaks to measure ion temperature, ion density, toroidal and poloidal plasma rotation velocities. CXRS will be one of the most important diagnostics at the ITER tokamak, as it would be used to measure main plasma parameters determining the efficiency of the fusion reaction. This work describes CXRS- Edge diagnostics development for ITER. The CXRS spectra modelling for ITER tokamak is considered. The main principles of spectra modelling in presence of the diagnostic neutral beam are considered. Simulation of Spec- tra code [2], created specially for CXRS modelling is described. Spectral profiles, calculated for different ITER scenarios are pre- sented. Figure 1 shows an exam- Figure 1: Modelled HeII and BeIV spectrum for ITER CXRS- ple of modelled HeII and BeIV Edge. It is a superposion of active HeII CX line, passive HeII CX spectrum for 0.5 minor radius. line, edge lines and BeIV active lines. The main challanges of CXRS modelling for ITER are described. It is shown that CXRS-Edge diagnostic on ITER tokamak will allow performing an ion temperature, impurities concentration, toroidal and poloidal rota- tion velocity measurements in accordance with ITER requirements. References [1] R. Fonck et al., Physical Review A, 29, 6 (1984) [2] M.von Hellermann et al., Physica Scripta, Volume 2005, T120, 19

Speaker: Stanislav Serov

14:00 P4.1013 Neural networks for fast soft X-ray tomographic inversions in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1013.pdf Neural networks for fast soft X-ray tomographic inversions in tokamaks A. Jardin1, J. Bielecki1, D. Mazon2, J. Dankowski1, Y. Peysson2 and M. Scholz1 1 Institute of Nuclear Physics Polish Academy of Sciences (IFJ PAN), PL-31-342, Krakow, Poland 2 CEA, IRFM F-13108 Saint Paul-lez-Durance, France Reconstructing the local plasma emissivity in the soft X-ray (SXR) range 0.1 – 20 keV can be very useful to access essential information on particle transport, magnetohydrodynamic activity or impurity content in tokamaks. In particular, radiative cooling of heavy impurities like tungsten (W) could be detrimental for the plasma core performances of ITER and developing robust SXR diagnostics is thus a crucial issue for monitoring the impurities and the prevention or their central accumulation. 2D tomography is the usual method to access the local SXR emissivity from line integrated measurements of two or more cameras viewing the plasma in a poloidal cross-section. This mathematically ill-posed and quite challenging problem is traditionally solved using Tikhonov regularization, such as the minimum Fisher information method implemented on the ASDEX Upgrade, TCV and WEST tokamaks [1]. However, real-time impurity control will require fast inversion methods while Tikhonov regularization needs relatively significant computational time, although many efforts have been performed in the direction of real-time applications [2]. Neural networks have been recently used for plasma tomography with JET neutron camera [3] and bolometers [4], showing promising results in terms of computational time as well as quality of reconstruction. Thus, the aim of this contribution is to investigate the use of neural network for fast soft X-ray tomographic reconstructions in the prospect of real-time impurity control in tokamak plasmas. Using a large database of various synthetic emissivity phantoms to train the neural network, the robustness of the inversion will be investigated and benchmarked with traditional Tikhonov regularization techniques [5]. The influence of the network parameters (neuron activation function, hidden layers, regularization procedure…) will be studied with a specific attention to the net gain in computational time, to the robustness of the method with respect to the experimental noise in the measurements and to the intrinsic limitations of such approach. Acknowledgments. This work has received a financial support from the POLONIUM collaboration program between the French and Polish Ministers of Science. [1] A. Jardin et al, 2016 JINST 11 C07006. [2] J. Mlynar, V. Weinzettl, G. Bonheure, A. Murari, Fusion Sci. Technol. 58 (3) (2010) 733–741. [3] E. Ronchi et al, Nuclear Instruments and Methods in Physics Research A 613 (2010) 295–303. [4] F. Matos, D. Ferreira, P. Carvalho and JET contributors, Fusion Engineering and Design 114 (2017) 18–25. [5] A. Jardin, D. Mazon and J. Bielecki, Phys. Scr. 91 (2016) 044007.

Speaker: Axel Jardin

14:00 P4.1014 Feasibility of pedestal density fluctuation measurement by beam emission spectroscopy on the ITER diagnostic beam

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1014.pdf Feasibility of pedestal density fluctuation measurement by beam emission spectroscopy on the ITER diagnostic beam O. Asztalos1, S. Zoletnik2, G. Boguszlavszkij1, M.v. Hellerman3, M. De Bock4, G.T.A. Huijsmans5,6, G.I. Pokol1 1 Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest, Hungary 2 Wigner Research Center for Physics, Budapest, Hungary 3 Institue for Plasma Physics, IEK4 Forschungszentrum Jülich, 52428 Jülich, Germany 4 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France 5 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 6 Eindhoven University of Technology, Eindhoven, The Netherlands ITER constitutes a critical milestone on the road to fusion energy production, which requires understanding of the scaling of turbulent density fluctuations and pedestal dynamics to ITER sized machines. This need facilitates the development of various fluctuation diagnostics. Fluctuation beam emission spectroscopy (BES) is an active plasma diagnostic used for density measurements that has sufficient spatial and temporal resolution for the study of turbulent density fluctuations and associated flows. A high energy neutral beam is shot into the plasma consisting of hydrogen isotopes or light alkali metal atoms, and through various collisional processes with plasma particles the beam atoms get to excited states, and their spontaneous emission is collected by an observation system. In the present contribution, the feasibility of pedestal density fluctuation measurement by BES is discussed that would be proposed to make piggy-back use of the pedestal CXRS periscope viewing the diagnostic neutral beam. Forward modelling was used to estimate the signal to background (SBR) and signal to noise (SNR) ratios, as well as the spatial resolution. These were evaluated in view of possible applications of the diagnostic. A 10 x 15 channel observation system was put forward that would not interfere with the baseline CXRS diagnostic system using the same periscope. Narrow-band optical filters were optimized for each detector column to eliminate as much as possible of the high continuous background expected on ITER. Resulting SBR of each column was determined using Simulation of Spectra [1], which models the Doppler shifted BES spectrum for each detector channel. The RENATE 3D BES modelling code [2], which handles realistic magnetic geometries and accounts for the spatial effects of the diagnostic, was used to determine the expected photon flux on each detector channel in order to derive the expected SNR. Fluctuation response analysis was performed on the system to determine the extent of the fluctuation sensitive volumes for each detector revealing the amount of expected cross-talk between detector channels and the performance of the diagnostic system. Applications of turbulence models and non-linear MHD codes, such as JOREK [4], in conjunction with RENATE as a synthetic diagnostic are discussed, as well, to prove the performance of the proposed fluctuation diagnostic. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization. [1] M.v Hellermann, et.al. 2006 IAEA IT/P1-26 [2] D. Guszejnov, et.al. 2012 RSI 83, 113501 [3] G.T.A. Huijsmans, et.al. 2007 NF 47, 659

Speaker: Örs Asztalos

14:00 P4.1015 Collective Thomson Scattering in FTU: first comparison between numerical predictions and experimental observations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1015.pdf Collective Thomson Scattering in FTU: first comparison between numerical predictions and experimental observations B. Baiocchi , W. Bin , A. Bruschi , L. Figini , U. Tartari , E. Alessi , 1 1 1 1 1 1 P. Buratti , V. Cocilovo , O. D’Arcangelo , E. Giovannozzi , M. Lontano , G. Pucella 2 2 2 2 1 2 1 Institute of Plasma Physics “P.Caldirola”, National Research Council of Italy via R. Cozzi 53, 20125 Milan, Italy 2 ENEA Fusion and Nuclear Safety Department, C. R. Frascati via E. Fermi 45, 00044 Frascati (Roma), Italy The Collective Thomson Scattering (CTS) diagnostic allows the investigation of ion populations in fusion plasma devices, studying the characteristic emissions, stimulated by the injection of a powerful microwave probing beam. From the shape of the emitted spectrum, plasma parameters such as ion temperature, drift velocity and ion composition can be inferred [1, 2]. The availability in FTU of a CTS diagnostic system at 140 GHz and the possibility of “non-resonant” plasma scenarios, i.e. scenarios in which the Electron Cyclotron (EC) layer (and harmonics) resonant with the probe frequency are out of the plasma region, allow to carry out studies on ions characteristics. In fact, in presence of EC resonances, the Electron Cyclotron Emission (ECE) background (at probing frequency) can significantly overwhelm the signals due to thermal CTS. In recent experiments, focused on the investigation of the effects of Parametric Decay Instabilities (PDI) in plasma with magnetic islands stimulated by neon injection [3], a few shots were performed in non-resonant plasmas at 3.6 T, plasma 19 20 -3 current of 350 kA and densities ranging from 5*10 to 1.2*10 m . The scattered signal of the 140 GHz, 350 kW probe beam has been detected by the upgraded CTS system [4] and further analysed with the Thermal Collective Scattering code (TCS) [5]. The TCS has been developed for the analysis of thermal ions spectral functions and recently upgraded with tool providing absolute calibrated spectra (in eV). The CTS emission predicted by the code was compared with the new calibrated spectra collected during the non-resonant discharges. The fitting of these spectra allows an estimate of ion temperature and of the fraction of neon impurities (injected to stimulate magnetic island) whose characteristic emissions have been also simulated by the code. References [1] Stejner M et al 2015 Plasma Phys. Control. Fusion 57 062001 [2] Stejner M et al 2011 Plasma Phys. Control. Fusion 53 065020 [3] Bruschi A et al 2017 Nucl. Fusion 57 076004 [4] Bin W et al 2015 J. Instrum. 10 P10007 [5] Bin W et al 2015 Fusion Eng. Des. 96-97 733-737

Speaker: Benedetta Baiocchi

14:00 P4.1016 - Measurement of a tilting cylindrical probe in a RF magnetized plasma discharge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1016.pdf Measurement of a tilting cylindrical probe in a RF magnetized plasma discharge J. Ledig1 , E. Faudot1 , N. Lemoine1 , S. Heuraux1 , M. Usoltceva2 , J. Moritz1 1 Institut Jean Lamour, Nancy, France 2 Max-Planck-Institut für Plasmaphysik, Garching, Germany I-V curve coming from Langmuir probe measurements is assumed to provide many physical plasma parameters as density, temperature, plasma potential, and floating potential. In the presence of magnetic field, probe understanding becomes more difficult because the magnetic field breaks down isotropy. Some works had already been done in this field for electron collection on a wall and parallel to magnetic field [1] and for a semi-infinite cylindrical probe aligned with magnetic field [2]. However, probe measurements in magnetized plasma is still a challenge especially in the case of a tilted probe with respect to the field (which occurs in Tokamaks). For the present work measurements were done in a linear plasma reactor, ALINE, a chamber of 1 m length and radius of 35 cm. The 1.2 Pa helium plasma was generated by an RF antenna at frequency 25 MHz. The injected power went from 30 W to 200 W. The 1 cm long cylindrical probe of radius 75 µm compensates RF fluctuations thanks to a compensation electrode and small chokes. Magnetic field was set between 0 and 100 mT and few tilting angles were used for Ψ from 0° (probe aligned with B) to 90° (probe perpendicular to B). Comparaisons of IV curves showed that increasing Ψ tend to increase electron saturations curents, but ion saturations currents remains approximatly the same. For low Ψ a current bump between exponential part of I-V characteristics and electron saturation current was noticed. A previous theory of electron collection for Ψ=0 on cylindrical probe for different values of magnetic field was used here using a simple projection to calculate plasma parameters in every tilting angle. [1] J. Moritz et al., Plasma sheath properties in a magnetic field parallel to the wall, Physics of Plasma 23, 062509 (2016) [2] J.G. Laframboise et al., Theory of a cylindrical probe in a collisionless magnetoplasma, Physics of Fluids 19, (1976)

Speaker: J. Ledig

14:00 P4.1017 Wavelet analysis of Mirnov coils signals for disruption prediction at JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1017.pdf Wavelet analysis of Mirnov coils signals for disruption prediction at JET B. Cannas1, A. Fanni1, A. Murari2, A. Pau1, G. Sias1 and the JET contributors* 1 Electrical and Electronic Engineering Dept. - University of Cagliari, Italy 2 Consorzio RFX (CNR, ENEA, INFN, Università di Padova, Acciaierie Venete SpA), Corso Stati Uniti 4, 35127 *See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001 Disruption are often preceded by MHD modes slowing down, growing and locking when the amplitude exceeds a critical value. The fluctuations of the poloidal magnetic field recorded by the Mirnov coils could provide useful markers related to the presence of this kind of instabilities causing disruptions. This paper proposes a time-frequency analysis of the Mirnov signals recorded at JET by the high resolution probes of KC1M diagnostic. The work is a contribution toward the definition of new features characterizing disruptive behaviours to be used as input in a multisignal disruption predictor. Mirnov coil signals are non-stationary, thus, their spectrum changes with time. Compared to Fourier transform, wavelet transform (WT) is a step forward in the spectral characterization of a time series, since allows to study the temporal evolution of amplitude, frequency over time scales comparable with the wave period. The continuous WT of a discrete time series {x[i]} is defined as the convolution product of {x[i]} with a scaled (t → t/s) and shifted (t → t − τ) version of a mother wavelet ψ(t). The windowing is intrinsic in the wavelet and it depends on scale s. The smaller s, the more compressed the wavelet is, so it can catch rapidly changing details in the signal. The database taken into account in this work consists of 116 non disruptive and 78 disruptive pulses. The Mirnov signals are acquired at the frequency of 2MHz and resampled at 20kHz. Then, the wavelet coefficients are evaluated on a mobile window as in a real time application. The results of a preliminary analysis performed on a single probe show that, for all non disruptive pulses, several high scale (low frequency) coefficients stay smaller than an optimized value, whereas for 86% of the analysed disruptive shots they exceed this value more than 10ms before the disruption time. Thus, this technique seems promising to anticipate the alarm of a multisignal predictor in case of rotating precursors to locked mode. In the final paper, an analysis of more signals from several Mirnov coils will identify the presence of locked modes or other instabilities in order to interpret the results. The study will be extended integrating the information given by different wavelet coefficients.

Speaker: Barbara Cannas

14:00 P4.1018 The He/Ne beam diagnostic for active emission spectroscopy in the island divertor of Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1018.pdf The He/Ne beam diagnostic for active emission spectroscopy in the island divertor of Wendelstein 7-X T Barbui1, F. Effenberg1, M. Jakubowski2, R. König2, M. Krychowiak2, S. Loch3, J. Muños Burgos4, O. Schmitz1 and the W7-X Team2 1 University of Wisconsin, Madison WI, USA 2 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 3 Auburn University, Auburn AL, USA 4 Astro Fusion Spectre, San Diego CA, USA A dedicated line-ratio spectroscopy system on thermal helium (He) and neon (Ne) was implemented at Wendelstein 7-X to measure radial profiles of electron density n e(r) and temperature Te(r) in front of the horizontal target in the graphite island divertor of W7-X. The injection system consists of two boxes with 5 fast piezo valves each, mounted directly behind the divertor plates in one upper and one lower divertor module, which are magnetically connected in the 5/5 island configuration [1]. The new observation system includes 54 horizontal lines-of-sight which are channelled to a 19cm and a 32cm focal length Czerny-Turner spectrometer allowing observation of the He and Ne lines as well as impurities and hydrogen (H) lines with high spectral resolution (dispersion down to 1.3 nm/mm). In the first divertor campaign of W7-X solely He has been used to measure Te and ne profiles for the full radial width of the scrape-off layer in the divertor, across the 5/5 island in the standard magnetic configuration. The spatial resolution of the diagnostic is 3 mm and the time resolution is 25 ms. Edge parameter measurements with the He-beam have been carried out during different physics experiments, such as radiative edge cooling and detachment studies through H fuelling. Preliminary results show clear impact of the seeded impurities (N2 and Ne) and H fuelling on the measured Te and ne, in agreement with other edge diagnostics. Ne has been tested in order to extend the applicability of the diagnostic to the detached divertor regime at very low Te (≪10eV) to be achieved in the next campaigns. Results from Ne injection and the status of the development of a dedicated collisional-radiative model for Ne are here presented. Acknowledgements: This work was funded in part by the U.S. DoE under grant DE-SC0014210 References [1] M. Griener et al 2017 Review of Scientific Instruments 88 033509

Speaker: Tullio Barbui

14:00 P4.1019 Atomic Beam Probe diagnostic for plasma edge current measurements at COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1019.pdf Atomic Beam Probe diagnostic for plasma edge current measurements at COMPASS D. I. Réfy1, P. Hacek2,3, S. Zoletnik1, D. Dunai1, G. Anda1, M. Lampert1, M. Aradi4, A. Bencze1, M. Berta5, J. Krbec2,6, V. Weinzettl2, R. Panek2 and the COMPASS Team2 1 Wigner RCP, Budapest, Hungary, 2Institute of Plasma Physics of the CAS, Prague, Czech Republic, 3Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic, 4Graz University of Technology, Fusion@ÖAW, Austria, 5Széchenyi István University, Győr, Hungary, 6Faculty of Nuclear Sciences and Physical Engineering, CTU, Prague, Czech Republic The measurement of the plasma edge current density distribution and temporal evolution during the edge localized mode (ELM) cycle is of particular interest on the field of magnetically confinement plasmas, since the theoretical models recognize it as a key element for the trigger mechanism of the ELMs. The atomic beam probe (ABP [1]) is an extension of the beam emission spectroscopy (BES) diagnostic [2]. The beam atoms are ionized due to the collision with the plasma particles, deflected through a curved path due to the magnetic field and may be detected close to the wall of the machine. The arrival location and intensity of the ions carry information about the toroidal plasma current distribution, the density profile and the electric potential in the plasma. Detecting the few microampere ion current close to the plasma edge requires a special detector. The measurements with a preliminary test detector head has been carried out, and a final detector head design was proposed based on the results [3]. A new detector head for the ABP was designed and tested in the lab. The new setup utilizes a shallow Faraday cup matrix, produced with printed-circuit board technology, and double mask for secondary electron suppression. Noise characterization, switching time, cross talk and fluctuation sensitivity test results in the lab setup will be presented, along with the first measurement results with the new setup at COMPASS tokamak [4]. [1] M. Berta et al., Development of atomic beam probe for tokamaks, Fus. Eng. Des. 88 (2013) 2875 [2] G. Anda et al., Lithium beam diagnostic system on the COMPASS tokamak. Fus. Eng. Des. 108 (2016) [3] P. Hacek et al., Measurements with ABP Diagnostic on the COMPASS Tokamak, WDS'15 proceedeings (2015) [4] R. Panek et al., Plasma Phys. Control. Fusion 58 014015 (2016)

Speaker: Dániel Imre Réfy

14:00 P4.1020 Requirements for an Imaging Heavy Ion Beam Probe at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1020.pdf Requirements for an Imaging Heavy Ion Beam Probe at ASDEX Upgrade G. Birkenmeier1,2 , J. Galdon-Quiroga1,3 , J. F. Rivero-Rodriguez3 , M. Garcia-Munoz1,3 , M. Griener1 , G. Harrer4 , N. Leuthold1 , E. Wolfrum1 , U. Stroth1,2 , and the ASDEX Upgrade Team. 1 Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany 2 Physik-Department E28, Technische Universität München, 85748 Garching, Germany 3 Department of Atomic, Molecular and Nuclear Physics, University of Seville, 41012 Seville, Spain 4 Institute of Applied Physics, TU Wien, Vienna, Austria We present a conceptual study and hardware investigations in preparation of an imaging heavy ion beam probe (i-HIBP) for the ASDEX Upgrade tokamak [1]. The main feature of this new type of a heavy ion beam probe (HIBP) is the imaging of the secondary beams by means of an in-vessel scintillator screen in combination with a high speed camera. The spatio-temporal pattern on the scintillator contains two-dimensional information about the plasma density, the plasma potential and the poloidal magnetic field at the points of ionization of the primary beam, where the secondaries are created. Due to the use of a neutral beam as primary beam and the in-vessel imaging of the secondaries, the i-HIBP system is much more compact than a classical HIBP [2] consisting of large accelerators and bulky electrostatic energy analyzers. A numerical study for a neutral 80 keV cesium beam as primary beam has shown [1], that information about the density, the plasma potential and the poloidal magnetic field from 10 cm inside the last closed flux surface up to the far scrape-off layer can be obtained for a typi- cal low-density ASDEX Upgrade plasma. The variation of the pattern on the scintillator has shown to depend linearly on the perturbation amplitude of the measured quantities, and local- ized measurements of plasma potential fluctuations down to 10 eV seem possible if certain beam properties are fulfilled. Laboratory tests with a neutral cesium beam and a scintillator material, which is typically used in fast ion loss detectors [3], have shown that we can meet all necessary requirements for a high measuring sensitivity of an i-HIBP at ASDEX Upgrade. We present details of the planned technical implementation and show the capabilities of this new diagnostic for investigations of plasma edge phenomena like edge localized modes, zonal flows, geodesic acoustic modes and blob filaments. References [1] J. Galdon-Quiroga et al., Journal of Instrumentation 12, C08023 (2017) [2] A.V. Melnikov et al., Nucl. Fusion 57, 072004 (2017) [3] M. Garcia-Munoz et al., Rev. Sci. Instrum. 80, 053503 (2009)

Speaker: Gregor Birkenmeier

14:00 P4.1021 Deuterium retention in tungsten with and without helium fuzz after irradiation by a pulsed high-temperature plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1021.pdf Deuterium retention in tungsten with and without helium fuzz after irradiation by a pulsed high-temperature plasma O. V. Ogorodnikova1, K.S. Klimov2, Yu.M. Gasparian1, V.S. Efimov1, А.G. Poskakalov1 1NationalResearch Nuclear University MEPHI (Moscow Engineering Physics Institute), Kashirskoe sh. 31, 115409 Moscow, Russia 2State Research Centre of Russian Federation Troitsk Institute for Innovation and Fusion Research, ul. Pushkovykh, vladenie 12, Troitsk, 108840 Moscow, Russia Tungsten (W) is the reference material for the divertor of ITER and DEMO reactors. In the fusion reactor, W will be exposed to energetic particles of hydrogen isotopes and helium, high heat flux, neutrons (14 MeV-peak neutron spectrum) and transmutation products. In this regard, a study of accumulation of hydrogen isotopes and helium in W under normal operation conditions and transit events is necessary for assessment of safety of fusion reactor due to the radioactivity of tritium and material performance and for the plasma fuel balance. In the present work, W samples were exposed to pulsed heat loads using deuterium (D) plasma in quasi-stationary high-current plasma gun QSPA-T. The pulse duration was 1 ms and number of pulses was varied from one to ten. The irradiation was performed below and above the melting threshold and sample temperature was kept during irradiation either 300 or 1273 K. We examined the impact of (i) ELMs-like events, (ii) sample temperature and (iii) formation of low-energy ion-induced helium (He) nano-structured ‘fuzz’ on the D retention in W. The He ‘fuzz’ on W was produced by exposure of W to low-energy He plasma at 1273 K prior to pulsed high-temperature D plasma exposure. The D and He retention in each irradiated sample was measured by a method of thermal desorption spectroscopy (TDS) up to 1700 K. We found that the total D retention was the highest for samples irradiated by plasma gun above the melting threshold. The D retention after 10 pulses of plasma gun exposure was much higher than that after stationary low-energy plasma exposure at sample temperature of either 600 or 700 K indicating the dominate influence of ELM’s-like events on the D retention compared to normal operation regime. The D retention in W samples with the presence of ion-induced He ‘fuzz’ was lower than without. The pulsed plasma exposure at base sample temperature of 1273 K indicates a reduction in the density of He ‘fuzz’ and decrease of the D retention compared to the base sample temperature of 300 K. The results obtained give possibility to assess the hydrogen isotope and helium retention in divertor areas subjected to high thermal loads at different operation regimes.

Speaker: Olga Ogorodnikova

14:00 P4.1022 Neutral particle fluxes on the divertor during overload mimic scenarios in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1022.pdf Neutral particle fluxes on the divertor during overload mimic scenarios in Wendelstein 7-X A. LeViness1, P. Drewelow2, J.D. Lore3, G. Schlisio2, G. Wurden4, B. Cannas6, K. Hammond2, M. Jakubowski2,5, F. Pisano6 and W7-X team 1 Universität Greifswald, Greifswald, Germany 2 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 3 Oak Ridge National Laboratory, Oak Ridge, United States 4 Los Alamos National Laboratory, Los Alamos, United States 5 Faculty of Mathematics and Physics, University of Szczecin, Szczecin, Poland 6 Università degli Studi di Cagliari, Cagliari, Italy Wendelstein 7-X will perform high-power long-pulse discharges with the actively cooled divertor from the early 2020’s. It is predicted [1] that in some configurations, during the first 100 s of the discharge, the toroidal current in the plasma will evolve and change the magnetic topology such that the edges of the divertor may be overloaded. The planned solution to this is the installation of ‘scraper element’ components. Two of these components are expected to be installed for OP 1.2b [2] to test their effectiveness and influence on plasma performance. One of the key questions is whether neutral divertor compression will be reduced too much due to strong interaction of the plasma with the surface of the scraper element. Because of the limits on pulse length and energy input, the overload scenario cannot occur during OP 1.2. Instead, five magnetic configurations were designed to mimic the topology created by the toroidal current as it evolves from 0 to 43 kA, including the peak overload case of 22 kA. In order to compare actual heat and particle loads to those predicted by EMC3-EIRENE simulations, and to establish baseline measurements for comparing performance with and without the test divertor scraper elements, experiments were performed during the previous campaign using these mimic configurations. In this work, we analyze the H-alpha camera diagnostic data in order to quantify divertor particle fluxes and relate them to neutral divertor pressure measured by pressure gauges. Results showed heat and particle flux patterns closely matching those predicted by simulations. References [1] H. Hoelbe, et al., Nucl. Fusion 56, 025015 (2016) [2] J.D. Lore, et al., IEEE TPS 42, 539 (2014)

Speaker: Alex LeViness

14:00 P4.1023 Comparison of experimental and predicted divertor fluxes in W7-X scraper element mimic scenarios

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1023.pdf Comparison of experimental and predicted divertor fluxes in W7-X scraper element mimic scenarios J.D. Lore1, H. Hoelbe2, P. Drewelow2, F. Effenberg3, H. Frerichs3, J. Geiger2, M. Jakubowski2, S. Lazerson4, H. Niemann2, G.A. Wurden5, and the W7-X team 1 Oak Ridge National Laboratory, Oak Ridge, USA 2 Max Planck Institute for Plasma Physics, Greifswald, Germany 3 University of Wisconsin-Madison, Madison, WI, USA 4 Princeton Plasma Physics Laboratory, Princeton, NJ, USA. 5 Los Alamos National Laboratory, Los Alamos, NM, USA Experiments were performed in the first diverted operational phase of W7-X (OP1.2a) to mimic the spatial evolution of the divertor strike points that is expected for long-pulse operation in the actively cooled operational phase (OP2). These experiments mimic the evolution of the toroidal current and plasma beta [1] on the edge topology and boundary island size that is predicted to cause overload of the edges of the main divertor components and baffle regions in certain operational scenarios. One proposed solution to this overload problem is the installation of a set of new divertor components known as scraper elements, that intercept the flux to the overloaded divertor edges. Two test divertor scraper elements will be installed before the next operational phase (OP1.2b). The scraper elements are predicted to prevent overload but have the consequences of reducing the pumping efficiency and acting as an additional neutral and impurity source that may deleteriously affect the core plasma. The experiments performed in OP1.2 confirm the predicted scenario and establish the parameters before the installation of scraper elements. Data were obtained in five magnetic configurations, corresponding to five points in the mimicked OP2 current and beta evolution [2]. We focus on comparison of the predicted divertor and baffle heat fluxes to the infrared camera measurements. Initial analysis indicates good qualitative agreement to calculations made using field line diffusion [3] and EMC3-EIRENE, indicated both that rapid diffusion-type calculations are appropriate for approximating divertor fluxes and that the approach of mimicking the effect of otherwise inaccessible plasma parameters such as toroidal current is valid. [1] J. Geiger, et al., Contrib. Plasma Phys. 50 (2010), 770. [2] H. Hoelbe, et al, Nucl. Fusion 56 (2016) 025015. [3] J.D. Lore, et al., IEEE TPS 42, (2014) 539.

Speaker: Jeremy Lore

14:00 P4.1024 Langevin approach for plasma-surface interaction: turbulent sputtering and surface morphology

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1024.pdf Langevin approach for plasma-surface interaction: turbulent sputtering and surface morphology D. Reiser Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, 52425 Jülich, Germany The eminent role of plasma instabilities and related turbulent effects in fusion research is well known. Prominent examples relevant for future experiments and reactor operation are the anomalous transport degrading confinement properties and the Edge Localized Modes (ELM’s) leading to intermittent expulsion of particles and heat onto the divertor plates. However, an integrated simulation taking into account the temporal evolution of the multi-scale plasma dynamics and the interaction of the plasma with plasma-facing components is currently not within reach due to limitations in computational resources. On the other hand, if the focus of research is not that much on the detailed origin of the plasma turbulence but rather on the interaction with material boundaries, a half-empirical approach is available via the use of so-called synthetic turbulence models. Such models can be employed to mimic the basic statistical features of the plasma dynamics known from more detailed sim- ulations and/or from experiment. With the knowledge of spatiotemporal correlations and am- plitudes the plasma turbulence can be parametrized and its time evolution can be modelled by means of fast algorithms. This approach has been successfully adopted already for the analy- sis of plasma-wall interaction in linear devices [1]. The extension to tokamak geometries is straightforward and might be applied to the studies of impurity transport in the presence of ELM’s. Moreover, this approach can be extended consistently by implementing additionally a Bradley-Harper-like model [2] for the morphological changes in the plasma-facing material, which is based on similar numerical methods like the generation of synthetic plasma turbulence. In this work we present a Langevin computational model for the linear device PSI-2 [3, 4] based on this combination of plasma turbulence with impurity sputtering and morphological changes of the target material. Scans through relevant parameter ranges of PSI-2 operational conditions are presented. References [1] D. Reiser et al., Phys. Scr. 2017, 014039 (2017). [2] V. O. Kharchenko and D. O. Kharchenko, Condensed Matter Physics 14, 23602 (2011). [3] A. Kreter et al., Fusion Sci. Technol. 68 (1), 8-14 (2015). [4] A. Kreter, Fusion Sci. Technol. 59 (1), 51-56 T (2011).

Speaker: Dirk Reiser

14:00 P4.1025 Visible spectroscopy with liquid tin limiter on FTU plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1025.pdf 45 EPS Conference on Plasma Physics 12696 Visible spectroscopy with liquid tin limiter on FTU plasma G.M. Apruzzese , M.L. Apicella , M. Iafrati , G. Mazzitelli , F.Bombarda , L.Gabellieri , A. 1 1 1 1 1 1 Romano and FTU Team 1 1 1 ENEA, Fusion and Technologies for Nuclear Safety Department, C.R. ENEA Frascati, via E. Fermi 45, 00044 Frascati (Rome), Italy In the Frascati Tokamak Upgrade (FTU), two different liquid metals, as plasma facing materials, have been studied, lithium and tin. The successful experiments with liquid lithium limiter, started since 2006, have pointed out the importance to explore other liquid metal materials such as tin whose operating window is much larger than that of lithium. The liquid tin limiter, TLL, has been tested on FTU in the experimental campaign, started at the end of 2016 [1]. The preliminary analysis of the experimental data has been focused in detecting the presence of tin in the discharge: suitable monitors are the spectroscopic diagnostics in the visible, VUV and XUV ranges [2]. The experimental observation of the tin spectral lines represents a new goal for extending the database of atomic nuclear data in the plasma tokamak research. The observed spectra are compared with the NIST database. In particular, the strong spectral lines of SnII, 607.8 nm and 645.3 nm, have been identified together with other weaker ones in the visible and VUV range, while the XUV spectra have been analysed and discussed in [3]. Moreover the quantity of the impurity in the plasma, in the presence of tin limiter, has been analysed. Since the presence of the tin in the discharge is strongly dependent on the heat load on the TLL, the correlation among the observed spectra and the heat load on the TLL has been explored. Particular attention has been placed for experiments with high heat load on TLL, performed operating with high electron density and with additional heating power. For FTU standard discharges with I = 0.5MA and B = 5.4T, the tin p T limiter has been exposed to the plasma with a heat loads up to 18 MW/m , reaching the 2 maximum temperature value of 1700 C. The paper reports on the spectroscopic o measurements obtained during experiments with the tin limiter in FTU tokamak. * Corresponding author: gerarda.apruzzese@enea.it (G.M. Apruzzese) 1. G.Mazzitelli et al., IAEA 2016,’Liquid metal experiments on FTU’,Ex/P8-21 2. G.M.Apruzzese et al., ISLA-V 2017, ‘First spectroscopic results with tin limiter on FTU plasma’, paper submitted to Plasma Physics Reports 3. F.Bombarda et al.’High Resolution EUV Spectroscopy on FTU with Tin Liquid Limiter’, submitted to this conference

Speaker: Gerarda Maria Apruzzese

14:00 P4.1026 High heat loads producing dust particles in the Alcator C-Mod tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1026.pdf High heat loads producing dust particles in the Alcator C-Mod tokamak a b c a a b b C. Arnas , J. Irby , G. De Temmerman , C. Martin , C. Pardanaud , I. Faust , Y. Lin , b d d S. Pierson , A. Autricque , C. Grisolia a CNRS, Aix-Marseille université, laboratoire PIIM, 13397 Marseille, France b M.I.T. Plasma Science and Fusion Center, 175 Albany Street, Cambridge, MA02139,USA c ITER Organization, Route de Vinon-sur-Verdon, 13067 St Paul Lez Durance, France d IRFM/CEA Cadarache, 13108 St Paul Lez Durance, France Plasma facing units in the ITER divertor will be formed with chains of tungsten monoblocks (MB). One identified key issue with this configuration is linked to the MB misalignment [1]. Under cycles of heat loads and transient high heat loads, the MB leading edges could be melted and induce molten material droplet emission [2]. Resulting surface damage could compromise plasma operation by changing the mechanical structure of MBs and reducing their lifetime. One effect of the tile misalignment was evidenced in the full-metal tokamak, Alcator C-Mod. During plasma operation, camera videos have shown an over-light emission of various leading edges of plasma facing components. These regions likely already melted during plasma operation were destabilized during disruptions and led to an emission of droplets across the vacuum chamber. Resulting typically rounded dust particles (splashes and spheres) were collected. Another characteristic is their large average size (50µm) compared to the size of dust produced in other tokamaks [3]. To reduce the emission of molten material droplets, a slight rotation (~1° tilt) of all the modules of the low outer divertor was done in 2015 in order to shadow their leading edges. The dust weight after the 2015 plasma campaign was from 3 to 6 times lower than the dust weight coming from the same modules in 2007. These results, added to the fact that the average energy injected in 2280 discharges in 2015 was 0.66 MJ/discharge against 2026 discharges in 2007 with 0.45MJ/discharge shows that less dust was produced in 2015. [1] R.A. Pitts, et al., Nucl. Mater. Energy 12, 60 (2017) [2] B. Bazylev, et al., Phys. Scr. T138, 014061 (2009) [3] C. Arnas, et al., Nucl. Mater. Energy 11, 12 (2017)

Speaker: Cecile Arnas

14:00 P4.1027 The EUROfusion JET-ILW pedestal database

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1027.pdf The EUROfusion JET-ILW pedestal database L. Frassinetti1, S. Saarelma2, F. Imbeaux3, P. Bilkova4, P. Bohm4, R. Fridström1, E. Giovannozzi5, M. Owsiak6, M. Dunne7, B. Labit8, R. Scannell2, J.C. Hillesheim2 and JET contributors9* 1 Division of Fusion Plasma Physics, KTH Royal Institute of Technology, Stockholm SE 2 CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, UK 3 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 4 Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic 5 ENEA, Fusion and Nuclear Safety Department, Via E. Fermi 45, 00044 Frascati, Italy 6 Poznan Supercomputing and Networking Center, IChB PAS, Noskowskiego 12/14, Poznan, Poland 7 Max-Planck-Institut für Plasmaphysik, Garching, Germany 8 Swiss Plasma Center (SPC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne,Switzerland 9 EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK * see X. Litaudon et al., Nuclear Fusion 57, 102001 (2017) To enhance the scientific output of multi-machine comparisons, EUROfusion has promoted the creation of several databases with common definitions and with a common platform. This work is an overview of the EUROfusion pedestal database of JET-ILW. The definitions of the pedestal quantities have been agreed among the EUROfusion machines AUG, JET-ILW, MAST-U and TCV, allowing future consistent multi-machine comparisons and scaling laws. The databases will be stored into the IMAS format (ITER integrated modelling and analysis suite) [1]. The JET-ILW pedestal database contains all the JET-ILW H-mode plasmas with stationary phases at least 0.5s long (longer than ≈2τE) and with good Thomson scattering data. The pedestal structure is determined using the pre-ELM profiles of the High Resolution Thomson Scattering [2] processed as described in [3]. From the point of view of the pedestal structure, the main parameters stored are: (i) height, (ii) width (iii) position of the maximum gradient, and (iv) maximum gradient of electron density, temperature and pressure, (v) separatrix density and (vi) normalized pressure gradient. Pedestal parameters are extracted by fitting the experimental data with both a mtanh function [4] and a combination of linear functions. In the JET-ILW database, the two fitting functions produce qualitatively similar results. Version 1 of the JET-ILW database contains the discharges till the C37 experimental campaign (end of 2016) with a total of ≈1200 entries. Figure 1 shows the scatter plot of Teped and neped in version 1. The database will be kept up to date. To complement the experimental data, the JET-ILW database contains the results of the peeling-ballooning stability analysis. This was done by self-consistent runs of ELITE [5] Figure 1. Pedestal temperature and density for the deuterium unseeded plasmas of the EUROfusion (using the bootstrap current from the Sauter JET-ILW pedestal database (version 1). Colors model [6]), which provide the normalized highlight the total input power. Circles: low-δ pressure gradient αcrit and the temperature Tecrit plasmas (δ<0.25). Triangles: high-δ plasmas expected by the P-B stability. (δ>0.25). The present work discusses both the technical aspects of the database (such as parameters definition and workflow) and the preliminary analysis, with particular emphasis on the comparison between experimental results and P-B stability predictions. References [1] F. Imbeaux et al., Nucl. Fusion 55 (2015) 123006. [4] R. Groebner et al., Nucl. Fusion 41 1789 (2001) [2] R. Pasqualotto et al., Rev. Sci. Instrum. 75, 3891 (2004). [5] S. Saarelma et al., Phys. Plasmas 22 056115 (2015) [3] L. Frassinetti et al., Rev. Sci. Instrum. 83, 013506 (2012) [6] O. Sauter et al., Phys. Plasmas 6 2834 (1999)

Speaker: Lorenzo Frassinetti

14:00 P4.1028 Preliminary research on the island divertor configuration by applying 3/1 RMP in J-TEXT

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1028.pdf Preliminary research on the island divertor configuration by applying 3/1 RMP in J-TEXT Nengchao Wang1, Y. Liang1, 2, 3, Xiaolong Zhang1, Jie Yang1, Qiming Hu4, Song Zhou1, Zebao Song1, Da Li1, Zhuo Huang1, Linzi Liu1, Chengshuo Shen1, Bo Rao1, Y. H. Ding1 and the J-TEXT team 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, Huazhong University of Science and Technology, Wuhan, China 2 Forschungszentrum Jülich, Jülich, Germany 3 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China 4 Princeton Plasma Physics Laboratory (PPPL), Princeton, USA *E-mail: wangnc@hust.edu.cn The island divertor configuration [1] was first proposed in 1977 for tokamak. It has been established successfully in various tokamaks, e.g. TEXTOR, and stellarators [2], such as W7-AS, LHD and recently in W7-X, leading to the impurity screening effect and the heat flux reduction on the target. In the recent campaign of J-TEXT tokamak, an experimental attempt have been made to form an island divertor configuration. An edge 3/1 island has been excited by applying the resonant magnetic perturbation (RMP) with dominate m/n = 3/1 component to a plasma with edge safety factor qa >~ 3. The 2/1 component of external RMP fields was kept at a low level to avoid exciting large 2/1 locked mode. Once the 3/1 island has been excited, the radial and poloidal profiles of the floating potential, the intensity of CIII radiation, the edge toroidal rotation varied significantly. The poloidal profiles of the floating potential measured at the limiters, varied during the formation of 3/1 island, indicating the impact of the 3/1 island on the footprints. In addition, the preliminary design for building a set of island divertor coils utilizing 4/1 island will also be discussed. [1] F. Karger and K. Lackner, Physcis letters A 61 (1977) 385 [2] R. König, et al., Plasma Phys. Control. Fusion 44 (2002) 2365

Speaker: Nengchao Wang

14:00 P4.1029 Manifold tracing for symplectic maps of magnetic field lines

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1029.pdf Manifold Tracing For Symplectic Maps Of Magnetic Field Lines D. Ciro, I. L. Caldas Institute of Physics, University of São Paulo, São Paulo, Brazil Invariant manifolds of unstable closed magnetic field lines (periodic saddles), organize the dynamics of chaotic field lines in magnetically confined plasmas. They are fundamental to understanding the structure of the chaotic field lines and provide insight into the mechanisms of transport at the plasma edge. In some situations, the geometry of the manifolds can be estimated through the mapping of a large collection of orbits close to the periodic saddle. However, without an ordering scheme and refinement this method is computationally expensive and limited in resolution. Here, we apply a recently proposed approximation technique [1], based on an intuitive geometrical decomposition of the manifolds in bare and fine details, for tracing the invariant manifolds of the unstable periodic orbits of the Ullmann Map, a symplectic map describing large aspect-ratio tokamaks perturbed by a magnetic limiter. The manifold tangles obtained for remnant internal islands near the last closed magnetic surface explain the field line stickiness and escape channels to the tokamak wall [2]. References 1- Efficient manifold tracing for planar maps. D. Ciro, T. Evans, I. L. Caldas. arXiv:1710.10140 (2018). 2- Escape patterns of chaotic magnetic field lines in a tokamak with reversed magnetic shear and an ergodic limiter. T. Kroetz, M. Roberto, E. C. Silva, I. L. Caldas, R. L. Viana. Physics of Plasmas 15, 092310 (2008).

Speaker: Ibere Luiz Caldas

14:00 P4.1030 Parameter dependence of small Edge Localized Modes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1030.pdf Parameter dependence of small Edge Localized Modes G.F. Harrer1 , E. Wolfrum2 , M.G. Dunne2 , P. Manz2 , M. Cavedon2 , P.T. Lang2 , T. Eich2 , B. Labit3 , F. Aumayr1 , the Eurofusion MST1 Team4 and the ASDEX Upgrade Team2 1 Institute of Applied Physics, TU Wien, Vienna, Austria 2 Max Planck Institute for Plasma Physics, Garching, Germany 3 Swiss Plasma Center, EPFL, Lausanne, Switzerland 4 see author list in H. Meyer et al. Nuclear Fusion 57 102014 (2017) The development of small Edge Localized Mode (ELM) scenarios is important to reduce the strain on plasma facing components. Such a scenario can be found at high density, close to double-null plasmas as small ELMs or type-II ELMs in ASDEX Upgrade, which are character- ized by a frequency fELM > 300 Hz and a low energy loss. Large type-I ELMs and small ELMs can occur simultaneously. While type-I ELMs can be described by a global peeling-ballooning model [1], the size and occurence of small ELMs is experimentally observed to depend for ex- ample on the density around the separatrix [2]. Experiments changing the edge density via different fuelling mechanisms and varying the plasma shape have been performed [3]. These experiments showed that small ELMs increase in size (divertor current amplitude) with the density at the separatrix, but they are reduced when the magnetic shear gets stronger. Both observations are in line with small ELMs being local ballooning modes driven by the pressure gradient and stabilized by magnetic shear. They cause transport and flatten the gradient region around the separatrix and thereby consequently nar- row the effective pedestal width. Because a narrower pedestal is more stable against global PB modes, the stability boundary is shifted towards higher pressure gradients and type-I ELMs do not occur. As both, the local pressure gradient and the magnetic shear, strongly influence the amplitude of small ELMs, a series of additional discharges at high triangularity and at high separatrix density has been performed varying the toroidal magnetic field at constant plasma current to vary the magnetic shear. The influence of the flux surface averaged and the local magnetic shear on the amplitude and frequency of small ELMs will be shown. References [1] J.W. Connor et al. Physics of Plasmas 5 2687 (1998) [2] H. Meyer et al. Nuclear Fusion 57 102014 (2017) [3] G.F. Harrer et al. Nuclear Fusion to be submitted (2018)

Speaker: Georg Friedrich Harrer

14:00 P4.1031 Li solution of the steady-state problem of tokamak in the light of the last experimental results

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1031.pdf 45 EPS Conference on Plasma Physics 13069 Li solution of the steady-state problem of tokamak in the light of the last experimental results S.V.Mirnov1,3,4, A.S.Dzhurik1, A.T.Komov4,V.B.Lazarev1, I.E. Lyublinski2,3, V.G.Otroshchenko1, A.N. Shcherbak1, A.N.Varava4, Ya. A.Vasina3, A.V.Vertkov2, A.V.Zaharenkov4, M.Yu. Zharkov2 1 JSC “SSC RF TRINITI” 108 840RussiaМoscowTroitsk Dep. Pushkovih St 12, 2 JSC «Red Star», 113230, Russia, Moscow, Elektrolitny dr. 1A, 3 NRNU MEPhI, 115409, Russia, Moscow, Kashirskoe sh.,31, 4 NRU MPEI, 111250, Russia, Moscow, Krasnokasarmennaya St.,14 Recent experiments made on tokamak T-11M [1] for the purpose of full-scale simulation of behavior of lithium, injected into the peripheral (SOL) region of tokamak for protection its first wall from the direct plasma-contact, forced us to bring some correction in the temperature operation limits of individual elements of a closed lithium circuit that implements this protection in the steady-state mode of tokamak. Its main elements are presented in figure: the lithium emitter and collector on the basis of capillary porous structure (CPS), the first wall with of Li-coated steel, and the system of D,T recovery from the lithium stream. It was found that the first wall of the steel chamber coated during discharge by lithium and heated over 350-400oC reflects to the plasma cord almost the whole entire flow of H+ and D+ which falls on the first wall. Thus the first wall can play role of a "mirror" in relation to both of them (and T in future) and prevent their gradual accumulation in the chamber of the tokamak. It is proposed to carry out the capture of D+ and T+, and its following removal from the camera by using of the liquid Li surface of CPS collectors in the temperature range of 200-300°C. To control the temperature of the collectors in the specified range assumed to apply both hot water and the recently developed cooling method by the dispersed gas-water flow formed by the special spray generator. The work supported by RSF grant № 16-19-10457 [1] A.N.Shcherbak, S.V.Mirnov e.a. 44 EPS Conf. on Plasma Phys. (2017, Belfast), P5 112

Speaker: Sergey Vasilievich Mirnov

14:00 P4.1032 High bandwidth electron temperature measurements in DIII-D divertor

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1032.pdf 45 EPS Conference on Plasma Physics 13103 High bandwidth electron temperature measurements in DIII-D divertor* D.L. Rudakov1, J.A. Boedo1, A.G. McLean2, J.G. Watkins3 1 University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0417, USA 2 Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA 3 Sandia National Laboratory, 7011 East Avenue, Livermore, CA 94550, USA For the first time electron temperature (Te) fluctuations have been measured in different regions of a tokamak divertor using a fast (100 kHz bandwidth) Langmuir probe based diagnostic. The diagnostic, recently installed on the fast reciprocating probe in the lower divertor [1], is based on the digital detection of harmonics in a single probe current spectrum, and is similar to that used on the mid-plane reciprocating probe in DIII-D [2]. Here we report the initial measurements of Te fluctuations in the divertor and compare their properties to those measured in the outboard SOL by the pre-existing diagnostic. Measurements were performed at the outboard divertor scrape-off layer (SOL) radially outside of the Outer Strike Point (OSP), private flux region, and inboard divertor SOL (inboard of the inner divertor leg) of Lower Single Null discharges. For this initial work, results concentrate on low-density low-confinement (L-mode) discharges with attached OSP, where the Te data from the new harmonic diagnostic are in reasonable agreement with the Divertor Thomson Scattering measurements. In all cases the relative (root-mean-square to mean) Te fluctuation levels in the divertor were between 0.3 – 1.0, which is higher than 0.2 – 0.5 measured in the same discharges in the outboard SOL by the mid-plane probe. Spectral characteristics of Te fluctuations vary with position in the SOL; comparisons between the divertor and outboard SOL are presented and discussed. The fluctuation spectra have measurable energy up to the bandwidth of the diagnostics (100 kHz) in both regions, while the frequency roll-off tends to be slower in the divertor compared to the outboard SOL. [1] J.G. Watkins, et al., Rev. Sci. Instrum. 68, 373 (1997) [2] D.L. Rudakov, et al., Rev. Sci. Instrum. 72, 453 (2001) ______________________________ *This material is based upon work supported by the U.S. Department of Energy under Award Number(s) DE- FG02-07ER54917, DE-FC02-04ER54698 DE-AC52-07N27344, and DE-NA0003525.

Speaker: Dmitry L. Rudakov

14:00 P4.1033 Generation of supersonic plasma flow in DiPS-2

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1033.pdf Generation of supersonic plasma flow in DiPS-2 I.J. Kang, M.-K. Bae, I.S. Park, S.H. Lee, S.J. Jeong, K.-S. Chung, Department of Electrical Engineering, Hanyang University, Seoul, South of Korea Flow measurements near X-points including E × B shear velocity and supersonic flow are still under debate [1, 2] in fusion devices, although the progress of edge plasma physics has been advanced in recent years. Various kinetic and fluid models have been developed on plasma flow phenomena at fields of fusion plasmas. However, subsonic plasma flow has been mostly studied for verification of models, which requires further verification for supersonic plasmas. Also, the generation and measurements of supersonic plasma flow have been studied at pulsed plasma system or transient phenomena, which are still insufficient in steady state plasma conditions, even. In this experiments, a concept of ion extraction system [3] has been adopted to generate supersonic plasma flows (M∞ > 1) at weakly magnetized plasma in steady state condition. A cylindrical ion extraction electrode of stainless steel, which has a diameter = 5 cm and an axial length = 4 cm, was used. In test for generation of supersonic plasma flow, the first result on the ion velocity distribution with supersonic plasma flow ( M∞ = ~ 1.2) was obtained in a capacitively coupled plasma with electron temperature (Te) ~ 2 eV and plasma density (ne) ~ 1010 cm-3 by using Mach probe. Ion extraction system was applied to a linear plasma device called DiPS-2 (Divertor Plasma Simulator - 2: length = 3560 cm, diameter = 20 cm, source = LaB6 cathode, average density ~ 1011 - 1013 cm-3, Te ~ 1 - 20 eV for Ar plasmas) [4]. To analyze drift velocity in supersonic plasma flow in terms of discharge currents and biased voltages to ion extraction electrode, a laser induced fluorescence (LIF) system was adopted with measurement of Mach probe. The LIF system composes of a tunable diode laser with a master oscillator power amplifier (MOPA), which has typical ouput power = 10 - 100 mW, line width = 1 MHz, coarse tuning range = 665 - 675 nm with a rotating grating, fine tuning range = 0.45 nm with piezo-electric actuator control from 0 to 100 Volt, and a mode-hop free tuning region > 16 GHz, with current coupling method, to pump Ar II transition 3d4F7/2 metastable level to the 4p4D5/2 level at 668.43 nm. The 442.60 nm fluorescence light emitted from 4p4D5/2 level to 4s4P3/2 level was collected to determine drift velocity in supersonic plasma flow. For validity of experimental results on supersonic plasma flow, LIF data was compared with Mach probe results with various calibration factors introduced from Mach probe theory. [1] Y. Nishimura et al., Contrib. Plasma Phys. 44 (2004) 194. [2] N. Asakura et al., J. Nucl. Mater. 363 (2007) 41. [3] Y. Nambu, J. Plasma Fusion Res. SERIES 8 (2009) 920. [4] I. J. Kang et al., Curr. Appl. Phys. 17 (2017) 358.

Speaker: In Je Kang

14:00 P4.1034 An exploration of a low temperature regime in EDGE2D-EIRENE simulations of JET ITER-like wall L-mode discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1034.pdf An exploration of a low temperature regime in EDGE2D-EIRENE simulations of JET ITER-like wall L-mode discharges K D Lawson1, M Groth2, D Harting1, S Menmuir1, D Reiter3, S Brezinsek3, G Corrigan1, C F Maggi1, A G Meigs1, S Wiesen3 & JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 2 Aalto University, Otakaari 1, Espoo, 02150, Finland 3 Forschungszentrum Jülich Gmbh, Institut für Energie- und Klimaforschung – Plasmaphysik, 52425 Jülich, Germany JET with its ITER-like wall (ILW) of Be in the main chamber and W in the divertor is ideally suited to gain understanding of the behaviour of the plasma edge and divertor, which is essential for predicting the performance of next-step machines such as ITER. Simulations by Groth et al. [1] of L-mode discharges run during JET-ILW campaigns and the previous JET-C campaigns, in which the plasma-facing surfaces were predominately C, have consistently shown a shortfall in the radiated power below that measured by bolometry, this bringing into question the predictions for the radiated power and cooling of a radiative divertor in a next step-machine. A similar result is found for unseeded ELMy H-mode discharges by Järvinen et al. [2]. A series of JET-ILW L- mode discharges, which reach detachment, provide a stringent test of the simulations in that most (~90%) of the radiated power from the divertor is due to atomic and molecular D, with impurities only playing a small role. In EDGE2D-EIRENE simulations, the molecular contribution is, typically, only ~10-15% and these results suggest that the simulated Te is too high throughout the divertor volume, in particular not reaching the very low Te (~1eV) required to give significant atomic D radiative recombination and high molecular densities with their associated power losses, this being especially so near the inner divertor target [3]. To test the sensitivity of the simulated temperature to the atomic and molecular power loss terms, these were artificially varied. A sensitivity to small changes (a few per cent) in the atomic power loss term, within the expected accuracy of the controlling atomic physics, was found to lead to a step down or transition in the temperature with increasing power loss [4]. This low temperature regime is explored by determining the temperature sensitivity to the power losses within particular temperature ranges. To understand better the acceptable variation of the D emission at different temperatures a reassessment of the D atomic data has been carried out, in particular to determine the likely accuracy of the data relating to collisional excitation, ionization and recombination. When combined with recently completed sensitivity calibrations for a VUV survey and a poloidally scanning VUV spectrometer [5] they will enable line-of-sight measurements of D line emission and consequently the power radiated by D to be estimated. The use of ratios of the line emission from low n shells, which measured along a divertor view are experimentally found to be independent of temperature, together with the absolute measurements of the D radiation and line intensities will be used to guide the simulations in order to achieve a more satisfactory agreement with the bolometric measurements of radiated power. [1] Groth et al., 2013, Nuc. Fus., 53, 093016 [2] Järvinen et al., 2015, JNM, 463, 135 [3] Lawson et al., 2015, JNM, 463, 582 [4] Lawson et al., 2017, NME, 12, 924 [5] Lawson et al., 2012, Rev. Sci. Instrum, 83, 10D536 *See the author list of X. Litaudon et al., 2017, Nucl. Fusion, 57, 102001

Speaker: Kerry David Lawson

14:00 P4.1035 JET ITER-like and JET Carbon wall discharges: 2 different scaling for the frequency of type I ELMs. Consequences for the pedestal structure.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1035.pdf JET ITER-like and JET Carbon wall discharges: 2 different scaling for the frequency of type I ELMs. Consequences for the pedestal structure. P. Devynck1 and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CEA, IRFM, F-13108 St. Paul-lez-Durance cedex, France We compare the results of the scaling previously obtained for the frequency of type I ELMs in JET ITER-like wall ( ILW) with new results in JET carbon wall obtained over a database of 270 shots. The frequency scaling in JET ILW has been found to be a linear function of Np/dNp [1] where Np is the pedestal density and dNp is the density drop of the pedestal after the ELM crash. We find that in JET carbon wall discharges; this is no more the case. The frequency scaling is a linear function of Psep/dWp, where Psep is the power through the separatrix and dWp is the energy drop after the ELM crash. Such a result is in agreement with what has been found in the literature [2]. We propose a simple interpretation for these two different scaling. After the ELM crash, energy and density are expelled from the plasma and must be recovered before the next ELM crash can be triggered. In both cases, the recovery is the result of an imbalance between source terms and outward transport. For the recovery of the energy, the source term is the additional heating (Psep) while for the density recovery the source term is provided by the neutrals fueling the plasma. These two processes occur on different time scales and the slowest one will set the frequency scaling of the ELMs. In the case of JET carbon wall, it is speculated that the wall releases during the discharge a very high flux of trapped particles towards the plasma providing a strong fueling. The density is faster than the energy recovery and one must wait for the additional heating to rise the temperature to the threshold pressure gradient. In the case of JET ILW, the situation is reversed. The wall does not outgas anymore and only the recycling and gas fueling are available to feed the plasma. The top pedestal temperature saturates and one must wait for the density to reach the peeling ballooning threshold pressure gradient. We expect the competition between these two processes to have some consequences for the pedestal structure. In carbon wall, the pedestal density will reach first the maximum allowed by the instabilities and a lower temperature will be sufficient to reach the threshold pressure gradient for the ELM crash. In ILW, it will be the opposite. As a result for the same pedestal pressure and pressure gradient, density and temperature are expected to be different in the two machines. A very simplified simulation of the competition between these two processes, allows recovering this behavior. Additionally we show that the coupling between these two nonlinear processes through the pressure can generate in some cases the appearance of several mixed frequencies for the ELMs. [1]P. Devynck et al. Plasma Phys. Control. Fusion 58 (2016) 125014 (9pp) [2] H. Zhom, Plasma Phys. Control. Fusion 38 (1996) 105–128 • See the author list of X. Litaudon et al., Nuclear Fusion 57, 10 (2017)

Speaker: Pascal Devynck

14:00 P4.1036 Analysis of Wendelstein 7-X divertor load symmetrization

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1036.pdf Analysis of Wendelstein 7-X divertor load symmetrization S. A. Lazerson1 , S.A. Bozhenkov2 , M. Otte2 , Y. Gao3 , H. Niemann2 , A. Ali2 , P. Drewelow2 , M. Jakubowski2 , F. Pisano4 , A. Puig Sitjes2 , T. Andreeva2 , V. Bykov2 , M. Endler2 , and the W7-X Team2 1 Princeton Plasma Physics Laboratory, Princeton, USA 2 Max-Planck Institut für Plasmaphysik, Greifswald, Germany 3 Forschungszentrum Jülich, Jülich, Germany 4 University of Cagliari, Cagliari, Italy The achievement of long pulses in the first divertor campaign (OP1.2a) on Wendelstein 7-X (W7-X) required the development of trim coil scenarios which ensured heat load symmetry among the ten divertor modules. Application of magnetic fields from these five copper coils located outside the cryostat, allowed actuation of the n = 1 components of the error fields. A series of compass scans were performed where the amplitude of the applied n = 1 field and phase (relative to the device) were varied [1]. The corresponding change in divertor heat loads were measured using thermocouples located in the carbon divertor tiles and through a set of infrared camera measurements. These scans were used to develop a map of the divertor asym- metry allowing prediction of trim coil currents which best symmetrize the divertor heat loads. This method was employed to characterize the correcting field for many of the magnetic con- figurations produced by the superconducting coil set. Correction was found to require around 10% the rated trim coil capacity, confirming previous limiter results that error fields were small [2, 3, 4, 5]. Comparison with flux surface measurements suggests that error fields comprise the majority of the symmetry breaking phenomena. From this we infer that the divertor structures themselves are well aligned and that any misalignment is small and easily correctible by appli- cation of trim coil currents. Assessments of the ten in-vessel control coils capability to correct both n = 1 and n = 2 fields are presented. References [1] S.A. Lazerson et al., Plas. Phys. Cont. Fusion, (submitted) (2018) [2] T.S. Pedersen et al., Nature Comm. 7 (2016) [3] S.A. Lazerson et al., Nuclear Fusion 56, 10 (2016) [4] S.A. Lazerson et al., Nuclear Fusion 57, 4 (2017) [5] S.A. Bozhenkov et al., Nuclear Fusion 57, 12 (2017)

Speaker: Samuel Aaron Lazerson

14:00 P4.1037 Optimizing 3D spectra for rotation control

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1037.pdf Optimizing 3D spectra for rotation control N.C. Logan1, S.R. Haskey1, B.A. Grierson1, R. Nazikian1, C. Chrystal2, C. Paz-Soldan2 1 Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA 2 General Atomics, PO Box 85608, San Diego, CA 92186, USA A new matrix formulation utilizing the multi-modal plasma response to optimize multi-coil spectra for desired neoclassical toroidal viscosity (NTV) torque profiles has been developed in the Generalized Perturbed Equilibrium Code (GPEC) and applied in experimental optimization on the DIII-D tokamak. The new GPEC formulation [1] solves the single-fluid quasi-neutral anisotropic pressure perturbed equilibrium in the first gyro-radius ordering, representing the nonlinear torque as a function of coil array currents; τ(ψ) = Ic · T(ψ) · Ic. With this representation in hand, the optimal coil configuration for localized torque between any two surfaces ψ1 and ψ2 is immediately calculable as the first eigenvector and of Tb-1[T1 - T2], where Tb is the boundary matrix. A single perturbed equilibrium calculation thus provides the optimal coil configurations for the maximum, minimum, core localized, and edge localized NTV torque profiles. Experiments have validated this model in nonresonant field space, providing accurate predictions of quiescent (having little impact on density and energy confinement) braking profiles that could be used in rotation control algorithms with little impact on the particle or energy confinement. Large edge resonant magnetic perturbations, however, caused large density pumpout not accounted for in the neoclassical model, significantly distorting the equilibrium from the perturbative model prediction. The impact of the pumpout is quantified here and used to motivate future work using integrated 3D (GPEC) and 2D (TRANSP) transport models for full momentum profile evolution predictions. This experimental application and test of the new GPEC torque matrix predictions represents a significant step in building successful error field correction models towards new practical applications for rotation profile control. The torque profile manipulation with the poloidal 3D field spectrum is a direct application of the multi-mode phenomena [2, 3] for concrete performance enhancements, and validated predictions provide a path towards reduced rotation profile control schemes for the optimization of tokamak stability and performance. This work is supported by US DOE contracts DE-AC02-09CH11466 & DE-FC02-04ER54698. [1] J.-K. Park and N.C. Logan, Physics of Plasmas 24, 32505 (2017). [2] C. Paz-Soldan, et al., Physical Review Letters 114, 105001 (2015). [3] N.C. Logan, C. Paz-Soldan, J. Park, and R. Nazikian, Physics of Plasmas 23, 56110 (2016).

Speaker: Nikolas Logan

14:00 P4.1038 Electromagnetic global gyrokinetic simulation for the analysis of MHD instabilities and turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1038.pdf Electromagnetic global gyrokinetic simulation for the analysis of MHD instabilities and turbulence A. Ishizawa1, K. Imadera1, Y. Nakamura1, Y. Kishimoto1 1 Graduate School of Energy Science, Kyoto University, Uji, Janan Sustaining burning plasmas requires good confinement of energetic particles produced by fusion reaction and of bulk plasmas heated by these particles. In order to achieve good confinement of them simultaneously, we need to understand turbulent transport of bulk plasma and transport of energetic particles due to macro-MHD instability such as toroidal Alfven eigen-modes. The electromagnetic turbulence dominates bulk plasma transport at finite beta [1] and interacts with MHD instabilities, and their saturation levels depend on their mutual interactions [2], and thus understanding interaction between MHD instabilities and turbulence is one of the critical issues. Our study is aim to understand MHD instabilities in burning plasmas, which are influenced by high energy particles produced from fusion reaction. In addition, we will study the MHD instabilities interacting with micro-turbulence through multi-scale nonlinear interactions. We are constructing a first principle simulation code of magnetically confined plasmas to evaluate the transport of energetic particles and of bulk plasmas simultaneously and self-consistently by means of numerical simulations of the MHD instabilities and micro-turbulence. The code is developed by extending GKNET [3] which is a global electrostatic gyrokinetic simulation code, so that the new code is applicable to the analysis of electromagnetic instabilities. The code enables us to investigate electromagnetic drift-wave instabilities such as the electromagnetic ion temperature gradient (ITG) modes mode and electromagnetic trapped electron modes (TEM) as well as MHD instabilities such as kinetic ballooning modes (KBM) and the tearing mode. We will evaluate the transport of energetic particles and bulk plasmas due to MHD instabilities and micro-turbulence, and invesitigate nonlinear interaction between them by using the new code. [1] A. Ishizawa, S. Maeyama, T.-H. Watanabe, et.al., J. Plasma Phys., (2015) 435810203. [2] A. Ishizawa and N. Nakajima, Nucl. Fusion, (2009) 055015. [3] K. Imadera, Y. Kishimoto, et.al., IAEA-FEC, (2014).

Speaker: Akihiro Ishizawa

14:00 P4.1039 Exciting of MHD modes during the penetration of massive gas jet on J-TEXT tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1039.pdf Exciting of MHD modes during the penetration of massive gas jet on J-TEXT tokamak Y. Huang1, Z. Y. Chen1,*, Qiming Hu2,*, Mingxiang Huang1, Y N Wei1, Daojing Guo1, Z.J.Yang1, X.M.Pan1,Tong Wang1, Z. F. Lin1, R. H. Tong1, W. Yan1, Z.P.Chen1, Y. H. Ding1, Y. Liang1 and J-TEXT Team 1 International Joint Research Laboratory of Magnetic Confinement Fusion and Plasma Physics, State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China 2 Princeton Plasma Physics Laboratory, Princeton NJ 08543-0451, USA *Corresponding author: Z.Y.Chen and Qiming Hu E-mail: zychen@hust.edu.cn and qhu@pppl.gov The massive gas injection and the shattered pellet injection of a large amount of impurities is essential to the mitigation of disruptions on large scale tokamaks. The deposition of impurities to the center of plasma is the key for the radiation of plasma energy and runaway suppression. The penetration of gas jet has been found to be limited by the q=2 surface. The interaction of the gas jet with the rational surfaces has been studied by scan the plasma current. Experimental results show that injection of massive argons can cool the plasma from edge to core region and the cooling process is accompanied by different magnetohydrodynamics (MHD) modes when the gas jet reach corresponding rational surface. It is observed that with different edge safety factors, electron density, gas injection can induce different poloidal mode at first. Then the poloidal mode will traverse lower m (poloidal mode number) MHD activities until 2/1 mode initiated and thermal quench (TQ) was onset. The experimental results show that the penetration of gas jet across the rational surfaces is faster in the plasmas with pre-existing large 2/1 tearing mode, which indicates that 2/1 mode plays an important role in the penetration process.

Speaker: Yuan Huang

14:00 P4.1040 Impact of ECCD on Alfvén Eigenmodes in the TJ-II stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1040.pdf Impact of ECCD on Alfvén Eigenmodes in the TJ-II stellarator. Á. Cappa1 , E. Ascasíbar1 , F. Castejón1 , J.M. García Regaña 1 , M. García Muñoz 2 A. González-Jerez3 , D. López-Bruna1 , M. Liniers1 , N. Marushchenko4 , M. Ochando1 J.L. Velasco1 , S. Yamamoto5 1 Laboratorio Nacional de Fusión, Madrid, Spain 2 Universidad de Sevilla, Sevilla, Spain, 3 Universidad Complutense de Madrid, Madrid, Spain 4 Max Planck Institut fur Plasmaphysik, Greifswald, Germany 5 Institute of Advanced Energy, Kyoto University, Japan The impact of Electron Cyclotron Current Drive (ECCD) on NBI-driven modes has been investigated in the TJ–II low shear stellarator. Experimental results show that a small amount of EC driven current may modify dramatically the spectrum of observed modes (Fig. 1). Applying 240 kW of on-axis ECRH power in counter-ECCD configuration (N|| = +0.2) provokes ∼ 0.5 kA reduction in plasma current. This mild reduction of current is accompanied by a strong change in the behaviour of alfvénic magnetic fluctuations [1]. Changes in rotational transform profile (ι), having a strong influence on the Shear Alfvén Spectrum (SAS) of the device, are the main candidate to explain the observations. The high sensitivity of the SAS structure on ι(ρ) suggests that the interpretation of the re- sults should be made considering all the rele- vant contributions to the plasma current (NBCD, ECCD and to a lesser extent, the boostrap current Iboot ). For modelling purposes, the STELLGAP and AE3D codes are used to calculate the spec- trum and spatial structure of possible gap modes in several shots with different values of the total current. No experimental information on the cur- rent profile is available and therefore, the input Figure 1: Spectrogram of magnetic fluctuations VMEC magnetic equilibrium, which should be with (bottom) and without ECCD (top). consistent with the plasma current profile, will be obtained using a rough approximation to the unknown NBCD profile and a rigorous theoret- ical calculation of the ECCD profile (TRAVIS) and the bootstrap current profile. References [1] S. Yamamoto et al., 21th International Stellarator-Heliotron Workshop, Kyoto, Japan (2017).

Speaker: Álvaro Cappa

14:00 P4.1041 Improvements of magnetic diagnostic systems and bootstrap current characterization at the stellarator Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1041.pdf Improvements of magnetic diagnostic systems and bootstrap current characterization at the stellarator Wendelstein 7-X K. Rahbarnia1, T. Andreeva1, U. Neuner1, H. Thomsen1, J. Schilling1, J. Svensson1, N. Lauf1, J. Geiger1, Y. Turkin1, T. Bluhm1, M. Zilker1, B.B. Carvalho2, D. Hathiramani1, M. Endler1 and the Wendelstein 7-X Team 1 Max Planck Institute for Plasma Physics, 17491 Greifswald, Germany 2 Instituto de Plasmas e Fusao Nuclear Instituto Superior Tecnico, Lisbon, Portugal The second operational phase (OP1.2a) at the stellarator Wendelstein 7-X (W7- X) took place from August to December 2017. Significant improvements of the magnetic diagnostic system have been implemented compared to the previous operational phase. About 90% of the installed sensors were put into operation, which include 2 diamagnetic loops, 6 Rogowski coil arrangements, 36 saddle coils and 125 Mirnov coils, distributed in all 5 modules of W7-X. Measured raw data is directly streamed into the W7-X archive. After each plasma pulse automatized data analyzing software calculates magnetic fluxes of all sensors, as well as the compensated diamagnetic energy and plasma current. Based on this data source, implemented in the MINERVA framework, the reconstruction of magnetic equilibria has been developed using the Variational Moments Equilibrium Code VMEC. Plasma pulses with a duration of up to 20s in combination with plasma density feedback allowed the application of the magnetic diagnostics for studies of the bootstrap current which are complemented by theoretical predictions. In these studies the minimization of bootstrap currents in certain magnetic field configurations could be confirmed. Additionally, a plasma heating interlock signal, which is generated from the measurement signal of the diamagnetic energy has been tested and prepared for the upcoming operational phases.

Speaker: Kian Rahbarnia

14:00 P4.1042 Fast and reliable reconstruction of the current distribution at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1042.pdf Fast and reliable reconstruction of the current distribution at ASDEX Upgrade R. Fischer1 , A. Bock1 , A. Burckhart1 , S.S. Denk1 , M. Dunne1 , O. Ford1 , L. Giannone1 , A. Gude1 , M. Maraschek1 , R.M. McDermott1 , A. Mlynek1 , E. Poli1 , M. Rampp2 , D. Rittich1 , M. Weiland1 , M. Willensdorfer1 , and the ASDEX Upgrade Team 1 Max-Planck-Institutfür Plasmaphysik, Boltzmannstr. 2, D-85748 Garching, Germany 2 Max Planck Computing and Data Facility, Giessenbachstr. 2, D-85748 Garching, Germany Fast and reliable reconstruction of the current distribution is of particular interest for exper- imental on-the-fly plasma scenario development. This is of major importance for the develop- ment of advanced scenarios where fine-tuning of the q-profile using heating and current-drive actuators is desired. The goal is to reconstruct the most reliable equilibrium achievable from all available experimental data and modelling constraints before the setting of the next plasma discharge has to be decided. The number of plasma discharges for the typically challenging per- formance optimization is often large but required to be as small as possible for budget reasons. At ASDEX Upgrade the goal is to have the most reliable current and q-profiles within 20 min to be available for plasma parameter optimization before the next discharge. The first 10 min after the previous discharge are foreseen for kinetic profile reconstruction employing an integrated data analysis (IDA) approach of all profile diagnostics available shortly after the previous plasma discharge (not necessarily in real-time). The second 10 min are ded- icated for equilibrium reconstruction with a temporal resolution of 5 ms for a typical plasma discharge of 8 s. The equilibrium reconstruction is based on the coupling of a Grad-Shafranov (GS) solver with the integration of the current diffusion (CD) equation employing a physical coupling of neighboring time points. The ingredients are reliable electron and ion temperature and density profiles from the IDA approach, fast-ion pressure and driven current profiles from the recently developed RABBIT code, the electron-cyclotron driven current from the recently upgraded TORBEAM code, an improved bootstrap-current evaluation, all magnetic data of an extended set of poloidal-field and diamagnetic-loop measurements, internal current measure- ments from (imaging)MSE and polarimetry, and an automized sawtooth detection algorithm. The fast and reliable current reconstruction is achieved with the equilibrium code IDE paral- lelized using an OpenMP scheme within the Grad-Shafranov solver, within the RABBIT code of up to 8 NI-beams and within the TORBEAM code. On top of this, an MPI (Message Passing Interface)-based approach is applied for parallel calculations of the GS-solver response ma- trix and for parallel TORBEAM evaluations of up to 8 EC-beams for the CD-integration. This enables parallel calculations on up to approx. 40 CPU cores of a server-class machine.

Speaker: Rainer Fischer

14:00 P4.1043 JOREK simulations of Shattered Pellet Injection with high Z impurities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1043.pdf JOREK simulations of Shattered Pellet Injection with high Z impurities D. Hu1 , E.Nardon2 , G.T.A. Huijsmans1,2 , M. Lehnen1 . 1 ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France 2 CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France The effect of Shattered Pellet Injection (SPI) using pure impurity pellets on the electron density and MHD modes is studied in the reduced MHD model of the JOREK code with a JET L-mode equilibrium as the target plasma and an injection configuration resembling that of the upcoming JET SPI system [1]. The pellet fragment ablation is described by considering the Neutral Gas Shielding (NGS) model for each fragment [2], and the fragment size distribution is set according to the Statistical Fragmentation Model [3]. The momentum transfer between the neutrals and the ionised plasma due to charge-exchange is assumed to be frequent enough so that the neutrals are convected along with the plasma flow. A simplified model based on coronal-equilibrium is used for the impurity radiation function, which, despite the fact that the plasma is not really in coronal-equilibrium, results in only small deviation from more detailed analysis so long as the plasma is cooled down fast enough. The impact of local radiation cooling at the rational surfaces as well as the global current contraction are investigated and their impact on MHD instability will be discussed. The MHD spectrum excited by the impurity SPI is qualitatively compared with that of the deuterium one for which only dilution cooling is present. The difference in injection penetration and assi- milation as a result of the difference in MHD activity will be compared. Also, the radiation asymmetry of SPI is investigated and compared to that of a Massive Gas Injection (MGI) case. Furthermore, the impact of injection parameters such as the injection velocity and the cha- racteristic fragment size on the penetration and assimilation is demonstrated by varying the injection parameters. The effect of SPI for different target equilibria, such as those with diffe- rent q profiles or pre-injection thermal energy, will also be discussed. Such analysis will provide insight for the preferable SPI parameters for the future ITER disruption mitigation system. References [1] L. Baylor, “Developments in Shattered Pellet Technology and Implementation on JET and ITER”, PPPL TSD workshop report, 2017. (http://tsdw.pppl.gov/Talks/2017/Lexar/Monday%20Session%201/Baylor.pdf) [2] V. Yu. Sergeev, O. A. Bakhareva, B. V. Kuteev and M. Tendler, Plasma Phys. Rep. Vol. 32, No. 5, 363 (2006); [3] P. Parks, “Modeling Dynamic Fracture of Cryogenic Pellets”, GA report GA-A28352, 2016. (https://www.osti.gov/scitech/servlets/purl/1344852)

Speaker: Di Hu

14:00 P4.1044 Using rotating current ribbons to model MHD: the EHO

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1044.pdf Using rotating current ribbons to model MHD: the EHO Emilia R. Solano1, K. Burrell2, T. Strait2, T. Evans2, S. Haskey3, T. Osborne2, X. Chen2, B. S. Victor4, C. P. von Thun5,6, DIII-D team# and JET Contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK. 1 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain; 2General Atomics, San Diego, California 92186-5608, USA;3Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543-0451,U.S.A.;4Lawrence Livermore National Laboratory, Livermore, California 94550, USA; 5Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, 52425 Jülich, Germany; 6EUROfusion PMU, Culham Science Centre, Abingdon, United Kingdom. From the earliest studies of MHD modes [1] it was assumed that field aligned current distributions might be responsible for the magnetic fluctuations observed, but now analysis is typically carried out in terms of mode numbers n (toroidal) and m (poloidal) of the measured magnetic field fluctuations, taking into account toroidicity [2,3] and plasma shape [4] as corrections on an effective poloidal angle. Here we present a model of the MHD instability based on Mirnov’s initial assumption, now taking into account the plasma shape. We assume there is ribbon of current parallel to the magnetic field at a rational surface in the plasma. We reconstruct the plasma equilibrium with kinetic constraints, trace candidate rational field lines with the TRIP3D code [5], and compute the field from a unit current along a field line spinning past each of the Mirnov probes, matching the frequency of the observed modes and their n number. The comparison of the amplitude and shape of the synthetic signals with measured dB/dt informs us of the accuracy of the reconstructed equilibrium, the width of the ribbon, and the applicability of this model to the mode observed. Mode frequency is matched against measurements of the main ion rotation profile, to obtain mode location and compare with the q profile. This procedure can be used to model solitary modes, such as the Outer Mode in JET [6], and possibly some EHOs in DIII-D [7]. The preliminary results obtained so far are promising when compared to [8]. This material is based upon work supported by the Department of Energy under Award Number DE-FC02-04ER54698. [1] S.V. Mirnov, I.B. Semenov, Soviet Atomic Energy Vol.30, 1, 22 (1971); [2] V.G. Merezhkin, Sov. J. Plasma Phys. 4, 152 (1978); [3] O. Klüber et al., Nucl. Fus. 31 907 (1991); [4] D. Testa et al., Rev. Sci. Inst. 74, 1694 (2003); [5] T.E. Evans et al., Phys. Plasmas 9, 4957 (2002); [6] E.R. Solano et al., Phys. Rev. Lett. 104, 185003 (2010) [7] K. H. Burrell et al., Physics of Plasmas 8, 2153 (2001); [8] E J Strait, Rev. Sci. Inst. 77, 023502 (2006) # See the author list of “W.M. Solomon 2017 Nucl. Fusion 57 102018” * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″

Speaker: Emilia R. Solano

14:00 P4.1045 Alfvén eigenmode driven by alpha particles and NBI energetic particles

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1045.pdf Alfvén eigenmode driven by alpha particles and NBI energetic particles L. García1 , J. Varela2 , D.A. Spong2 and Y. Todo3 1 Universidad Carlos III de Madrid, 28911 Leganés, Madrid, Spain 2 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 3 National Institute for Fusion Science, Toki, Gifu, 509-5292, Japan Alfvén eigenmodes (AE) can be destabilized by populations of energetic particles (EP). We use a linearized gyrofluid model to investigate the properties of the instabilities driven by ener- getic particles in ITER and LHD. The model consists of the reduced MHD equations in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles [1]. Landau damping and resonant destabilization effects are included using a closure relation [2]. In the case of ITER, we consider two energetic particle sources: neutral beam injection (NBI) and alpha particles. The results show that the AEs are mainly destabilized by alpha particle drive. In addition, modifying the NBI injection intensity, beam energy or energetic particle den- sity profile only slightly changes the AE growth rate and frequency. The combined effect of alpha and NBI energetic particles leads to AEs with lower growth rates compared with AEs destabilized by NBI or alpha energetic particles individually, indicating that the instability Lan- dau damps on the lower energy NBI population. The AEs destabilized are n > 11 toroidal AE (TAE) localized in the reverse shear region (n is the toroidal number) showing a larger toroidal coupling compared to low-n TAE (n < 11), that are stable. In the case of LHD, the sources are two neutral beam injectors with different injection ener- gies. For low density / magnetic field discharges, an n = 1 TAE is stabilized if one of the NBI lines is deposited off axis and the EP density profile is flatter compared to the other EP species, although lower growth rates are observed if the energy of one NBI line is smaller than the other. Including two fluid effects in the LHD case leads to the destabilization of Beta Acoustic AE (BAAE). Adding helical coupling effects in the LHD case leads to a stronger damping in multi- NBI simulations for the n = 2, 8, 12 helical family and weaker damping for the n = 1, 9, 11 helical family compared to simulations with only toroidal couplings. References [1] J. Varela, D.A. Spong and L. Garcia, Nucl. Fusion 57, 046018 (2017) [2] D.A. Spong, B.A. Carreras and C.L. Hedrick, Phys. Plasmas B 4, 3316 (1992)

Speaker: Luis Garcia

14:00 P4.1046 Dependence of the shattered-pellet-mitigated thermal quench radiation efficiency on the plasma thermal energy in DIII-D with uncertainties derived from disruption energy flow models

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1046.pdf Dependence of the shattered-pellet-mitigated thermal quench radiation efficiency on the plasma thermal energy in DIII-D with uncertainties derived from disruption energy flow models R. Sweeney1, R. Raman2, N. Eidietis3, J. Herfindal4, E. Hollmann5, D. Hu1, M. Lehnen1, D. Shiraki4, J. A. Snipes1 1 ITER Organization, Rte. de Vinon-sur-Verdon, 13067 St. Paul-Lez-Durance, France 2 University of Washington, Seattle, Washington, USA 3 General Atomics, P.O. Box 85608, San Diego, CA 92186, USA 4 Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, USA 5 University of California-San Diego, 9500 Gilman Dr., La Jolla, CA 921093, USA Experiments were conducted on DIII-D using the shattered pellet injection (SPI) system to study how the required quantity of neon for full thermal quench (TQ) mitigation changes with thermal energy. A super H-mode discharge was used and terminated with the SPI as the thermal energy reached Wth=1.9 MJ. The radiation efficiency (Wrad,th/Wth) as a function of injected neon quantity for this discharge will be shown and compared with the previously investigated Wth=0.75 MJ discharge [Shiraki et al., Phys. Plasmas, 2016]. The change in the required neon quantity for full TQ mitigation will be compared in the high and low energy cases, and implications for the ITER disruption mitigation strategy will be discussed. To determine this required neon quantity, the fraction of thermal energy radiated is investigated using the fast diode arrays and the foil bolometer arrays. The fast diode arrays can temporally resolve the radiation flash during the TQ, but an estimation of the amount of magnetic energy dissipated during the TQ is required. The relatively low temporal resolution of the foil bolometers requires integrating both the radiated thermal and magnetic (Wmag) energies, but requires modelling the fraction of Wmag dissipated by the vessel and other conductors in close proximity to the plasma, and requires an estimate of the fraction of Wmag that is not radiated. For proper energy accounting, a cylindrical 0D model is developed that describes the evolution of Wmag during the TQ and current spike. The measured current spikes will be compared with this 0D model, and the implications on the total radiated energy throughout the disruption will be discussed. Separately, a simple toroidal wire loop model is developed to describe the work done by the vertical field during the major radial contraction. Implications of the dissipated vertical field energy on the predicted radiation efficiency will be discussed. This material is based upon work supported in part by the U.S. Department of Energy under DE-FC02-04ER54698.

Speaker: Ryan Sweeney

14:00 P4.1047 Parametric dependence analysis of disruption forces in tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1047.pdf Parametric dependence analysis of disruption forces in tokamaks F. Villone1, V. Pustovitov2, G. Rubinacci1 1 Consorzio CREATE, DIETI, Università degli Studi di Napoli Federico II, Italy 2 National Research Centre Kurchatov Institute, pl. Kurchatova 1, Moscow 123182, Russia Disruptions are among the fundamental issues to be tackled in future tokamaks [1]. With rapid transfer of the magnetic energy, they generate significant (eddy and halo) currents in the conducting structures. Interaction of these currents with the strong magnetic field present in the tokamaks is expected to produce substantial electromagnetic forces and torques, which might challenge even the integrity of the device elements. Consequently, theoretical and experimental studies on disruption modelling, prediction, avoidance and mitigation are currently in progress. In this paper, we investigate the dependence of the disruption-induced global electromagnetic forces on various parameters (resistive wall time, plasma current quench time, vertical instability growth rate and stability margin). This is a highly debatable area with contradictory indications and huge scatter of the results [2-5]. The modelling tool that we use is the CarMa0NL code [6], solving evolutionary axisymmetric equilibrium equations in the plasma, coupled to 3D volumetric conductors described by the eddy currents equations. This code is used here to provide predictions for ITER-relevant geometry and range of parameters, since it has been recently proven adequate to such studies [7]. Indeed, the CarMa0NL results have been found consistent with the counterintuitive, but theoretically founded property [8] that the total global electromagnetic force acting on a perfect conductor circumventing the toroidal plasma must be zero, neglecting plasma inertia. The simulations reproduced this property despite circulation of significant total current in such ideal wall (up to several MA in ITER) and strong local electromagnetic force density. Moreover, the results obtained suggested the proposal of an electromagnetic disruption force damper [7], able to “drain” global force from the conducting wall. Here we make next steps in analyzing the high-priority disruption issues. [1] T. Hender et al, Nucl. Fusion 47 (2007) S128 [2] H. Strauss, Phys. Plasmas 25 (2018) 020702 [3] D. V. Mironov and V.D. Pustovitov V.D., Phys. Plasmas 24 (2017) 092508 [4] L. E. Zakharov et al., Phys. Plasmas 19 (2012) 055703 [5] H. Strauss et al., Phys. Plasmas 17 (2010) 082505 [6] F. Villone et al., Plasma Phys. Control. Fusion 55 (2013) 09500 [7] V. D. Pustovitov, G. Rubinacci, F. Villone, Nucl. Fusion 57 (2017) 126038 [8] V.D. Pustovitov, Nucl. Fusion 55 (2015) 1130302

Speaker: Fabio Villone

14:00 P4.1048 Experimental investigations on plasma current quench during disruptions in the KSTAR tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1048.pdf Experimental investigations on plasma current quench during disruptions in the KSTAR tokamak Jun Gyo Bak, Heung Su Kim, Sang Hee Hahn, Jahyun Kim, Hyun Seok Kim, Jeong Won Lee and KSTAR team National Fusion Research Institute (NFRI), Daejeon, Korea The study on the plasma current quench in the phase of disruptions are carried out for the plasma current Ip0 of 0.4 -1.0 MA in the KSTAR tokamak. The disruption data in the experimental campaign of 2012 - 2017 are used for the study. Firstly, the relationship between instantaneous current quench rate (ICQR) and the pre-disrupted plasma current Ip,pred is investigated by using the ICQR obtained from the time derivative of plasma current at the phase of current quench (CQ). The magnitude of the ICQR is up to ~ 200 MA/s and the increment of the ICQR becomes smaller for higher value of Ip,pred, which means that the relationship between ICQR and Ip,pred is not linear. Secondly, several linear (or averaged) current quench rates (LCQRs) are evaluated from the linear fits for several ranges (for an example, 90 % - 60 % level of Ip0) in the time evolution of plasma current during the CQ, and the best linear fit for evaluating the LCQR can be selected from the comparison between the ICQR and the LCQRs. From the investigation of the CQRs, the minimum current quench time is evaluated as ~ 2 ms. Thirdly, the characteristics of the toroidal vessel current IVC and eddy current IPS induced on the passive stabilizer as a conducting shell used for plasma control are investigated by using experimental data in the phase of the CQ. The magnitude of IVC is up to ~ 60 % of Ip,disrup. There is a correlation between the CQR and magnitudes of both IVC and IPS. In addition, the vertical growth rate and shrink rate of plasma size during the vertical displacement events (VDEs) are investigated by using the EFIT reconstructed data in the phase of the CQ. There is a weak linear correlation between the vertical growth rate and the shrink rate of plasma size. In this work, the results from the further investigations on plasma current quench during disruptions in the KSTAR comparing to the previous work presented at the 44th EPS meeting, together with behaviors during the VDE in the phase of the CQ, are reported.

Speaker: Jun-Gyo Bak

14:00 P4.1049 Anisotropic heat diffusion on stochastic magnetic fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1049.pdf Anisotropic heat diffusion on stochastic magnetic fields Yasuhiro Suzuki National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan SOKENDAI, Graduate University for Advanced Studies, 322-6 Oroshi-cho, Toki 509-5292, Japan suzuki.yasuhiro@LHD.nifs.ac.jp The magnetic topology is a key issue in fusion plasma researches. An example is the Resonant Magnetic Perturbation (RMP) to control the transport and MHD activities. However, the physics how the RMP affects the transport and MHD is not clear. One reason is the change of the magnetic topology by the plasma response. Since the vacuum approximation cannot interpret experimental observations in many cases, the magnetic topology might be changed by the plasma response. In addition, the change of the magnetic topology is predicted by numerical simulations. However, the identification of the magnetic topology in the experiment is very difficult. Recently, ideas to identify the magnetic topology experimentally are proposed in many experiment devices. Those are the heat pulse propagation by modulated ECH and measurements of the radial electric field. However, those techniques give only one dimensional profiles. In the peripheral region of the perturbed tokamak and stellarator, the magnetic field structure is very sophisticated because island chains are overlapped by strong magnetic shear. Thus, the heat pulse propagation and radial electric field might be distributed by two- or three- dimensionally. That means the experimental study of the magnetic topology is still very difficult. In this study, we study numerically the anisotropic heat diffusion on the stochastic magnetic field. The anisotropic heat diffusion is given by a following equation, 𝜕𝑇 = ∇ ∙ (𝜅∥ ∇∥ 𝑇 + 𝜅∥ ∇⊥ 𝑇) + 𝑄. 𝜕𝑡 Numerically solving this equation, we can simulate the heat transport on the stochastic magnetic field. A difficulty is the time scale of the parallel and perpendicular to the magnetic field. In the realistic case, the parallel heat transport is much faster than the perpendicular transport. So, the numerical integration of the anisotropic heat diffusion equation is very difficult, because the time step of the numerical integration is defined by the parallel transport. If a ratio of 𝜅∥ and 𝜅⊥ is huge, the time step must be small and that is very time consuming. To resolve that problem, we are developing an implicit scheme of the time integration in fully three-dimensional geometry. In this study, we discuss initial results from a new code to solve the anisotropic heat diffusion based on the implicit scheme. We applied the new code to a perturbed tokamak and a stellarator. The distribution of the electron temperature on the stochastic magnetic field is obtained. Hudson et al pointed out the KAM surface is a barrier to keep the finite temperature. We simulate those results in realistic magnetic field of the perturbed tokamak and stellarator.

Speaker: Yasuhiro Suzuki

14:00 P4.1050 Smoothed particle hydrodynamics and its application to the solution of fusion-related MHD problems

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1050.pdf Smoothed Particle Hydrodynamics and its application to the solution of fusion-relevant MHD problems L.Vela Vela1 , R. Sanchez1 , J.M.Reynolds-Barredo1 , J.Geiger2 1 Universidad Carlos III, Leganes, Spain 2 Max-Planck Institute for Plasma Physics, Greifswald, Germany The present contribution aims at demonstrating the potential advantages of simulating MHD scenarios typically considered among the magnetically-confined-plasma community using SPH. The SPH method, or Smoothed Particle Hydrodynamics, is a Lagrangian numerical method originally designed to solve the equations of Hydrodynamics and later extended to Magnetohy- drodynamics [1]. In SPH every particle corresponds not only to a small portion of the fluid but also serves as an in- terpolation node for its neighbours. Using this in- terpolation procedure one can discretise the spatial derivatives of ideal/resistive MHD on a co-moving frame and obtain evolution equations for the par- ticle’s position, velocity, mass density and internal energy. In contrast to PIC codes, the magnetic field in SPH is not solved with an underlying regular grid but is evolved with all the other plasma properties. This makes SPH completely mesh-free and opens Figure 1: Simulation of an unstable Z-pinch. up the possibility of an efficient parallel implemen- The m=0 (kink) mode, shown here, is the most tation. unstable mode of the system. The contribution presents first a series of numer- ical tests where the properties of the SPH method are explored (Energy Conservation, Dissi- pation, Symplectic Integrators, Interpolation Kernels, etc) and second, a battery of realistic 3D cylindrical plasma columns (Theta pinch, Zeta pinch and Screw pinches) where the accuracy of the method is quantitatively tested, its solutions benchmarked against known MHD stability solutions and its suitability for future toroidal applications demonstrated. References [1] J.D.Price, "Smoothed particle hydrodynamics and magnetohydrodynamics", Journal of Computational Physics, 231, 759-794, (2012)

Speaker: Luis Ernesto Vela Vela

14:00 P4.1051 Experimental validation of the reconnection model (full or partial) in the sawtooth instability in KSTAR

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1051.pdf Experimental validation of the reconnection model (full or partial) in the sawtooth instability in KSTAR H.K. Park1, J.S. Ko2, Y.B. Nam3, S. Jardin4 1, Ulsan National Institute of Science and Technology, Ulsan, Korea 2, National Fusion Research Institute, Daejeon, Korea 3, CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 4 Princeton Plasma Physics Laboratory, Princeton, NJ, United States The long-standing issue whether the central safety factor (q0) goes back to above ~1.0 or not after the crash of the sawtooth instability was revisited in this paper. In this study, it was found that the “full reconnection model” in which the q0 goes back to above ~1.0 after the crash, originally proposed by Kadomtsev, is likely to be the correct model [1]. This model was discarded for a long time due to the first q0 measurements (Faraday rotation and Motional Stark Effect (MSE)) where the measured q0 was remained well below ~1.0 (~0.8) after the crash. Now we have learned that the unfolding techniques of these polarimetry measurements are much more complex and understanding has evolved since the first measurement. Some of the critical issues in unfolding techniques will be addressed in this paper. Recent MSE measurement of the q0 for sawtoothing plasmas on KSTAR has been ~1.0 ± 0.03 and this value is consistent with the previous MSE measurements in DIII-D. Since the change of the q0 (or core current density) is relatively small, the required absolute accuracy of ~2% of the MSE system for a definitive proof of the model is too stringent. A controlled supplementary experiment employing the higher order tearing modes that are extremely sensitive to the background q0 in conjunction with the measured q0~1.0 successfully validated the full reconnection model [2]. Here, a resistive MHD code, M3D-C1 was employed to identify the growth rate of the excited modes and compared with the experiment. The dynamics of the high m tearing modes in non-sawtoothing plasmas (hybrid mode) are studied and the results are consistent with the conclusion from the sawtoothing discharges. This work is supported by the NRF of Korea under Contract No 2014M1A7A1A03029865 [1] B.B. Kadomtsev, Sov. J. Plasma Phys. 1, 389 (1975). [2] Y.B. Nam, et al., Validation of “full reconnection model” of the sawtooth oscillation, to be published in Nuclear Fusion, 2018.

Speaker: Hyeon K. Park

14:00 P4.1052 Observations of electron-driven Alfvén eigenmodes in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1052.pdf Observations of electron-driven Alfvén eigenmodes in Wendelstein 7-X E. M. Edlund1, M. Porkolab2, and the W7-X Team3 1 SUNY Cortland, Cortland, NY, USA 2 Massachusetts Institute of Technology, Cambridge, MA, USA 3 Max Planck Institut für Plasmaphysik, Greifswald, Germany Experiments conducted in the Wendelstein 7-X OP1.2a campaign regularly achieved electron temperatures in the range of 1-4 keV with densities of 1-4´1019 m-3 with H and He gas puffing, though pellet fueling was able to substantially increase the density toward the X2 cutoff around 8´1019 m-3. Despite the absence of energetic ions, clear signatures of Alfvénic modes were observed in many experiments covering a wide range of conditions. Calculations from the CKA-EUTERPE code suggested that Alfvénic modes identified during the W7-X OP1.1 experimental campaign may have been driven by the gradient of the thermal electron pressure. In this work, we summarize the observations and present the trends compiled over and exhaustive search of all experiments from the OP1.2a campaign. The observed Alfvénic activity falls under two major classes of behavior: modes that are excited during the early plasma within about 100 ms of breakdown, and those that are excited later in the plasma. In the early transient phase, Alfvénic modes tend to be short-lived and with rapid frequency variation, suggesting a sensitive response to evolution of the local equilibrium, perhaps similar to reversed shear Alfvén eigenmodes observed in tokamak experiments. With few exceptions, the Alfvén modes observed at later times are long-lived with steady frequency signatures, and tend to closely track the density evolution. We compare measurements from the phase contrast imaging diagnostic, Mirnov coils, and the soft x- ray diagnostic system (XMCTS).

Speaker: Eric Edlund

14:00 P4.1053 Features of the high field ultra-low aspect ratio tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1053.pdf Features of the high field ultra-low aspect ratio tokamak C. Ribeiro1 1 Laboratório de Física de Plasmas e Fusão, Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande, Rio Grande do Sul, Brazil (celso_ribeiro@hotmail.com) The basic features of the medium-size high field ultra-low aspect ratio tokamak (HF-ULART) has been recently proposed[1]. The major objective is to explore very high beta under the minimum toroidal field as a target plasma, and then explore higher pressure values using the combined minor and major radius adiabatic compression (AC) technique. This might be one of potential pathways scenario for an ultra-compact pulsed neutron source based on the spherical tokamak(ST) concept. The major characteristics of typical target plasma are: Ro=0.51m, a=0.47m, aspect ratio A=1.1, k=2, δ0.8, B(Ro)=0.1T (0.4T max.), Ip=0.5MA (2MA, max.), ne(0)~1x1020m-3, Te(0)~1keV, and discharge duration τd~100ms. The vessel is spherical, made of SS, and insulated from the natural diverted (ND) plasma by thin (few centimetres) tungsten (W) semi-spherical limiters. The central stack is made of cooper cover by a thin (~2mm) W sleeve. No internal PF coils or solenoid is envisaged. This helps the compactness due to the close plasma-vessel fitting, capitalizing of wall stabilization as previously envisaged in the RULART proposal[2], while also potentializes easier H-mode (small edge neutral source volume), which has already been observed in Pegasus ohmic H-mode ND plasmas, using inboard gas fuelling[3]. The major source of initial heating is provided by Ip generated from RF (e.g. EC and EBW) in combination with transient Coaxial/Local Helicity Injection (CHI/LHI) techniques, as both have been successfully demonstrated in STs. By applying the AC technique over a very high beta plasma, that is, Ip=0.5MA, B(Ro)=0.1T, Ro=0.51m, a=0.47m, A=1.1, k=2, δ0.8, q(Peng)=22, Te/Ti =263/486eV (scaled from ref.4), ne(0)~0.15x1020m-3[4], the following final values can be reached for short period (ms): Ip=1.0MA, B(Ro)=0.61T, Ro=0.33m, a=0.28m, A=1.2, k=1.6, δ0.1, q(Peng)=12, Te/Ti=1.9/3.4keV, ne(0)~2.8x1020m-3. Preliminary neutron yield and MHD stability calculations and some fixed and free-boundary equilibrium simulations by VMEC[5] and FIESTA codes, respectively, will be also presented. [1] Ribeiro C., 59th American Physical Society Meeting, Plasma Phys. Division, Milwaukee, WI, US, 2017. [2] C. Ribeiro, Proc. 26th Symposium on Fusion Eng., Austin, TX, US, June 2015. [3] K.E. Thome et al, Nucl. Fusion 57 022018, 2017. [4] D.J. Schlossberg et al., Phys. Rev. Letters 119, 035001, 2017. [5] private communication with M. R. Cianciosa.

Speaker: Celso Ribeiro

14:00 P4.1054 A relativistic Langevin approach for runaway electrons in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1054.pdf A RELATIVISTIC LANGEVIN APPROACH FOR RUNAWAY ELECTRONS IN TOKAMAK PLASMAS* J. A. Mier1 , J. R. Martı́n-Solı́s2 and R. Sánchez2 1 Universidad de Cantabria, Avda. de los Castros s/n, Santander, 39005-Cantabria, Spain 2 Universidad Carlos III de Madrid, Avda. de la Universidad 30, Leganés, 28911-Madrid, Spain ABSTRACT The Langevin approach to the kinetics of a collisional plasma is developed for relativistic electrons such as runaway electrons (RE) in tokamak plasmas. In this work, we consider Coulomb collisions between very fast, relativistic electrons and a relatively cool, thermal background plasma. The model is developed using the stochastic equivalence of the Fokker-Planck and Langevin equations [1]. The resulting Langevin model equation for relativistic electrons is an stochastic differen- tial equation (SDE), amenable to numerical simulations by means of Monte-Carlo type codes. The approach will be used to analyze the two-dimensional runaway electron dy- namics in momentum space (runaway probability and conditions for runaway, runaway distribution function and generation rate) and the results of the simulations will be com- pared with those from the non-relativistic Langevin equation for runaway electrons used in the past [2]. Synchrotron radiation losses will be also included which: (1) increase the critical (mini- mum) electric field for runaway generation; (2) set a limit on the maximum energy that the runaways can reach. The resulting critical field and runaway limiting energy are found to be in agreement with the values provided by a test particle description of the runaway dynamics [3]. [1] V. I. Tikhonov and M. A. Mironov, Markovian Processes (1977). Soviet Radio, Moscow. [2] I. Fernández-Gómez, J. R. Martı́n-Solı́s and R. Sánchez, Phys. Plasmas 19 (2012) 102504. [3] J. R. Martı́n-Solı́s, J. D. Álvarez, R. Sánchez and B. Esposito, Phys. Plasmas 5, 2370 (1998). * This work was carried out with financial support from Dirección General de Investigación, Cientı́fica y Técnica, Project No. ENE2015-65444-R (MINECO-FEDER, UE).

Speaker: José Ángel Mier

14:00 P4.1055 Circuit analysis of nested current element to explain Ohmic current diffusion in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1055.pdf Circuit Analysis of Nested Current Element to Explain Ohmic Current Diffusion in Tokamak Plasmas ByoungHo Park1, H. H. Lee1 1 National Fusion Research Institute, Daejeon, Korea A seemingly simple question sometimes is not that simple to answer in simple way. The direction of current diffusion in the tokamak is one example. The inductive Ohmic current when the central solenoid current is varying, we all know that the effects are start from outside to inside. The answer may given by the wave propagation and skin depth effect but if you compare the system size of the tokamak with the wave length caused by the central solenoid current variation, the answer should be given in a simpler way. The most simple and successful description of the start up of the tokamak operation is the circuit theory. The circuit theory does not miss any essential feature of the tokamak start up in this aspect. Therefore this question also should be able to be answered by circuit model. Each circuit comprised in the circuit model does not direct information of distance from the CS coils they just communicate each other through the mutual inductance. How do they know which one is higher rank? This work is inspired by the following statement: At the very moment of CS coils current are varied the loop voltages applied on any closed paths surrounding the center stack are the same. Therefore all closed paths start to build current on their paths and at the same time they are screening the induced electric field or loop voltage each other by mutually interacting through the mutual inductance. They seem to be equal when we write down them in a circuit model. We modeled the tokamak current consists of nested circuit elements conformal with the flux surface and we found that the matrix of mutual inductance of circuit model has specific symmetry. Intuitive explanation of this question and analysis of some of KSTAR Ohmic discharges are studied.

Speaker: Hyung-Ho Lee

14:00 P4.1056 Tomographic inversion of Wendelstein 7-X stellarator plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1056.pdf Tomographic inversion of Wendelstein 7-X stellarator plasmas C. Brandt1 , H. Thomsen1 , T. Andreeva, N. Lauf1 , U. Neuner1 , K. Rahbarnia1 , J. Schilling1 , T. Broszat1 , R. Laube1 and the Wendelstein 7-X Team 1 Max-Planck-Institute for Plasma Physics, Greifswald, Germany In the operational phase OP1.2a (Aug-Dec 2017) of the Wendelstein 7-X (W7-X) stellarator experiment the soft X-ray tomography diagnostic (XMCTS: soft X-ray multi camera tomogra- phy system) has been commissioned. Soft X-ray tomography systems are powerful diagnostics for high temperature plasmas measuring spatiotemporal X-ray emissivity profiles. The XMCTS consists of 20 poloidally arranged pinhole cameras at one toroidal location observing a triangu- lar shaped up-down symmetric plasma cross section. X-ray radiation is mainly emitted in the hot plasma core (electron temperatures > 1 keV). In the pinhole cameras the plasma radiation is filtered by a beryllium foil of 12.5 µm thickness being transmissible for X-ray radiation above 1 keV. Taking into account the detector silicon thickness of 100 µm the detectable energy range is limited to approximately 1 − 10 keV. With 18 available cameras in OP1.2a the soft X-ray emissivity has been recorded along 324 lines-of-sight with a time resolution of 0.5 µs. The presentation concentrates on the preparation and first results of the tomographic inver- sion. For correct calculation of the tomograms, both, the knowledge of the exact geometry of the lines-of-sight and the sensitivity of each photodiode are of crucial importance. The as-built coordinates of the cameras have been measured after the in-vessel installation. The deviations from the designed lines-of-sight are smaller than 1◦ . Changes of the lines-of-sight geometry according to mechanical deformations of the vacuum vessel in the pumped down state and its systematic effects on the tomography are discussed. The amplitude responses of all cam- eras measured before and after in-vessel installation are considered. The tomography code used bases on the regularization applying a minimum Fisher constraint. First tomography results of selected discharges from OP1.2a are discussed.

Speaker: Christian Brandt

14:00 P4.1057 Role of MHD activity triggered by fast ions in tungsten transport in JET hybrid discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1057.pdf Role of MHD activity triggered by fast ions in tungsten transport in JET hybrid discharges M.Goniche1, P.Buratti2, R.Dumont1, C.Challis3, J. Graves4, P.Jacquet3, E.Lerche5, M.Mantsinen6, T.Pütterich7 and JET Contributors* Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2 ENEA, C.R. Frascati, 00044 Frascati (RM), Italy 3 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 4 1Barcelona Supercomputing Center(BSC),Barcelona, Spain 5 Laboratory for Plasma Physics, Brussels, Belgium, 6 EPFL, Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland 7 Max-Planck-Institut für Plasmaphysik, Garching, Germany MHD activity is known to be acting on impurity transport and in particular the sawtooth crash is found to flush out the tungsten accumulated inside the q=1 surface. On JET, when ICRH power is added to a NBI-heated H-mode discharge, the resulting increase of fast ion pressure gradient inside the q=1 surface may trigger the fishbone instability. When a regime with large amplitude and frequency span of the fishbones is achieved, the tungsten profile peaking decreases strongly and flat profiles can be observed before the sawtooth crash. In the hybrid scenario (Bt=2.8-3.2T, Ip=2.0-2.4MA, PNBI+ICRH=25-32MW) with on-axis ICRH power exceeding 3MW, fishbones are also triggered in 40% of the 39 analysed pulses. The fishbone structure (amplitude, frequency span, cycling time) varies during the high power phase and the mode may alternate with the continuous (1,1) internal kink mode. In that latter case, the tungsten peaking increases strongly with the continuous mode. On average for this data base, it is found that the tungsten peaking of the pulses with fishbone activity is lower than those with no fishbones and is compatible with operation at high normalized beta (βN>2) for more than 4 s. In fishbone-free discharges, the tungsten transport is found to be dominated by neo-classical transport unless tearing modes, mainly with toroidal number n=2 or n=3, are triggered and strong tungsten peaking occurs in the plasma core. *See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″

Speaker: Marc Goniche

14:00 P4.1058 Gas assimilation during thermal quench and runaway beam phase

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1058.pdf Gas assimilation during thermal quench and runaway beam phase G. Pautasso1, D. Coster1, M. Bernert1, M. Dibon1, M. Dunne1, R. Dux1, E. Fable1, P. Lang1, P. McCarthy2, A. Mlynek1, G. Papp1, the ASDEX Upgrade team1 and the EUROfusion MST1 team3 1 Max-Plank-Institute für Plasma Physik, D-85748, Garching, Germany 2 Department of Physics, University College Cork, Cork, Ireland 3 see author list in H. Meyer et al 2017 Nucl. Fusion 102014 The massive injection of material (MMI) - mostly noble gases in the gaseous or frozen state - has been shown to be suitable for thermal quench (TQ) and force mitigation in induced tokamak disruptions. This mitigation method is believed to be also applicable to ITER. In principle, runaway electron (RE) suppression or mitigation in a full current ITER disruption should also be possible by increasing the plasma density sufficiently, i.e. up to the so-called critical density of the order of 1021–1023 m-3, depending on the current quench time. But in practice, this density is very large and it has not yet been reached in present devices. In addition, the density increase must occur on a short time scale (< 10 ms in ITER) in the plasma centre – where the REs are confined or are going to be generated - and these requirements call for the development of dedicated injectors. Besides the technological issues, it is unknown whether or under which conditions the plasma can assimilate enough material to suppress the REs. Ultimately, this RE mitigation scheme awaits confirmation. In this contribution we discuss what can be learned from experiments of massive gas injection induced TQ and during the RE beam lifetime, conducted on the medium size tokamak ASDEX Upgrade. In addition we report on whether simulations can reproduce the experimental observations and then used for extrapolation to an ITER plasma. ASDEX Upgrade is equipped with fast gas valves close to the plasma, density and radiation measurements. RE beam current up to 400 kA can be created by argon injection into a low density circular plasma. A 2nd massive gas injection into the RE beam can also be performed to study its dissipative effect on the RE current and energy. The assimilation of argon in the pre-TQ plasma is rather large (up to 50 %) but it decays to 10 % after the 2nd injection into the RE beam. The argon (and neon) density rise in the RE background plasma is slow, of the order of tens of milliseconds. This observation is in qualitative agreement with the results of JET experiments: The RE suppression with MGI is not effective on JET, probably because the gas penetration into the beam is slow compared to the vertical movement of the plasma (some tens of milliseconds) [2]. An effective radial diffusion coefficient can be inferred from the density measurements on ASDEX Upgrade and transport simulations. However, is the physics behind the diffusion mechanism known? The injection of deuterium pellets into the RE beam does not lead to density increase but to gradual plasma recombination. This observation also awaits an explanation. In summary, knowing whether RE suppression and/or dissipation is feasible with MMI requires understanding and being able to model particle and energy transport in a cold background plasma interacting with the fast electrons. This contribution begins to tackl this lack of understanding. [1] G. Pautasso et al., ”What can be learned from ASDEX Upgrade experiments on gas assimilation and its interaction with runaway electrons”, 2017 PPPL Workshop: Theory and Simulation of Disruptions, Princeton, USA, July 17-19 2-17, https://tsdw.pppl.gov/Program.html [2] C. Reux et al., Nuclear Fusion, 55 (2015) 093013

Speaker: Gabriella Pautasso

14:00 P4.1059 ELM suppression characterisation by plasma response computation on ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1059.pdf ELM Suppression Characterisation by Plasma Response Computation on ASDEX Upgrade D A Ryan1, L Piron1, A Kirk1, Y Q Liu2, M Dunne3, L Li4, B Dudson5, W Suttrop3, the ASDEX Upgrade team 3 and the EUROfusion MST1 team[1] 1] CCFE, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB, UK 2] General Atomics, P. O. Box 85608, San Diego, California 92186-5608, USA 3] Max Planck Institute for Plasma Physics, Garching, Germany 4] College of Science, Donghua University, Shanghai 201620, China 5] York Plasma Institute, Department of Physics, University of York, York, YO10 5DQ, UK Edge Localised Modes (ELMs) in H-mode tokamak plasmas may be controlled or entirely suppressed by applying 3D magnetic perturbations (MPs). The applied perturbation is amplified by the plasma response, and it has previously been established that the size of the peeling component of this response is a reliable indicator for expected ELM control on ASDEX Upgrade [2] and MAST [3]. This motivates further studies of the connection between the peeling response and ELM behaviour. Using the MARS-F linear MHD code [4], the global plasma response to applied n=2 MP fields was computed at 33 points in time from 3 recent ELM suppression experiments on ASDEX Upgrade. The amplified peeling response was characterised using a previously employed [5] set of figures of merit, based on the total magnetic perturbation and plasma displacement. The computed amplified peeling response for poor mitigation, good mitigation, and suppression were compared. Good mitigation is defined here as an increase in ELM frequency over the natural frequency of more than 50% (not referring to target plate heat load reduction). It is found that the values of the peeling response of the ELM suppressed cases occupy a relatively small subspace of that occupied by the ELM mitigated cases. Although the sample size is small, it appears that the peeling response may take larger maximum values for ELM mitigated cases than suppressed cases, consistent with a previous suggestion a sufficiently large peeling response may inhibit or reverse ELM suppression [6]. However, the peeling response for suppressed cases does not appear to be systematically higher or lower than for mitigated cases. It has been previously suggested [7], that the observation that ELM suppression access is easier at high triangularity may be related to the larger pedestal pressure gradient in these cases amplifying the peeling response. To investigate this, the pedestal pressure gradient of a standard ASDEX Upgrade equilibrium is scanned from shallow to steep. The plasma response to an applied MP is then computed for this scan. The results indicate that the amplitude of the amplified peeling response is not strongly sensitive to the magnitude of the pedestal pressure gradient. These observations appear inconsistent with the suggestion that a larger pressure gradient leads to a more strongly amplified peeling response which eases the transition from mitigation to suppression. These results are discussed in the context of the broader pursuit of a predictive theory for ELM suppression access, and the outlook for this effort briefly examined. Further investigation into the cause of the lower spread of peeling response values in ELM suppressed relative to ELM mitigated cases is underway and will be reported. [1] See authorlist of H Meyer et al, 2017, Nuclear Fusion, 57, 102014 [2] A Kirk et al, 2015, Nuclear Fusion, 55, 043011 [3] A Kirk et al, 2013, Plasma Phys. and Contr. Fusion, 55, 015006 [4] Y Q Liu et al, 2000, Physics of Plasmas, 7, 3681 [5] L Li et al, 2016, Nuclear Fusion, 56, 126007 [6] A Wingen et al, 2015, Plasma Phys. and Contr. Fusion, 57, 104006 [7] R Nazikian et al, 2016, First observation of ELM suppression by magnetic perturbations in ASDEX Upgrade and comparison to DIII-D matched-shape plasmas. 26th IAEA Int. Conf. on Fusion Energy, Kyoto, Japan

Speaker: David Anthony Ryan

14:00 P4.1060 Plasma stability in a tokamak with q~1 and forces acting on the conducting wall during disruption

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1060.pdf Plasma stability in a tokamak with q~1 and forces acting on the conducting wall during disruption S.Yu.Medvedev1,2, A.A. Martynov1,2, S.V. Konovalov2, V.E. Lukash2, V.D. Pustovitov2, R.R. Khayrutdinov2 1 Keldysh Institute of Applied Mathematics, Moscow, Russia 2 National Research Centre Kurchatov Institute, Moscow, Russia The stability of the tokamak plasma in the process of disruption and the sideways forces acting on the conducting wall due to the eddy currents are investigated. The plasma is considered to be isolated from the wall and halo currents are not taken into account. The basis for calculating the stability is the equilibrium configuration, obtained in the simulation of the disruption in ITER by the DINA code taking into account the generation of runaway electrons with the corresponding current profile [1]. A plasma with minor radius of 1 m and almost circular shape with a large current (> 5 MA) and the safety factor of q ~ 1 is close enough to the wall of the vacuum chamber at its top so that the ideal kink mode n = 1 becomes stable. Using the stability code KINX [2], the conditions for wall stabilization (stability gaps) at the Alfvén timescale are determined varying the current profile and the value of q at the plasma boundary. Taking into account a finite conductivity in the thin wall approximation, the growth rates of resistive wall modes (RWM), the plasma displacement structure and the currents induced in the wall are calculated. The sideways force acting on the wall is determined as the Ampere force from the surface current in a thin wall and the equilibrium field. The results of the calculations show that for a peaked current density profile in the plasma there is a gap of ideal stability at q > 1 and a slow RWM can develop. The resonant harmonic m = 1 dominates the plasma displacement. The sideways force is almost completely determined by the interaction of the perturbed poloidal surface current and the toroidal field in the ITER (5.3T). The magnitude of this force with respect to the maximum of the perturbed radial field at the plasma boundary corresponds to the analytical model [3], despite the differences in the displacement structure. A possible development of the model with allowance for a plasma with open magnetic surfaces interacting with the wall is discussed. [1] S. Konovalov et al. Integrated Modelling of ITER Disruption Mitigation. 25th IAEA Fusion Energy Conference, TH/P3-31, St. Petersburg, Russian Federation, 2014. [2] L. Degtyarev et al. Computer Phys. Commun. 103 (1997) 10-27. [3] D. V. Mironov, V. D. Pustovitov. Physics of Plasmas 24 (2017) 092508.

Speaker: Sergey Medvedev

14:00 P4.1061 Numerical simulations of edge localised modes in MAST-U plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1061.pdf Numerical Simulations of Edge Localised Modes in MAST-U Plasmas S.F. Smith1,2, S.J.P. Pamela1, H.R. Wilson1,2, G.T.A. Huijsmans3,4 and MST1 Team* 1 CCFE, Culham Science Centre, Abingdon, Oxon, UK. 2 York Plasma Institute, Department of Physics, University of York, York, UK. 3 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 4 Eindhoven University of Technology, Eindhoven, The Netherlands. Edge localised modes (ELMs) are magneto-hydrodynamic (MHD) instabilities that drive filamentary plasma eruptions in high confinement tokamak discharges [1]. Gaining an improved understanding of ELMs is important [2]; in future fusion reactors such as ITER, ELM heat fluxes will need to be limited to ensure durability of divertor materials [3]. A new divertor configuration, the Super-X, will be tested on the MAST-U tokamak. The Super-X has a closed divertor designed to retain neutrals and could offer a solution for divertor heat flux control due to the increased connection length and magnetic flux expansion [4]. The effect of the new magnetic configuration on ELMs is unknown. First simulations of ELM dynamics in MAST-U plasmas are presented using the nonlinear MHD code JOREK [5], which is being developed to establish quantitative validation against current experiments [6]. The evolution of a model MAST-U plasma has been simulated, showing filamentary structures of higher density forming in the nonlinear phase. The simulations predict energy and particle losses that are compared with data from previous MAST experiments. A fluid neutrals model has been implemented in JOREK and will be presented, including the impact on ELM dynamics in MAST-U, considering configurations with varying divertor leg length. References: [1] A. W. Leonard Phys. Plasmas 21, 090501 (2014) [2] P. B. Snyder et al., Physics of Plasmas 12, 056115, (2005) [3] R.A. Pitts et al., Journal of Nuclear Materials 438, S48-S56, (2013) [4] I. Katramados et al. Fusion Eng. Des. 86 (2011) 1595–1598 [5] G T A Huysmans and O. Czarny, Nucl. Fusion 47 (2007) 659–666 Fig: Poloidal plane during the simulation showing high density [6] S.J.P. Pamela et al., Nucl. Fusion 57 076006 (2017) filaments forming in the plasma * Author list H.Meyer et al, Nucl. Fusion 57 102014 (2017) edge.

Speaker: Siobhan Faye Smith

14:00 P4.1062 Properties of Alfvén waves in ohmic plasma in the TUMAN-3M tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1062.pdf Properties of Alfvén waves in ohmic plasma in the TUMAN-3M tokamak G.I. Abdullina, L.G. Askinazi, A.A. Belokurov, V.A. Kornev, S.V. Krikunov, S.V. Lebedev, D.V. Razumenko, A.I. Smirnov, A.S. Tukachinsky, N.A. Zhubr Ioffe Institute, St. Petersburg, Russian Federation The study is devoted to properties of Alfvén waves (AWs) in ohmic plasma in the TUMAN-3M tokamak [1 – 4]. One of the important parameters of AWs is their location in the poloidal cross-section of the tokamak plasma. This information is necessary for identification the type and source of the observed oscillations. The AW location is found to be in the region r a  0.5 [4], by matching the frequency calculated from electron density profile to the experimentally measured one. The fact that this region occupies an essential part of plasma cross-section points to the global nature of the mode. Also, this approximately corresponds to the region in which q  1 . These characteristics make it possible to identify the observed mode as GAE (Global Alfvén Eigenmode), and at the same time, exclude the TAE mode (Toroidal Alfvén Eigenmode). As a result, the distortion of the linear dependence of AW frequency on AW velocity in [3] is eliminated if the local plasma density values in the region of AW propagation are used instead of the chord-averaged values for calculation the AW velocity. Mode structure of AWs, namely poloidal and toroidal mode numbers, was determined with the in-vessel array of sixteen poloidal fast magnetic probes and two toroidal ones. The dependence of AW frequency on increased carbon impurity content has been studied in deuterium plasma. It is experimentally confirmed that in the case of equal mass-to-charge ratio for both the main and impurity ions AW frequency is independent of the impurity density and is determined by the electron plasma density and the main ion mass. The study of the Alfvén wave location was supported by Russian Science Foundation (Project # 16-12-10285). The investigation of the Alfvén waves in deuterium plasma with increased carbon impurity content was supported by Ioffe Institute. [1] Askinazi L.G. et al 2015 Nucl. Fusion 55 104013 [2] Tukachinsky A.S. et al 2016 Technical Physics Letters 42 pp 1167-1169 [3] Lebedev S.V. et al 2016 Proc. 43rd EPS Conf. on Plasma Phys. P5.036 [4] Abdullina G.I. et al 2018 Technical Physics Letters 44 p 108

Speaker: Gulnara I. Abdullina

14:00 P4.1063 Acceleration of beam ions during edge localized modes in the ASDEX Upgrade tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1063.pdf Acceleration of beam ions during edge localized modes in the ASDEX Upgrade tokamak J.Galdon-Quiroga1*, M.Garcia-Munoz1, K.G.McClements2, M.Nocente3, S.S.Denk4, S.Freethy4, M. Hoelzl4, A.S. Jacobsen4, F.Orain4, J.F.Rivero-Rodriguez1, M.Salewski5, L.Sanchis-Sanchez1, W.Suttrop4, D. van Vugt6, E.Viezzer1, M.Willensdorfer4, the ASDEX Upgrade4 and EUROfusion MST1§ Teams 1 Dept. of Atomic, Molecular and Nuclear Physics, University of Seville, Seville, Spain 2 CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom 3 Dipartimento di Fisica ‘G Occhialini’, Università di Milano-Bicocca, Milano, Italy 4 Max Planck Institute for Plasma Physics, Garching, Germany 5 Department of Physics, Technical University of Denmark, Kgs. Lyngby, Denmark 6 Eindhoven University of Technology, Eindhoven, The Netherlands Acceleration of charged particles is ubiquitous in space, astrophysical and laboratory plasmas. Magnetically confined fusion plasmas with in-situ measurements are an ideal testbed to elucidate the physics underlying the different acceleration mechanisms. Experiments at the ASDEX Upgrade tokamak provide, for the first time, evidence of beam ion acceleration during edge localized modes (ELMs). Fast-ion loss detector (FILD) measurements show bursts of enhanced fast-ion losses associated with individual ELM filaments [1]. Tomographic inversion techniques applied to the FILD signal allow us to determine the velocity distribution of the lost ions with unprecedented resolution in pitch angle and energy. A high-energy feature tens of keV above the main neutral beam injection energy is observed, which shows multiple pitch angle structures varying with the beam source and q95 values. These well-defined velocity space structures suggest that the acceleration results from a resonant interaction between the beam ions and parallel electric fields arising during ELM filament eruption, when magnetic reconnection is believed to take place. Consistent with the FILD measurements, at the onset of ELMs, bursts are often detected in electron cyclotron emission and also in soft X-ray channels with lines of sight tangential to the plasma edge. Similar bursts reported in the MAST spherical tokamak have been attributed to electron acceleration [2]. Full orbit fast ion simulations have been carried out including the 3D perturbation fields of the ELM modelled with JOREK [3]. The filamentary-like pattern of the temporal evolution of fast-ion losses can be reproduced and resonance structures associated with the energy gain of the ions are obtained. These findings motivate the incorporation of a kinetic description of fast particles in ELM models, which may shed light on the role of these fast particles in ELM stability as well as in the overall particle and energy loss during the ELM cycle. [1]M.Garcia-Munoz et al, Plasma Phys. Control. Fusion 55 124014 (2013) [2]S.Freethy et al, Phys. Rev. Lett. 114 125004 (2015) [3]G.T.A. Huysmans and O.Czarny, Nucl. Fusion 47 659 (2007) § H.Meyer et al, Nucl. Fusion 57 102014 (2017)

Speaker: Joaquin Galdon-Quiroga

14:00 P4.1064 Threshold Effect In Tearing Mode Stabilization

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1064.pdf Conferenceonon Plasma Plasma Physics, Physics 2018, Prague, Czech Republic P4.1064 Synchrotron spectra, images, and polarization measurements from runaway electrons in the Alcator C-Mod tokamak R.A. Tinguely1, R.S. Granetz1, M. Hoppe2, O. Embréus2, and T. Fülöp2 1 Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, USA 2 Department of Physics, Chalmers University of Technology, Göteborg, Sweden In the high-field, compact Alcator C-Mod tokamak, relativistic runaway electrons (REs) generated during flattop plasma discharges emit synchrotron radiation in the visible wavelength range. Thus, spectrometers, cameras, and the Motional Stark Effect diagnostic installed on C-Mod measure absolutely-calibrated spectra, distortion-corrected images, and polarization information, respectively, of REs throughout the plasma. Due to the complex interplay of the RE phase-space distribution, plasma magnetic topology, and detector geometry, the synthetic diagnostic SOFT [1] is used to simulate all three measurements and compare theory with experiment. As inputs, the RE momenta and density distributions are calculated using both a test-particle model [2 – 4] and kinetic solver CODE [5]. In particular, this work explores the following: (1) Synchrotron spectra observed from REs generated at three magnetic fields (B0 = 2.7, 5.4, and 7.8 T) indicate a decrease in RE energy as synchrotron power loss is enhanced at higher fields [6]. (2) Transport and MHD activity are incorporated into the analysis of synchrotron images to better explain interesting spatiotemporal features. (3) Profiles of linearly-polarized synchrotron emission intensity and polarization angle are explored as a novel diagnostic of RE dynamics. [1] M. Hoppe, et al., Nucl. Fusion 58 (2018). [2] J.R. Martín-Solís, et al., Phys. Plasmas 5 (1998). [3] J.W. Connor and R.J. Hastie, Nucl. Fusion 15 (1975). [4] M.N. Rosenbluth and S.V. Putvinski, Nucl. Fusion 37 (1997). [5] M. Landreman, et al., Comput. Phys. Commun. 185 (2014). [6] R.A. Tinguely, et al., submitted to Nucl. Fusion (2018). This work is supported by the US DOE (grant DE-FC02-99ER54512), using Alcator C-Mod, a DOE Office of Science User Facility; Vetenskapsrådet (Dnr 2014-5510); and the European Research Council (ERC-2014-CoG grant 647121).

Speaker: Nathaniel Joseph Fisch

14:00 P4.1065 First results of plasma experiment on the spherical tokamak Globus-M2

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1065.pdf First results of plasma experiment on the spherical tokamak Globus-M2 V.B. Minaev1, V.K. Gusev1, N.V. Sakharov1, Yu.V. Petrov1, V.I. Varfolomeev1, N.N. Bakharev1, E.N. Bondarchuk2, F.V. Chernyshev1, A.A. Kavin2, N.A. Khromov1, G.S. Kurskiev1, A.B. Mineev2, A.N. Novokhatskii1, K.Yu. Oshuev1, M.I. Patrov1, P.B. Shchegolev1, A.E. Shevelev1, A.D. Sladkomedova1, V.V. Solokha1, A.Yu. Telnova1, V.A. Tokarev1, S.Yu. Tolstyakov1, E.G. Zhilin3 1 Ioffe Institute, St. Petersburg, Russia 2 JSC «NIIEFA», St. Petersburg, Russia 3 Ioffe Fusion Technology Ltd., St. Petersburg, Russia The Globus-M2 spherical tokamak [1] is an upgraded version of the Globus-M machine [2] with substantial increase of engineering parameters (the toroidal magnetic field up to 1 T, the plasma current up to 0.5 MA). The goal of the project is to achieve the improved plasma performance with sub-fusion temperature value and collisionality much less than unity in compact geometry. Magnetic field and plasma current increasing in Globus-M2 led to complete redesign of the electromagnetic system as compared to Globus-M [3] due to new plasma equilibrium requirements and significant rise of the mechanical and thermal load. The upgraded machine was assembled by the end of 2017. During first experimental campaign the toroidal magnetic field and plasma current were increased only to 0.6 T and 300 kA respectively. Ohmically and auxiliary heated plasma shots were performed. One neutral beam injector of 1 MW power with particle energy up to 30 keV was used. Limiter and divertor plasma magnetic configurations were available in experiment. Plasma density behaviour was controlled by means of RF reflectometer. Electron temperature and density profiles were measured with the help of Thomson scattering diagnostic. Two NPAs were used to investigate thermal and fast ion behaviour. Some other routine diagnostics such as SXR, D-alfa and neutron detectors were available too. Promising improvement in plasma confinement was found. The results of first experimental campaign are discussed in the report and compared to Globus-M data. References: [1] V.B. Minaev, V.K. Gusev, N.V. Sakharov, et al. // Nucl. Fusion, 57 (2017) 6, # 066047. [2] V.K. Gusev, V.E. Golant, E.Z. Gusakov, et al. // Tech. Phys., 44 (1999) 9, 1054. [3] V.K. Gusev, E.A. Azizov, A.B. Alekseev, et al. // Nucl. Fusion, 2013, 53 (9), #093013.

Speaker: Vladimir B. Minaev

14:00 P4.1066 Investigation of pellet cloud dynamics in the magnetic geometry of Wendelstein 7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1066.pdf Investigation of pellet cloud dynamics in the magnetic geometry of Wendelstein 7-X stellarator G. Kocsis1, N. P. Alvarez2, J. Baldzuhn3, C. Biedermann3, S. Bozhenkov3, G. Cseh1, K.J. McCarthy2, T. Szepesi1 and the W7-X Team 1 Wigner RCP RMI, Budapest, Hungary 2 CIEMAT, Madrid, Spain 3 Max-Planck-Institute for Plasma Physics, Greifswald, Germany Cryogenic pellet injection is one of the prime candidates to fuel large-scale fusion devices such as tokamaks and stellarators. In the second experimental campaign (OP1.2a) of the Wendelstein 7-X (W7-X) stellarator, started in 2017, a cryogenic pellet injector capable of both inboard and outboard injection was began operation. Additionally, a tangentially viewing fast-frame video observation system, designed for ultra fast (up to 600 kHz) pellet observation, was also developed and commissioned. The system observes both inboard and outboard injected pellets and is triggered for each individual pellet by the light emission from the ablating Hydrogen pellets. For OP1.2a island divertors were installed to ensure good pumping and controlled plasma-wall interaction. The island divertor is implemented by creating large 5/5 magnetic islands at the plasma boundary intersected by the divertor plates. Significant pellet ablation was observed only when pellets penetrated into the confined plasma region, independently of the pellet injection direction. No significant pellet ablation was observed in the island region, independently of whether the pellet trajectory crossed the O or X point regions. Similar to the fast-frame video observations in ASDEX Upgrade pellet experiments, the radiation from both the cloud attached to pellet and from drifting (already detached) clouds could be observed if the temporal resolution was better than 10 µs. The W7-X video observation system allowed us to track both the attached and the drifting clouds, which showed that the pellet cloud always drifts outward from the plasma for both inboard and outboard injected pellets. This observation is in contradiction with tokamak results where the inboard injection case is always accompanied by favourable inboard pellet cloud drift. It appears that at the W7-X stellarator, the inboard pellet injections did not show this advantageous behaviour for fuelling which can be the consequence of the complex 3D stellarator magnetic geometry.

Speaker: Gabor Kocsis

14:00 P4.1067 Neutral Beam Injection on JET : Effect on neutron discrepancy and energy balance

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1067.pdf Neutral Beam Injection on JET : Effect on Neutron Discrepancy and Energy Balance D.B. King1, C.D. Challis1, E.G. Delabie2, D. Keeling1, G.F. Matthews1, S. Silburn1 and JET contributors* Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 Culham Centre for Fusion Energy, UK, 2ORNL, USA, The dependence of JET neutron discrepancy and energy balance on neutral beam (PINI) selection has been investigated experimentally. There has been a consistent discrepancy between neutrons predicted and measured during JET pulses, with the measured neutrons typically being lower than interpretive simulation results. A number of investigations into this have been carried out [1] with many explanations excluded. Further to this the energy balance on JET has shown a discrepancy of ~25% [2]. The neutron production on JET is split between thermal fusion reactions and beam-target reactions, with beam-target reactions making the larger contribution in most deuterium-deuterium discharges. Given this dominance of beam-target reactions and the ubiquity of NBI heating in JET plasmas it is important to have a good understanding of both the behaviour of JET NBI in the plasma and the NBI power calibration. To improve this understanding a series of experiments were carried out involving a single PINI at a time into a stable, L-mode plasma. These pulses were then analysed using the TRANSP [3] code to determine how the predicted & measured neutrons varied with PINI selection. To further aid the analysis beam emission spectroscopy was also carried out and the change in plasma stored energy at beam turn-on was analysed and compared with the beam power. The variation of neutron discrepancy with PINI selection will be shown, with some off-axis PINIs showing a 50% or higher difference in the discrepancy. Other PINI positions showed ~5% variation in both neutron discrepancy and energy balance. Where possible a comparison between the same PINI positions on different beamlines will be shown to indicate any separation between technical and plasma physics causes of a deficit. The details of the method used for NBI power calibration will also be shown with the systematic errors recalculated to be ~10%. First results of the stored energy analysis show no disagreement with the beam power calibration within these errors. *See the author list of “Overview of the JET results in support to ITER” by X. Litaudon et al. to be published in Nuclear Fusion Special issue: overview and summary reports from the 26th FEC (Kyoto, Japan, 17-22 Oct 2016) [1] H. Weisen et al, Nuclear Fusion 57, 7 (2017) [2] G.F. Matthews et al, Nuclear Materials and Energy 12, 227-233 (2017) [3] R.J. Goldston et al, J. Comp. Phys 43 (1981) 61

Speaker: Damian Bryan King

14:00 P4.1068 Particle sources and SOL dynamics in JET strike point sweeping experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1068.pdf Particle sources and SOL dynamics in JET strike point sweeping experiments A. Salmi1, Tala1, A. Järvinen2, D. Dunai3, R. Gomes4, P. Lomas5, L. Meneses4,6, S. Mordijck7, V. Naulin8, J. Juul Rasmussen8, M. Romanelli4, A.C.C. Sips9,10, and JET contributors* Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 VTT, Espoo, Finland; 2LLNL, Livermore, USA; 3Wigner Research Centre for Physics, Budapest, Hungary; 4 IPFN, IST, Universidade de Lisboa, Portugal; 5CCFE, Abingdon, UK; 6ITER Organization, France; 7College of William & Mary, Virginia, USA; 8DTU Physics, Lyngby, Denmark; 9JET Exploitation Unit, Culham, UK; 11 European Commission, Brussels, Belgium; JET experiments to study plasma fuelling, edge transport and scrape-off-layer (SOL) behaviour have been performed for the first time using a technique based on strike point sweeping. Sweeping itself is routinely used in JET high power discharges to, e.g., spread the heat flux or to measure high radial resolution SOL profiles with Langmuir probes. Here, however, we employ this technique at the highest feasible frequencies (limited by machine safety) to study its feasibility for edge plasma fuelling studies to complement gas puff modulations [1, 2]. The sweep modulations are performed in various strike point configurations and in plasmas with Ohmic and L/H-mode confinement and in two isotopes H/D. By comparing the core and SOL electron density measurements, line radiation across the Figure 1 Strike point sweeping poloidal plane and divertor Langmuir probe data we can observe: perturbs the recycled particle fluxes in the vicinity of the strike (1) periodic LH transitions facilitated by the strike point movement points as well as the divertor from horizontal to vertical target and back in < conditions in general thus affecting upstream SOL profiles 2 conditions, (2) frequency independent (4/8/18.5Hz) midplane and core fuelling. The main SOL electron density changes (3) radial SOL ‘communication plasma shape as well as other heating and fuelling parameters times’ of the order of 10-20 ms (4) parallel SOL communication are kept constant. times within measurement accuracy (<5ms). Present observations seem to suggest that sweeping is not generating significant modulated neutral particle sources inside the separatrix but that the effect at the pedestal comes via SOL density modulation as a boundary condition. EDGE2D/EIRENE [3,4] modelling is underway to identify the dominant physics mechanisms (pumping, recycling, flux expansion etc) responsible for these observations and to develop this experimental technique for plasma fuelling studies. [1] A. Salmi et al. EPS, Belfast, Ireland, 2017 [3] R Simonini et al., CPP, 34 (1994) (368-373). [2] T. Tala et al. IAEA FEC, Ahmedabad, India, 2018 [4] D. Reiter et al. FS&T, 74 (2005) (172-186). * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001ʺ

Speaker: Antti Salmi

14:00 P4.1069 The role of pinch, fueling in determining the pedestal density structure

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1069.pdf The role of pinch, fueling in determining the pedestal density structure S. Mordijck1, R. Groebner2, J. Hughes3, A. Järvinen4, P. Kress1, T. Osborne2, A. Salmi5, T. Tala5, F. Laggner6, G.R. McKee7, R.A. Moyer8, T. Rhodes9, L. Zeng9 1 The College of William and Mary, Williamsburg, VA, USA 2 General Atomics, San Diego, CA, USA 3 MIT, Cambridge, MA, USA 4 LLNL, Livermore, CA, USA 5 VTT, Helsinki, Finland 6 Princeton University, Princeton, NJ, USA 7 University of Wisconsin – Madison, Madison, WI, USA 8 UCSD, San Diego, CA, USA 9 UCLA, Los Angeles, CA, USA Experiments were performed on the DIII-D tokamak to examine the impact on H-mode density pedestal structure to widely varying gas puff rates. At high plasma current and density, we observe that the ratio of pedestal to separatrix density n e,ped/ne,sep is insensitive to fueling rate and absolute density. There is a clear shift of the density profile outward into the SOL and an increase in the separatrix density from 3 to 5x10 19 m-3, accompanied by a larger precentage increase in the SOL density, from 0.3 – 1.6x10 19 m-3. Though the increased separatrix density enhances the neutral opacity at the plasma edge, there is no degradation in the pedestal density height. In addition to increasing the opacity by increasing the electron density, we added a modulated perturbative gas puff. At the separatrix we observe a phase shift between the puff modulation and the local n e response, which decreases with increasing opacity/fueling. Similarly, we find that a reversal in how the amplitude of the electron density responds to the gas puff modulation in the SOL versus at the top of the pedestal. In the SOL the amplitude modulation of the electron density (δne/ne) is strongly reduced from 25% to 5% with increased fueling and n e,sol. At the top of the pedestal the inverse is observed; at low density and no steady-state gas fueling the perturbation is nearly negligible (<1%), whereas at high density, the perturbation is close to 4%. Analysis and modelling of this new experimental data will address a longstanding question: does plasma transport facilitate the density pedestal formation in the regime of strong neutral screening and reduced pedestal ionization? This work is supported by the US DOE under DE-SC0007880 1,2, DE-FG02-08ER549842, DE-AC05- 06OR231003, DE-FC02-04ER54698, and DE-SC0014264.

Speaker: Saskia Mordijck

14:00 P4.1070 Plasma heating and neutron production in the TUMAN-3M

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1070.pdf Plasma heating and neutron production in the TUMAN-3M V.A. Kornev, L.G. Askinazi, A.A. Belokurov, F.V. Chernyshev, S.V. Lebedev, A.D. Melnik, A.S. Tukachinsky, N.A. Zhubr Ioffe Institute, 194021, Saint-Petersburg, RF Intense energetic neutral beams injection (NBI) is used for auxiliary plasma heating in experiments on TUMAN-3M compact tokamak [1]. Recently, it was found that efficiency of plasma heating and neutron production in the TUMAN-3M are hampered when NBI energy exceeds some critical value ~14keV [2]. Among possible reasons for this degradation in plasma heating and neutron production is plasma pollution by impurity influx, or neutral beam attenuation in beam transmitting port [3]. This loss of beam power may results from the process in which a fraction of the neutral beam is re-ionized and the tokamak magnetic field deflects it to the port’s wall. A series of experiments on TUMAN-3M was conducted with the injection of high- energy atoms, aimed at clarifying the mechanism of saturation of neutron rate and ion temperature with beam energy. A new transmission port was installed between the injector and the tokamak, which, thanks to a larger cross-section, reduced beam-wall interaction, and a risk of the beam attenuation. The efficiency of NBI was estimated through ion temperature, fast particle spectra and neutron rate measurements. Observation of impurity lines from tokamak plasma and D emission in the transmitting port was used to identify a possible reason of plasma heating saturation at higher energy and power of the beam, and to clarify a possible role of beam-wall interaction in the transmitting port. Numerical simulation of neutron rate as function of beam power was carried out using the NUBEAM code. The experiments presented in this paper were supported by Russian Science Foundation (Project # 16-12-10285). Modeling of the neutron production was supported by Ioffe Institute. References: [1] V.A. Kornev, L.G. Askinazi, M.I. Vildjunas et al., Techn. Phys. Lett., v 39 (2013), No 3, p 290 [2] V.A. Kornev, L.G. Askinazi, A.A. Belokurov et al., Nuclear Fusion, 57 (2017), 12, #126005, DOI: http://dx.doi.org/10.1088/1741-4326/aa7d13 [3] A.C. Riviere, J. Sheffield, Nuclear Fusion, 15, 944 (1975)

Speaker: Vladimir Alexandrovich Kornev

14:00 P4.1071 Expected performances of the DTT heating systems

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1071.pdf Expected performances of the DTT heating systems G. Granucci , S. Garavaglia , P. Agostinetti , T. Bolzonella , A. Cardinali , C. Castaldo , S. 1 1 2 2 3 3 Ceccuzzi , D. Farina , L. Figini , R. Maggiora , D. Milanesio , A. Moro , G. L. Ravera , M. 3 1 1 4 4 1 3 Vallar , P. Vincenzi 2 2 1 Istituto di Fisica del Plasma IFP-CNR, Milano, Italy 2 Consorzio RFX, Padova, Italy 3 ENEA, Dipartimento FSN, Frascati (RM), Italy 4 Politecnico di Torino, Dipartimento di Elettronica, Torino, Italy The main purpose of the Divertor Tokamak Test is to study solutions to mitigate the issue of power exhaust in conditions relevant for DEMO. The tokamak proposed by Italy, I-DTT [1] (BT=6T, IP=5MA, ne~2⋅1020m-3, R0=2.05m, a=0.7m and pulse duration of ~100s), is being designed to allocate the optimal divertor magnetic configuration under reactor relevant power flow (P /R>15 MW/m) in the scrape off layer. To achieve this goal it is SEP planned to equip the machine with a significant amount of auxiliary heating power (45 MW). The heating power foreseen to get the target value of 45 MW at the plasma will consist of a mix of ECRH (28-40MW), ICRH (8-12MW) and NNBI (10MW). The final choice of each system contribution will be fixed at the end of the design review phase. In this work we present the preliminary studies on the capability of each system to couple the target power to the plasma. The EC system is based on gyrotrons sources (1MW/170GHz/100s) and front steerable launchers to fulfill several requirements as bulk electron heating, additional current drive generation, avoidance of impurities accumulation and MHD control. The IC (f=60-90MHz) system is mainly dedicated to central plasma heating with the use of antennas designed to maximize the coupled power. NNBI with beam energy of 300 keV will be provided by two injectors with optimized tangential injection geometry to support plasma current generation. A description of the three systems and estimations of the deposition profiles will be discussed in this work, underlining the specific technical solutions adopted to fulfill the requirements and maximize the performances. [1] R. Albanese et al, Fusion Eng. Des. 122 (2017) pp. 274-284.

Speaker: Saul Garavaglia

14:00 P4.1072 Kinetic full wave analysis of electron cyclotron waves in a tokamak plasma using finite element method

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1072.pdf Kinetic full wave analysis of electron cyclotron waves in a tokamak plasma using finite element method A. Fukuyama1 , S.A. Khan1,2 , H. Igami3 , H. Idei4 1 Department of Nuclear Engineering, Kyoto Univerisity, Kyoto, Japan 2 National Center for Physics, Islamabad, Pakistan 3 National Institute for Fusion Science, Toki, Japan 4 Research Institute for Applied Mathematics, Kyushu University, Kasuga, Japan Full wave analysis including kinetic effects of plasmas has been extensively employed in studying ion-cyclotron (IC) heating and lower-hybrid (LH) current drive in tokamak plasmas. Most of previous analyses of wave propagation and absorption in an inhomogeneous plasma are based on the response in a uniform plasma and the wave number has an essential role in describing the plasma-wave interactions. The dielectric tensor in a hot plasma has been usually expressed as a function of wave number. In order to describe the response of plasma without wave number, it is appropriate to use an integral form of dielectric tensor derived by integrating along an unperturbed particle orbit. Maxwell’s equation with the integral form of dielectric ten- sor is numerically solved as a boundary-value problem by means of the finite element method (FEM). Numerical analysis with FEM may have higher performance with parallel processing owing to sparse coefficient matrix. Though the integration is localized in an element in usual FEM for differential equations, coupling between elements in a localized region occurs in the FEM for integro-differential equations. In a magnetized plasma, guiding center motion along an inhomogeneous magnetic field and cyclotron motion perpendicular to the magnetic field are considered for deriving the dielectric tensor as an integral operator. This scheme was applied to electron-cyclotron (EC) waves. In the first case of one-dimensional analyses, cyclotron damp- ing in the presence of magnetic field inhomogeneous along the field line is studied to obtain the power deposition profile in magnetic beach heating. In the second case, the O-X-B mode conversion in spherical tokamaks is studied. Mode conversion to the electron Bernstein wave and strong absorption at the cyclotron resonance are described. The mode-conversion efficiency is consistent with analytical estimates. The extension to two-dimensional analyses in an equa- torial plane and a poloidal cross section of tokamak plasmas is also discussed. Computational performance of integro-differential equation solver using FEM will be also discussed.

Speaker: Atsushi Fukuyama

14:00 P4.1073 New powerful ion source for Globus-M2 spherical tokamak injector

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1073.pdf New powerful ion source for Globus-M2 spherical tokamak injector P.B. Shchegolev1, A.Yu. Telnova1, V.B. Minaev1, N.N. Bakharev1, V.K. Gusev1, E.O. Kiselev1, G.S. Kurskiev1, A.A. Panasenkov2, G.N. Tilinin2 1 Ioffe Institute, St. Petersburg, Russia 2 NRC “Kurchatov Institute,” Moscow, Russia Neutral Beam Injection (NBI) is one of the main methods for additional heating of tokamak plasma. In Globus-M2 spherical tokamak [1], toroidal magnetic field and plasma current will more than double and plasma density will be significantly higher than in Globus-M [2]. Thereby, in order to ensure the optimal depth of atomic beam penetration into plasma before beam ionization, it is necessary to increase the energy of injected particles. For this purpose, we developed a new three-electrode ion source with peripheral magnetic field (ISPM-1M). While ISPM-1M retains the advantages of an arc discharge plasma emitter, the design of its high-voltage insulator junction and slit ion-optical system is different from its analogues ISPM-1 and ISPM-2 [3]. The main characteristics of ISPM-1M are as follows: - maximum atomic beam power – 1MW; - maximum accelerating voltage – 40kV; - maximum ion beam current – 50A; - emission surface area – 115cm2; - number of electrode arrays – 4 pcs.; - cathode heating voltage – 10.5V; - cathode heating current – 1200A; - discharge voltage – up to 70V; - discharge current – up to 1300A. This presentation details ISPM-1M structure, explains of ion-optical system geometry, and discusses experimental results on discharge characteristics and parameters of arc discharge plasma, as well as the emissivity of the new ion source and the dependence of the optimum value of emission electrode current on accelerating voltage. Furthermore, the presentation introduces calculations of fast particle losses in Globus-M2 plasmas during NBI and predictive modeling results of heating and current drive created by the neutral beam for Globus-M2 discharges. References: [1]. Minaev V.B., Gusev V.K., Sakharov N.V., et. al., Nuclear Fusion, 57 (2017) 066047 [2]. Gusev V.K., Golant V. E., Gusakov E. Z., et al., Technical Physics, 44 (1999) No. 9, 1054-1057 [3]. Gusev V.K., Dech A.V., Esipov L.A., et al., Technical Physics, 52 (2007) No. 9, 1127-1143

Speaker: Petr Borisovich Shchegolev

14:00 P4.1074 Discharge recovery by means of EC assisted start-up

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1074.pdf Discharge recovery by means of EC assisted start-up D. Ricci1, G. Granucci1, S. Coda3, D. Farina1, F. Figini1, S. Garavaglia1, C. Galperti3, F. Maviglia2, A. Moro1, J. Sinha3, the TCV team*, and the MST1 team** 1 IFP-CNR, Milan, Italy 2 EUROfusion Consortium, Garching, Germany 3 Swiss Plasma Center, EPFL, CH-1015 Lausanne, Switzerland In view of an efficient pulsed operation scenario of future nuclear fusion reactors, the effectiveness of a prompt and reliable plasma start-up is essential to improve plasma performance and reproducibility, especially after a disruptive event, as well as to reduce dwell time between pulses. The foreseen solution to widen the operational window with respect to the pre-pulse conditions (background pressure and impurity content) is the use of Electron Cyclotron (EC) additional heating, which can compensate for radiation losses and sustain the plasma burn-trough phase. In order to design the operational scenario of future demonstration reactors (DEMO) it is mandatory to set appropriate codes capable of extrapolating from present experiments to future scenarios. Experiments on the TCV tokamak focused on discharge recovery by means of EC assisted start-up (82.7 GHz, XM2) have been carried out with toroidal electric field of 0.7 V/m, pressure before startup ranging between 2 and 10 mPa and neutral composition dominated by Ar impurity. In the deuterium-dominated plasma, the use of EC makes start-up effective even at reduced pumping speed (to mimic the DEMO dwell phase) assuming enough power (>400KW). As expected, on this background, adding Ar as impurity leads to an increased power threshold for a sustained startup. Experimental results have been reproduced successfully with simulations provided by BKD0 code, which models in detail the burn- though phase and includes a consistent calculation of the EC absorbed power computed by the beam-tracing code GRAY in low density plasma and with a realistic description of the beam injection conditions, including polarization mix after beam reflection at the inner wall. The required additional power and impurity impact on startup have been determined for TCV and extrapolated to ITER, JT-60SA and DEMO. * See the author list of ’S. Coda et al 2017 Nucl. Fusion 57 102011’ ** See the author list of ‘H. Meyer et al., Nucl. Fusion 57, 102014 (2017)’

Speaker: Daria Ricci

14:00 P4.1075 Development of RF wave simulation using the open source MFEM library

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1075.pdf Development of RF wave simulation using the open source MFEM library S. Shiraiwa1, J. C. Wright1, P. T. Bonoli1, T. Kolev2, J. Myra3 and M. Stowell2 1 MIT Plasma Science and Fusion Center, 190 Albany St Cambridge, 02139, USA 2 Center for Applied Scientific Computing, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA 3Lodestar Research Corporation, 2400 Central Avenue P-5, Boulder, CO 80301, USA The finite element method (FEM) can handle complicated computational geometry and its mathematical formulation is suitable for modeling cold plasma wave propagation, in which the dielectric response to the RF electric field is local. Indeed, FEM has been widely used to analyze the propagation of RF waves in antenna and edge regions [1]. One can readily build such an RF wave simulation code nearly out-of-box, using the scalable open-source FEM library MFEM (http://mfem.org) and Petra-M (Physics equation translator for MFEM). This paper reports application of MFEM/Petra-M to model various types of RF wave antennas including the field-aligned ICRF antenna on Alcator C-Mod, proposed DIII- D HFS LHCD launcher, and capcacitivily coupled comb-line antenna for LHCD. MFEM/ Petra-M has been successfully coupled with the TORIC core spectrum solver to solve RF wave problem in entire tokamak plasma poloidal cross-section self-consistently [2-4]. We will also discuss including advanced physics models such as the mode-conversion to Bernstein waves and RF rectified sheath BC [5]. [1] S. Shiraiwa et al., Physics of Plasmas 17, 056119 (2010) [2] S. Shiraiwa, J. C. Wright, et al., Nucl. Fusion 57, 086048 (2017) [3] J. Wright and S. Shiraiwa, EPJ Web of Conferences 157, 02011 (2017) [4] S. Shiraiwa, J. C. Wright, et. al., EPJ Web of Conferences 157, 03048 (2017) [5] H. Kohno and J.R. Myra Computer Physics Communications 220 (2017) 129–142 Work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using User Facility Alcator C-Mod, under Award Number DE- FC02-99ER54512 and by US DoE Contract DE-SC0018090 under a Scientific Discovery Through Advanced Computing Initiative. The work at Lawrence Livermore National Laboratory was performed under the auspices of DoE under Contract DE- AC52-07NA27344, LLNL-PROC-703397.

Speaker: Syun'ichi Shiraiwa

14:00 P4.1076 Development of a caesium free hydrogen negative ion source based on a pulsed ICP discharge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1076.pdf Development of a Caesium Free Hydrogen Negative Ion Source Based on a Pulsed ICP Discharge M. J. Barnes and M. D. Bowden Department of Electrical Engineering and Electronics, University of Liverpool, UK The negative ion sources planned for use in ITER’s NBI system will utilise caesium to enhance the surface production of H- and D- ions. However it has been suggested [1] that for DEMO/commercial fusion reactors that a similar Cs injection rate to ITER is likely to lead to NBI operational problems during the reactor’s lifetime. Fusion NBI ion sources of the future will need to dramatically reduce their rate of Cs consumption, or will require alternatives to Cs for H- surface production. The aim of this work is to evaluate the performance of a Cs free RF inductively coupled ion source, operated in a pulsed regime to generate a high density of volume produced negative ions. Such sources have been developed for use in damage free plasma etching of future Ultra-Large Scale Integrated circuits [2]. Source performance has been characterised by Langmuir probe measurements of plasma density and temperature at the centre of the discharge and in proximity to the extraction grid, together with RFA measurements of the extracted ion beam. The source will also be used for testing materials which have shown promise as Cs alternatives for H- surface production, such as boron doped diamond [3], for comparison with conventional magnetically filtered, caesiated fusion H- ion sources. References: [1] R.S. Hemsworth, D. Boilson, ”Considerations for the development of neutral beam injection for fusion reactors or DEMO,” AIP Conference Proceedings, 1869, 2017. [2] S. Samukawa, ”Ultimate Top-Down Etching Processes for Future Nanoscale Devices: Advanced Neutral- Beam Etching,” Japanese Journal of Applied Physics, 45, 4A, pp. 2395-2407, 2006. [3] A. Ahmad, C. Pardanaud, M. Carr`ere, J.-M. Layet, G. Cartry et. al., ”Negative-ion production on carbon materials in hydrogen plasma: Influence of the carbon hybridization state and the hydrogen content on H- yield,” Journal of Physics D: Applied Physics. 47, 2014.

Speaker: Michael Barnes

14:00 P4.1077 Predictive integrated modelling simulations in preparation of the JET Deuterium-Tritium campaign

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1077.pdf Predictive integrated modelling simulations in preparation of the JET Deuterium-Tritium campaign J. Morales1, J. Garcia1, C. Challis2, J.-F. Artaud1 and JET contributors∗ EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 2 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK (*) See the author list of X Litaudon et al. 2017 Nucl. Fusion 57 102001 The main objective of the future JET tokamak experimental campaigns is to prepare the future D-T scenarios of JET and ITER. Together with these experiments an important effort in modelling is needed to be able to test and improve the predictive capability of integrated modelling tools for D-T burning plasmas. Alpha particles along with isotope effects [1] on plasma confinement need to be further studied and understood. A particular topic of interest is the validity of first principle models for predicting turbulence in D-T conditions. Therefore, a significant effort towards that direction is required by analysing the physics of extrapolated D-T plasmas. Weakness of the models can be mitigated by proposing experiments specifically designed to improve such predictive capabilities in plasmas different than D, for instance in the future T campaign. To help in the present modelling effort of D-T tokamak plasmas we have carried out integrated modelling simulations with the CRONOS code [2] using GLF23 [3], TGLF [4] and QuaLiKiz [5] turbulence transport models. A baseline JET shot (92436) has been extrapolated to higher power and D-T plasma conditions. This shot has been chosen because it is one with the highest neutron rate yield from the last campaign. In the present study we have carried out simulations varying the injected NBI power, first in deuterium and then in D-T plasmas. A scan in plasma current and in toroidal rotation velocity is performed. The results show the improvement of the plasma confinement with increasing toroidal rotation and the decrease of transport for D-T plasmas in some particular plasma regions (inner core and edge) compared to pure deuterium. The fusion power calculated from the different D-T plasmas simulations range between 13 and 16 MW for 41 MW of total injected power (6 MW of ICRH and 35 MW of NBI). [1] J. Garcia et al. 2017 Nucl. Fusion 57 014007, [2] J.-F. Artaud et al. 2010 Nucl. Fusion 50 043001, [3] R. E. Waltz et al. 1997 Phys. of Plasmas 4 2482, [4] G. M. Staebler et al. 2005 Phys. of Plasmas 12 102508, [5] C. Bourdelle et al. 2016 Plasma Phys. And Control. Fusion 58 014036

Speaker: Jorge Morales

14:00 P4.1078 How predict-first will change our approach to experimental planning

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1078.pdf How predict-first will change our approach to experimental planning F. Poli1, B. Grierson1, M. Podestà1, Z. Wang1, J. Ferron2, C. Holcomb3, B. Victor3, K. Thome4 1 Princeton Plasma Physics Laboratory, NJ 08543, USA 2 General Atomics, San Diego, CA 92121, USA 3 Lawrence Livermore National Laboratory, Livermore, CA 94551, USA 4 Oak Ridge Associated Universities, Oak Ridge, TN, 37831, USA Time-dependent, transport simulations of experiments ahead of time can improve the efficiency of our experimental studies and might become a game changer. High-fidelity, validated models are critical for the success of the predict-first approach, which relies entirely on the fidelity of the models used to evolve transport and magnetic equilibrium. We are going to show an example of successful application of the predict-first approach on DIII-D, for the optimization of access to steady-state operation with sustained high qmin at mid-radius. A feed-forward scheme has been proposed using free-boundary time-dependent simulations with TRANSP, combining EC and NBI injection in the ramp-up to delay the relaxation of the safety factor profile. Simulations indicate that a combination of Electron Cyclotron heating and current drive for pre-heating in L-mode and Neutral Beam injection sustain a broad and flat safety factor profile in the flattop phase, which has been a posteriori verified in the experiment, a successful demonstration of the predict-first approach towards experimental planning and optimization of runtime resources. The limits of predictive modeling will be discussed and examples will be provided to show what assumptions are critical for the success of the predict-first approach. In particular, self- consistent particle transport, with realistic feedback control on the line-averaged density, like it is done in experiments, is critical for experimental projections. These examples provide directions for improvement of modeling capabilities in time- dependent solvers. This work is supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under contract numbers DE-AC02-09CH11466 and DE-FC02-04ER54698.

Speaker: Francesca Poli

14:00 P4.1079 Robust plasma position, current, and shape control system simulated on plasma evolution code for the spherical tokamak Globus

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1079.pdf Robust plasma position, current, and shape control system simulated on plasma evolution code for the spherical tokamak Globus-M Y.V. Mitrishkin1,2, A.A. Prokhorov,1,2, P.S. Korenev1,2, M.I. Patrov3 1 Lomonosov Moscow State University, Faculty of Physics, Moscow, Russia 2 V.A. Trapeznikov Inst. of Control Sciences, Russian Academy of Sciences, Moscow, Russia 3 Ioffe Physical-Technical Inst. of the Russian Academy of Sciences, Saint Petersburg, Russia To simulate plasma shape and position during tokamak discharges a new plasma evolution code was developed in MATLAB. To obtain plasma position and coil currents the plasma motion equation, Faraday’s law equations for PF coils, vacuum vessel and plasma circuits are numerically solved with input voltages. Forces acting on plasma and inductance matrices are obtained from a plasma current density distribution, which is calculated to satisfy Grad-Shafranov equation. To design feedback controllers, linear plasma models were obtained on the Globus-M (Ioffe Inst.) experimental data. Then these controllers were applied on the developed plasma evolution code. The hierarchical multi-loop control system includes cascades for controlling the plasma position and current with robust SISO PID controllers tuned by QFT [1]. The outer cascade of plasma shape control incorporates a plasma reconstruction code, which is created on moving filaments and has sufficient accuracy and Fig. 1. Control process of the plasma shape: Br, Bz speed of response [2]. A plasma shape MIMO in X-point, δΨ1= ΨX‒Ψ1 , δΨ2= ΨX‒Ψ2 , ΨX is the flux at X-point, Ψ1, Ψ2 are fluxes at the separatrix. controller was designed by the H∞ robust loop-shaping approach [3] for magnetic field at X-point Br, Bz and poloidal fluxes on the plasma separatrix Ψ1, Ψ2. Full thyristor current inverter models operating in self-oscillation mode up to 3 kHz were used as original fast actuators for plasma position control [4]. The plasma shape controller is turned on at 0.18 s of the discharge and transfers the plasma boundary to the desired position in less than 5 ms during the divertor phase (Fig. 1). That is critically important due to comparatively short plasma discharges on the Globus-M tokamak of about 200-250 ms. [1] Garcia-Sanz M. Robust Contr. Eng.: Practical Quantitative Feedback Theory Solutions, CRC Press, 2017. [2] Mitrishkin Y.V., Prohorov A.A. Korenev P.S.et al. Proc. IFAC WC, Toulouse, France, pp. 11883-11888, 2017. [3] McFarlane D. and Glover K. IEEE Trans. Automatic Control, Vol. 37, No. 6, pp. 759-768, June 1992. th [4] Kuznetsov E.A., Mitrishkin Y.V., Yagnov V.A., and Shcherbitsky V.N. Proc. 11 IEEE Intern. Conf. AICT2017, Inst. of Control Sciences, September 20-22, 2017, Moscow, Russia, pp. 485-489, 2017.

Speaker: Pavel Korenev

14:00 P4.1080 Application of modified ASTRA-SPIDER code to simulation of free boundary equilibrium evolution

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1080.pdf Application of modified ASTRA-SPIDER code to simulation of free boundary equilibrium evolution A.Yu. Dnestrovskiy 1, A.A. Ivanov 2, S.Yu. Medvedev1,2, V.V. Drozdov3, M.P. Gryaznevich3, A.R. Polevoi4 1 National Scientific Centre Kurchatov Institure, Moscow, Russian Federation 2 Keldysh Institute of Applied Mathematics, Moscow, Russian Federation 3 Tokamak Energy Ltd, Culham Science Centre, Abingdon, OXON, OX14 3DB, UK 4 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St Paul Lez Durance, France In our studies a coupling of the equilibrium solver with a transport code is considered. In such 1.5D codes the evolution of poloidal magnetic flux, density and temperatures of plasma species are simulated in 1D approximation on the flux grid and with metric coefficients calculated consistently by 2D equilibrium solver. Our simulations are based on the Automated System for Transport Analysis (ASTRA) [Pereverzev et al 2002 IPP Report 5/98] and equilibrium solver SPIDER [Ivanov et al 2005 32nd EPS Conf. on Plasma Physics vol 29C (ECA) P-5.063]. In the original coupling of the SPIDER to ASTRA7.0 [E Fable et al 2013 Plasma Phys. Control. Fusion 55 124028] the evolution of the poloidal magnetic flux is computed outside the equilibrium solver. We modified the iteration loop to include the poloidal flux evolution into the internal iteration loop of the equilibrium solver and circuit equations using the grid adapted to magnetic fluxes. The comparison has shown that such a modification noticeably improves the convergence reducing number of iterations in the equilibrium solver with evolving shape and profiles. It also reduces the total computational time of 1.5D transport evolution, where 2D equilibrium is the most time-consuming part. Such a modification noticeably improves the convergence for the cases with strong pressure and current density gradients near the edge for H-mode operation in tokamak plasmas thus proving to be the most efficient approach to free boundary simulations with 1.5D transport codes. The efficiency of the proposed scheme further increases for highly shaped plasmas and fast evolution of plasma parameters. As an application of the modified 1.5D solver we demonstrate free boundary simulations of plasma evolution with increasing elongation in the tokamak ST40 [M. Gryaznevich, et al 2017 Fus. Eng. & Des. 123 177-180]. Plasma density, temperature and current density evolution is simulated with the coupled transport and equilibrium code consistently with the free boundary plasma shape change. The scenario of current and voltage control in the poloidal field coils is developed. The dependence of the plasma shape evolution on the scenarios of plasma heating, fueling and the initial plasma current value is discussed.

Speaker: Alexey Dnestrovskiy

14:00 P4.1081 Confinement improvement triggered by the impurity injection in T-10 ECR heated plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1081.pdf Confinement improvement triggered by the impurity injection in T-10 ECR heated plasmas N.A.Kirneva1,2, G.M.Asadulin1, V.M.Bajkov1, A.A.Borschegovskij1, M.M.Dremin1, A.Ya.Kislov1, L.A.Kluchnikov1, V.A.Krupin1, S.V.Krylov1, A.V.Melnikov 1,2, N.A.Mustafin1, A.R.Nemets1, Yu.D.Pavlov1, I.S.Pimenov1, G.N.Ploskirev1, D.V.Ryjakov1, D.V.Sarychev1, D.S.Sergeev1, N.A.Solovev1, A.V.Sushkov1, V.M.Trukhin1, E.V.Trukhina1 1 National Research Center “Kurchatov Institute”, Moscow, Russia 2 National Research Nuclear University MEPhI, Moscow, Russia Effect of the increase of the central electron temperature triggered by the Neon injection in T-10 was observed for the first time in discharges with ECRH/ECCD (EC current drive in co-direction to the total plasma current). Time evolution of the typical discharge is presented in Figure 1 in comparison with the discharge without Ne puffing. Increase of the electron temperature, plasma density and plasma energy content due to the impurity injection is clearly seen. Experiments were carried out at moderate edge safety factor value qL~3. Toroidal magnetic field was changed in the range of BT=2.42…2.18 T, which led to the shift of the EC resonance position from the center to the high field side, ~a/2 (a- minor radius). The phenomenon was observed in regime with slightly off-axis ECRH/ECCD, BT~2.25 T, when the ECR power was absorbed in the vicinity of q=1 position and sawtooth oscillations were suppressed. Destruction of the improved confinement is linked to the odd MHD mode development (most possibly m=1 mode). Dependence of the value of the temperature gain on the ECCD power has been investigated. Confinement improvement seems to be a result of interplay between core current profile redistribution (with the increase of the gap between resonance surfaces in vicinity of the q=1) and the increase of radiation losses from the edge due to the Ne puffing. 3.5 Figure 1. Time evolution of the electron density 19 -3 a) Te(0), keV ne, 10 m 3.0 (a), central electron temperature (b) and plasma 2.5 2.0 energy content (c) in similar T-10 discharges 1.5 2.5 b) with (red curves) and without (blue curves) 2.0 Neon puffing. Time and duration of Ne puffing 1.5 1.0 and ECRH/ECCD are presented in subplot (c). c) Ne puffing 20 Wdia, kJ 15 ECRH/ECCD 10 700 750 800 850 900 time, ms This work is supported by Rosatom and by RSF (project 14-22-00193).

Speaker: Natalia A. Kirneva

14:00 P4.1082 Fast ion confinement study by NB blips in the LHD deuterium plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1082.pdf Initial Results of a Machine Learning-based Real Time Disruption Predictor on DIII-D C. Rea1, R.S. Granetz1, N. Eidietis2, K. Erickson3, M.D. Boyer3, R. Johnson2 1 MIT Plasma Science & Fusion Center, Cambridge, MA, US 2 General Atomics, San Diego, CA, US 3 Princeton Plasma Physics Laboratory, Princeton, NJ, US A disruption prediction algorithm, developed using machine learning, runs in real time in the DIII-D plasma control system (PCS), and accurately predicts impending major disruptions with several hundred milliseconds warning time, while also having a very low rate of false alarms. The algorithm is based on the Random Forests machine learning method, and has been developed starting from an extensive database of more than 10000 DIII-D discharges, both disruptive and non-disruptive ones. The algorithm uses 9 plasma parameters that are derived from several real time diagnostic signals and real time EFIT equilibrium reconstructions, which are provided by the PCS on a cycle time of 250 µs. Most of the parameters are dimensionless (e.g. li, βp, …) or cast in a dimensionless form (e.g. n/nG, Bpn=1/Btor …), which facilitates multi-machine analyses. The prediction algorithm was trained on all types of major disruptions occurring during the flattop phase, without differentiation by cause, and the initial results do indeed show good success at recognizing multiple types of major disruptions during the flattop, and even during the rampdown phase of discharges. A reliable prediction warning time of several hundred milliseconds allows, at least conceptually, for the possibility of actively avoiding an impending disruption, if the specific cause(s) of the disruption can be identified, and if control ‘knobs’ exist to modify the identified cause(s). However, although Artificial Intelligence (AI) methods can accurately make predictions, it is not well-understood how to determine which input features are responsible for the output prediction. Determining how to do this is currently a high-priority topic of AI research, which we are now pursuing in order to effectively close the disruption avoidance control loop. This work was supported by the U.S. Department of Energy under DE-FC02-04ER54698, DE-SC0014264 and DE-AC02-09CH11466. DISCLAIMER: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Speaker: Takeo Nishitani

14:00 P4.1083 Multiplet effects in radiation losses during discharge quenching by intense argon injection in ITER

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1083.pdf Multiplet effects in radiation losses during discharge quenching by intense argon injection in ITER P.A. Sdvizhenskii1, A.B. Kukushkin1,2, M.G. Levashova1, V.E. Zhogolev1, V.M. Leonov1, V.S. Lisitsa1,2, S.V. Konovalov1 1 National Research Center “Kurchatov Institute”, Moscow, Russia 2 National Research Nuclear University MEPhI, Moscow, Russia One of conditions of the experimental tokamak reactor ITER’s safe operation is the possibility of disruption instability mitigation by massive injection of inert gases, in particular, of argon and neon. While modeling in [1] of Ar and Ne massive gas injection (MGI) in the ITER 15 MA Q=10 baseline scenario, the MGI is carried out at the quasi- stationary stage of discharge (flat-top of the current). For modeling of main plasma parameters, the ASTRA transport code was used, integrated with the ZIMPUR [2] code which describes the dynamics of charge states, radiation losses and transport of impurities (radiation losses were simulated in [1] for optically thin coronal plasma). Here we present the results of estimating the following effects in scenario [1]: (i) radiation imprisonment, using the Escape Probability model, (ii) deviations from coronal model, caused by collisional quenching, (iii) fine structure of atomic levels (multiplet splitting). This consideration is stimulated by the results [3] where the impact of plasma opacity on the disruption mitigation by the MGI in tokamaks was found (only the first two effects were considered there). For the most strongly radiating ions at various stages of discharge quenching (e.g., highly ionized atoms at the initial stage of penetration of impurity into plasma and weakly ionized atoms at the stage of impurity stirring practically throughout the entire plasma volume), the optical thickness for the ionic strongest lines appears to be about 10. However, it has no significant effect on the total radiation power losses of plasma in the quenching scenario [1]. The most significant effect appears to be the multiplet splitting, which provides the increase of radiative losses, e.g., for weakly ionized atoms at low temperatures, because of the contribution from ∆n=0 transitions with lower excitation energy than that in the model of multiplet-averaged energy levels. References [1]. Leonov V.M., Konovalov S.V., Zhogolev V.E., 27th IEEE Symposium on Fusion Engineering (SOFE 2017) Shanghai, China, W.POS.026. [2]. Leonov V.M., Zhogolev V.E., Plasma Phys. Control. Fusion, v. 47 (2005) 903. [3]. Lukash V.E., Mineev A.B., Morozov D.Kh. Nucl. Fusion, 2007, v. 47, pp. 1476–1484.

Speaker: Petr A. Sdvizhenskii

14:00 P4.1084 Real-time capable neural network approximation of NUBEAM for use in the NSTX-U control system

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1084.pdf Real-time capable neural network approximation of NUBEAM for use in the NSTX-U control system M.D. Boyer1, S. Kaye1, D. Liu2, K. Erickson1, W. Heidbrink2, O. Menegheni3, S.A. Sabbagh4 1 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 2University of California-Irvine, Irvine, CA, USA 3General Atomics, San Diego, CA, USA 4Columbia University, New York, NY, USA Present-day and next step tokamaks will require precise control of plasma conditions, including the spatial distribution of rotation and current profiles, in order to optimize performance and avoid physics and operational constraints. The coupled nonlinear dynamics of equilibrium profiles and the complex effects of actuators on the equilibrium evolution motivates embedding physics-based models within real-time control algorithm designs. Due to the important role of beam heating, current drive, and torque in establishing scenario performance and stability, a high-fidelity beam model suitable for use in real-time applications is desired. This work describes a neural network that has been developed to enable rapid evaluation of the beam heating, torque, and current drive profiles based on measured equilibrium profiles. The training and testing database has been generated from the NUBEAM calculations output from interpretive TRANSP analysis of shots from the 2016 NSTX-U campaign, including scans of Zeff and fast ion diffusivity. Neural network predictions made for the testing data demonstrate the ability of the model to generalize and accurately reproduce NUBEAM calculated profiles and scalar quantities. Results of hardware-in-the-loop simulations of the model within the NSTX-U plasma control system will be presented, along with plans and progress toward application of the neural network for accelerated offline analysis and real-time control. * Work supported by U.S.D.O.E. Contract No. DE-AC02-09CH11466.

Speaker: Mark Daniel Boyer

14:00 P4.1085 Collisional transport of heavy impurities with flux-surface density variation in stellarators

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1085.pdf Collisional transport of heavy impurities with flux-surface density variation in stellarators S. Buller1 , H.M. Smith2 , P. Helander2 , A. Mollén2 , S.L. Newton3 , I. Pusztai1 1 Department of Physics, Chalmers University of Technology, SE-41295, Göteborg, Sweden 2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany 3 CCFE, Culham Science Centre, Abingdon, Oxon OX14 3DB, UK Due to their ability to cause intolerable radiation losses, heavy impurities cannot be allowed in the core of a magnetic fusion reactor. In addition, heavy impurities can have observable density variations on flux-surfaces due to their sensitivity to any flux-surface variations in electrostatic potential. Such density variations have been analytically shown to significantly affect the colli- sional impurity transport in tokamaks [1, 2], while their importance in stellarators have mainly been investigated numerically [3]. We have included impurity density flux-surface variations in an analytic calculation for a stellarator in the mixed-collisionality regime, building on recent analytical results in stellarator impurity transport [4, 5] – and have thus generalized the calculation in Ref. [2] to stellarator geometry. Specifically, we have derived an expression for the radial transport of a heavy impu- rity, using a mass-ratio expanded ion-impurity collision operator. In contrast to both the general tokamak case, and the stellarator case with flux-function impurity density, the neoclassical flux includes an electrostatic flux term [6], which must be retained. We have found the neoclassical transport to be sensitive to the distribution of impurities over the flux-surface in simple test cases with a W7-X vacuum field – even changing sign compared to the homogeneous case when the impurity density becomes sufficiently localized around extrema in the magnetic field strength. Interestingly, for these test cases, this effect on the neoclassical transport is overshadowed by classical transport, which appears to be the dominant collisional transport mechanism for a collisional species in W7-X. Work is currently being carried out to investigate in which scenarios classical transport is relevant. References [1] P. Helander, et al., Physics of plasmas 5 3999 (1998). [2] C. Angioni & P. Helander, Plasma Physics and Controlled Fusion 56 124001 (2014). [3] J. M. García-Regaña et al., Nuclear Fusion 57 056004 (2017). [4] P. Helander, et al., Physical Review Letters 118 155002 (2017). [5] S.L. Newton, et al., Journal of Plasma Physics 83 5 (2017). [6] S.P. Hirshman & D.J. Sigmar, Nuclear Fusion 21 1079 (1981), page 1098.

Speaker: Stefan Buller

14:00 P4.1086 Transport of Li and W impurities and their influence on discharge parameters of the T-10 tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1086.pdf Transport of Li and W impurities and their influence on discharge parameters of the T-10 tokamak I.A. Zemtsov, V.A. Krupin, M.R. Nurgaliev, L.A. Klyuchnikov, A.R. Nemets, A.Yu. Dnestrovskij, G.M. Asadulin, A.A. Borschegovskij, V.A. Vershkov, S.A. Grashin, T.B. Myalton, D.V. Sarychev, D.S. Sergeev, N.A. Solovyev, A.V. Sushkov, V.M. Trukhin National Research Centre "Kurchatov Institute", Moscow, Russia In 2016, a W-limiter made of ITER-grade WMP "POLEMA" tungsten and the moveable Li- limiter has been installed on the T-10 tokamak [1]. The transport of Li and W impurities and their influence on the parameters of T-10 OH and ECRH-discharges are studied in this paper. Experiments in OH-discharges were performed with two positions of the Li-limiter: outside and inside of the W-limiter radius. In the first case, short lifetime of Li1+ in scrape-off layer is severely limiting lithium flux in the plasma that results in low concentration of Li nuclei in the plasma center (nLi3+ < 0.3% of ne , which is insufficient to perform CXRS-measurements). In the second case, the flow of lithium is significantly increased and high concentration of Li nuclei in the plasma center is achieved (up to 26% of ne , according to CXRS-measurements). Reliable data on nLi3+ made it possible to establish that the transport of lithium ions and nuclei follows the same dependences as all impurities in T-10 plasma and can be described by the transport model worked out for Ar, K, C, O, W impurities [2, 3]. The main influence of Li on the parameters of OH discharges is a strong reduction of light impurities level. This leads to a decrease of the effective charge Ze f f and opens the possibility for a strong peaking for both the Ze f f (r) profile and the PW (r) radiation loss profile on W ions. Study of the influx, transport, and radiation of W impurity in a plasma cord with a tungsten limiter at high (Ze f f ≥ 4) and low (Ze f f ≈ 1) levels of light impurities is carried out. The follow- ing recurring scenario is observed in the experiments: first, Ze f f (r) peaks, then W accumulates at the plasma center, PW (r) peaks and suppresses the sawtooth oscillations (SO). Further the peaking of PW (r) causes flattening and broadening of Te (r), which ends with the evolution of the MHD mode m = 2 and the occurrence of a "small" disruption with the impurities removal and loss of 30 ... 50% of the plasma stored energy. This scenario (W-cycle) can repeate many times during the discharge, often resulting in a disruption. The conditions for development of the W-cycle in T-10 plasma are determined in this work. It was found that off-axis ECRH leads to the acceleration of the W-cycle due to the mitigation of SO suppression and the enhanced accumulation and peaking of W. The on-axis ECRH prevents the development of W-cycle at any stage due to the effective removal of tungsten from the plasma center [4]. References [1] V.A. Vershkov et.al., Nuclear Fusion, Vol. 57 (10), 102017 (2017) [2] V.A. Krupin et.al., 12th EPS Conference on Plasma Physics, Vol. 9F, 207-210 (1985) [3] I.A. Zemtsov et.al., Problems of Atomic Science and Technology, Ser. Thermonuclear Fusion, Vol. 40, P. 29-35. [4] V.A. Krupin et.al. Nuclear Fusion, Vol. 57 (6), 066041 (2017)

Speaker: Ivan Zemtsov

14:00 P4.1087 Test particles dynamics, quasi-linear and nonlinear transport in low-frequency tokamak turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1087.pdf Test particles dynamics, quasi-linear and nonlinear transport in low-frequency tokamak turbulence J. Médina, M. Lesur, E. Gravier, T. Reveille, M. Idouakass, P. Bertrand, T. Drouot Université de Lorraine, CNRS, IJL, F-54000 Nancy, France In the context of magnetic confinement fusion, we compare the quasi-linear particle and heat fluxes obtained from an analytical expression, to the nonlinear fluxes obtained with a gyroki- netic code. We then study the transport and the diffusion in toroidal turbulent plasma simulations using statistics on a relevant number of test particles. TERESA is a gyrokinetic code based on the bounce-averaged Vlasov-Poisson model[1], which reduces drastically the numerical computation costs by averaging out the cyclotron and banana bounce motions of trapped particles. TERESA[2, 3] (Trapped Element REduction in Semi lagrangian Approach) is therefore relevant to study phenomena at the order of the trapped particle precession timescale. Such phenomena include macroscopic anomalous transport driven by the plasma turbulence, which degrades the confinement of the fusion plasma. We find that the quasi-linear fluxes predictions are accurate for a certain range of parameters and radii. Furthermore test particles diffusion is in qualitative agreement with quasi-linear theory. References [1] G. Depret, X. Garbet, P. Bertrand, A. Ghizzo, Plasma Phys. Cont. Fusion 42, 949 (2000) [2] T. Cartier-Michaud, P. Ghendrih, V. Grandgirard, and G. Latu, ESAIM: PROC 43, 274 (2013) [3] T. Drouot, E. Gravier, T. Reveille, A. Ghizzo, P. Bertrand, X. Garbet, Y. Sarazin, T. Cartier-Michaud, Eur. Phys. J. D 68, 280 (2014)

Speaker: Julien Médina

14:00 P4.1088 Turbulent transport model validation at JET using integrated modelling enhanced by Gaussian process regression

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1088.pdf Turbulent transport model validation at JET using integrated modelling enhanced by Gaussian process regression A. Ho1 , J. Citrin1 , F. J. Casson2 , F. Auriemma3 , C. Bourdelle4 , P. Manas5 , G. Szepesi2 , H. Weisen6 , and JET Contributors∗ 1 DIFFER, De Zaale 20, 5612 AJ, Eindhoven, The Netherlands 2 EURATOM-CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK 3 Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Padova, Italy 4 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 5 Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany 6 Swiss Plasma Center, EPFL, 1015 Lausanne, Switzerland ∗ See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001" Due to increasing complexity and costs of experimental fusion plasma devices, more empha- sis is being placed on plasma models to assist in the design process. To have confidence in these model predictions, a self-consistent connection between the predictions and experimental mea- surements must be ensured via model validation. However, the high sensitivity and non-linear nature of plasma models demand a more rigourous uncertainty treatment in order to determine the significance of any reported agreement between model and experiment. By using Gaus- sian Process Regression (GPR) techniques [1, 2] on the measurement data, which can provide both fit and fit gradient envelopes while maintaining tractability for large-scale data processing, validation and sensitivity studies can be performed with increased statistical rigour. This study outlines the application of GPR techniques to profile fitting for use in tokamak turbulence transport model validation within integrated modelling. With properly tuned opti- mizers, the developed profile fitting tool can process a single time window in ∼2 min., allowing the processing of measurements from an entire discharge in reasonable time. The advantages of this approach were demonstrated through a JETTO integrated modelling simulation [3, 4] of the JET ITER-like-wall discharge #92436 with the QuaLiKiz quasilinear turbulent transport model [5, 6]. Excellent agreement was achieved between the fitted and simulated profiles for ne , Te and Ωtor simultaneously but the simulation underpredicts Ti for this discharge. This un- derprediction is suspected to be from known physics which is currently being included in the transport model. The fit envelopes have allowed for more rigourous error propagation through the model, such as Monte Carlo studies of transport model boundary conditions within the fit uncertainties, and the definition of a figure-of-merit to assess the quality of this agreement. References [1] M.A. Chilenski et al., Nuclear Fusion 55, 2 (2015) [2] C.E. Rasmussen, C.K.I. Williams, Gaussian Processes for Machine Learning, (2006) [3] M. Romanelli et al., Plasma and Fusion Research 9, 01 (2014) [4] G. Cenacchi, A. Taroni, JETTO: A free boundary plasma transport code, JET-IR (1988) [5] J. Citrin et al., Plasma Physics and Controlled Fusion 59, 12 (2017) [6] C. Bourdelle et al., Plasma Physics and Controlled Fusion 58, 1 (2016)

Speaker: Aaron Ho

14:00 P4.1089 Gyrokinetic Simulation for Trapped Electron Mode during dominant electron heating in EAST Tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1089.pdf Gyrokinetic Simulation for Trapped Electron Mode during dominant electron heating in EAST Tokamak X.M. Zhang1*, W.D. Chen1, E.B. Xue 1, L.M. Yu1, and the EAST Team2 1 Department of Physics, School of Science, East China University of Science and Technology, Shanghai 200237, China 2 Institute of Plasma Physics, Chinese Academy of sciences, Hefei 230031, China The mechanism and behavior of trapped electron mode (TEM) is very important to study confinement and transport during electron dominant heating in tokamak [1-3]. Simulations of TEM have been performed for some typical discharges with dominant electron heating by using gyro-kinetic simulation code GTC in EAST. Calculation results show that the ratio of electron temperature to ion temperature Te/Ti and logarithmic density gradient R/Ln are main factors of affecting on TEM linear growth rate 𝛾 rather than electron temperature Te individually and normalized electron ion temperature logarithmic gradient R/LTe. For safety factor q and magnetic shear 𝑠̂ , the dependences of TEM linear growth rate are complex with different 𝑠̂ value in the range of normalized minor radius  <0.6. When 𝑠̂ is larger than 0.5 within  <0.6, 𝛾 increases with q while decreases with 𝑠̂ , which is consistent with theoretical analysis by the reduced model. However, when 𝑠̂ is smaller than 0.5 within  <0.6, the opposite results are obtained, namely 𝛾 decreases with q while increases with 𝑠̂ . References: [1] Horton W. 1999 Rev. Mod. Phys. 71 735 [2] Ryter F et al. 2005 Phys. Rev. Lett. 95 085001 [3] Bonanomi N et al. 2015 Nucl. Fusion. 55 113016 [4] Xie H S et al. 2017 Phys. Rev. Lett. 118 095001 [5] Xiao Y et al. 2007 Phys. Plasmas. 14 055910 [6] Bravenec R V et al. 2013 Phys. Plasmas. 20 104506 [7] Anderson J et al. 2006 Plasma Phys. Contr. F. 48 651

Speaker: Xianmei Zhang

14:00 P4.1090 Interaction between magnetic island, plasma perpendicular flow and turbulence in HL-2A ohmic plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1090.pdf Interaction between magnetic island, plasma perpendicular flow and turbulence in HL-2A ohmic plasmas M. Jiang1, W.L. Zhong1, Y. Xu2, Z.B. Shi1, W. Chen1, X.Q. Ji1, X.T. Ding1, Z.C. Yang1, P.W. Shi1, A.S. Liang1, J. Wen1, J. Q. Li1, Y. Zhou1, Y.G. Li1, D.L. Yu1, Y. Liu1, Q.W. Yang1 and M. Xu1 1 Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, People’s Republic of China 2 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, People’s Republic of China Corresponding author: jiangm@swip.ac.cn The multi-scale physics such as the interaction between large scale MHD modes and turbulence were reported to play a crucial role in the transport regulation in the core plasma [1, 2] and the interaction between sheared zonal flow and turbulence was considered to be the key ingredient for the low-to-high confinement mode transition [3, 4]. In this work, we present the first experimental observations of the interaction between magnetic island, plasma perpendicular flow and turbulence in the presence of the naturally rotating m/n = 2/1 tearing mode in the HL- 2A ohmic plasmas using a hopping Doppler backward scattering reflectometer system, which provides direct experimental evidence for the simulations. It has been observed that across the O-point cut the perpendicular flow is near zero at the center of the island and strongly enhanced around the boundary of the island, resulting in a large increase of the flow shear in the outer half island, while across the X-point cut the flow is almost flat in the whole island region. Meanwhile it was found that the density fluctuations drop near the O-point region while elevated at the X-point region, which is in agreement with the gradient drive of the turbulence. The results indicate that both the perpendicular flow and the density fluctuation level are modulated by the naturally rotating tearing mode near the island boundary. The cross- correlation between the perpendicular flows and the oscillating electron temperature further reveals that the modulation of the perpendicular flow occurs mainly inside and in the vicinity of the island. [1] Bardóczi L. et al 2016 Phys. Rev. Lett. 116 215001 [2] Choi M.J. et al 2017 Nucl. Fusion 57 126058 [3] Kim E.J. and Diamond P.H. 2003 Phys. Rev. Lett. 90 185006 [4] Schmitz L. et al 2012 Phys. Rev. Lett. 108 155002

Speaker: Min Jiang

14:00 P4.1091 Real-time multichannel tokamak plasma profile simulations using the RAPTOR code and the QLK-NN first-principle transport model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1091.pdf Real-time multichannel tokamak plasma profile simulations using the RAPTOR code and the QLK-NN first-principle transport model F. Felici1 , J. Citrin2 , K. van de Plassche2 , A.A. Teplukhina1 , A. Ho2 , C. Bourdelle3 , O. Sauter1 , the EUROFusion MST1 Team4 and JET contributors5 1 EPFL-SPC, CH-1015, Lausanne, Switzerland. 2 DIFFER, Eindhoven, The Netherlands. 3 CEA, IRFM, France. 4 See http://www.euro-fusionscipub.org/mst1 5 See the author list of: X. Litaudon et al 2017 Nucl. Fusion 57 102001 Real-time capable yet accurate simulations of the plasma profile evolution have important ap- plications in discharge preparation and optimization, real-time profile reconstruction and con- trol.For the first time, real-time-capable coupled simulations of the kinetic profiles Te , Ti and ne and q profile have been obtained that agree well with experimental data. The RAPTOR rapid profile evolution code was used for this purpose, coupled to a first-principle based model to pre- dict the transport coefficients for the kinetic profiles. This transport model, named QLK-NN, is a neural network emulation of results from the QuaLiKiz quasilinear gyrokinetic code [1]. This allows the fluxes to be evaluated in less than a millisecond per radial point per time step. An initial version of QLK-NN, named QLK-NN4Dkin, extending the original proof of principle in [2] to include kinetic electrons, takes as inputs the normalised logarithmic ion temperature gra- dient R/LTi , the ion to electron temperature ratio Ti /Te , the safety factor q, and magnetic shear s and returns the electron and ion heat flux, and electron diffusion and pinch coefficients. This model was trained in the regime where turbulence drive is dominated by ITG modes and has proven successful in reproducing kinetic profiles from a well-diagnosed JET discharge by set- ting only the kinetic profile boundary conditions at the top of the pedestal [3]. First results using RAPTOR with a more advanced version of the neural network transport model, QLK-NN10D [4], are also presented. This model is trained on an extended parameter space including further dependence on the electron temperature gradient, the density gradient, local aspect ratio, colli- sionality, impurity content, and perpendicular flow shear, and covers ITG/TEM/ETG turbulence regimes. First experimental tests are foreseen on JET and MST1 devices in 2018. References [1] Citrin, J. et al. 2017 Plasma Physics and Controlled Fusion 59 124005 [2] Citrin, J. et al. 2015 Nuclear Fusion 55 092001 [3] Felici, F. et al. 2018 Submitted to Nuclear Fusion [4] v.d. Plassche, K. et al. This conference

Speaker: Federico Felici

14:00 P4.1092 Fluctuations measurements in TEM and ITG dominated negative triangularity plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1092.pdf Fluctuations measurements in TEM and ITG dominated negative triangularity plasmas M. Fontana1 , L. Porte1 , O. Sauter1 , S. Coda1 , Ajay C. K.1 , S. Brunner1 , G. Merlo2 , A. Fasoli1 and the TCV team 1 Swiss Plasma Center-EPFL, Lausanne, 1015, Switzerland 2 University of Texas at Austin, Austin, TX 78712, United States Past experiments on TCV have shown that fluctuations in negative triangularity discharges are suppressed with respect to positive triangularity plasmas with comparable profiles and hea- ting [1][2]. These past observations had been only conducted in ohmic or EC heated discharges where Te /Ti > 1. Gyrokinetic simulations show these plasmas to be dominated by electron driven turbulence, especially Trapped Electon Modes (TEM) [3]. If such confinement impro- vements were retained also in low Te /Ti plasmas, where Ion Temperature Gradient (ITG) driven turbulence is dominant, it would be particularly interesting for the design of negative triangula- rity DEMO-like machines. For this reason, recent experiments have exploited the versatile heating system of TCV to investigate the effects of triangularity on transport and fluctuations in plasmas with Te /Ti ≤ 1. Discharges with symmetric positive and negative triangularity, characterized by comparable density and temperature profiles, have been obtained using different levels of Neutral Beam Injector (NBI) power. The CECE diagnostic has been used to measure temperature fluctuations in the region 0.7 < ρ < 0.85. These measurements show reduced relative fluctuations in negative triangularity plasmas, compared to positive triangularity discharges, also in cases where NBI is the dominant source of heating. Linear gyrokinetic simulations, performed with the GENE code, suggest that turbulence, in these plasmas, is dominated by ITG modes. Non-linear gyrokinetic simulations will be employed to investigate the effects of Te /Ti on the dominant instability regime. The foreseen fluctuations levels, calculated with the use of a synthetic diagnostic, will be compared with the experimentally measured ones. References [1] Zhouji Huang. Experimental study of plasma turbulence in the TCV tokamak. PhD thesis, 2017. [2] M. Fontana, L. Porte, S. Coda, O. Sauter, and The TCV Team. The effect of triangularity on fluctuations in a tokamak plasma. Nuclear Fusion, 58(2):024002, 2018. [3] Gabriele Merlo. Flux-tube and global grid-based gyrokinetic simulations of plasma microturbulence and comparisons with experimental TCV measurements. PhD thesis, EPFL, 2016.

Speaker: Matteo Fontana

14:00 P4.1093 Shear effect on edge turbulence during the L-H transition in JET and ASDEX Upgrade plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1093.pdf Shear effect on edge turbulence during the L-H transition in JET and ASDEX Upgrade plasmas F. Clairet1, A. Medvedeva2, C. Bottereau1, G. Dif-Pradalier1, X. Garbet1, U. Stroth2,3, L. Meneses4, ASDEX Upgrade team2,a), JET contributorsb) and EUROfusion MST1 teamc) 1 CEA, IRFM, 13108 St-Paul-Lez-Durance, France 2 Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany 3 Physik-Department E28, Technische Universität München, 85747 Garching, Germany 4 IPFN, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal a) For a list of members, see Appendix of A. Kallenbach et al, Nucl. Fusion 57 102015 (2017) b) For a list of members, see Appendix of X. Litaudon et al Nucl. Fusion 57 102001 (2017) c) For a list of members, see Appendix of H. Meyer et al, Nucl. Fusion 57 102014 (2017) It is widely accepted that the improvement of the confinement in an L to H-mode transition is the result of the suppression of the edge turbulence and that the radial electric field (Er) plays a key role in the explanation of transport. In fact, sheared poloidal flows can influence the turbulence via shear decorrelation mechanisms and, as a consequence, modify the induced transport. We have performed high radial resolution turbulence measurements using fast frequency swept reflectometry which is especially well suited for the study of the narrow pedestal region. Measurements during intermediate transitions, such as the I-phase in AUG and the M-mode in JET plasmas, have been performed. These L to H transition phases allow following the evolution of the turbulence and the mechanisms involved as they can provide time for statistics. We observe that both I-phase and M-mode offer similar characteristics in the modifications of their turbulence frequency spectra, changing from broadband to coherent modes in the pedestal region along with the deepening of the diamagnetic contribution of the radial electric field well. Moreover, a detailed analysis of the complex reflected signal displays a single side band feature at low frequency around few kHz and reverses of sign radially. This feature is discussed in terms of eddy tilting in changing ExB shear flow. The result is consistent with previous observations [1] of eddy breaking and tilting by edge sheared flows and could be the cause [2] for the observed particle transport reduction. [1] I. Shesterikov et al. Phys. Rev. Letter 111, 055006 (2013) [2] P. Manz, Phys et al. Rev. Letter 103, 165004 (2009)

Speaker: Frederic Clairet

14:00 P4.1094 Core impurity rotation in TJ-II plasma scenarios in which combined ECRH and NBI heating is used to mitigate impurity accumulation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1094.pdf Core impurity rotation in TJ-II plasma scenarios in which combined ECRH and NBI heating is used to mitigate impurity accumulation B. López-Miranda1, B. Zurro1, A. Baciero1, I. Pastor1, G. Rattá1 and TJ-II team1 1 Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain In stellarators and tokamaks, long impurity confinement times, or impurity accumulation, is observed in some regimes [1, 2]. It is well known that avoidance of this deleterious effect is critical for present day devices and future fusion reactors. Electron Cyclotron Resonance Heating (ECRH) has been demonstrated as an effective tool to mitigate this problem, as its application has the capability to avoid impurity accumulation [1]. The goal of the present study is to investigate solid-rigid core rotation, in TJ-II plasma scenarios where Neutral Beam Injection (NBI) heating and ECRH are combined, and its role in particle and impurity confinement mitigation. For this purpose, the main plasma rotation diagnostic has been a high spectral resolution spectrometer [3]. It has been upgraded to permit collection of plasma light emissions without the need for a fibre bundle. Moreover, in order to overcome reduced impurity light emission, long exposure times and flexibility in the number of spatial channels employed (19 to 29) permit compatibility with the purpose of the experiment. The behaviour of core plasma poloidal rotation, as measured by passive Doppler spectroscopy of emission lines for the carbon ions C+4 and C+5, versus line-averaged electron plasma density has been evaluated for reference NBI discharges in which ECRH is applied at different power levels and is focused at different plasma radii. Representative results, obtained for a range of ECRH overlapped with NBI heating scenarios, are shown in order to assess whether changes in radial electric field resulting from this operational method are a key parameter to mitigate impurity confinement in this hybrid heating regimes. [1] Tamura N et al., Phys. Plasma 24 056118 (2017) [2] Sertoli M et al., Plasma Phys. Contrl. Fusion 57 7 (2017) [3] Baciero A, Zurro B et al., Rev. Sci. Instr. 72 971 (2001)

Speaker: Belen Lopez-Miranda

14:00 P4.1095 Turbulent impurity transport in DIII-D plasmas with additional on-axis electron heating

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1095.pdf Turbulent impurity transport in DIII-D plasmas with additional on-axis electron heating T. Odstrcil1 , N.T. Howard1 , F. Sciortino1 , P. Rodriguez-Fernandez1 , K. Thome2 1 MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139, USA 2 Oak Ridge Associated Universities, Oak Ridge, TN 37831, USA Impurities in the plasma present a serious threat to the operation of fusion reactors due to fuel dilution and excessive radiative cooling. On-axis electron heating is considered the most effective tool to control central impurity density. However, the actual mechanism of impurity removal is not trivial; the heating is known to modify neoclassical and turbulent transport [1] as well as the MHD activity associated with a core 1/1 mode [2]. To disentangle such complex behavior, experiments on the DIII-D tokamak were designed using a “predict-first” approach with TGYRO coupled with the TGLF and NEO codes to clarify role of turbulent flux driven by electron heating. Neoclassical and MHD contributions were reduced via optimization of im- purity poloidal asymmetry profiles [3] in ELMy H-mode discharges without sawteeth activity. Initial modeling predicted a factor of five variation in the mid-radius impurity transport coeffi- cients D and v caused by changes in NBI/ECRH heating mix. Impurity transport will be probed experimentally by trace injection of silicon and tungsten particles utilizing a new laser blow off (LBO) system recently installed on DIII-D. LBO is capable of producing multiple short injec- tions (∼0.1 ms) in a single discharge, which is essential for a seperate determination of diffusion and pinch effects. Low-k and intermediate-k plasma fluctuation are monitored by beam emis- sion spectroscopy (BES) and Doppler back scattering (DBS) diagnostics, which combined with TGLF modelling allow for the determination of the dominant turbulent regime. Comparison of the measured transport coefficients for mid-Z and high-Z impurity transport with the TGLF modeling will be presented for various heating levels and deposition locations, spaning a wide range electron/ion heat fluxes. This work was supported by U.S. Department of Energy award DE-SC0014264 and DIII-D cooperative agreement DE-FC02-04ER54698. References [1] R. Dux, R. Neu, A. G. Peeters et al., Plasma Phys. Controlled Fusion 45, 1815-1825 (2003). [2] M. Sertoli, T. Odstrcil, C. Angioni and ASDEX Upgrade Team, Nucl. Fusion 55, 113029 (2015) [3] T. Odstrcil, T. Putterich, C. Angioni et al., Plasma Phys. Controlled Fusion 60.1 (2017).

Speaker: Tomáš Odstrčil

14:00 P4.1096 Multi-species model for study of ion plasma filaments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1096.pdf Multi-species Model for study of Ion Plasma Filaments A. S. Poulsen1, V. Naulin1, J. J. Rasmussen1 1 Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark In future devices as ITER the main fuel will be comprised of a mix of deuterium and tritium to achieve burning plasma conditions. Additionally, in a burning plasma Helium and radiating impurities are often main components which should be considered. In order to further the understanding of the efect the plasma mix has on plasma turbulence and transport it is necessary to be able to model the individual species separately. We present results on the use of a multi-species model for simulating the infuence of isotopes on transport and turbulence in the edge and SOL. The model is an extension of on the four feld HESEL model¹, ion density and pressure equations for each new species is considered. We examine the infuence on multiple species with diferent mass and charge on the propagation of blobs as a frst application of the enhanced code. Simulations of seeded blobs show that ions with similar charge but diferent mass can be sufficiently well described by using an efective mass for ions. However, when dealing with multiple charge states, the system can no longer be described using an efective charge as in particular the associated FLR efects difer leading diferent dynamics. In general the use of a multi ion species model present a much more versatile tools as it can describe systems that are ill suited for efective mass studies, such as local seeding of neutral impurities. ¹Madsen, J. et al, Physics of Plasmas 23, 032306 (2016)

Speaker: Aslak Sindbjerg Poulsen

14:00 P4.1097 Isotope effect in energy confinement in high density FT-2 tokamak regimes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1097.pdf Isotope effect in energy confinement in high density FT-2 tokamak regimes. D.V. Kouprienko1, A.B. Altukhov1, L.A. Esipov1, A.D. Gurchenko1, E.Z. Gusakov1, S.I. Lashkul1, S. Leerink2 1 Ioffe Institute, St. Petersburg, Russia 2 Aalto University, Espoo, Finland The isotope effect in a tokamak confinement resulting, in contradiction to the theory expectations, in the anomalous transport decrease in numerous experiments with growth of the hydrogen isotope number remains a long-standing puzzle for the period of 40 years [1]. The novel approach to explanation of this effect, which is favorable for fusion applications, is based on accounting for the multi-scale turbulence nonlinear interactions. Within this approach the isotope effect in particle confinement, but not energy, was demonstrated recently in FT-2 tokamak in hydrogen (H) and deuterium (D) ohmic discharges with modest electron density ~ (1.5-2.5)×1019 m-3. The higher particle confinement in D-discharges was correlated in these experiments to a higher excitation level of the GAM in agreement with results of specially performed global full-f gyrokinetic modeling by ELMFIRE code [2, 3]. In this paper we present the results of further development of energy confinement studies [4] in FT-2 tokamak at high densities. Special series of Ohmic discharges are performed in H and D plasmas within the chord averaged density range ~ (5–9)×1019m-3. The energy confinement time calculations based on measured kinetic profiles demonstrate essential difference in τE behavior for different gases. Hydrogen plasma follows the LOC to SOC transition that happens at the densities above ~ 6×1019 m-3. At the same time deuterium plasma behavior at the highest densities shows further increase of τE with growing density typical of LOC scenario. In vicinity of tokamak operational density limits lim~ 9×1019 m-3 the energy confinement time in D is twice as high as in H. Confinement improvement in D- discharge is accompanied by the flattening of the electron density profile in the central region and its steepening at the edge, followed by essential decrease of radiation losses. The turbulence evolution with growing plasma density in these regimes is studied both with reflectometry diagnostics and by the gyrokinetic modeling. [1] F. Wagner and U. Stroth 1993 Plasma Phys. Control. Fusion 35 1321 [2] A.D. Gurchenko et al. 2016 Plasma Phys. Control. Fusion 58 044002 [3] P. Niskala et al. 2017 Plasma Phys. Control. Fusion 59 044010 [4] D.V. Kouprienko et al. 2017 44th EPS Conference on Plasma Physics, P4.179

Speaker: Denis Kuprienko

14:00 P4.1098 Numerical investigation of fast-ion driven modes in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1098.pdf Numerical investigation of fast-ion driven modes in Wendelstein 7-X C. Slaby1 , A. Könies1 , R. Kleiber1 , S. Äkäslompolo1 1 Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstaße 1, 17491 Greifswald, Germany Fast ions in fusion plasmas are typically generated by heating methods such as neutral beam injection or ion cyclotron resonance heating. In future fusion reactors, there will additionally be fast alpha particles created from the deuterium-tritium fusion reaction. The fast ions need to remain in the plasma for a time period that is comparable to the slowing-down time in order to thermalize. If they leave the plasma prematurely, energy losses and possibly damage to plasma- facing components are the consequences [1]. Especially in a stellarator, due to the lack of a continuous symmetry, the confinement of fast particles is not guaranteed in general. Hence, one of the optimization goals of Wendelstein 7-X is the good confinement of fast ions [2]. However, in the process of slowing down, even the well-confined the fast particles can excite Alfvénic perturbations in the plasma, which have been shown to enhance fast-ion transport [1]. This paper investigates the resonant interaction of fast particles with Alfvénic perturbations in the Wendelstein 7-X stellarator using the non-linear CKA-EUTERPE code package [3]. The approach is perturbative in the sense that an MHD mode structure is calculated by CKA, which is used by the gyro-kinetic code EUTERPE to compute the power transfer from the fast particles to the mode. The mode structure remains fixed for the entire simulation run. Our simulations include a triple-slowing-down distribution of the fast ions coupled with re- alistic fast-ion density profiles computed by the ASCOT code [4, 5]. A fast-ion collision oper- ator is included in the EUTERPE modeling to assess the effects of pitch-angle collisions and slowing-down drag on the non-linear dynamics of the mode and its transport properties. References [1] H. H. Duong et al., Nucl. Fusion 33, 749 (1993) [2] G. Grieger et al., Phys. Fluids B (7), 2081 (1992) [3] T. B. Fehér, Ph.D. thesis, University Greifswald, 2013 [4] J. A. Heikkinen, S. K. Sipilä, Phys. Plasmas 2, 3724 (1995) [5] E. Hirvijoki et al., Comp. Phys. Comp. 185, 1310 (2014)

Speaker: Christoph Slaby

14:00 P4.1099 Evolution of energy losses and of microturbulence at modulated ECRH of L-2M stellarator plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1099.pdf Evolution of energy losses and of microturbulence at modulated ECRH of L-2M stellarator plasmas G.M. Batanov, V.D. Borzosekov, S.E. Grebenshchikov, N.K. Kharchev, A.A. Kharchevsky, Yu.V. Kholnov, L.V. Kolik, E.M. Konchekov, A.A. Letunov, A.E. Petrov, N.N. Skvortsova V.D. Stepakhin, D.G. Vasilkov A.M. Prokhorov General Physics Institute RAS, Moscow, Russia After recent upgrade of the electron-cyclotron resonance heating (ECRH) system of the L-2M stellarator it is possible to study plasma dynamics at 100% modulated ECRH. Such modulation implies that heating goes in a form of a sequence of microwave pulses and between pulses high-temperature current-free plasma is confined without auxiliary heating. One of many interesting aspects to study in this operational regime is evolution of energy losses namely the steep increase of energy losses that happens shortly after (~ 1 ms) start of each heating pulse (Fig.1). Fig.1. Diamagnetic signal – black solid line; shaded rectangle is the time interval with steep increase of energy losses. Experiments reported here were carried out at average electron density ne = 2·1019 m-3 and 400 kW of central X2 ECRH. Lengths of microwave pulses and time interval between pulses (quiet interval) were varied. Main focus of this report is an attempt to find relation between the steep increase of energy losses and evolution of microturbulence that was investigated using microwave scattering techniques at the L-2M. Four collective scattering diagnostics operate in the ECRH cross-section while Doppler reflectometry is installed in another cross-section. For density fluctuations in the local region near plasma axis it was found that intensity of density fluctuations 𝑛2~ is maximal in the time interval of the energy losses increase. Line averaged measurements of density fluctuations yielded same results. However, results of edge localized measurements of Doppler reflectometry demonstrate no change of fluctuations intensity. But change of Doppler reflectometry spectra is prominent: till the onset of the energy losses steep increase the peak near zero-frequency dominates in the spectrum and when the increase starts the spectrum becomes broader while the side peak arises near 750 kHz. The reported study was funded by RFBR project № 18-02-00621.

Speaker: Valentin Borzosekov

14:00 P4.1100 Direct determination of background neutral density profiles from neutral particle analyzers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1100.pdf Direct determination of background neutral density profiles from neutral particle analyzers K. Mitosinkova1,2 , B. Geiger3 , P. A. Schneider3 , A. van Vuuren3 , A. N. Karpushov4 , the ASDEX Upgrade team5 , the TCV team6 and the EUROfusion MST1 team7 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 3 Max-Planck Institute für Plasmaphysik, Garching, Germany 4 Swiss Plasma Center, EPFL, Lausanne, Switzerland 5 See author list of A. Kallenbach et al 2017 Nucl. Fusion 57 102015 6 See author list of S Coda et al 2017 Nucl. Fusion 57 102011 7 See author list of H Meyer et al 2017 Nucl. Fusion 57 102014 Profiles of the background neutral density, n0 , are important for plasma transport understanding because n0 is responsible for charge-exchange losses, as well as, for plasma fuelling. However, detailed n0 profiles are not routinely available at most fusion devices. Here we present a fast reconstruction of n0 , directly from neutral particle analyzer (NPA) data, which has become possible thanks to the steady improvement of ion temperature and ion density measurements. NPAs measure energy resolved fluxes of neutrals escaping the plasma, Γ(En ), formed by charge-exchange collisions between the plasma ions and the background neutrals. Calculated fluxes Γ(En ), based on knowledge of the other plasma parameters, are fitted to measured ones by optimizing n0 profile parameters. The method is successfully benchmarked by comparing the actual NPA measurements with synthetic NPA fluxes from FIDASIM simulation with calculated n0 used as the input. In addition the reconstructed n0 profiles are compared with predictions from KN1D, TRANSP/FRANTIC and DOUBLE. As a fist application of the n0 profiles obtained from the new direct analysis, ELM-resolved neutral densities will be presented. Moreover, the impact of the inferred neutral densities on the level of charge-exchange losses will be discussed for ASDEX Upgrade and TCV cases.

Speaker: Klara Mitosinkova

14:00 P4.1101 Fast-ion transport study in the plasma periphery of ASDEX Upgrade using fast-ion D-alpha spectroscopy

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1101.pdf Fast-ion transport study in the plasma periphery of ASDEX Upgrade using fast-ion D-alpha spectroscopy A. Jansen van Vuuren1 , B. Geiger1 , P.A. Schneider1 , A.S. Jacobsen1 , K. Mitosinkova2 , T. Lunt1 , J. Gonzalez-Martin3 and the ASDEX Upgrade and EUROfusion MST1 Teams1∗ 1 Max-Planck Institute for Plasma Physics, Garching, Germany 2 Institute of Plasma Physics of the CAS, Prague, Czech Republic 3 Dept. of Mechanical and Manufacturing Engineering, University of Seville, Seville, Spain Good confinement of fast ions in the plasma periphery is of particular importance for fusion devices since these particles can easily be transported to unconfined orbits, become lost and potentially damage first wall components. Several mechanisms exist that can redistribute fast ions, of which the mode-induced transport might be the most critical one. However for a detailed fast-ion transport analysis first, charge exchange (CX) losses and drifts in perturbed equilibria must be considered. Low density experiments were performed at ASDEX Upgrade with 5 MW of off-axis NBI heating that show high fast-ion densities at the edge. During those experiments strong CX losses were observed by a new edge fast-ion Dα (FIDA) diagnostic that measured intense signals originating from CX reactions between fast ions and background neutrals. In order to model this so called passive FIDA light first, the background neutral density is modelled with KN1D and EMC3-EIRENE. The neutral density is then incorporated in TRANSP simulations which include CX losses in the prediction of the fast-ion distribution. Finally the predicted fast-ion and background neutral-density profiles are translated into synthetic passive FIDA spectra using FIDASIM. When comparing measured and simulated spectra the best agreement is found for high neutral densities that cause a reduction of up to 15% of the total fast-ion density. This shows that CX losses can have a strong impact on the fast-ion density at the edge of ASDEX Upgrade. In addition, the experimental measurements show a clear modulation of the passive FIDA signal during edge localised modes (ELMs) and after the application of RMPs. This is partly explained by a modification of the background neutral density and possibly by fast-ion losses, as observed using the fast-ion loss detectors [1]. Detailed modelling results will be presented, including ELM resolved simulations and predictions of the 3D perturbations induced by RMPs. References [1] M. García-Muñoz et al, Plasma Phys. Control. Fusion 55, 12 (2013) ∗ See H. Meyer et al, Nucl. Fusion 57 102014 (2017)

Speaker: Anton Jansen van Vuuren

14:00 P4.1102 Non-local reduction of the electron heat flux and changes in impurities transport in certain T-10 experiments with W-limiter

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1102.pdf Non-local reduction of the electron heat flux and changes in impurities transport in certain T-10 experiments with W-limiter S.V. Neudatchin, A. A. Borschegovskiy, I.S. Pimenov, D.A. Shelukhin, NRC Kurchatov Institute, Russia, Moscow,123182, Kurchatov sq 1 The new phenomenon has been found in some shots with W-limiter (and Li-coating) in the plasmas with two EC-beams with power injected in opposite directions under approximately equals toroidal angles and EC-power 1.5 MW. The spontaneous rise of the electron density nearly in the all plasma column occurs simultaneously with the rise of Te in the wide region (0

Speaker: Sergey Neudatchin

14:00 P4.1103 Rotation-induced electrostatic-potentials and density asymmetries in NSTX

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1103.pdf Rotation-induced electrostatic-potentials and density asymmetries in NSTX L. F. Delgado-Aparicio1, R. E. Bell1, G. J. Kramer1, M. Podestà1, B. P. LeBlanc1, A. Diallo1, S. Gerhardt1 and M. Ono1 1 Princeton Plasma Physics Laboratory, Princeton, NJ, 08540, USA The computation of rotation-induced electrostatic potentials is currently being used to study the associated two-dimensional distribution of impurity density asymmetries in NSTX and NSTX-U plasmas. This calculation relies on flux-surface quantities like electron and ion temperature (Te,i) and rotation frequency (ωφ) and finds the 2D electron, deuterium and carbon density profiles self-consistently assuming the presence of a poloidal variation due to centrifugal forces. The iterative solution [1] for the electrostatic potential difference [Δϕ = ϕ(θ) - ϕ(θ =0)] are routinely obtained and compared with the values derived from the ideal solution to quasi-neutrality, which assumes that the main low-Z intrinsic impurity (e.g. carbon) is in the trace limit. An ad-hoc solution, which attempts to extend the ideal Fig. 1. Rotation-induced potential and overall effect in approximation beyond the trace limit [2], NSTX does not adequately captures the physics of finite mass and Zeff. Nevertheless, the net-change of the plasma potential profile due to the presence of the rotation-induced electrostatic well is smaller than 6%. This calculation also finds 2D asymmetries for medium- to high-Z impurity density profiles that are at the trace limit with very small changes to quasi-neutrality and Zeff. While the asymmetry in the core radiated power density from low-Z ions (e.g. D, C, O, Ne) is relatively small, the core density and radiation from medium- to high-Z’s (e.g. Ar, Fe, Mo, W) will be strongly affected by centrifugal forces. This work is supported by the U.S. Department of Energy, Office of Fusion Energy Sciences under contract number DE-AC02-09CH11466. [1] E. Belli and J. Candy, PPCF, 51, 075018, (2009). [2] T. Odstrcil, at al., PPCF, 60, 014003, (2018).

Speaker: Luis F. Delgado-Aparicio

14:00 P4.1104 The helicity and the generation of large scale flows in confined plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1104.pdf The helicity and the generation of large scale flows in confined plasma F. Spineanu, M. Vlad National Institute of Laser, Plasma and Radiation Physics, Bucharest, Romania The formation of quasi-coherent, large scale structures in turbulent plasma is known from numerical simulations and from experimental observations. In particular, formation of a layer of sheared quasi-laminar poloidal rotation which acts as a transport barrier (ITB, Internal Transport Barrier) has been observed. It is not always clear what are the conditions which trigger ITB formation and in gyrokinetic simulations some additional factor, beyond the Reynolds stress, appears to be necessary. We prove that an essential element leading to the formation of coherent, sheared poloidal flows, is the turbulent helicity. Currently, this term is absent from the statistical analysis of the turbulence, with the consequence that the Reynolds stress seems ineffective to convert the tur- bulence into Internal Transport Barrier. In a basic statistical analysis of turbulence the two-point correlations must include a term which breaks the parity invariance and in spectral representa- tion is purely imaginary. It is not possible to include this contribution in a renormalization of the linear propagator. We propose a fundamental justification and a detailed description of the helical content of the fluctuating field for current turbulent models, like ITG. The connection between laminar sheared flow (like in the H-mode rotation layer) and the filamentary structures (like in Edge Localized Modes or, more generally, in Kelvin-Helmholtz fluid instability) is examined as a conversion of the uniform vorticity into topological linking of helical streamlines. We will provide a quantitative description of this process. Conversely, the effect of turbulent distribution of Gaussian linking is shown to contribute to an inverse cascade. The approach developed in this work is inspired by neutral turbulent fluids. However, the plasma instabilities have a natural helical content at the scale of the vorticity advection (of the order of sonic Larmor radius).

Speaker: Florin Spineanu

14:00 P4.1105 Monte-Carlo simulation of fast ion transport in magnetic island regions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1105.pdf Monte-Carlo simulation of fast ion transport in magnetic island regions Rodrigo Saavedra1 and Julio J. Martinell1 1 Instituto de Ciencias Nucleares, UNAM, A. Postal 70-543, México D.F., Mexico There is theoretical evidence of the formation of magnetic islands in rational magnetic sur- faces in toroidal fusion devices. Furthermore it has been shown that, in electron cyclotron reso- nance heating (ECRH) experiments, such regions may act as transport barriers for suprathermal electrons [1]. When the plasma heating is produced by neutral beam injection (NBI), a popula- tion of fast ions arises which interacts with the magnetic islands altering its transport. Here we study the transport of a population of fast particles in the presence of a magnetic is- land configuration produced by collisions with a Maxwellian plasma background consisting of electrons and a single species of ions, which are described by Lorentz scattering [2]. We obtain the time evolution of the distribution function by solving Langevin equations for a large popu- lation of particles corresponding to ECRH or NBI. Then, transport coefficients are calculated. The equations of motion for the guiding center (GC) of a charged particle in a strong magnetic are solved in 3 spatial dimensions (x, y, z) and 2D in velocity space represented by the normal- ized kinetic energy v2 and the pitch angle λ . The set of equations which give the evolution of phase space variables can be expressed in the form of Langevin equations which simulate the effect of collisions of the test particle with the plasma background [3]. They include the energy and pitch angle stochastic collision operators [2]. In order to determine transport coefficients the time evolution of a test distribution function of N particles is obtained with Monte Carlo simulations, which is equivalent to solving the Fokker- Planck equation. The equations are solved with a fourth order Runge-Kutta algorithm with a random choice of the sign in the Lorentz collision operators at each time step. Additionally a radial electric field was included, which enhances the transport of particles. The diffusion 1 coefficient was calculated from the standard expression D = 2tN ∑Nj=1 (x j (t) − x j (0))2 where x j (t) is the position of a particle at time t. The results show that the island acts as a transport barrier for electrons, and the ions experi- ence a significant modification of their transport across the island. References [1] M. A. Ochando et. al., Plasma Phys. Control. Fusion 45, 221 (2003). [2] A. H. Boozer and G. Kuo-Petravic, Physics Fluids 24, 851 (1981) [3] A. De Bustos-Molina, PhD thesis, Universidad Complutense de Madrid (2013).

Speaker: Rodrigo Saavedra

14:00 P4.1106 Highly collisional two-fluid and gyrokinetic simulations of tokamak edge turbulence and the transition between kinetic and fluid regime

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1106.pdf Highly collisional two-fluid and gyrokinetic simulations of tokamak edge turbulence and the transition between kinetic and fluid regime K. Hallatschek1 , J. Candy2 , E.A. Belli2 1 Max-Planck-Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany 2 General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA To arrive at a common basis, the gyrokinetic code CGYRO [1] and the non-local two-fluid code NLET [2] have both been applied to identical parameters sets ranging from highly collisional, resitive ballooning turbulence scenarios - which approach the fluid limit - relevant to the edge of a tokamak, up to the ITG turbulence at higher temperatures in the core-edge transitional regime. Earlier attempts with a less sophisticated collision operator in the gyrokinetic code were un- successful to come close to the expected transport values in the edge regime. Surprisingly, it has been much easier to match fluid and gyrokinetic results in the lower collisionality ITG regime in the core-edge transitional region. Even in the collisionless core the transport difference between fluid and gyrokinetic results for non-marginal instabilities are . 30% [3]. A non-trivial, novel result is that the linear growth rate and nonlinear transport agree be- tween the codes in the fluid limit of high collision numbers (νe ∼ 500 − 2000ci /R), not least, because the kinetic code treats the collisions fully implicit and employs the Sugama collision operator with momentum and energy conservation, Galileian invariance and numerically exact self-adjointness property. For example, runs with resistive ballooning turbulence in the edge regime using the CGYRO and the NLET code were performed at the parameters R/Ln = 10, R/LT = 0, ε = r/R = 0, q = 3.2, Ti = Te , νee = 586ci /R. For the fully developed turbulence the amplitude, pattern, time- and length-scales of the turbulence agree within the statistical errors, indicating that the proper fluid limit has been obtained. E.g., the gyro-Bohm particle diffusivities in the mentioned case are χCGY RO = 772, χNLET = 796 (in units of ρi2 ci /R). The cross ion and electron heat diffusivities i,Q i,Q e,Q e,Q are slightly less then 3/2 times that, χCGY RO = 1047, χNLET = 1131, χCGY RO = 1034, χNLET = 1120. Regarding the structure of the turbulence the typical fluid-like Kelvin-Helmholtz plumes ap- pear in the simulations, which is very different from the case of collisionless turbulence, with its strongly dispersive behaviour and rather diffuse and random perturbations [1] J. Candy, E.A. Belli, R.V. Bravenec, J. Comput. Phys. 324, 73 (2016) [2] K. Hallatschek, A. Zeiler, Phys. Plasmas 7, (2000) 2554 [3] K. Hallatschek, Phys. Rev. Lett. 93, 065001 (2004)

Speaker: Klaus Hallatschek

14:00 P4.1107 Turbulent impurity transport of electrostatic drift wave in tokamak plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1107.pdf Turbulent impurity transport of electrostatic drift wave in tokamak plasmas M. K. Han1,2, J. Q. Dong2,3, Z. X. Wang1 and Yong Shen2 1 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian, 116024, China 2 Southwestern Institute of Physics, Chengdu, 610041, China 3 Institute of Fusion Theory and Simulation, Zhejiang University, Hangzhou, 310027, China Abstract Experiments in tokamaks show that, in addition to neoclassical transport, small-scale turbulence induced by drift instabilities plays a significant role in particle transport [1-3]. In recent experiments on HL-2A, Tore Supra el al., it is found that the experimental threshold (especially the critical gradients) is in well agreement with the one calculated with gyrokinetic model [4]. Meanwhile, it is well known that the impurity problem is of great importance since even a small quantity of impurity strongly enhances the radiation loss and leads to the dilution of plasma reactivity [5-6]. In order to investigate the turbulent impurity transport of electrostatic drift wave, the quasilinear particle transport is considered in the toroidal gyrokinetic integral code HD7. Detailed analyses about the dependence of particle flux on plasma parameters, especially the gradient thresholds are performed. Comparing various electrostatic drift instabilities, it reveals that the impurity transport induced by impurity ions is of great significance in contrast with other electrostatic instabilities and is expected to have significant influence on plasma transport and confinement. References [1] X. Garbet et al, Phys. Rev. Lett. 91; J. Weiland et al, Nucl. Fusion 29 [2] C. Angioni et al, Plasma Phys. Control Fusion 51 [3] M. K. Han et al, Nucl. Fusion 57 [4] D. Villegas et al, Phys. Rev. Lett. 105; W. L. Zhong et al, Phys. Rev. Lett. 117 [5] B. Coppi et al, Phys. Rev. Lett. 17 [6] Yong Shen et al, Nucl. Fusion 58

Speaker: Mingkun Han

14:00 P4.1108 Explaining cold-pulse dynamics in tokamak plasmas using local turbulent transport models

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1108.pdf 45 EPS Conference Conference onon Plasma Plasma Physics, Physics 2018, Prague, Czech Republic P4.1108 Explaining Cold-Pulse Dynamics in Tokamak Plasmas using Local Turbulent Transport Models P. Rodriguez-Fernandez1, A.E. White1, N.T. Howard1, B.A. Grierson2, G.M. Staebler3, J.E. Rice1, X. Yuan2, N.M. Cao1, A.J. Creely1, M.J. Greenwald1, A.E. Hubbard1, J.W. Hughes1, J.H. Irby1, F. Sciortino1 1 MIT Plasma Science and Fusion Center, Cambridge, USA 2 Princeton Plasma Physics Laboratory, Princeton, USA 3 General Atomics, San Diego, USA It has been observed for more than twenty years that rapid edge cooling of fusion plasmas triggers core electron temperature increases on timescales faster than a diffusion time, and that the effect disappears as plasma density is increased. These temperature inversions have been interpreted as strong evidence of nonlocal transport, and have therefore challenged the local transport paradigm encapsulated in predictive electromagnetic drift-wave turbulent transport models. In this work, the TRANSP power balance code coupled with the quasilinear transport model TGLF-SAT1 [1], with a new saturation rule motivated by cross-scale coupling physics and that captures the nonlinear upshift of the critical gradient, are shown to fully describe the cold-pulse phenomenology [2]. The TGLF-SAT1 model is able to quantitatively capture the prompt onset of the core electron temperature inversion, with a magnitude that is qualitatively consistent with experimental trends, as well as the disappearance at high-density. These new results provide further confidence that local transport models can be used to reliably predict plasma behavior in future tokamaks, such as ITER. [1] G.M. Staebler et al., 2017 Nucl. Fusion 57 066046 [2] P. Rodriguez-Fernandez et al., Phys. Rev. Lett. 120, 075001 (2018) This work was supported by U.S. Department of Energy Award No. DE-FC02-99ER5451, using Alcator C-Mod, a DOE Office of Science User Facility. P.R.F. was also supported by U.S. Department of Energy Award No. DE-SC0014264 and a La Caixa Fellowship.

Speaker: Pablo Rodriguez-Fernandez

14:00 P4.1109 Measurement of neon impurity transport by ME-SXR diagnostic in the EAST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1109.pdf Measurement of Neon impurity transport by ME-SXR diagnostic in the EAST tokamak Y. L. Li,1,2* G. S. Xu,1 K. Tritz,3 Y. Liang,1,2 X. Lin,1 H. Q. Liu,1 Q. Zang,1 T. Zhang,1 W. Zhang,1 L. Wang,1 W. Feng,1 X. L. Li,1 and the EAST team 1 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – 2 Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 3 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA *y.li@fz-juelich.de The neon impurity transport has been analysed by multi-energy soft x-ray (ME-SXR) diagnostic in the EAST tokamak. ME-SXR contains five arrays, of which one non-foil is bolometric while four different foil filters (5 μm beryllium, Be, 15 μm Be, 25 μm Be and 50 μm Be foil) are used to measure the radiation spectrum of soft x-ray emitted by plasma. For typical plasma temperature (~450 eV), the bolometer signal is dominated by L-shell emission, while the 5, 15 and 25 μm Be filter arrays primarily measure K-shell lines and the 50 μm Be array measures continuum emission from fully stripped neon. To study the neon transport, the time derivative of the emissivity is introduced to describe the neon impurity transport. The radial perturbation velocity of K-shell line emission emitted by neon impurity is measured about 40 m/s in H mode regime and is originally propagated near the separatrix along with forming two perturbed emissivity peaks in the movement path. In contrast, the perturbation velocity of continuum emission is much slower and is observed to begin to spread near the pedestal top. The estimated electron pressure obtained by multiplying the electron density and electron temperature, which is measured by POINT and ME-SXR respectively, shows that the pedestal top pressure gradually decreases during the neon impurity propagating to the core plasma region. The mitigation of edge localized modes is delayed for 20 ms after the neon injection, after which the recovered ELM eruption time measured by the emissivity in 5 μm Be is twice that in 50 μm Be array. Reference D J Clayton, et al., Plasma Phys. Control. Fusion 54 (2012) 105022 Y. L. Li, et al., Review of Scientific Instruments 86, 123512 (2015)

Speaker: Yongliang Li

14:00 P4.1110 Kinetic flux limiters for the ITER Scrape-Off Layer

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1110.pdf Kinetic flux limiters for the ITER Scrape-Off Layer I. Vasileska1 , D. Tskhakaya2 , L. Kos1 , R. A. Pitts3 , EUROfusion-IM Team∗ 1Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia, 2 Institute of Applied Physics, TU Wien, Fusion@ÖAW, A-1040 Vienna, 3 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France In next generation tokamaks such as ITER, Edge Localized Mode (ELM)-induced transient heat loads on the divertor targets represent the greatest threat to target lifetime. Predicting the ex- pected consequences through modelling is especially challenging and is often attempted through the use of fluid plasma boundary modelling codes, such as SOLPS, in which the ELM is crudely approximated as a fixed increase in anomalous cross-field transport coefficients for particles and heat for a short duration consistent with a specified total ELM energy loss from the plasma, ∆WELM . However, one problem with this approach is that the boundary conditions at the target sheath interface are expected to vary strongly in time through the ELM transient, whilst fixed kinetic heat flux limiters are typically applied in the fluid codes. This contribution describes the first results of efforts to address this issue for ITER simulations under high performance condi- tions using the 1D3V electrostatic parallel Particle-in-Cell (PIC) code BIT1 [1] to provide time dependent kinetic target sheath heat transmission factors (SHTF) for given ∆WELM . In a later stage of the work, these will be used as boundary conditions for calculations of ELM target heat loads using the SOLPS-ITER code [2]. The first, and most challenging step, is to establish BIT1 simulations of the stationary parallel transport in the inter-ELM scrape-off layer (SOL). This has been performed for burning plasma conditions corresponding to the ITER Q = 10, 15 MA baseline at q95 = 3, for which the poloidal length of the 1D SOL is ∼ 20 m from inner to outer target. Typical upstream separatrix param- eters of ne ∼ 3 − 5 · 1019 m−3 , Te ∼ 100 − 150 eV and Ti ∼ 200 − 300 eV are assumed, guided by SOLPS-ITER code runs. Inclined magnetic fields at the targets of (∼ 5◦ ) are included, as are particle collisions, with a total of 3.4 · 105 poloidal grid cells giving shortening factors of 20. Secondary electron emission at the tungsten targets is neglected. In the first instance, a SOL flux tube just outside the separatrix is considered. A typical simulation requires up to 60 days running massively parallel 1152-2304 cores of the EU Marconi super-computer. On this back- ground the ELM transient is then launched, by injecting an ambipolar, Maxwellian source of particles distributed around the midpoint between the two targets and at the Ti,ped , Te,ped , ne,ped characteristic of the H-mode pedestal. The focus of the first ELM simulations will be mitigated Type I ELMs with ∆WELM in the range 0.1 − 1.0 MJ. The ELMs are "switched on" stepwise by increasing the strength of the particle source and incoming particle temperatures (corresponding to ne,ped , Te,ped ). The duration of the ELM pulse is taken to be between 100-200 µs. References [1] D. Tskhakaya et al., Plasma Phys. Control. Fusion,59, 114001 (19pp), (2017); [2] X. Bonnin et al., Plasma and Fusion Research, 11, 1403102, (2016). ∗ See http://www.euro-fusionscipub.org/eu-im

Speaker: Ivona Vasileska

14:00 P4.1111 Reduced fluctuations in high confinement plasmas at negative triangularity on DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1111.pdf Reduced fluctuations in high confinement plasmas at negative triangularity on DIII-D∗ A. Marinoni1 , M.E. Austin2 , M.L. Walker3 , E.M. Davis1 , A.W. Hyatt3 , C.C. Petty3 , M. Porkolab1 , J.C. Rost1 , O. Sauter4 , K.E. Thome5 and the DIII-D Team 1 Plasma Science & Fusion Center, MIT, Cambridge (USA) 2 University of Texas-Austin, Austin (USA) 3 General Atomics, San Diego (USA) 4 Swiss Plasma Center, EPFL, Lausanne (CH) 5 Oak Ridge Associated Universities, Oak Ridge (USA) Plasmas with negative triangularity (δn ) shape on the DIII-D tokamak are characterized by high confinement and normalized beta (H98,y2 = 1.2, βN = 2.6), despite featuring edge pressure profiles typical of an L-mode plasma without Edge Localized Modes. This work was inspired by previous results from the TCV tokamak [1], where the energy con- finement time of collisionless (νeff ∼ 0.2) L-mode plasmas subject to pure Electron Cyclotron Heating (ECH) was shown to double when reversing δ , with other parameters held fixed. The experiments on DIII-D investigated δn plasmas at moderate collisionalities (νeff ' 0.5) in both pure ECH and mixed ion-electron (ECH/NBI) heating regimes, thus exploring for the first time a more reactor relevant regime where Te ∼ Ti . For both heating schemes, plasmas at δn show up to 30% increase in stored energy compared to discharges with matched actuators but positive δ (δ p ). In the high power phase, during which δ p plasmas develop an H-mode pedestal, the δn matched discharges produced 30% more neutrons than the δ p counterpart, which a TRANSP analysis shows to be due to a reduced main ion dilution owing to lower impurity content. The intensity of density fluctuations measured by the Phase Contrast Imaging (PCI) diagnostic [2] is seen to decrease by 50% and 30%, respectively, in the two heating phases at δn . The relative intensity of fluctuations at positive and negative wavenumbers is seen by the PCI to depend on the shape. A linear gyro-kinetic analysis indicates that, in both heating schemes, discharges are dominated by Trapped Electron Modes at ion scale but, unlike the TCV discharges, strong electron scale fluctuations are present in the core. Growth rates are seen to decrease at δn in the spectral region kθ ρs < 2, with the largest decrease seen in the ECH-only phase. References [1] Y. Camenen et al., Nucl. Fusion 47 (2007) 510 [2] J.R. Dorris et al., Rev. Sci. Instrum. 80 (2009) 023503 ∗ Work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility under Award DE-FC02-04ER54698, and under Award DE-FG02-94ER54235.

Speaker: Alessandro Marinoni

14:00 P4.1112 First Results of Transport Studies of injected impurities in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1112.pdf First Results of Transport Studies of injected impurities in Wendelstein 7-X Th. Wegner1 , B. Geiger1 , R. Burhenn1 , F. Kunkel1 , B. Buttenschön1 , A. Langenberg1 , N. Pablant2 , P. Traverso3 , D. Zhang1 and the W7-X Team1 1 Max-Planck Institute for Plasma Physics, Greifswald, Germany 2 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 3 Auburn University, Auburn, AL, USA This contribution explains in detail the experimental setup of the new laser blow-off system on W7-X and presents initial results regarding transport properties of injected impurities which were introduced in plasmas with different conditions. The understanding of impurity transport is a demanding task for stellarators which have a high potential for steady state operation. The accumulation of impurities in confined plasma in certain operation regimes can cause an early pulse termination due to a radiative collapse. The development of favorable operating scenarios that avoid these accumulations is therefore one of the main objectives of W7-X operation. Hence, the investigation of transport properties is inevitable and a new laser blow-off system was installed to inject non-intrinsic, non-recycling impurities in a controlled manner. The system was available from the beginning of the second operation phase OP1.2a and successfully performed more than 300 injections of different mate- rials with varying material thicknesses, spot diameters and injections frequencies. The ablated amount was large enough to measure the emission of several ionization stages from the X-ray to XUV wavelength range with temporal and spatial resolution in different magnetic field con- figurations and plasma parameters. From the temporal decay of the emission one can estimate a confinement time of the injected impurities of about 100 ms. The detailed analysis of the emission by means of the radiation and transport code STRAHL enables the characterization of transport properties, e.g., diffusion and convection coefficient.

Speaker: Thomas Wegner

14:00 P4.1113 Simulation of penetration supersonic beam in fusion plasma using neutral/HESEL model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1113.pdf Multi-species Model for study of Ion Plasma Filaments A. S. Poulsen1, V. Naulin1, J. J. Rasmussen1 1 Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark In future devices as ITER the main fuel will be comprised of a mix of deuterium and tritium to achieve burning plasma conditions. Additionally, in a burning plasma Helium and radiating impurities are often main components which should be considered. In order to further the understanding of the efect the plasma mix has on plasma turbulence and transport it is necessary to be able to model the individual species separately. We present results on the use of a multi-species model for simulating the infuence of isotopes on transport and turbulence in the edge and SOL. The model is an extension of on the four feld HESEL model¹, ion density and pressure equations for each new species is considered. We examine the infuence on multiple species with diferent mass and charge on the propagation of blobs as a frst application of the enhanced code. Simulations of seeded blobs show that ions with similar charge but diferent mass can be sufficiently well described by using an efective mass for ions. However, when dealing with multiple charge states, the system can no longer be described using an efective charge as in particular the associated FLR efects difer leading diferent dynamics. In general the use of a multi ion species model present a much more versatile tools as it can describe systems that are ill suited for efective mass studies, such as local seeding of neutral impurities. ¹Madsen, J. et al, Physics of Plasmas 23, 032306 (2016)

Speaker: A. S. Poulsen

14:00 P4.2002 Relativistic Doppler-boosted gamma-rays in High Fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2002.pdf Relativistic Doppler-boosted γ-rays in High Fields R. Capdessus1 M. King1, D. Del Sorbo2, M. J. Duf1, C. P. Ridgers2 and P. McKenna1 1. Department of Physics SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom 2. York Plasma Institute, Department of Physics The relativistic Doppler efect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. It occurs in the case of a plasma sail accelerated to relativistic velocities by an external driver, such as an ultra-intense laser pulse. The construction of several international multi-petawatt laser facilities (e.g. APOLLON in France, ELI-NP in Bucharest and ELI-Beamlines in Prague) are anticipated to produce field intensities on the order of 10 23-1024 W/cm2, where the gamma ray emission and pair production will be copious [1]. In such interaction regimes involving ultra-strong electromagnetic fields, the ions can no longer be considered as “background plasma particles” since the quiver electron energy can be comparable with the ion rest mass [2]. Through an analytical model and 2D QED-PIC simulations, we show that the relativistic Doppler efect on the high energy synchrotron photon emission (∼ 10 MeV), strongly depends on the intrinsic properties of the plasma (charge state and ion mass) and the transverse extent of the driver [3]. When the moving plasma becomes relativistically transparent to the driver, we show that the γ-ray emission is Doppler-boosted and the angular emission decreases; optimal for the highest charge-to-mass ratio ion species (i.e. a hydrogen plasma). This new fundamental insight into the generation of γ -ray sources in various extreme conditions will be significant for experiments on multi-petawatt laser facilities. [1] A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, and C. H. Keitel Mod. Rev. Phys. 84 (2012). [2] R. Capdessus, E. d’Humieres, and V. T. Tikhonchuk Phys. Rev. Lett. 110 , 215003 (2013). [3] R. Capdessus, M. King, D. Del Sorbo, M. J. Duf, C. P. Ridgers, and P. Mckenna, submitted to Scientific Reports.

Speaker: Remi Capdessus

14:00 P4.2003 Fast Neutron Detection in Super-intense γ Radiation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2003.pdf Fast Neutron Detection in Super-intense γ Radiation Hongjie Liu 1,2, Yuqiu Gu1,2, Bo Cui1, Leifeng Cao1,2 1 Research Center of Laser Fusion, CAEP, Mianyang, China 2 Science and technology on plasma physics laboratory, Mianyang, China Scintillator detectors in inertial confinement fusion experiments are predominantly used to measure neutron yield and ion temperature of the primary fusion reactions. The detection of neutrons in fast-ignition experiments is very challenging since it requires the neutron detection system to recover within 100 ns from a high background orders of magnitude stronger than the signal of interest. Liquid scintillator with different compositions was investigated. We present several designs of liquid scintillator using the Geant4 Code and the X-Lab Code. Our liquid scintillator is based on PPO, dissolved in xylene and enriched with molecular O2. The detector consists of a 2-3 liters volume of liquid scintillator coupled to a gated MCP. The gating performance under high-intensityγrays was experimentally checked. The typical flight time spectrum of the neutrons from (p,n) reaction driven by a PW laser is shown in Fig.1. The neutron yield in the fast ignition experiments on Shenguang-II laser facility was successfully measured using this detector. Our neutron detection system could suppress the background signal and eliminate the afterglow present in conventional plastic scintillators. Fig. 1 Neutron flight time spectrum obtained in PW laser References: 1. Abe Y. Hosoda H. Arikawa Y, et. al, Characterizing a fast-response, low-afterglow liquid scintillator for neutron time-of-flight diagnostics in fast ignition experiments, Review Scientific Instruments, 85 (2014). 2. Stoeckl C, Cruz M, Glebov V.Y, et.al, A gated liquid-scintillator-based neutron detector for fast-ignitor experiments and down-scattered neutron measurements. Review Scientific Instruments, 81 (2010), 10D302

Speaker: Hongjie Liu

14:00 P4.2004 Hybrid SRS-TPD instability in inhomogeneous femtosecond laser plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2004.pdf Hybrid SRS-TPD instability in inhomogeneous femtosecond laser plasma I.N. Tsymbalov1, K.A. Ivanov1, S.A. Shulyapov1, D.A. Gorlova1, A. M. Sen’kevich1, R.V. Volkov1, A.B. Savel'ev1, A.V. Brantov2, V.Yu. Bychenkov2 1 Faculty of Physics and International Laser Center M.V. Lomonosov Moscow State University Moscow, Russia 2 P.N. Lebedev Physical Institute Russian Academy of Sciences Moscow, Russia Electron acceleration in femtosecond laser plasma with scalelength L/λ~1 is due to nonlinear plasma wave excitation [1]. Optimization of high energy electrons generation requires study of nonlinear laser-plasma interaction and wave excitation. Radiation scattered by waves carries information about their frequencies, wave numbers and space localization and can be used for plasma wave diagnostics. Studies of instability in femtosecond plasma have already been carried out in papers [2,3], a feature of this work is the short plasma gradient (L/λ~1) and subrelativistic intensities of the laser pulse. The PIC simulation showed that the main feature of the oblique incidence laser pulse interaction with short plasma gradient is refraction, which leads to the appearance of new components in the spatial spectrum. So, the instability pump wave should now be considered as a sum of plane waves, and this leads to the appearance of new features for instability growth rate. The analysis of electromagnetic fields showed that in addition to the electrostatic component in the ponderomotive forces corresponding to the TPD, there is an electromagnetic component corresponding to SRS. SRS and TPD have a common plasma wave. This agrees with the observed values of the plasmon wave vector kx=1.1-1.6k0 [4] The scattering of the fundamental wave by plasma generates a radiation source with an even broader spectral ky component and a rather narrow kx component, which determines the angular distributions of the scattered radiation at frequencies 3/2ω and 1/2ω. The angular distributions of 3/2ω radiation from PIC simulation are in good agreement with the experimental data. [1] K. Ivanov, I. Tsymbalov, S. Shulyapov, D. Krestovskikh, A. Brantov, V.Y. Bychenkov, R. Volkov, and A. Savel’ev, Phys. Plasmas 24, 063109(2017) [2] L. Veisz, W. Theobald, T. Feurer, H. Schillinger, P. Gibbon, R. Sauerbrey, and M. S. Jovanovic, Phys. Plasmas 9, 3197 (2002). [3] A. Tarasevitch, C. Dietrich, C. Blome, K. Sokolowski-Tinten, and D. von der Linde, Phys. Rev. E 68, 026410 (2003) [4] B. Quesnel, P. Mora, J.C. Adam, A. Heron, and G. Laval, Phys. Plasmas 4, 3358 (1997).

Speaker: Ivan Tsymbalov

14:00 P4.2005 Kinetic Simulations of Parametric Instabilities and Hot Electrons Production in the Context of the Shock Ignition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2005.pdf Kinetic Simulations of Parametric Instabilities and Hot Electrons Production in the Context of the Shock Ignition Y. J. Gu1, 2, O. Klimo1, 4, Ph. Nicolai3, V. T. Tikhonchuk1, 3, S. Weber1 1) Institute of Physics of ASCR, ELI-Beamlines, Na Slovance 2, Prague, Czech Republic E-mail: stefan.weber@eli-beams.eu 2) Institute of Plasma Physics of the CAS, Za Slovankou 1782/3, Prague, Czech Republic 3) University of Bordeaux, CNRS, CEA, CELIA, Talence, France 4) Czech Technical University in Prague, FNSPE, Prague, Czech Republic The shock ignition (SI) scheme in laser-driven Inertial Confinement Fusion (ICF) is attractive since it allows significant reduction of the driving energy requirements and improved hydrodynamic stability. It is achieved with a strong shock which is launched at the end of implosion phase by abruptly raising the laser intensity by one or two orders of magnitude. However, laser–plasma interactions at this stage are strongly nonlinear and the physics of laser spike absorption is important, while it is still one of the major unknowns in the shock-ignition scenario. Recent experiments at Prague Asterix Laser System (PALS) conducted under the conditions compatible with SI and at wavelength of 1.315 µm have shown that a large portion of laser energy can be reflected by Stimulated Raman Scattering (SRS) with a relatively small number of generated hot electrons. A big difference in the absorption process and hot electron generation is not well understood. Simulations of the laser-plasma interaction for the conditions of this experiment are necessary. In this work, we demonstrate the kinetic simulations of laser interacting with the plasma corona. The Particle-in-cell (PIC) simulations are based on the relativistic electromagnetic code EPOCH. The initial conditions are obtained from the hydrodynamics simulations. A large fraction of laser energy is transferred into hot electrons with temperature higher than hundreds keV and strong SRS accompanied with cavitation at quarter critical density and density profile modification (steepening around critical density). It is observed that the SRS becomes stronger and shifts to the less dense plasma in front of the quarter critical density region. The temperature of hot electrons oscillates due to the competition between different instabilities. A broad SRS spectrum is observed with many fractional harmonics which is a signature of strong secondary parametric instabilities. The processes of laser beam filamentation and two-plasmon decay are also discussed. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: Stefan Weber

14:00 P4.2006 Magnetic controlling of high-power laser pulses and their interactions with plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2006.pdf Magnetic controlling of high-power laser pulses and their interactions with plasmas S. M. Weng1, Q. Zhao1, Z. M. Sheng1,2, W. Yu3, L. S. Luan3, M. Chen1, M. Murakami4, W. B. Mori5，B. Hidding2, D. A. Jaroszynski2, Jie Zhang1 1 Laboratory for Laser Plasmas, Shanghai Jiao Tong University, Shanghai, China 2 SUPA, Department of Physics, University of Strathclyde, Glasgow, UK 3 Shanghai Institute of Optics and Fine Mechanics(SIOM), CAS, Shanghai, China 4 Institute of Laser Engineering, Osaka University, Osaka, Japan 5 Department of Physics and Astronomy, University of California, Los Angeles, USA In the talk, we will firstly report an extreme case of the Faraday effect that a linearly polarized ultrashort laser pulse splits in time into two circularly polarized pulses of opposite handedness during its propagation in a highly magnetized plasma. This offers a new degree of freedom to manipulate ultrashort and ultrahigh power laser pulses. Together with technologies of ultra-strong magnetic fields, it may pave the way for novel optical devices, such as magnetized plasma polarizers. The latter could allow the generation of circularly polarized laser pulses as high power as 10 PW in up-to-date laser facilities. The resultant high-power circularly polarized pulses are particularly attractive for laser-driven ion acceleration, and optical control of mesoscopic objects. In addition, it may offer a powerful means to measure strong magnetic fields broadly existing in objects in the universe and in laser–matter interactions in laboratories. Besides the manipulating of laser pulses by strong magnetic fields, we will also discuss about the magnetic controlling of laser-plasma interactions, such as laser wakefield acceleration. The ultrahigh acceleration gradients of laser wakefield accelerators (LWFAs) make them a promising next-generation ultra-compact technology suitable for high impact applications. However, controlling injection and optimizing beam loading are outstanding, unresolved issues, which have a crucial impact on the reliability and quality of beams from LWFAs. Here we propose a scheme to control the injection persistence and rate, through a combination of ionization and magnetic fields. Furthermore, beam loading is naturally compensated for because of the ensuing trapezoidal-shaped charge profile. Our scheme enables robust generation of high-charge electron beams with narrow energy spread suitable for applications that have wide impact.

Speaker: Su-Ming Weng

14:00 P4.2007 NCD plasma dynamics driven by ultraintense femtosecond laser pulse

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2007.pdf NCD plasma dynamics driven by ultraintense femtosecond laser pulse X.H. Yuan1, 2, *, Y.Q. Deng1, 2, N. Haq1, 2, D.N. Yue1, 2, X.L. Ge1, 2, W.Q. Wei1, 2, Y.J. Li1, 2, X. Zhao1, 2, F. Liu1, 2, M. Chen1, 2, L.M. Chen1, 2,3, Z.M. Sheng1, 2, 4 and J. Zhang1, 2 1 Key Laboratory for Laser Plasmas (MoE), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China 2 Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China 3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 4 SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK Email: xiaohui.yuan@sjtu.edu.cn High-density gas-jet target has superior advantages in laser-driven particle and radiation sources development. The near-critical-density gas is especially attractive for both ion acceleration and high-brilliance Betatron x-ray generation due to highly efficient laser absorption and a variety of nonlinear coherent structures. In this talk, I will present our experimental work on the spatiotemporal evolution of near-critical-density gas-plasma produced by high-contrast relativistically intense femtosecond laser pulses with helium gas jet of peak atom density of 8x1020 cm-3. The underlying physics will be discussed with the help of 2D and 3D particle-in-cell simulations. Figure 1 Typical plasma structure detected with second-harmonic optical probe References: F. Sylla, etc. Short Intense Laser Pulse Collapse in Near-Critical Plasma. Phys. Rev. Lett. 110, 085001 (2013) F. Sylla, etc. Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction. Phys. Rev. Lett, 108, 115003 (2012)

Speaker: Xiaohui Yuan

14:00 P4.2008 Perspectives of Ion Acceleration with PW-lasers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2008.pdf Perspectives of Ion Acceleration with PW-lasers S. Ter-Avetisyan1, A. Andreev1, P. K. Singh2, H. Ahmed3, M. Borghesi3 and V. Yu. Bychenkov4 1 ELI-ALPS, Szeged, Hungary 2 Center for Relativistic Laser Science, Institute of Basic Science, Gwangju, South Korea 3 School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, UK 4 P. N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow, Russia Experiments on ion acceleration driven by high intensity lasers over the past ∼15 years have demonstrated the generation of proton and ion beams with remarkable. Nowadays accessible intensities, beyond 1021 W/cm2, have provided for the first time the opportunity to access new ion acceleration regimes and to extend scaling laws for the acceleration process. It will be discussed the recent experimental findings on ion acceleration obtained on PW laser. In most laser-driven ion acceleration studies the sheath field established by relativistic electrons at target surface accelerates ions, via the so-called Target Normal Sheath Acceleration (TNSA). Newly found scenario at PW laser power offers more favorable proton energy scaling with laser intensity than “ordinary” TNSA, the ions are accelerated in the electrostatic field of charged cavity created by relativistic laser pulse at the target front and in the enhanced sheath field at the target rear. A separate mechanism, Radiation Pressure Acceleration (RPA), where Radiation pressure is exerted via laser ponderomotive force on a foil surface, which results in local electron-ion displacement, and ion acceleration via the ensuing space-charge field. These phenomena will be discussed by careful study of complex dynamics of laser-plasma processes through characteristics of the ion source and accelerated beam properties. This presentation is closely related to recent development or imminently anticipated development of laser technology to bring the existing laser power to a multi-PW level to study relativistic plasma phenomena and for application, e.g., ion acceleration. The findings pave a way to achieving an ion source and beam desire parameters and they encourage further activities for optimisation of laser plasma-based accelerators.

Speaker: Sargis Ter-Avetisyan

14:00 P4.2009 Phase-space analysis of the Schwinger effect in inhomogeneous electromagnetic fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2009.pdf Phase-space analysis of the Schwinger effect in inhomogeneous electromagnetic fields Christian Kohlfürst1,2 1 Helmholtz-Institute Jena, Fröbelstieg 3, 07743 Jena, Germany 2 Theoretisch-Physikalisches Institut, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany We have studied Schwinger pair production in spatially and temporally inhomogeneous high- intensity few-cycle pulses [1, 2] 2 2 2t sin (ωt + φ ) − ωτ 2 cos (ωt + φ ) ε z t E(t, z) = −∂t A(t, z) = exp − 2 − 2 × ex , (1) ω λ τ τ2 2 t 2 2z sin (ωt + φ ) ε z B(t, z) = ∇ × A(t, z) = − exp − 2 − 2 ey , (2) ω λ τ λ2 where ε determines the electric field strength in units of m2 /e, τ sets the temporal scale and λ specifies the spatial scale. The parameters ω and φ control the pulse structure. Employing advanced numerical methods, we have been able to produce accurate numeri- cal solutions of a quantum kinetic theory. We have computed particle (electrons and positrons) momentum spectra, see Fig. 1, as well as spatial-momentum distribution functions in order to thoroughly investigate how spatial and temporal variations in the electric and magnetic fields affect the particle distribution n (z, px , pz ). Moreover, we have introduced a semi-classical model on the basis of an effective theory for the particle production rate taking into account instantaneous pair production and relativistic single-particle dynamics. We have found remarkable signatures of quan- tum interferences and spin-field interactions. Addi- tionally, we observed the formation of characteristic patterns strongly depending on the carrier-envelope phase of the background fields. Figure 1: Density plot of the particle dis- References tribution function n (px , pz ) (quantum kinetic [1] C. Kohlfürst and R. Alkofer, Phys. Lett. B 756 (2016) 371 calculation) in momentum space. [2] C. Kohlfürst, arXiv:1708.08920 [quant-ph]

Speaker: Christian Kohlfürst

14:00 P4.2010 Radiation-pressure-driven ion Weibel instability and collisionless shocks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2010.pdf Radiation-pressure-driven ion Weibel instability and collisionless shocks A. Grassi1, M. Grech1, F. Amiranoff1, A. Macchi2,3 and C. Riconda1 1 Laboratoire d'Utilisation des Lasers Intenses, Paris, France 2 Dipartimento di Fisica Enrico Fermi, Pisa, Italy 3 Istituto di Ottica, Pisa, Italy The Weibel instability driven from counter-streaming plasma flows is a basic process of outmost importance for the formation of collisionless shock in astrophysics. It has motivated recent experimental efforts worldwide that aim at recreating collisionless shocks using high-energy moderately intense laser systems such as NIF [1]. In this work, we investigate the possibility to recreate similar collisionless processes using ultra-high intensity picosecond laser systems [2]. Using two- and three-dimensional Particle-In-Cell (PIC) simulations, we investigate suitable configurations for driving the ion Weibel instability (IWI) from a fast quasi-neutral flow launched into a target via the radiation pressure of an ultra-intense laser pulse. The use of S-polarized light at oblique incidence is found to be optimal to drive a fast neutral flow that in turns triggers the IWI into the dense target. This configuration is shown to mitigate the production of hot electrons, thus preventing the growth of competing (electron) instabilities and allowing for a longer operating time of the laser piston. This configuration is also shown to eventually lead to the formation of a Weibel-mediated collisionless shock. [1] J. S. Ross et al., Phys. Rev. Lett. 118, 185003 (2017). [2] A. Grassi et al., Phys. Rev. E 96, 033204 (2017).

Speaker: Anna Grassi

14:00 P4.2011 Realising single shot measurements of radiation reaction for inverse Compton sources

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2011.pdf Realising Single Shot Measurements of Radiation Reaction for Inverse Compton Sources 1 1 2 3 4 C. D. Baird , C. D. Murphy , T. G. Blackburn , A. Ilderton , S. P. D. Mangles , M. 2 1 Marklund , and C. P. Ridgers 1 York Plasma Institute, Department of Physics, University of York, York YO10 5DD 2 Department of Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden 3 Centre for Mathematical Sciences, University of Plymouth, PL4 7AA 4 Blackett Laboratory, Imperial College London, South Kensington, London SW7 2BZ Modern, high-intensity laser systems can accelerate electrons to multi-GeV energies in laser-wakefield schemes. By employing a second, counter-propagating laser, those electrons can then be used to drive high-brightness X-ray sources via inverse Compton scattering (ICS). In order to increase the brightness of such sources, it is desirable to increase the intensity of the scattering laser. This leads to nonlinear ICS where multiple photons interact with a single electron and radiation reaction (RR) effects where the motion of the electron is significantly altered by its own emission. At the highest intensities pair production may occur, providing a laboratory analogue for some of the most extreme environments in the universe. Recent experiments have shown that high-intensity laser-plasma experiments can reach the RR regime [1], however shot-to-shot fluctuations in laser pointing and electron beam profiles limit the precision with which RR can be measured. Using the 3D PIC code, EPOCH, we simulate laser-electron collisions and investigate a method for measuring RR effects in a single laser shot by comparing different regions of an electron bunch post-interaction. With the aid of improved detection methods, this may allow detailed, on-shot measurements to be made. 1. Cole, J. M., et al., Physical Review X, 8, 011020 (2018). 2. Arber, T. D., et al., Plasma Physics and Controlled Fusion, 57(11), 113001 (2015)

Speaker: Christopher David Baird

14:00 P4.2012 Recent results on quantum radiation reaction effects in laser plasma interaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2012.pdf Recent results on quantum radiation reaction effects in laser plasma interaction F. Niel1 , C. Riconda1 , F. Amiranoff1 , R. Duclous2 , and M. Grech3 1 LULI, UPMC Université Paris 06: Sorbonne Universités, CNRS, École Polytechnique, CEA, Université Paris-Saclay, F-75252 Paris cedex 05, France 2 CEA, DAM, DIF, F-91297 Arpajon, France 3 LULI, CNRS, École Polytechnique, CEA, Université Paris-Saclay, UPMC Université Paris 06: Sorbonne Universités, F-91128 Palaiseau cedex, France Radiation reaction (RR) in the interaction of ultra-relativistic electrons with a strong external electromagnetic field is investigated using a kinetic approach in the non-linear moderately quan- tum regime. Analyzing the system of kinetic equation for the electron and photon distribution functions, we deduce three complementary descriptions depending on the average quantum parameter of the electron population : a deterministic one relying on the quantum-corrected radiation reac- tion force in the Landau and Lifschitz (LL) form, a linear Boltzmann equation for the electron distribution function, and a Fokker-Planck (FP) expansion in the limit where the emitted photon energies are small with respect to that of the emitting electrons. [1] Quantum RR effects can affect significantly the electron distribution function. Our treatment allows us to evidence that both the average quantum parameter and the initial shape of the electron distribution function are important to determine the influence of quantum RR on the system. This has important implications for the experimental observation of quantum RR effect and for the implementation of RR in PIC codes. The results established for the electron distribution function allow to reinterpret the differ- ences in the radiation spectrum in the three models. In particular, we observe that the features of RR are much more subtil on the radiation spectrum than on the electron distribution function. [2] References [1] F. Niel, C. Riconda, F. Amiranoff, R. Duclous and M. Grech, arXiv:1802.02927, (2017) [2] F. Niel, C. Riconda, F. Amiranoff, M. Lobet, J. Derouillat, F. Pérez, T. Vinci, M. Grech, arXiv:1802.02927 (2018)

Speaker: Caterina Riconda

14:00 P4.2013 Relativistic laser pulse peak intensity evaluation based on vacuum acceleration of electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2013.pdf Relativistic laser pulse peak intensity evaluation based on vacuum acceleration of electrons K.A. Ivanov1, I.N. Tsymbalov1, O.E. Vais2, S.G. Bochkarev2 and A.B. Savel’ev1 1 Physics faculty of M.V. Lomonosov MSU, Moscow, Russia 2 P.N. Lebedev Physical Institute of RAS, Moscow, Russia Recent results on acceleration of electrons in the electromagnetic field of tightly focused relativistically strong femtosecond laser radiation are presented. The vacuum acceleration of free electrons by laser pulse is characterized by direct connection between laser radiation characteristics and accelerated electron distributions with no influence of additional plasma collective effects. It opens the opportunity to evaluate the main pulse parameters for ultra-high power laser systems by means of measurement of high energy electrons properties. In our work we used the radiation of a Ti:Sa laser system (805nm, 10Hz, 100 mJ, 50 fs) focused by an off-axis parabolic mirror (F/D=3) to a focal diameter D=2.2 microns (FWHM), which provided the estimated peak intensity >1019 W/cm2. The focusing optics was mounted inside a vacuum chamber filled with noble gas (Helium or Argon) at pressure of ~10-1 mb (gas purity >99%). Electrons appearing due to nonlinear ionization by the EM field of the pulse were registered in the polarization plane by energy calibrated MediPix matrix detector which covered angles from 0o to 90o in respect to the beam propagation axis. It was found that electrons are dominantly emitted in a relatively narrow range of angles. With the growth of laser pulse energy the direction of electron scattering moves closer to the beam axis. Particles residual energy exceeded 500 keV. Numerical simulations of relativistic laser interaction with particles using two independent models (PIC code and test particles method) revealed that electrons gain energy dominantly due to the ponderomotive action of the pulse. A good agreement between numerical and experimental data was observed for electrons angular and energy distributions. Moreover in the considered range of laser peak intensity (1018-1020 W/cm2) the results are weakly depended on beam transvers profile and we found a direct correlation between the peak intensity and the scattered particles properties. This gives the opportunity to build a simple method of in-situ single shot peak intensity measurement at full energy of the pulse. With the use of our technique the peak intensity of the laser pulse with 70 mJ energy was evaluated on the level of 2.9x1019 W/cm2, being very close to 2.6x1019 W/cm2, obtained from beam diameter and energy. The work was supported by RFBR grant 16-32-60174.

Speaker: Konstantin Ivanov

14:00 P4.2015 Structured plasmas for enhanced gamma emission at relativistic laser intensities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2015.pdf Structured plasmas for enhanced gamma emission at relativistic laser intensities K.Ivanov1,2, A.Lar’kin1, D.Gozhev1,2, A.Brantov2, V.Bychenkov2, A.Savel’ev1 1 Lomonosov Moscow State University, Moscow, Russia 2 Lebedev Physical Institute RAS, Moscow, Russia We present experimental & numerical studies of interaction of femtosecond laser radiation with intensity up to 5х1018 W/cm2 with structured plasma created using terawatt femtosecond laser facility at MSU. Main stress was on the control of plasma parameters (luminosity in X-ray and gamma ranges, generation of bunches of relativistic electrons) and their optimization. Two approaches are discussed: (i) target surface/volume structuring on nano- or microscale before interaction by different techniques and (ii) in situ liquid metal plasma structuring with short pre-pulse giving rise to microjets. (i) We employed different techniques for structuring of a target surface such as laser ablation with additional chemical etching, chemical etching of bulk silicon, germanium and molybdenum, volume structuring of CH films, etc. We paid special attention to the optical damage of structures under action of femtosecond radiation prepulse. We found out irradiation regimes and structures provided for prominent increase both in the fast electron energy and gamma yield. Numerical simulations using PIC code Mandor allowed to get insight into the mechanisms of the electron acceleration in structured targets. (ii) By using a liquid metal as a target, one may significantly enhance the yield of hard x-rays with a sequence of two intense femtosecond laser pulses. The influence of the time delay between the two pulses is studied experimentally and interpreted with numerical simulations. It was suggested that the first arbitrary weak pulse produces microjets from the target surface, while the second intense pulse provides an efficient electron heating and acceleration along the jet surface. These energetic electrons are the source of x-ray emission while striking the target surface. This work was supported by RSF (grant #17-12-01283, nanostructured targets studies), RFBR (grant#16-02-00263, gamma & electron detection techniques, 16-02-00302, liquid metal targets study).

Speaker: Andrei Savel'ev

14:00 P4.2016 Synchrotron emission from nanowire-array targets irradiated by ultraintense laser pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2016.pdf Synchrotron emission from nanowire-array targets irradiated by ultraintense laser pulses B. Martinez1,2 , E. d’Humières2 , L. Gremillet1 1 CEA, DAM, DIF, F-91297 Arpajon, France 2 CELIA, UMR 5107, Université de Bordeaux-CNRS-CEA, 33405 Talence, France Forthcoming multi-petawatt lasers will enable scientists to access a new regime of laser- plasma interactions where collective plasma processes are intertwined with radiative and quan- tum electrodynamics effects, offering exciting prospects for fundamental and applied research [1, 2, 3, 4]. One underlying mechanism common to all these applications is the copious gen- eration of hard x-ray or γ-ray photons through synchrotron emission–equivalent to nonlinear inverse Compton scattering in the strong-field regime. Here we present the results of two-dimensional particle-in-cell simulations of the synchrotron emission from carbon nanowire arrays irradiated by femtosecond laser pulses of intensities I = 1021 − 1023 Wcm−2 . The realization of intense laser-driven synchrotron sources is but the latest application of nanowire arrays, whose capability in strongly enhancing the laser energy absorption and hot-electron generation is now well established and exploited [5, 6]. Through an extensive parametric scan on the laser-target parameters, we identify and characterize sev- eral dominant radiation mechanisms, mainly depending on the transparency or opacity of the plasma produced by the laser-driven wire expansion, and on the quasistatic fields self-induced around the wires. At I = 1022 Wcm−2 , the emission of high-energy (> 10 keV) photons attains a maximum energy conversion efficiency of ∼ 10% for ∼ 30 − 50 nm wire widths and 1 µm inter- spacing. While this maximum radiation yield does not exceed that achieved in uniform plasma of same average (sub-solid) density, we show that nanowire arrays provide efficient radiation sources over a broader parameter range. Finally, we demonstrate that the radiation efficiency can be further boosted by adding a plasma mirror at the backside of the nanowire array. References [1] A. Di Piazza, C. Müller, K. Z. Hatsagortsyan, and C. H. Keitel, Rev. Mod. Phys. 84, 1177 (2012). [2] C. P. Ridgers et al., Phys. Rev. Lett. 108, 165006 (2012). [3] L. L. Ji et al., Phys. Rev. Lett. 112, 145003 (2014). [4] M. Lobet et al., Phys. Rev. Lett. 115, 215003 (2015). [5] L. Cao et al., Phys. Plasmas 17, 043103 (2010). [6] M. A. Purvis et al., Nature Photon. 7, 796 (2013).

Speaker: Bertrand Martinez

14:00 P4.2017 Fast ignition fusion by counter beam illumination for the CANDY project-Hole boring on injected CD spherical pellet targets-

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2017.pdf Fast ignition fusion by counter beam illumination for the CANDY project -Hole boring on injected CD spherical pellet targets- Y. Kitagawa1 , R. Hanayama1 , Y. Mori1 , K. Ishii1 , S. Okihara1 , O. Komeda2 , H. Suto2 , Y. Umetani2 , J. Okijima2 , T. Hioki3 , T. Motohiro3 , A. Sunahara4 , Y. Sentoku5 , Y. Arikawa5 , Y. Abe5 , E. Miura6 , H. Sakagami7 , S. Ozaki7 , A. Iwamoto7 , T, Johzaki8 1 The Graduate School for the Creation of New Photonics Industries, 2 Advanced Material Engineering Div., TOYOTA Motor Corporation, 3 Nagoya University, GREMO, 4 CMUXE, Perdue University, 5 Institute of laser Engineering, Osaka University, 6 National Institute of Advanced Industrial Science and Technology, 7 National Institute for Fusion Science, 8 Faculty of Engineering, Hiroshima University A kJ-class mini reactor CANDY, as in Fig. 1, is pro- posed for an engineering feasibility study of the power plant in the counter beam fast ignition scheme fusion. To develop the CANDY, we are performing fast ignition ex- periments using both single-shot petawatt lasers[1] and Figure 1: CANDY image. DT cryo- a high-repetition-rate laser-diode(LD)-pumped laser with genic fuel pellets are injected at 10 Hz counter beam configuration[2]. by the counter implosion beams fol- Fuel pellet injection and repetitive laser illumina- lowed by coaxial heating beams. tion are key technologies for realising inertial fusion energy[3]. Relating to the fast ignition fusion, hot electron transports through a dense core are big issues. We have succeeded in 1 Hz injection of solid spherical deuterated polystyrene bead pellets, whose diameter is 1mm, which two ultra-intense laser beams engaged from both sides. A straight channel (hole boring) with about 10µ m diameter was formed inside the injected pel- lets, as in Fig. 2. The laser provides 0.63 J/beam in 100 fs at 811 nm: 4.7 × 1018 W/cm2 . Only the injected pellets have the holes, but no other shaped or earthed targets have. The experiments show that the short pulse laser driven hot electrons bore the holes. Some possible mechanism due to such as preplasmas will be presented. References [1] Y. Kitagawa et al., Phys. Rev. Lett. 114 195002(2015); Nu- clear Fusion 57 076030(2017). [2] Y. Mori et al., Phys. Rev. Lett. 117 055001(2016);Nuclear Fu- sion 57 116031(2017). Figure 2: Hole through in an injected and [3] O. Komeda et al., Scientific Reports 3 2561(2013). counter-laser beam engaged CD bead.

Speaker: Yoneyoshi Kitagawa

14:00 P4.2018 All-optical studies of high-field QED processes: experimental limitations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2018.pdf All-Optical Studies of High-Field QED Processes: Experimental Limitations G. M. Samarin1, M. Zepf1, 2, G. Sarri1 1 School of Mathematics and Physics, Queen’s University Belfast, Belfast, UK 2 Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany Uncovering the physics of processes such as quantum radiation reaction and photon-photon pair production remain some of the biggest challenges of experimental investigations in the realm of high-field Quantum Electrodynamics. The experimental limitations in the conventional dual beam all-optical setups which are standard to study these phenomena1 are reviewed. Particular emphasis is made on the topics of spatial-temporal overlap of laser beams and how this translates to particle-laser synchronisation, spectral range and reproducibility of conventional laser wakefield accelerators2, and the difficulty of measuring the products of extremely low cross-section events. Potential solutions for these problems and how they can be implemented in both current and prospective laser facilities are outlined. [1] Cole, J. M., Behm, K. T., Gerstmayr, E., Blackburn, T. G., Wood, J. C., Baird, C. D, Duff, MJ, Harvey, C, Ilderton, A, Joglekar, AS, Krushelnick, K, Kuschel, S, Marklund, M, McKenna, P, Murphy, CD, Poder, K, Ridgers, CP, Samarin, GM, Sarri, G, Symes, D, Thomas, AGR, Warwick, J, Zepf, M, Najmudin, Z & Mangles, S. P. D. (2018). Experimental evidence of radiation reaction in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam. Physical Review X, 8(1), [011020]. DOI: 10.1103/PhysRevX.8.011020 [2] G. M. Samarin, M. Zepf & G. Sarri (2017) Radiation reaction studies in an all-optical set- up: experimental limitations, Journal of Modern Optics, 64:21, 2281-2288, DOI: 10.1080/09500340.2017.1353655.

Speaker: G. M. Samarin

14:00 P4.2019 Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2019.pdf Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interaction T. Silva1 , J. Vieira1 , M. Hoshino2 , R.A Fonseca1,3 , L. O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 2 Departament of Earth and Planetary Science, University of Tokyo, 113-0033 Tokyo, Japan 3 DCTI/ISCTE Insituto Universitário de Lisboa, 1649-026 Lisbon, Portugal The interaction of intense electromagnetic waves with plasmas is a rich research topic be- cause of its importance in basic plasma science and in potential scientific and societal applica- tions, ranging from advanced fusion devices to compact plasma based accelerators and radiation sources. Magnetic fields play a crucial role in this context: they may stabilise hot electron cur- rents against beam-break up instabilities, are vital to reproduce extreme astrophysical scenarios in the laboratory, and make plasma-based radiation emission processes more efficient. There are several processes that can lead to the generation and amplification of magnetic fields. Re- cent experiments, for instance, demonstrated the generation large-scale [1] due to hot electron currents in underdense plasmas, and determined the turbulent [2] dynamics of intense magnetic fields in laser-solid interactions. In general, magnetic field generation depends on the specific temperature distribution of hot electrons. Thus, controlling how heating occurs is important to enhance magnetic field gen- eration in laser-plasma interactions. In this work we explore a novel mechanism to drive the Weibel instability in laser-plasma interactions by controlling the temperature of background plasma electrons in each direction, independently. The scheme employs an intense laser pulse propagating in an underdense plasma. Using two and three-dimensional particle-in-cell simula- tions with the code OSIRIS [3], we show that the interaction is subject to Raman side-scattering. We find that electron heating is stronger along the direction where the scattered plasma wave phase velocity is lower due to Landau damping. Thus, our work shows that this setup creates an angle-dependent temperature distribution capable of driving the Weibel instability. We discuss the role of the laser polarisation in our findings. References [1] A. Flacco et al Nature Physics 11, 409 (2015). [2] G. Chatterjee et al Nat. Comms. 8, 15970 (2017). [3] R. Fonseca, et al., Lecture Notes in Computer Science 2331, 342 (2002)

Speaker: Thales Silva

14:00 P4.2020 Calibration of a compact gamma ray spectrometer for an energy range of 4-20 MeV

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2020.pdf Calibration of a compact gamma-ray spectrometer for an energy range of 4-20 MeV S. Singh1, A. Laso Garcia2, R. Versaci1, A. Ferrari2, M. Molodtsova2, L. Morejon1, R. Schwengner2, D. Kumar,1 and T. Cowan2 1) ELI Beamlines, Institute of Physics of the ASCR, Dolni Brezany, Czech Republic 2) Institute for radiation physics, Helmholtz-Zentrum Dresden-Rossendorf, Germany E-mail: Sushil.Singh@eli-beams.eu With currently available high intensity lasers and the upcoming multi-PW facility at ELI- Beamlines, copious amounts of gamma rays are expected to be generated in high intensity laser-matter interaction experiments. Measurement of multi-MeV gamma-ray spectra in such experiments provide direct indication of hot electrons generated inside the target. To determine the spectrum of hot electrons and gamma rays, an appropriate spectrometer with absolute calibration is essential. We report on the design of a compact gamma ray spectrometer (GRS) of size 70 cm x 25 cm x 25 cm based on measuring forward Compton scattered electrons by incoming gamma rays. In this presentation, we describe the design parameters and calibration results of the GRS. The calibration was performed using the bremsstrahlung facility gELBE [1] at the ELBE accelerator of HZDR, Dresden. The calibration was conducted at different electron end point energies, i.e. 11, 13, 15 and 18 MeV. Experimental spectra show systematic increase in the maximum cut-off energy, temperature and flux. These results indicate that the spectrometer is effective for an energy range of 4−20 MeV with 20-30% energy resolution. GRS provides an opening angle of 23 mrad and experiments to measure bremsstrahlung spectrum from laser- solid interaction are currently planned. The preliminary results from the experiment will also be presented at the conference. Our work is supported by Czech Science Foundation project 18-09560S. References [1] R. Schwengner et al., Nucl. Instrum. Meth. A: Accelerators, 555.12, pp. 211-219, (2005).

Speaker: Sushil Kumar Singh

14:00 P4.2021 Characterization of ellipsoidal plasma mirrors beyond the paraxial approximation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2021.pdf Characterization of ellipsoidal plasma mirrors beyond the paraxial approximation D. Kumar1 , M. Šmíd1 , E. Chacon-Golcher1 , J. Fuchs2 , M. Morrissey1 , M. Nakatsutsumi3 , O. Klimo1 , S. Weber1 1 Institute of Physics of the ASCR, ELI-Beamlines project, Prague, Czech Republic 2 LULI, Ecole Polytechnique, Palaiseau, France 3 European XFEL, Hamburg, Germany Ellipsoidal plasma mirrors (EPM) can demagnify the focal spot from a conventional off axis parabolic (OAP) optic to yield ultra high focused intensities beyond the range of 1023 W/cm2 in upcoming laser facilities[1, 2]. The design of these EPMs have traditionally used paraxial approximation to estimate the achievable demagnification[3]. However, numerical codes do exist to characterize the focal spot diameter under tightly focused condition when the output focal spot diameter is comparable to the laser wavelength[4]. In this presentation we compare the measured focal spots to the theoretically predicted values (without paraxial approximation). These results thus guide us to design the simplest geometry of the EPM to achieve a tightly focused spot for a given OAP. Our work is supported by Czech Science Foundation project 18-09560S. References [1] M. Nakatsutsumi, A. Kon, S. Buffechoux et al, Optics letters 35, 13 (2010) [2] R. Wilson, M. King, R.J. Gray et al, Physics of Plasmas 23, 033106 (2016) [3] A. Kon, M. Nakatsutsumi, S. Buffechoux et al, Journal of Physics: Conference Series 244, 032008 (2010) [4] T. M. Jeong, S. Weber, B. LeGarrec et al, Optics Express 23, 9, pp. 11641-11656 (2015)

Speaker: Deepak Kumar

14:00 P4.2022 Effects of strong external magnetic field on high-intense laser propagation into dense plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2022.pdf Effects of strong external magnetic field on high-intense laser propagation into dense plasma M. Hata , H. Sakagami , T. Sano , Y. Sentoku , H. Nagatomo 1 2 1 1 1 1 Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, Japan 2 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu, Japan The establishment of method for generating kilo-tesla class magnetic field using high-power laser allows us to perform experiments of high-intense laser plasma interactions (LPI) under strong external magnetic field [1,2]. Such strong magnetic field affects not only fluid dynamics but also fast electrons and laser propagation. Recently, it is proposed that fast electrons of which divergence is very large are guided by kilo-tesla class external magnetic field and heat core efficiently, and related experiments have been intensively performed [3,4]. With recent progress of strong magnetic field generation in laboratory, fundamental studies using such strong magnetic field have been performed and high-intense laser plasma interactions under strong magnetic field have been opened up as new research area. In this study, we pay attention to high-intense laser propagation into dense plasma under strong magnetic field and have conducted two-dimensional Particle-In-Cell (PIC) simulations of high-intense LPI with strong magnetic field. Target plasma is made of hydrogen and its density profile in x direction consists of preplasma which has exponential profile with scale length of 20 µm and flat plasma with density of 40 n . The density profile in y direction is uniform. Applied external magnetic cr field along the direction of laser propagation, namely x direction, is set to 50 kilo-tesla. Linearly polarized laser that has temporally flattop and spatially Gaussian profiles with spot diameter of 20 µm irradiates the target with normal incidence. At least 500 fs of simulation has been done using 2D PIC code. According to the linear theory of cold plasma in strong magnetic field, right-handed circularly polarized (RCP) component of electromagnetic wave propagates into dense plasma without cut-off density. Simulation results show that initially RCP component of injected laser can propagate in dense plasma, but after a while following laser cannot propagate. It is found that strong ion acoustic wave generates at the area where laser cannot propagate and it triggers the reflection of RCP component of the injected laser. In the presentation, inhibition mechanism of laser propagation will be discussed in detail. [1] S. Fujioka et al., Sci. Rep. 3, 1170 (2013). [2] H. Yoneda et al., Phys. Rev. Lett. 109, 125004 (2012). [3] T. Johzaki et al., Nucl. Fusion 55, 053022 (2015). [4] M. Bailly-Grandvaux et al., Nature Comm. 9, 102 (2018)

Speaker: Masayasu Hata

14:00 P4.2023 Formation of power law electron energy distribution in picosecond interaction of relativistic laser and dense plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2023.pdf Formation of power law electron energy distribution in picosecond interaction of relativistic laser and dense plasma N. Iwata , Y. Sentoku , T. Sano and K. Mima 1 1 1 1,2 1 Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, Japan 2 The Graduate School for the Creation of New Photon Industries, 1955-1 Kurematsu, Nishiku, Hamamatsu, Shizuoka, Japan High power lasers with relativistic intensities above 1018 W/cm2 and pulse lengths exceeding picosecond (ps) have been developed in recent years. In over-ps laser-plasma interactions, energy slope of high-energy electrons tends to be higher than the scaling laws used in the sub-ps regime. One of the key mechanisms of such a superthermal electron generation is stochastic heating in a laser-irradiated thin foil, where fast electrons recirculate around and suffer multiple kicks from the laser field during the pulse duration [1]. The blowout of hot plasma towards the laser, which takes place under the ps laser heating [2], also enhances the multiple interactions of fast electrons with laser light. Understanding characteristics of the energy distribution resulted from the new accelerations arise in ps relativistic regime is essential for various applications for intense lasers. Furthermore, the stochastic acceleration by superthermal fields is related to the acceleration of cosmic rays which exhibit power law spectrum in high energy tail. For a non-relativistic laser interaction with underdense plasma, the electron energy spectrum is found to be a kappa distribution which becomes power law in high energy limit [3]. Here, we model the electron acceleration in the laser-thin foil interaction and study the resulting electron energy distribution based on the relativistic Fokker-Plank equation in momentum space. We introduce new diffusion and friction coefficients that represent the stochastic heating at the front side and the energy dissipation by the sheath potential trap at the rear side, respectively. We find that the steady solution of the Fokker-Plank equation becomes a power law when the diffusion by the laser kick is in proportion to the momentum p. This analysis can specify the origin of the power law formation, and provide an insight for further development of theoretical models for complex laser interactions in multi-ps time scale. [1] N. Iwata et al, Phys. Plasmas 24 (2017) 073111 [2] N. Iwata et al., Nat. Commun. 9:623 doi: 10.1038/s41467-018-02829-5 (2018) [3] A. Hasegawa, K. Mima and M. Duong-van, Phys. Rev. Lett. 54 (1985) 2608

Speaker: Yasuhiko Sentoku

14:00 P4.2024 Influence of the peak density of near-critical gas targets on the spectrum features using ultra-high laser intensity through numerical modeling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2024.pdf Influence of the peak density of near-critical gas targets on the spectrum features using ultra-high laser intensity through numerical modeling D. Tatomirescu1,2, D. Vizman1, E. d'Humières2 1 Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania 2 CELIA, University of Bordeaux – CNRS – CEA, 33405 Talence, France In the past two decades, laser-accelerated ion sources and their applications have been intensely researched due to the increased focus in developing potential laser plasma sources with applications in proton radiography [1], fast ignition [2], hadrontherapy [3], [4], radioisotope production [5] and laboratory astrophysics [6]. Recently, it has been shown through experiments that proton beams with characteristics comparable to those obtained with solid targets can be obtained from gaseous targets. By means of Particle-In-Cell simulations, this paper studies in detail the effects of a near-critical density gradient on ion and electron acceleration after the interaction with ultra high intensity lasers. We can observe the influence of the peak density of the gas jet on the accelerated particle spectrum features. We can observe that as the gas jet density increases, so does the peak energy of the central quasi-monoenergetic ion bunch due to the increase in laser absorption while at the same time having a broadening effect on the electron angular distribution. Furthermore, the gamma photon production is studied for all cases comprised in the study in order to ascertain the feasibility of such targets as secondary sources. References: [1] M. Borghesi et al., Plasma Phys. Control. Fusion 43, A267 (2001) [2] M. Roth et al., Phys. Rev. Lett. 86, 436 (2001) [3] V. Malka et al., Med Phys. 31, 1587 (2004) [4] S. Bulanov et al., Phys. Lett. A 299, 240(2002) [5] S. Fritzler et al., Applied Phys. Lett. 83, 3039 (2003) [6] S. Davis et al., High Energy Density Phys. 9, 231 (2013)

Speaker: Dragos Emilian Tatomirescu

14:00 P4.2025 Integrated simulation analysis of core heating property for ion assisted fast ignition using low-density structured plastic foam

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2025.pdf Integrated simulation analysis of core heating property for ion assisted fast ignition using low-density structured plastic foam H. Sakagami 1, T. Johzaki 2, A. Sunahara 3, H. Nagatomo 4 and Y. Sentoku 4 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 2 Hiroshima University, Higashi-hiroshima, Japan 3 Purdue University, West Lafayette, IN, US 4 Institute of Laser Engineering, Osaka University, Osaka, Japan To mitigate quite low energy coupling from fast electrons to the core, guiding fast electrons to the core by external magnetic field and improving pulse contrast of the heating laser are conducted at up-to-date FIREX experiments [1]. To enhance the core heating moreover, the ion assisted fast ignition scheme [2,3] is also suggested, where low-density structured plastic (CH) foam is introduced at the bottom of the cone to adapt the radiation pressure ion acceleration [4]. In recent FIREX experiments, solid ball targets are introduced to stably achieve compressed dense core instead of shell targets, and this target configuration also enables to remove the Au cone tip, in which extra energy loss and scattering of fast electrons occur during propagation. As collisional effects of ions in the cone tip are much larger than those of electrons, the tipless cone is very useful for ion assisted fast ignition. On the other hand, a longer pulse of the heating laser is going to be introduced to enlarge the total heating energy without increasing laser intensity. The longer pulse requires thicker foam to continuously obtain ion beams, but the stability of ion generation is still unknown for such long pulses. Thus integrated simulations should be carried out to evaluate core heating properties for there cases. *This work is partially supported by JSPS KAKENHI Grant number JP16K05638 and JP15H05751, and is performed with the support and under the auspices of the NIFS Collaboration Research program (NIFS17KUGK110 and NIFS12KUGK057). References [1] S. Fujioka, et al., Phys. Plasma 23, 056308 (2016). [2] H. Sakagami, et al., J. Phys.: Conf. Series 688, 012096 (2016). [3] H. Sakagami, et al., J. Phys.: Conf. Series 717, 012046 (2016). [4] S. C. Wilks, et al., Phys. Rev. Lett. 69, 1383 (1992).

Speaker: Hitoshi Sakagami

14:00 P4.2026 Investigation of radiation reaction at ELI-NP

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2026.pdf Investigation of radiation reaction at ELI-NP K. Seto1, T. Moritaka2, K. Homma3,4, Y. Nakamiya1, J. F. Ong1, L. D’Alessi1 and O. Tesileanu1 1 Extreme Light Infrastructure - Nuclear Physics (ELI-NP)/ Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Ilfov, Romania 2 National Institute for Fusion Science, Gifu, Japan 3 Graduate School of Science, Hiroshima Univ., Hiroshima, Japan 4 International Center for Zetta-watt Science and Technology, École Polytechnique, France In the rapid development of high-power and high-intensity lasers in the world, the maximum laser power and intensity will reach O(10PW-1023W/cm2) soon. Extreme Light Infrastructure – Nuclear Physics (ELI-NP) is one of the research centers which has the 2 arms of the 10PW lasers to create such extremely high-intensity light, and the electron LINAC up to 720MeV to create gamma photons of O(~19.5MeV) via the inverse Compton scattering [1]. Radiation reaction (RR), the back-reaction acting on a radiating electron, has become important in laser-plasma science due to the construction of these high-intensity lasers. One of its typical predictions is that more than 80% of the electron’s energy is lost in RR in the case of beam parameters similar to the ones of ELI-NP [2]. The work was performed in purely classical dynamics, however, the importance of the quantum corrections depending on laser intensity has been recently suggested [3]. Theoretical models with quantum corrections have been proposed by many authors. To investigate this, we plan to examine the RR effect by the head-on collision between the high-energy electrons of 720MeV from LINAC and the high-intensity laser (>1022W/cm2) at ELI-NP [4]. In this presentation, we will give the schematic idea of the RR experiment at ELI-NP. In addition, we will also show the theoretical model of RR developed, “RR acting on a relativistic and Brownian scalar electron”, as the quantization of the Lorentz-Abraham-Dirac equation in classical dynamics [5]. [1] ELI-NP: https://www.eli-np.ro/ [2] J. Koga, Phys. Rev. E 70,046502 (2004). [3] For example, K. Seto, Prog. Theor. Exp. Phys. 2015, 103A01 (2015). [4] K. Homma, et. al., Rom. Rep. Phys. 68, Supplement, S233 (2016). [5] K. Seto, arXiv:1603.03379v5 (2017).

Speaker: Keita Seto

14:00 P4.2027 Laser-induced vacuum birefringence beyond idealized setups

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2027.pdf Laser-induced vacuum birefringence beyond idealized setups R. Torres1 , T. Grismayer1 , R.A. Fonseca1,2 , L.O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 2 DCTI/ISCTE - Instituto Universitário de Lisboa, 1649-026 Lisbon, Portugal The prospect of coupling ultra-intense lasers with x-ray sources (e.g. at SLAC or XFEL) will allow to perform the first experiments on probing the quantum vacuum. For this scenario, ei- ther an analytical solution cannot be found or the analytic methods are inefficient due to the increasing complexity coming from the setup or the electromagnetic profiles of the laser pulses. Consequently, we have developed a numerical method to self-consistently solve the nonlinear system of Maxwell’s equations including quantum corrections of the vacuum polarization [1]. This will allow modelling future planned experiments aiming to measure the induced ellipticity on an x-ray pulse after probing a strong optical laser due to quantum vacuum fluctuations [2]. Realistically, experimental conditions are not ideal and one should study the impact of these imperfections in the signatures resulting from quantum electrodynamic processes. In this way, we will be able to optimize the experimental setup in order to perform the first direct detection of the photon-photon scattering. We present simulation results of the ellipticity induced for a set of non-ideal setups: misalignment of the central axis of the x-ray probe and the ultra-intense optical pump pulse, different polarization angles between the x-ray and optical laser pulses, temporal mismatch of the pulses focuses (timing jitter) and finite-size multi-dimensional ef- fects [3]. This code has been benchmarked for simpler cases, giving us the confidence to tackle realistic setups. Ultimately, our code is capable of exploring regimes unachievable by a theoret- ical analysis, which is going to be of great utility for the extremely high-intensity laser physics society. References [1] P. Carneiro, T. Grismayer, R.A. Fonseca and L.O. Silva, arXiv:1607.04224v2 (2017) [2] V. Dinu, T. Heinzl, A. Ilderton, M. Marklund, G. Torgrimsson, Phys. Rev. D 90, 045025 (2014) [3] B. King and C.H. Keitel, New J. Phys. 14, 103002 (2012)

Speaker: Rui Pedro Torres

14:00 P4.2028 Multiple-core hole states production in the interaction of solid-state density plasmas with a relativistic optical and x-ray free electron laser

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2028.pdf Multiple-core hole states production in the interaction of solid-state density plasmas with a relativistic optical and x-ray free electron laser Cheng Gao1, Jiaolong Zeng1, Yong Hou1, Jianmin Yuan1,2,3 1 Department of Physics, National University of Defense Technology, Changsha Hunan 410073, P. R. China 2 Graduate school of China Academy of engineering Physics, Beijing 100193, P. R. China 3 IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, P. R. China Much research on SCH and DCH states have been carried out in the past decades1-3, however, very few work is reported in the literature on the observation of production for triple-core-hole (TCH) states4. The investigation of TCH states gives rise to a great challenge both experimentally and theoretically. Multiple-core states of a silver foil are investigated in the interaction with a relativistic femtosecond optical laser and x-ray free electron laser. Strong x-ray emission of TCH atoms with three L-shell electrons being ionized can be observed at pulse intensities of 3  10 21W / cm 2 . Detailed kinetic calculations showed that the emissivity originating from the TCH states exceeds that from the single- and double-core-hole states in Ne-like Ag37+ and is comparable in the neighbouring ionization stages of Ag36+ and Ag38+ in the produced plasmas at electron temperature of ~500 eV and raidative temperature of ~1500 eV using optical laser. These extremely exotic dense matter states are produced by an intense polychromatic x-ray field formed by hot electrons produced in the interaction of the laser. This work opens new ways to the deep insight into investigation of extremely exotic states properties which is important in high energy density physics, astrophysics and laser physics. 1. Young, L. et al. Femtosecond electronic response of atoms to ultra-intense x-rays. Nature 466, 56-62 (2010). 2. Rudek, B. et al. Ultra-efficient ionization of heavy atoms by intense x-ray free-electron laser pulses. Nature Photon. 6, 858-865 (2012). 3. Tamasaku, K. et al. Double core-hole creation by sequential attosecond photoionization. Phys. Rev. Lett. 111, 043001 (2013). 4. Wallis, A. O. G., Banks, H. I. B. & Emmanouilidou, A. Traces in ion yields and electron spectra of the formation of Ar inner-shell hollow states by free-electron lasers. Phys. Rev. A 91, 063402 (2015). jmyuan@nudt.edu.cn, jlzeng@nudt.edu.cn

Speaker: Jiaolong Zeng

14:00 P4.2030 Photon dose lowering by fast electron energy loss induced by return current as a short-pulse high-intensity laser interacts on a metal solid target

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2030.pdf Photon dose lowering by fast electron energy loss induced by return current as a short-pulse high-intensity laser interacts on a metal solid target A. Compant La Fontaine CEA, DAM, DIF, F-91297 Arpajon, France During the interaction of a short-pulse high-intensity laser with the preplasma produced by the pulse’s pedestal in front of a high-Z metal solid target, high-energy electrons are produced, which in turn create an X-ray source by interacting with the atoms of the converter target. The current brought by the hot electron current is almost completely neutralized by a return current driven by the background electrons of the conductive target, and the force exerted on the hot electrons by the electric field induced by the Ohmic heating produced by the background electrons reduces the energy of the hot electrons and thus lowers the X-ray emission and photon dose. This effect is analyzed here by means of a simple 1-D temperature model which contains the most significant terms of the relativistic Fokker-Planck equations with electron multiple scattering, and the energy equations of ions, hot and cold electrons are solved numerically. The energy loss of the hot electrons by Ohmic heating varies with different parameters as the plasma scale length, the target thickness, and the laser characteristics. For instance for a ps laser pulse with 10 microns spot size on a tantalum target, the energy loss fraction by Ohmic heating is about 10 to 40%. Laser and plasma parameters may be optimized to reduce this effect, for instance at small plasma scale length or at small laser spot size. Conversely, the resistive heating is enhanced with a foam target or at long plasma scale length and high laser spot size and intensity, at which the incident hot electron bunch have a small mean emission angle given by the ponderomotive force. The X-ray emission and dose produced by a laser interacting in a gas jet may thus be inhibited under these circumstances. The resistive heating may also be maximized in order to reduce the X-ray emission to lower the radiation level for instance in a safety radiological goal.

Speaker: Antoine Yvon Compant La Fontaine

14:00 P4.2031 Simulation studies on transmissivity of silicon nitride plasma shutter for laser pulse contrast enhancement

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2031.pdf Simulation studies on transmissivity of silicon nitride plasma shutter for laser pulse contrast enhancement M. Matys1,2 , O. Klimo1,2 , J. Psikal1,2 1 FNSPE, Czech Technical University in Prague, Prague, Czech Republic 2 ELI-Beamlines project, Institute of Physics, AS CR, Prague, Czech Republic Tightly focused petawatt laser pulse is usually accompanied by low-energy prepulses, com- posed of Amplified Spontaneous Emission part and picosecond pedestal [1]. These prepulses can cause ionization and heating of the target and consequently create a low density preplasma [2] before the main pulse arrive. Mitigation of these effects, i.e., increasing the laser pulse con- trast, is beneficial for several application, e.g, Radiation Pressure Acceleration in the light sail regime [3], High Harmonic Generation in the relativistic regime [4] or use of nanostructures on the target [5]. Prepulses can be reduced either by reflecting plasma media [6] or by transmitting plasma media, so-called plasma shutter [7]. In this work we study the utilisation of silicon nitride target as a plasma shutter for laser pulse contrast enhancement in the sub picosecond time domain with realistic parameters with the help of numerical 2D3V particle-in-cell simulations [8]. We focus on the dependence of the laser pulse transmission through the shutter on its thickness, the properties of the transmitted pulse (pulse shape, spectrum) and the effects of preplasma located on the front side of the shutter. When the laser pulse burns through the shutter focusing of the transmitted pulse is observed. Using thin shutter targets (less 40 nm thickness) more than 5% of energy of a petawatt class laser beam is transmitted, with transmissivity of 35% in the case of 20 nm target. Our work is supported by Czech Science Foundation project 18-09560S. References [1] G. A. Mourou, T. Tajima and S. V. Bulanov, Rev. Mod. Phys. 78, 309 (2006) [2] F. Wagner, S. Bedacht, A. Ortner et al, Optics Express 22, (2014) [3] B. Qiao, S. Kar, M. Geissler et al., Phys. Rev. Lett. 109, 029901 (2012) [4] F. Dollar, P. Cummings, V. Chvykov et al., Phys. Rev. Lett. 110, 175002 (2013) [5] D. Margarone, O. Klimo, I. J. Kim et al., Phys. Rev. Lett. 109, 234801 (2012) [6] A. Levy, T. Ceccotti, P. D’Oliveira et al., Optics Letters 32, 3 (2007) [7] S. Palaniyappan, B. M. Hegelich, H. Wu et al., Nature Physics 8, (2012) [8] T. D. Arber, K. Bennett, C. S. Brady et al., Plasma Phys. Control. Fusion 57, 113001 (2015)

Speaker: Martin Matys

14:00 P4.2032 Velocity measurement of laser-induced shock using a spectral domain interferometer and a chirped pulse laser

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2032.pdf Velocity measurement of laser-induced shock using a spectral domain interferometer and a chirped pulse laser K. Ishii1, A. Sunahara2, Y. Mori1, R. Hanayama1, S. Okihara, Y. Kitagawa1, T. Sekine3, Y. Takeuchi3, T. Watari3, T. Kurita3, H. Kimura3, Y. Kabeya3, Y. Mizuta3, Y. Kato3, T. Hioki4, T. Motohiro4, H. Azuma5, Y. Sentoku6, E. Miura7, A. Iwamoto8, and H. Sakagami8 1 The Graduate School for the Creation of New Photonics Industries, Japan, 2 Purdue Univ., USA, 3 Hamamatsu Photonics, K. K., Japan, 4 Nagoya University, GREMO, Japan, 5 Aichi Synchrotron Radiation Center In “Knowledge Hub Aichi”, Japan, 6 Institute for Laser Technology, Japan, 6 Institute of laser engineering, Osaka Univ., Japan 7 National Institute of Advanced Industrial Science and Technology, Japan 8 National Institute of Fusion Science, Japan In the fast ignition scheme inertial fusion, shock waves driven by ultra-intense lasers are one of candidates for the core heating. To measure the velocity and pressure of shock wave, we have developed a spectral domain interferometer using a part of the chirped pulse amplified (CPA) laser of 800 nm wavelength, which we call the probe beam [1]. The laser pulse with the pulse width of 110 fs and the peak intensity of 1.73x1017 W/cm2 irradiates 150 μm-thickness solid Zirconia plate, which is coated with 20 nm-thick vanadium on the surface, The probe beam is illuminated from the backside of the plate. Figure 1 shows a measured interference fringe at the moment of the laser irradiation. From the fringe analysis, the velocity of shock wave is estimated to be 4×105 cm/s. In the presentation, we compare the velocity of shock wave with the numerical result obtained from the two-dimensional radiation hydrodynamic code (STAR2D) and discuss the pressure of the shock wave. References [1] K. Ishii et al., Proc SPIE, 10089, 1008916 (2017). Fig. 1 Interference fringe at the moment of the laser irradiation to a solid Zirconia plate. It is measured using a spectral domain interferometer and a chirped pulse laser.

Speaker: Katsuhiro Ishii

14:00 P4.2033 Experiments with Shanghai Super-intense Ultrafast Laser Facility and the Station of Extreme Light

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2033.pdf Experiments with Shanghai Super-intense Ultrafast Laser Facility and the Station of Extreme Light Baifei Shen1,2 1 Department of Physics, Shanghai Normal University, Shanghai 200234, China. 2 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P. O. Box 800-211, Shanghai 201800, China. bfshen@shnu,edu.cn The Shanghai Super-intense Ultrafast Laser Facility (SULF) with a ten PW laser will be completed in the end of 2018. The research platform for Ultrafast Sub-atomic Physics at SULF will be focused on the production of energetic beams and their applications. Laser driven proton acceleration with solid and gas targets is planned. [1] Protons will be polarized and accelerated in a special way. Laser driven electrons will be used to generate positron beams [2] and intense gamma rays, especially in the near QED regime. Nuclear physics by using laser driven protons and gamma rays are considered. The Station of Extreme Light (SEL) at Shanghai Coherent Light Facility (SCLF) has been approved to be built. The 100 PW laser of SEL will not only be used for exploring vacuum birefringence [3] and other vacuum QED effects with the help of the hard XFEL, but also accelerate protons to more than 10GeV which can be used for anti-proton production. [4] Thanks to the high production efficiency of gamma ray in the QED regime, nuclear photonics will be one of the most important research fields. [5, 6] 1．H. Zhang, B.F. Shen et al., Collisionless Shock Acceleration of High-Flux Quasi monoenergetic Proton Beams Driven by Circularly Polarized Laser Pulses, PHYSICAL REVIEW LETTERS 119, 164801 (2017) 2. Tongjun Xu, Baifei Shen et al.,Ultrashort megaelectronvolt positron beam generation based on laser-accelerated electrons, PHYSICS OF PLASMAS 23, 033109 (2016) 3. Baifei Shen et al., Exploring vacuum birefringence based on a 100 PW laser and an x-ray free electron laser beam, Plasma Phys. Control. Fusion 60, 044002(2018). 4. Shun Li, Zhikun Pei, Baifei Shen et al., Physics of Plasmas 25, 023111 (2018). 5. L. L. Ji, A. Pukhov, E. N. Nerush, I. Yu. Kostyukov, B. F. Shen, and K. U. Akli, Energy partition, gamma-ray emission, and radiation reaction in the near-quantum electrodynamical regime of laser-plasma interaction, PHYSICS OF PLASMAS 21, 023109 (2014) 6. Shun Li, Baifei Shen et al., Ultrafast multi-MeV gamma-ray beam produced by laser- accelerated electrons，PHYSICS OF PLASMAS 24, 093104 (2017)

Speaker: Baifei Shen

14:00 P4.2034 Interaction of multi-PW class laser pulses with underdense plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2034.pdf Interaction of multi-PW class laser pulses with underdense plasmas M. Yano 1, A. Zhidkov2, R. Kodama1,2,3 1 Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan 2 Country Photon Pioneers Center, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan 3 Country Institute of Laser Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan Petawatt class femtosecond lasers and x-ray free electron lasers open up a new page in research fields related to space and vacuum physics. Regular electron sub-systems undergoing super-acceleration generated by these new instruments, which may be important experimental objects for vacuum and space-time researches, are shown to be created in underdense plasma irradiated by multi-PW laser pulses with intensity over 1022 W/cm2. For the first time interaction of multi-PW laser pulses with underdense plasma, in the regime of strong relativistic wave-breaking, is investigated via 3D particle-in-cell simulation. Effects of pulse self-focusing, ion motion, and radiation reaction on the interaction and formation of regular electron sub-systems under super-acceleration are examined. We estimate scattering broadening of Thomson scattering from the electron sub-system for detection of space time effects.

Speaker: Masahiro Yano

14:00 P4.2035 Radiation friction induced enhancement of laser-driven longitudinal fields for pushing the ion acceleration limit

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2035.pdf Radiation friction induced enhancement of laser-driven longitudinal fields for pushing the ion acceleration limit E.G. Gelfer1,2 , A.M. Fedotov2 , S. Weber1 1 ELI Beamlines, Institute of Physics of the ASCR, Dolni Brezany, Czech Republic 2 National Research Nuclear University “MEPhI”, Moscow, Russia Due to the construction of high power laser facilities, ELI Beamlines [1] and alike, a pressing challenge is the search for novel regimes of laser-plasma interactions at the next intensity levels, in particular uncovering the role of radiation friction [2]. We consider the generation of longi- tudinal waves due to the propagation of a strong laser pulse through an underdense plasmas with account for radiation friction. Our goal is an analytical model of the process capable for estimating and optimizing the parameters of the wave [3]. In particular, we prove that both the amplitude and the period of the generated waves are essentially enhanced by radiation friction under the condition !2/3 5/6 1/3 I n 1/6 t λ pulse · · · & 1. 1022 W/cm2 1019 cm−3 100 fs 1 µm Our findings are confirmed by 1D and 2D PIC simulations. The resulting charge separation field can be so high that ions gain relativistic energies, hence the discovered effect can be ap- plied to laser-plasma acceleration. We also demonstrate that radiation friction notably enhances longitudinal field generation under the conditions realizable at ELI Beamlines [1], see Fig. 1. Figure 1: 2D simulation of the longitudinal field distributions created by a tightly focused 10 PW laser pulse of FWHM duration t pulse = 150 fs, propagating in a plasma (a) with and (b) without friction. References [1] http://www.eli-beams.eu. [2] A. Di Piazza, C. Muller, K.Z. Hatsagortsyan, and C.H. Keitel, Rev. Mod. Phys. 84, 1177 (2012). [3] E.G. Gelfer, N.V. Elkina and A.M. Fedotov, arXiv:1710.09253 (2017); E.G. Gelfer, A.M. Fedotov and S. Weber, arXiv:1801.03795 (2018).

Speaker: Evgeny Gelfer

14:00 P4.2036 Accessing the relativistic transparency regime in laser-ion acceleration experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2036.pdf Accessing the relativistic transparency regime in laser-ion acceleration experiments L. Obst1,2, P. L. Poole3, G. E. Cochran4, J. Metzkes-Ng1, H.-P. Schlenvoigt1, I. Prencipe1, T. Kluge1, T. E. Cowan1,2, U. Schramm1,2, D. W. Schumacher4, K. Zeil1 1 Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany 2 Technische Universität Dresden, Germany 3 Lawrence Livermore National Laboratory, USA 4 The Ohio State University, Columbus, USA In target normal sheath acceleration (TNSA), the onset of relativistic induced transparency (RIT) [1] can lead to increased proton energies due to volumetric heating of the target electrons by the transmitted laser light [2,3]. We present an experimental study investigating TNSA over a target thickness range spanning the typical TNSA-dominant regime (∼ 1 μm) down to below the onset of relativistic laser-transparency (< 40 nm) [4]. The experiment was conducted with a single target material in the form of freely adjustable films of liquid crystals along with high contrast (via plasma mirror) laser interaction (∼ 2.65 J, 30 fs, I > 5 × 1020 W cm−2) under oblique incidence. The proton energy and spatial distribution, measured along the laser axis and in both front and rear target normal directions, evidence predominant proton acceleration along the target normal during high contrast interaction, even for ultra-thin targets. For the latter, changes in light transmission, maximum proton energy, and proton beam spatial profile indicate the onset of relativistic transparency. References [1] V. A. Vshivkov et al. Nonlinear electrodynamics of the interaction of ultra-intense laser pulses with a thin foil. Phys. Plasmas 5, 2727–2741 (1998). [2] B. M. Hegelich et al. Laser-driven ion acceleration from relativistically transparent nanotargets. New J. Phys. 15, 085015 (2013). [3] A. Higginson et al. Near-100 MeV protons via a laser-driven transparency-enhanced hybrid acceleration scheme. Nat. Comm. 9, 724 (2018). [4] P. L. Poole et al. Laser-driven ion acceleration via target normal sheath acceleration in the relativistic transparency regime. New J. Phys. 20(1), 013019 (2018).

Speaker: Lieselotte Obst

14:00 P4.2037 High Harmonic Generation and QED Effects Induced by Relativistic Oscillating Mirror

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2037.pdf High Harmonic Generation and QED Effects Induced by Relativistic Oscillating Mirror Y. J. Gu1, 2, O. Klimo1, 3, S. V. Bulanov1, 4, 5, S. Weber1 1 Institute of Physics of the ASCR, ELI-Beamlines project, Na Slovance 2, Prague 18221, Czech Republic 2 Institute of Plasma Physics of the CAS, Za Slovankou 1782/3, Prague, Czech Republic 3 FNSPE, Czech Technical University in Prague, 11519 Prague, Czech Republic 4 Kansai Photon Research Institute, National Institutes for Quantum and Radiological Science and Technology, 8-1-7 Umemidai, Kizugawa-shi, Kyoto 619-0215, Japan 5 A. M. Prokorov Institute of General Physics, the Russian Academy of Sciences, Vavilova 38, 119991 Moscow, Russia E-mail: yanjun.gu@eli-beams.eu Intensities of the forthcoming laser facilities are approaching 1023-24 W/cm2. With such a high intensity, the laser-plasma interactions are dominated by the QED regime. In this work, we present the high brightness γ-photon emission and e+e- pair creation accompanied with the high harmonic generation. Relativistic oscillating mirror reflects the incident intense laser field and generates the focused attosecond pulse with intensity enhancement. A large number of high energy photons are emitted by the radiation trapped electron colliding with the high harmonic pulse. The corresponding photons are counter-propagating through the strong laser field which provide a high probability for pair creation. Relativistic positron bunches are obtained and further accelerated in the reflected laser field. This regime may be beneficial for the potential experiments carried on the large laser facilities such as ELI-beamlines1. References 1 G. Mourou, G. Korn, W. Sandner, and J. Collier, ELI Extreme Light Infrastructure (Whitebook). (THOSS Media GmbH, 13187 Berlin, Germany, 2011).

Speaker: Yanjun Gu

14:00 P4.2038 Kinetic and finite ion mass effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2038.pdf Kinetic and finite ion mass effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration E. Siminos1 , M. Grech2 , B. Svedung Wettervik3 , T. Fülöp3 1 Department of Physics, University of Gothenburg, Sweden 2 LULI, CNRS, UPMC, Ecole Polytechnique, CEA, 91128 Palaiseau, France 3 Department of Physics, Chalmers University of Technology, Gothenburg, Sweden We study kinetic effects responsible for the transition to relativistic self-induced transparency (RSIT) in the interaction of a circularly-polarized laser-pulse with an overdense plasma and their relation to hole-boring (HB) and ion acceleration. It is demonstrated using particle-in-cell simulations 8 HB IC) and an analysis of separatrices in single-electron 7 s (P 1 + a02 ion 2 1/2 6 b . ∝ a0 r phase-space, that ion motion can suppress fast elec- o imm n SW nc eff = tron escape to the vacuum, which would otherwise 5 n0 /nc lead to transition to the relativistic transparency 4 regime. A simple analytical estimate shows that 3 H for large laser pulse amplitude a0 the time scale 2 RSIT He over which ion motion becomes important is much 5 10 15 20 25 a0 shorter than usually anticipated. As a result, the threshold density above which hole-boring occurs Figure 1: Different transition thresholds be- decreases with the charge-to-mass ratio. Moreover, tween RSIT and HB: for infinite plane waves the transition threshold is seen to depend on the (black dashed line), cold-fluid threshold for laser temporal profile, due to the effect that the latter existence of a standing wave [1] (red solid has on electron heating. We report a new regime in line), PIC simulations with immobile ions [2] which a transition from relativistic transparency to (green triangles), PIC simulations for hydro- hole-boring occurs dynamically during the course gen and helium [3] (error bars). The dynamic of the interaction. It is shown that, for a fixed laser transition regime lies within the error bars. intensity, this dynamic transition regime allows op- timal ion acceleration in terms of both energy and energy spread. References [1] F. Cattani et al, Phys. Rev. E 62, 1234 (2000) [2] E. Siminos et al, Phys. Rev. E 86, 056404 (2012) [3] E. Siminos et al, New J. Phys. 19, 123042 (2017)

Speaker: Evangelos Siminos

14:00 P4.2039 Multipurpose single shot, offline and online, gamma calorimeters for ultra-high intensity laser-plasma experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2039.pdf Multipurpose single shot, offline and online, gamma calorimeters for ultra-high intensity laser-plasma experiments A. Laso Garcia1, M. Molodtsova1, A. Ferrari1, M. Downer2, A. Hannasch2, A. Irman1, J. Metzkes-Ng1, T. Cowan1 1 Institute of Radiation Physics, Helmholtz-Zentrum Dresden – Rossendorf, Dresden, Germany 2 Department of Physics, University of Texas at Austin, Austin, Texas 78712-1081, USA 3 Institute, City, Country Highly intense gamma ray bursts (>106 gamma/shot) are associated with the interaction of ultra-intense lasers with solid targets. In the case of underdense plasmas, burst of gamma rays can be generated via inverse Compton processes between the laser and the accelerated electrons. In both cases, a suitable diagnostic is required. In this talk, we present a multipurpose gamma calorimeter based on absorber materials and image plates that provides a single shot measurement of the gamma spectrum. Furthermore, measurement results from an online-readout calorimeter based on scintillators will also be presented. Both detectors have been successfully fielded at the high power laser facility DRACO at Helmholtz-Zentrum Dresden – Rossendorf. We report the results of bremsstrahlung measurements at ion acceleration with solid targets as well as inverse Compton measurements at laser wakefield acceleration in which the calorimeters have recorded data over more than a thousand shots.

Speaker: Alejandro Laso Garcia

14:00 P4.2040 High intensity physics and braided beam emissions in underdense plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2040.pdf High intensity physics and braided beam emissions in underdense plasmas E. Wallin1 , A. Gonoskov1,2,3 , M. Marklund1 1 Department of Physics, Chalmers University of Technology, SE?412 96 Göteborg, Sweden 2 Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia 3 University of Nizhny Novgorod, Nizhny Novgorod 603950, Russia Today, laser wakefield acceleration of electrons is a mature subject and one of the major appli- cations of high-power laser systems [1]. The weakly nonlinear regime of LWFA is known to be the optimal for reaching the highest possible electron energies, while the capabilities of upcom- ing large laser systems will provide the possibility of running highly nonlinear regimes of laser pulse propagation in underdense or near-critical plasmas. We show that such regimes can be implemented with external guiding for a relatively long distance of propagation and allow for the stable transformation of laser energy into other types of energy, including the kinetic energy of a large number of high energy electrons and their incoherent emission of photons. This is despite the fact that the high intensity of the laser pulse triggers a number of new mechanisms of energy depletion, which we investigate systematically. Notably, the production of pairs in these systems is very small even at very high intensities, and only becomes notable at extreme intensities (around 1026 W/cm2 ) [3]. Apart from the intensity parameter, one may also play with the geometry of the wakefield setup. In particular, if allowed to interact, two such wakefield systems will generate a rich dy- namics, where its characteristics depend on, e.g., the collision angle [?]. Here, we do a full parameter scan of different collision angles between the wakefields. In particular, we are inter- ested in the radiative properties of the interaction. We use analytics and 3D PIC simulations to investigate this as a means for controlling and tuning the radiation emission from such sys- tems. Two main regimes are compared: large angle collisions with the transverse acceleration due to the laser fields and small angle collisions with the transverse acceleration due to plasma fields. The latter provide a mechanism for generating soft x-rays. Moreover, for small angle collisions, the electron bunches oscillate behind the laser pulses in a braided pattern, extending the interaction time beyond the normal dephasing length and giving a tunable radiation source. References [1] E. Eseray, C.B. Schroeder, and W.P. Leemans, Rev. Mod. Phys. 81, 1229 (2009) [2] E. Wallin, A. Gonoskov, C. Harvey, O. Lundh, and M. Marklund, J. Plasma Phys. 83 2 (2017) [3] E. Wallin, A. Gonoskov and M. Marklund, Phys. Plasmas 24, 093101 (2017).

Speaker: Erik Wallin

14:00 P4.2041 Open, Any-Platform, Leadership-Scale PIC Simulations for Humans (No Hooks Attached)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2041.pdf Open, Any-Platform, Leadership-Scale PIC Simulations for Humans (No Hooks Attached) R. Pausch1,2, R. Widera1, M. Garten1,2, A. Debus1, I. Goethel1, A. Matthes1,2, B. Worpitz1,2, S. Starke1, J. Kelling1,2, S. Kossagk1,2, S. Bastrakov1, T. Kluge1, G. Juckeland1, U. Schramm1,2, T.E. Cowan1,2, M. Bussmann1, A. Huebl1,2 1 Helmholtz-Zentrum Dresden – Rossendorf, Dresden, Germany 2 Technische Universität Dresden, Dresden, Germany PIConGPU is a fully open, community-driven, 3D and 2D3V particle-in-cell code for the age of heterogeneous, many-core driven supercomputing. Running from a single source C++ code base PIConGPU supports both "legacy" CPU architectures as well as modern and highly parallel architectures such as OpenPOWER, XeonPHI, and Nvidia GPUs. Especially the latter enable few-hour turnaround full 3D simulations for complex studies such as laser-ion acceleration. The resulting dramatic demands in post-processing (PBytes+) are efficiently addressed with implemented in-situ data reduction techniques. Those allow asking e.g. for a wide range of observables relevant for experiments - up to 100x during the time frame of an actual beam time. This is complemented by modern Visualization of an LWFA simulation and a list of methods for photon generation, software used. transport, and X-ray interaction. Driving, re-using and publishing performance-portable libraries, PIConGPU aims to provide documented, installable and re-usable software components for the community, well suited for open data (openPMD) and open science workflows without restrictions. Latest developments further include a python-centric, extensive framework for specific experiments, which provides all of the above in an intuitive, non-expert user interface.

Speaker: Richard Pausch

14:00 P4.2042 2D and 3D modeling of bright X-ray sources on LMJ

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.2042.pdf 2D and 3D modeling of bright X-ray sources on LMJ L. JACQUET1, M. PRIMOUT1, L. VIDEAU1 1) CEA, dam, DIF, F-91297 Arpajon, France E-mail: laurent.jacquet@cea.fr Multi-keV bright X-ray sources are needed for many applications as material testing and plasma diagnostics for inertial confinement fusion. For that purpose, X-ray sources are designed using gas-filled pipes and metallic foils. These targets are expected to be illuminated by up to 12 quads of the LaserMegaJoule facility (LMJ). Here we focus on the simulations of pipes filled with xenon and foils made of silver. The radiative-hydrodynamics simulations are carried out with the 2D code FCI2 [1] and the 3D code Troll. The two codes use the same physics package to simulate radiation transfer, non-local-thermal-equilibrium atomic physics, flux-limited electron thermal conduction and laser propagation. For several target configurations, the energy emitted in multi-keV X-rays (with photon energies above 1 keV) is computed with FCI2 and Troll. The comparison of 2D and 3D results enables to quantify the effect of the asymmetric feature of the laser irradiation configuration on the X-ray fluence. Moreover, Troll provides a 3D characterization of the X-ray emission lobes that are of particular importance for radiographic purposes [2] and to optimize the location of samples for material testing within the LMJ experimental chamber. References [1] E. Buresi et al., Laser Part. Beams 4, 531 (1986). [2] L. Jacquet et al., High Energy Density Physics 9 (2013) 601-608.

Speaker: Laurent Maurice Jacquet

14:00 P4.3001 Non equilibrium vibrational and electron energy distribution functions in CO2/CO cold plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3001.pdf Non equilibrium vibrational and electron energy distribution functions in CO2/CO cold plasma L. D. Pietanza, G. Colonna, A. Laricchiuta and M. Capitelli PLASMI Lab NANOTEC CNR Bari (Italy) In recent papers [1-2], we have shown results obtained by implementing a self-consistent time-dependent kinetic model of a pure CO plasma applied to conditions generally met in microwave, dielectric barrier and nanosecond repetitively pulsed discharges. The model is based on the coupling between the Boltzmann equation for the electron energy distribution function (eedf), the CO vibrational and electronic excited state kinetics and a simplified global model for dissociation and ionization plasma chemistry. The results reported in [1-2] have shown the importance of the model to understand the energy exchange processes between the different vibrational and electronic modes of the plasma molecules and the free electrons. In the present contribution, we will show results obtained by inserting the CO kinetic model into the more complex model which describes the kinetics of a reacting CO2/ CO plasma mixture [3-8], focusing on the problem of CO2 activation by means of plasma technology. Attention will be made in the description of the most important processes linking the CO and CO2 kinetics and to the contribution of the CO and CO2 electronic excited state kinetics in affecting the time-dependent eedf of the reacting mixture. References [1] L. D. Pietanza, G. Colonna and M. Capitelli Plasma Sources Sci. Technol. 26, 12500 (2017) [2] L. D. Pietanza, G. Colonna and M. Capitelli J. Plasma Phys. 83, 6 (2017) [3] L. D. Pietanza, G. Colonna, G. D’Ammando, A. Laricchiuta and M. Capitelli Plasma Sources Sci. Technol. 24, 042002 (FTC) (2015) [4] L. D. Pietanza, G. Colonna, G. D’Ammando, A. Laricchiuta and M. Capitelli Chem. Phys. 468, 44 (2016) [5] M. Capitelli, G. Colonna G. D’Ammando, A. Laricchiuta and L.D. Pietanza Plasma Sources Sci. Technol. 26, 055009 (2017) [6] T. Kozak and A. Bogaerts Plasma Sources Sci. Technol. 23, 045004 (2014) [7] A. Bogaerts, A. Berthelot, S. Heijkers, S. Kolev et al. Plasma Sources Sci. Technol. 26, 063001 (2017) [8] T. Silva, M. Grovulovic, B. L. Klarenaar, A. S. Morillo-Candas et al. Plasma Sources Sci. Technol. 27, 015019 (2017)

Speaker: Lucia Daniela Pietanza

14:00 P4.3002 Self-consistent simulation of hydrogen-methane plasmas for CVD diamond deposition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3002.pdf Self-consistent simulation of hydrogen-methane plasmas for CVD diamond deposition S. Prasanna1 , A. Michau1 , C. Rond1 , K. Hassouni1 , A. Gicquel1 1 Laboratoire des Sciences des Procédés et des Matériaux, UPR3407, CNRS, Universite Paris 13, avenue Jean-Baptiste Clément, 93430 Villetaneuse (France) MW assisted hydrogen methane plasmas have been extensively used for growth of CVD dia- 3000 mond and graphene. In this article, we discuss the T (K) 2000 results of self-consistent simulation of hydrogen- CH4 0.5% 1000 CH4 4% Hyd methane plasmas in a microwave resonating cav- 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 ity at high pressure conditions (110-200mbar) and z (m) 0.5 different concentrations of methane. Details of the 0.4 self-consistent model is provided elsewhere [1]. XH 0.3 0.2 The results indicate that the pressure, power and 0.1 concentration of methanne in the H2 −CH4 methane 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 z (m) affect the characteristics of the coupling between MW and plasma. Figure 1 shows the gas temper- Figure 1: Effect of methane on the tem- ature and atomic hydrogen concentration at a pres- prature and atomic hydrogen mole frac- sure of 200 mbar and power 2500 W. The results tion at 200 mbar and 2500 W at the axis are in agreement with experimental observations. It of the plasma reactor is seen that the addition of methane increases the temperature of the reactor. As a result the the dissociation of hygrogen increases with addi- tion of methane. The results are similar at 110 mbar. n general, the plasma characteristics is a function of methane concentration, pressure and MW power. References [1] S. Prasanna et al. Plasma Sources Science and Technology 26.9 (2017)

Speaker: Khaled Hassouni

14:00 P4.3003 Impact of shock wave on weakly ionized gas: numerical evaluation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3003.pdf Impact of shock wave on weakly ionized gas: numerical evaluation V.A. Pavlov1 , J.V. Triaskin1 1 Physics Department, St. Petersburg State University, 1, Ulyanovskaya str., Petrodvorets, 198504, St. Petersburg, Russia The basic principles of nonlinear ion-acoustic waves formation in weakly ionized gas sub- jected to the shock wave of neutral gas were investigated by the numerical and analytical methods. The ion-acoustic approximation were employed to describe the plasma component of charged gas [1]. Within a such approach the ion-acoustic waves arise via the collisions of charges with the neutral particles only. For numerical simulation the initial and approximate boundary conditions for non-stationary problem are determined in assumption that the solution of runaway wave type can be found [2]. The strong anomalous nonlinear effects appear in this case. The competitive action of nonlinearity, dispersion and dissipation at the formation of spe- cific plasma "condensations" and "rarefactions" is shown [2]. In narrow range of the shock wave velocities the anomalous relaxation of plasma oscillations occurs behind the front. It appears in the total ambipolar entrainment by the shock wave of charged components. This effect possibly results from the strong nonlinear resonant (in respect to the shock wave velocity) perturbation in the region ahead of front. Nonlinear perturbations of weakly ionized non-isothermal gas (Te Ti ≈ Tn ) under the ac- tion of a strong stationary shock wave of the neutral component have been studied based on computer-aided calculations. The detected patterns reflect the most essential features of the additional mechanism of reduction of the intensity of a strong shock wave of the neutral com- ponent without energy release for heating the region ahead of the front. The reciprocal action of the charged components upon the neutral particles result in change of the structure and reduction of the intensity of the shock wave. In such a case, a paradoxical situation arises: low-ionized plasma (the nonperturbed state is meant) exerts a strong effect upon the neutral component and the reduction of the shock wave intensity. Laboratory experiment data to corroborate such influence are available [3]. References [1] V. A. Pavlov, Plasma Phys. Rep. 22, 167, (1996) [2] V.A. Pavlov. Ya. V. Tryaskin. Journal of Applied Mechanics and Technical Physics, Vol. 56, No. 3, (2015) [3] Yu. L. Serov, MODERN SCIENCE, No.2, Vol.10, 2012

Speaker: Jaroslav Triaskin

14:00 P4.3004 Internal energy relaxation processes of nitrogen plasmas at different electronic states in an entry flight condition

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3004.pdf Internal energy relaxation processes of nitrogen plasmas at different electronic states in an entry flight condition G. Yamada1, M. Kajino1, H. Kawazoe2 1 Tokai University, Hiratsuka, Japan 2 Tottori University, Tottori, Japan Entry flight is a technical issue on the development of space vehicles used for planetary exploration. Particularly, characteristics of plasma flows around the space vehicles should be clarified for the better prediction of aerodynamic forces and heating rates on the body during entry flight. In the present study, to investigate the internal energy relaxation process of nitrogen plasma behind a shock wave, spectroscopic measurements are conducted using a shock tube facility in an entry flight condition. The shock velocity and the spectrum position from the shock front are determined by the double laser schliren measurement system. Emission spectra of N2(1+), and N2+(1-) are obtained by means of the spatially- resolved imaging spectroscopy. The rotational and vibrational temperatures are derived from the measured spectra by a spectrum fitting method and finally temperature distributions correlated to the shock front are obtained as shown in Figs.1(a) and (b). In these figures, the calculated temperatures are plotted as solid lines for comparison. From Fig.1(a), it is found that the measured rotational temperatures of N2(1+) and N2(2+) are almost same behind the shock wave and much lower than the calculated rotational temperatures, showing the notational nonequilibrium process. On the other hand, from Fig.1(b), the measured vibrational temperature of N2(1+) is much higher than that of N2(2+) . This is considered to be due to the difference of internal energy relaxation process depending on the electronic energy state. The present result has indicated that the electronic state has great influence on the relaxation process behind the shock wave. (a) Rotational temperature (b) Vibrational temperature Fig. 1 The spatial distribution of temperatures correlated to the distance from shock front

Speaker: Gouji Yamada

14:00 P4.3005 Study of cavitation in liquid water under the action of inhomogeneous pulsed electric fields: application to sub-nanosecond electrical breakdown

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3005.pdf Study of cavitation in liquid water under the action of inhomogeneous pulsed electric fields: application to sub-nanosecond electrical breakdown M. Šlapanská1 , M. Kubečka1 , A. Obrusník1 , J. Hnilica1 and Z. Bonaventura1 1 Department of Physical Electronics, Faculty of Science, Masaryk University, Brno, Czech Republic Sub-nanosecond electrical breakdown in dielectric liquids is of vital interest, e.g. for ap- plications in high-voltage insulation and high-current switching. Liquid dielectrics in strong nonuniform electric fields are under influence of electrostrictive force that tents to move the fluid into the regions with higher electric field. If the voltage rise is fast enough, the liquid does not have enough time to set into motion thanks to inertia. Then the poderomotive force induces significant stress in the bulk of the liquid leading to generation of a negative pressure. At certain threshold, the negative pressure causes cavitation ruptures of the fluid. Free electrons then can be produced by emission from the surface inside the cavity and accelerated to energies exceed- ing the energy for ionization of water and contribute thus to formation of microstreamers. In this work we use hydrodynamic model for motion of dielectric fluid to study the dynamic of water in a pulsed strongly inhomogeneous electric fields in the approximation of compressible flow described by equation of continuity for mass and momentum [1, 2] ∂ρ + ∇ · (ρ~u) = 0 ∂t ∂~u ~ 2 1 ρ + (~u · ∇)~u = −∇p + F + η ∇ ~u + ∇(∇ ·~u) ∂t 3 where ρ is the fluid density, p is the pressure, ~u is the velocity, η is the dynamic viscosity, and ~F ≈ ε0 ε∇E 2 is the force acting on the body of the fluid thanks to inhomogeneous electric field E. The set of continuum equations is closed by the Tait equation of state for water [3, 4, 5]. The model allows to find pressure field in the liquid for considered electrode geometry and high voltage pulse and calculate probability for cavitation voids generation. This contribution is funded by the Czech Science Foundation grant no. 18-04676S. References [1] M. N. Shneider and M. Pekker, Phys. Rev. E 87, 043004 (2013) [2] M. N. Shneider and M. Pekker, J. Appl. Phys. 114, 214906 (2013) [3] R. I. Nigmatulin and R. Kh. Bolotnova, High Temperature 49 2, 303 (2011). [4] R. I. Nigmatulin and R. Kh. Bolotnova, High Temperature 46 3, 325 (2011). [5] Y.-H. Li, J. Geophys. Res. 70 10, 2665 (1967)

Speaker: Marta Šlapanská

14:00 P4.3006 Simulation of shock-waves in water induced by nanosecond-laser pulse

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3006.pdf Simulation of shock-waves in water induced by nanosecond-laser pulse M. Kubečka1 , A. Obrusník1 , Z. Bonaventura1 1 Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic One of the main advantages of using the nanosecond-laser pulses for generation of fast break- down of water is to avoid the presence of metal-liquid interface. The laser-produced breakdown is well known phenomenon that generates shock-waves in liquid. The main physical mech- anisms responsible for shock-waves in liquid by laser pulse were found to be linear optical absorption with subsequent bulk thermal expansion, explosive evaporation and dielectric break- down and ionization [1, 2]. We study this acoustic phenomenon by simulating the generation of shock-waves using hy- drodynamic model for motion of compressible liquid (water) described by equation of continu- ity for mass, momentum equation and the Tait equation [3] ∂ρ + ∇ · (ρ~u) = 0 ∂t ∂~u 2 1 ρ + (~u · ∇)~u = −∇p + η ∇ ~u + ∇(∇ ·~u) ∂t 3 γ ρ p = (p0 + B) −B ρ0 where ρ is the fluid density, p is the pressure, ~u is the velocity, η is the dynamic viscosity, B is the compressibility of the liquid and γ is a material parameter. The aim of our work is to simulate the propagation of shock-wave to reconstruct numerical Schlieren images for comparison with experimental data. Acknowledgements This research has been supported by the Czech Science Foundation grant no. 18-04676S. References [1] B. D. Strycker, et al., Optics express (21), 20 (2013) [2] F. V. Bunkin, A. A. Kolomensky, V. G. Mikhalevich, Lasers in Acoustics (12) (1991) [3] M. N. Shneider, M. Pekker, Physical Review E (87), 4 (2013)

Speaker: Martin Kubečka

14:00 P4.3007 Modelling of streamer propagation in dielectric liquids using a dense gas model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3007.pdf Modelling of streamer propagation in dielectric liquids using a dense gas model D. Trdlička1 , J. Karel1 , P. Bílek2 , J. Fořt1 and Z. Bonaventura2 1 Department of Technical Mathematics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Prague, Czech Republic 2 Department of Physical Electronics, Faculty of Science, Masaryk University, Brno, Czech Republic Ultrafast electrical breakdown in dielectric liquids is of considerable interest for applications in high-voltage insulation. For liquids with high mobility of charged particles, the breakdown takes place on a nanosecond time scale, and its mechanism is similar to the streamer breakdown of gases which is caused by the electron impact ionization of particles, with a distinction that the electron–ion recombination in the streamer channel plays a significant role compared to streamers in gases. Also very high-voltage pulses of sub-ns duration provide an extremely high electrical field in the plasma formation region in the liquid and allow ionization directly in the condensed phase by direct electron impact. Thanks to the sub-nanosecond time scale, the fluid lacks time to expand, and so the discharge is formed directly in the liquid phase [1, 2]. In this contribution we present a study positive streamer dynamics in dielectric liquid using a dense gas model [3]. The electric discharge propagation in liquid is described by the set of convection- diffusion equations with source terms for charged particles coupled with the Poisson equation for the electric potential. The equations are discretized by finite volume method (FVM) on 2D unstructured triangular grid. The convective terms are computed by upwind scheme and the accuracy of the scheme is increased by linear reconstruction restricted by the Barth-Jespersen limiter. The dissipative terms are discretized by the diamond scheme and central approxima- tion. The second order in time is guaranted by three steps Runge-Kutta method. The Poisson equation is discretized analogously as dissipative terms in convection-diffusion equations, and the system of linear equations is afterwards solved by LU decomposition. Implemented multi- level dynamic grid adaptation algorithm allows to capture sharp peaks and steep gradients of unknowns occurring in moving region of the streamer head. This contribution is funded by Czech Science Agency grant no. 18-04676S. References [1] Starikovskiy A 2013 Plasma Sources Sci. Technol. 22 012001. [2] Starikovskiy A, Yang Y, Cho Y and Fridman A 2011 Plasma Sources Sci. Technol. 20 024003. [3] Babaeva N Y and Naidis G V 1999 Tech. Phys. Lett. 25 91.

Speaker: David Trdlicka

14:00 P4.3009 A study of asymmetrical effects in a 3D Inductively Coupled Plasma discharge simulation of including multiphysics.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3009.pdf A study of asymmetrical effects in a 3D Inductively Coupled Plasma discharge simulation of including multiphysics. EunHee Choi1, YeJin Shon1, Dong-Gil Kim1, Deuk-Chul Kwon2, HeeHwan Choe1 1 School of Electronics and Information Engineering, Korea Aerospace University, Goyang, Gyeonggi 10540, Republic of Korea 2 Plasma Technology Research Center, National Fusion Research Institute, Gunsan, Jeollabuk 34133, Republic of Korea A 3-dimensional plasma simulation for an inductively coupled plasma (ICP) discharge based on the fluid model in semiconductor manufacturing process is conducted in this study. Heat transfer and gas flow are merged to the plasma simulation for considering several physical phenomena simultaneously. Electron energy distribution function (EEDF) has great role in determining important coefficients such as electron mobility, diffusion coefficient, electron-neutral reaction rates and so on. Therefore, EEDF was obtained by Two-term Boltzmann Solver using space-averaged plasma properties (electron density, electron temperature, gas temperature, ionization degree, molar fraction, etc). The effects of asymmetrical structure of the antenna coil and that of the discharge chamber are investigated. 3D effects were observed, which could not be found in the 2D axisymmetric simulation. Changes by an insertion of metal plate between antenna and plasma, including Faraday shield effect, were also observed. Acknowledgement This research was supported by the National Research Council of Science & Technology(NST) grant by the Korea government (MSIP) (No. CAP-17-02-NFRI).

Speaker: EunHee Choi

14:00 P4.3010 Self-consistent 1D modelling of the CO2 conversion in microwave discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3010.pdf Self-consistent 1D modelling of the CO2 conversion in microwave discharges Vladislav Kotov Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jüich, Germany Splitting of the atmospheric CO2 into CO and O2 together with water electrolysis are the basic processes required to transfer the intermittent electricity produced by the wind and solar power plants into storable chemical fuels. An up to 80 % energy efficiency of the CO2 splitting in microwave (2.4 GHz) induced plasmas was reported back in 1970s-1980s [1, 2]. To facilitate the theoretical understanding and, thus, optimization of the process, recently a very detailed model of the CO2 plasma chemistry has been compiled [3, 4, 5]. The model explicitly describes 72 heavy species, including vibrationally excited states, and takes into account more than 5000 reactions. With this reaction set, however, the maximum calculated efficiency of only around 30 % was obtained [4]. This result seem to contradict not only with the experimental values, but also with theoretical calculations reported in the past. In the present paper the energy efficiency of the process is investigated on the basis of a simple 1D model of the plasma flow. The electron density and temperature (average energy), as well as the translational-rotational temperature of heavy particles are calculated self-consistently. For the chemical kinetics the reaction set published in [5] is revised and implemented by translating it into Fotran code. Analysis in the relevant range of discharge parameters will be presented. Conditions of achieving the highest reported efficiency in the model will be discussed. References [1] V. D. Rusanov, A. A. Fridman, G. V. Sholin Sov. Phys. Usp. 24 447 (1981). [2] A. Fridman Plasma Chemistry, Cambridge: Cambridge University Press, 2008 [3] T. Kozak, A. Bogaerts Plasma Sources Sci. Technol 23 045004 (2014). [4] T. Kozak, A. Bogaerts Plasma Sources Sci. Technol 24 015024 (2015). [5] P. Koelman et al. Plasma Proceses and Polymers 14 1600155 (2017), https://plasimo.phys.tue.nl/resources/

Speaker: Vladislav Kotov

14:00 P4.3011 A two-dimensional study of the capacitively coupled plasma discharge considering the effects of multiphysics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3011.pdf A two-dimensional study of the capacitively coupled plasma discharge considering the effects of multiphysics Yejin Shon1, Eunhee Choi1, Deuk-Chul Kwon2, HeeHwan Choe1 1 School of Electronics and Information Engineering, Korea Aerospace University, Goyang, Republic of Korea 2 Plasma Technology Research Center, National Fusion Research Institute, Gunsan, Republic of Korea *Corresponding author. Email address: choehh@kau.ac.kr Plasma simulation methods were used to analyze discharge characteristics including the flow and heat transfer of the gas in the capacitively coupled plasma discharge. In this study, two - dimensional axisymmetric structure was assumed, which is common in the semiconductor device processes. Laminar flow model was used to calculate flow, heat transfer was considered to determine the temperature of the gas. Fluid description of plasma model was combined with flow and heat transfer models. Also, electron energy distribution function (EEDF) was obtained using two - term Boltzmann approximation. The plasma region was divided multiple zones, to consider the spatial variation of EEDF. Standing wave effect in the plasma discharge was added to investigate the electromagnetic field effect according to process conditions and driving frequencies. This research was supported by the National Research Council of Science & Technology(NST) grant by the Korea government (MSIP) (No. CAP-17-02-NFRI).

Speaker: Yejin Shon

14:00 P4.3012 Energy transfer pathways in CO2-containing DC discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3012.pdf Energy transfer pathways in CO2-containing DC discharges V. Guerra1, T. Silva1, P. Ogloblina1, M. Grofulović1, L. Terraz1, H. Rodrigues1, C. Gonçalves, A. Silva1, N. Pinhão1, C. D. Pintassilgo1,2, A. Tejero-del-Caz1, L. L. Alves1, A. S. Morillo-Candas3 and O. Guaitella3 1 IPFN, Instituto Superior Técnico, Universidade de Lisboa, Portugal 2 Dep. de Engenharia Física, Faculdade de Engenharia, Universidade do Porto, Portugal 3 LPP, Ecole Polytechnique, UPMC, Université Paris Sud-11, CNRS, Palaiseau, France CO2-containing plasmas constitute a hot topic nowadays, due to their importance in CO2 reforming and the production of solar fuels [1,2] and in Mars-related studies [3,4]. A key step seems to reside in the selective excitation of the CO2 asymmetric stretching vibrational mode, while limiting the losses by gas heating. The subsequent vibration-vibration (V-V) up-pumping may enhance dissociation and favour CO2 conversion at a low energy cost [1,2]. This work presents a thorough theoretical, modelling and experimental investigation of discharges in pure CO2 and in CO2 mixtures with N2, CH4 and Ar and their afterglows, operating at pressures around 1 Torr, discharge currents of 10s of mA, either in a continuous or a pulsed regime. The basis of the model was presented in [5]. It comprises a detailed state-to-state kinetics of CO2 vibrationally excited levels, coupled to the gas phase chemistry and to the homogeneous electron Boltzmann equation describing the electron kinetics. The model is validated from the comparison with the measurements of the populations of several heavy species, e.g. O, CO, CO2(v) and C2Hx. Several phenomena are presented and discussed, such as the transfer of vibrational energy from N2 to the CO2 asymmetric stretching mode, the efficiency of dry reforming of methane, the influence of shifting the electron energy distribution function to higher energies due to Ar addition, or the main routes towards enhanced reactivity. Acknowledgments: This work was partially supported by the Portuguese FCT, under Projects UID/FIS/50010/2013, PTDC/ FIS-PLA/1420/2014 (PREMiERE) and 1243/2014 (KIT-PLASMEBA), and grants PD/BD/ 105884/2014 and 114398/2016 (PD-F APPLAuSE). VG has been supported by LABEX Plas@par receiving financial aid managed by ANR under the reference ANR-11-IDEX-0004-02. References [1] A Bogaerts et al 2017 Plasma Sources Sci. Technol. 26 063001 [2] A. P. H. Goede et al 2014 EPJ Web of Conferences 79 01005 [3] A. Bultel and J. Annaloro 2013 Plasma Sources Sci. Technol. 22 25008 [4] V. Guerra et al 2017 Plasma Sources Sci. Technol 26 1 [5] T. Silva et al 2018 Plasma Sources Sci. Technol 27 015019

Speaker: Vasco Guerra

14:00 P4.3013 Charge Fluctuations of small Particles

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3013.pdf Charge Fluctuations of small Particles A. Michau1, S. Prassanna1, K. Hassouni and S. Longo2 1 LSPM, UPR 3407 CNRS, Université Paris 13, 93430 Villetaneuse, France 2 Department of Chemistry, University of Bari, via E. Orabona 4, 70126 Bari, Italy The charge distribution of small particle and in particular for particle less than 10 nm is critical for aerosol dynamics while it controls particle coagulation [1] . Particle charge distribution is well described by Gaussian distribution [2] but this assumption is no more valid for such small particle. In this study we developed a Fokker Planck method using Monte Carlo simulation to describe the charge state of particle in a plasma. The model captures gaussian distribution for large particle. However for small particle sizes the distribution is very narrow, large fraction of them are neutrals [3] and cannot be described by a gaussian. 0.6 2 nm 0.6 50 nm 0.5 0.5 0.4 0.4 frequency frequency 0.3 0.3 0.2 0.2 0.1 0.1 0.0 0.0 -4 -3 -2 -1 0 1 -10 -9 -8 -7 -6 -5 -4 -3 -2 q q Figure 1 : charge distribution for ne=ni, Te/Ti=3 for two particle size. This charge fluctuation effect has been studied for different plasma conditions and has to be taken into account when considering for coagulation in dusty plasmas. 1. Michau, A., C. Arnas, and K. Hassouni, Aerosol dynamics in a sputtering DC discharge. Journal of Applied Physics, 2017. 121(16): p. 163301. 2. Matsoukas, T. and S.K. Friedlander, Dynamics of aerosol agglomerate formation. Journal of Colloid and Interface Science, 1991. 146(2): p. 495-506. 3. Bouchoule, Dusty plasmas: physics, chemistry & technological impacts in plasma processing 1999: John Wiley and Sons Ltd.

Speaker: Armelle Michau

14:00 P4.3014 Kinetic theory of gas discharge under condition of longitudinal pressure and electric field gradient

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3014.pdf Kinetic theory of gas discharge under condition of longitudinal pressure and electric field gradient Viktoriya S. Golyak1, Alexander O. Kokovin1, Vasily Yu. Kozhevnikov2, Andrey V. Kozyrev1, Natalia S. Semeniuk2 1 Tomsk State University, Tomsk, Russia 2 Institute of High Current Electronics, Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia Investigation of phenomena caused by thunderstorm activity in the atmosphere is a strategic and applied value. Papers [1, 2] demonstrate a unique relationship between the occurrence of powerful X-ray flashes in the atmosphere and the formation of "blue jets". Proposed model is the beginning of a way to describe this phenomenon. The task conditions of our numerical experiment are similar to those observed in nature (no uniform distributions for field and pressure take place). We use a circuit with a series-connected discharge gap and a charged capacitance. The gap is the spherical sector filled with nitrogen with a pressure gradient from 1.0 to 0.1 of atmospheric value (from cathode to anode coordinates). We assume a generation of runaway electrons plays an important role in the breakdown phenomenon. Therefore, for an adequate simulation we use the fundamental principles of electron physical kinetics. Namely, the system of equations includes the Boltzmann kinetic equation for the electron distribution function with the modeling collision integral, the continuity equation for the discharge current, and the Kirchhoff equation for the electric circuit. The numerical solution is carried out by grid difference schemes. The proposed method makes it possible to simulate an electrical breakdown with sufficient accuracy and to obtain such important characteristics as the discharge current, the distribution of the electric field in the gap, the energy spectrum of the electron component at any time. The proposed method for describing the discharge was successfully tested earlier for high- pressure discharges and showed good agreement with experiment [3]. References [1] Dwyer et. al., (2010) J. Geophys. Res., 115, D09206; [2] Fishman et. al. (1994) Science, vol. 264, iss. 5163, pp.1313-1316. [3] Tarasenko et. al. (2017) High Voltage, 2, pp. 49-55.

Speaker: Natalia Stepanovna Semeniuk

14:00 P4.3016 Modelling 1D Dielectric Barrier Discharge in Nitrogen Mixtures

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3016.pdf Modelling 1D Dielectric Barrier Discharge in Nitrogen Mixtures Lucas W S Crispim1 , Hallak, P. H.1 , Maikel Y Ballester2 1 Programa de Pós-Graduação em Modelagem Computacional UFJF, Juiz de Fora, Brasil 2 Departamento de Física UFJF, Juiz de Fora, Brasil This work aims at analyzing the temporal evolu- 1012 tion of species (Fig. 1), heating and other physical e N2(A) 1010 N N2(B) 108 quantities in a gaseous mixture subjected to elec- −3 106 Density/cm 104 tric discharges. The mathematical model includes 102 100 the application of high voltage in a gaseous mix- 10 −2 −4 10 ture between electrodes. The simulation domain is 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Radius/10−1 mm a cartesian one-dimensional region. In the macro- scopic perspective, the effects of transport, i.e. heat Figure 1: Species density at 1.0×10−6 s transfer and mass, are considered [1], microcopies, effects of heat generation due to electronic collisions and chemical reactions are also consid- ered [2]. Reaction rate and transport coefficients depending upon the electron energy distribu- tion function are calculated from collision cross-section data by solving the electron Boltzmann equation (BE). The application of a technique of separation of operators in the mathematical model provides to two sub-models, a global for macroscopic effects and another one containing microscopic effects of the plasma. A discrete sub-model for the electron-species and species- species collisions [3] is solved in ZDPlasKin [4], a zero-dimensional plasma analysis tool, while BE solver BOLSIG+ [5] required for solved electron energy distribution function. Nitrogen is used as an initial gaseous mixture in the simulation. Due to the high computational cost, a do- main decomposition with Message Passing Interface (MPI) while OpenMP is used to solving a set of partial differential equations of each component in the gas mixture [6]. References [1] A. W. Date. Analytic Combustion: With Thermodynamics, Chemical Kinetics and Mass Transfer. Cambridge University Press, 2011. [2] A. Fridman. Plasma chemistry. Cambridge university press, 2008. [3] M. Capitelli, C. Ferreira, B. Gordiets, and A. Osipov. Plasma kinetics in atmospheric gases, 2001. [4] S. Pancheshnyi, B. Eismann, G. Hagelaar, and L. Pitchford. Zdplaskin: a new tool for plasmachemical simu- lations. Bulletin of the American Physical Society, 53, 2008. [5] G. Hagelaar and L. Pitchford. Solving the boltzmann equation to obtain electron transport coefficients and rate coefficients for fluid models. Plasma Sources Science and Technology, 14(4):722, 2005. [6] P. Pacheco. An introduction to parallel programming. Elsevier, 2011.

Speaker: Lucas W S Crispim

14:00 P4.3017 A Development of Atmospheric Pressure Dielectric Barrier-Discharge System Using Computational Tools

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.3017.pdf A Development of Atmospheric Pressure Dielectric Barrier-Discharge System Using Computational Tools B. Turkyilmaz1, E. Ipek1, D. Ozdemir1, E.I. Sungur1, I.U. Uzun-Kaymak1 1 Middle East Technical University Department of Physics, Ankara, Turkey The Dielectric Barrier Discharge (DBD) plasma systems have a wide range of applicability such as surface sterilization, surface property improvement, ozone generation1. In this study the main focus is to simulate and to design an atmospheric DBD system for the purpose of bifurcation studies. Previously, we have shown period doubling bifurcations in dc driven semiconductor-gas discharges2. The DBD system consists of two copper ring electrodes placed concentrically around a quartz tube of 4mm inner diameter and 6mm outer diameter. The quartz tube is preferred due to its dielectric characteristics and high melting point. When the Argon gas is fed to the quartz tube at an atmospheric pressure, the plasma is obtained by applying modulated high voltage to one of the electrodes while other one is grounded. Expected uniform microdischarges produce a well defined dielectric discharge behaviour. Applying a high frequency AC high voltage generally reignites the old microdischarge channels at every half period1. In order to take advantage of this memory effect, a high voltage high frequency square wave is applied. Spatial and temporal plasma properties are investigated for both 1-D and 3-D models of the system using COMSOL Multiphysics. In agreement with simulations, width and separation of electrodes are determined. It is observed that an order of 10 kV AC high voltage oscillating near 10kHz frequency is at least required effectively to generate the plasma. For plasma generation, a high voltage DC source is modulated using optocouplers and IGBT based H-bridges and transformers. Also, a matching network is designed to optimize the delivered power. Designs of circuits are done using NI Multisim simulations. The current and voltage characteristic of assembled circuits are evaluated with respect to values in simulations. 1. U. Kogelschatz, B. Eliasson, W. Egli .Journal de Physique IV Colloque. 07, (1997). 2. D. Mansuroglu, I. U. Uzun-Kaymak, I. Rafatov, Phys. of Plasmas, 24, 053503 (2017).

Speaker: I. U. Uzun-Kaymak

14:00 P4.4001 Filamentation of a short laser pulse in magnetized quantum plasma with spin polarization

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4001.pdf Filamentation of a short laser pulse in magnetized quantum plasma with spin polarization Punit Kumar and Nafees Ahmad Department of Physics, University of Lucknow-226007, India. The study of electron beam-wave interaction in the presence of background plasma has attracted a lot of interest over the past few decades. This interaction has widespread application in a number of area including inertial confinement fusion (ICF), plasma microwave electronics, x-ray burst sources, free electron lasers, cyclotron auto resonance maser oscillator, the solar corona and accelerator physics. As is well known that when an electron beam propagates in a plasma, it will induce a return current in the plasma, carried by plasma electrons, to keep neutralization of the system. The interaction results in filamentation. In plasmas, when the de Broglie wavelength of the charge carriers is comparable to the dimension of the plasma system, quantum mechanical effects are expected to play a major role in the behaviour of charged plasma particles. The QHD model, which consists of a set of equations dealing with the transport of charge, momentum and energy in a plasma is the most widely used model to describe quantum effects in plasma. In recent years, quantum effects have proved to play a crucial role in ultrasmall electronic devices, laser plasmas and dense astrophysical plasmas. Filamentation in quantum plasma have been studied by various authors but all the previous studies considered electrons as a single fluid of macroscopically averaged spin-1/2 plasma. The earlier papers did not show a full picture and didn’t took spin-up and spin-down interaction force into account. Very recently, a modified separate spin evolution (SSE) treatment of electrons in accordance with Pauli equation has been developed [1,2]. In the present paper, using the modified SSE-QHD model we have studied the filamentation of a short laser pulse in a magnetized quantum plasma. Spin-up and spin-down electrons have been taken to be separate species of particles and spin-spin interaction picture has been developed. The effects of quantum Bohm potential, electron Fermi pressure and spin have also been taken into account. The direction of the external field has been taken to be along the direction of electron beam propagation in the first case and oblique in the second case. The dispersion for both the cases have been obtained and growth rate evaluated. The numerical analysis for growth rate has been carried out. The results of both the cases have been compared and analysed. Comparison has also been done with earlier studies and the difference is critically analysed and interpreted. [1] P. A. Andreev, Phys. Plasmas 22, 062113 (2015). [2] P. A. Andreev, Phys. Rev. E 91, 033111 (2015).

Speaker: Punit Kumar

14:00 P4.4002 New Developments of the Energy Conserving Semi Implicit (ECsim) method

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4002.pdf New Developments of the Energy Conserving Semi Implicit (ECsim) method G. Lapenta, D. Gonzalez, M.E. Innocenti, J. Amaya, E. Boella Center for mathematical Plasma Astrophysics, Department of Mathematics, KULeuven, Belgium The Energy Conserving Semi Implicit (ECsim) method [1, 2] is a new approach to particle in cell plasma simulation based on a exactly energy conserving formulation. The method uses a new implicit particle mover and a mass matrix formation of the current to discrete the coupled particle-field equations with a semi-implicit temporal scheme. The new lines of investigation reported are: sub-cycling of the particle motion with respect to the field solution, stabilisation of spurious instabilities present in a drifting plasma, preservation of the Poisson constraint and detailed local charge conservation. Subcycling is the process whereby particles are moved multiple times during a field evolution time step. In the present case, this feature can be implemented in a different way for each particle and leads to a modification of the algorithm to compute the mass matrix. The procedure is beneficial in three ways: it increases the accuracy, it can lead to charge conservation and it can be modified to lead to a gyro-averaged approach Drifting cold plasmas are notoriously hard to model with PIC because of the insurgence of the finite grid instability. We report a new method developed within our ECsim approach to eradicate this nuisance. The Poisson eqaution and the solenoidal condition for the magnetic field are constraints that need to be valid at all times. In kinetic particle in cell the second is trivially enforced by choosing a discretisation of the curl whose discretised divergence is zero. But the first is a more complex matter, requiring to design an interpolation method for the charge and the current consistent with each other via the local charge conservation equation. We report our approach to resolve this issue. References [1] Lapenta, G. (2017). Exactly energy conserving semi-implicit particle in cell formulation. Journal of Compu- tational Physics, 334, 349-366. [2] Lapenta, G., Gonzalez-Herrero, D., & Boella, E. (2017). Multiple-scale kinetic simulations with the energy conserving semi-implicit particle in cell method. Journal of Plasma Physics, 83(2).

Speaker: Giovanni Lapenta

14:00 P4.4004 Effects of impurities and electron trapping in collisionless electrostatic shocks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4004.pdf Effects of impurities and electron trapping in collisionless electrostatic shocks I. Pusztai1 , A. Sundström1 , J. M. TenBarge2,3 , J. Juno4 , A. Hakim3 , and T. Fülöp1 1 Department of Physics, Chalmers University of Technology, Göteborg, Sweden 2 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08543, USA 3 Princeton Plasma Physics Laboratory, Prinecton, NJ 08543, USA 5 IREAP, University of Maryland, College Park, MD 20742, USA Electrostatic collisionless shocks appear in various laboratory and space plasmas; and they are also used in laser-plasma based acceleration schemes to produce mono-energetic ion beams [1]. We investigate the existence and properties of low Mach-number electrostatic collisionless shocks, with particular emphasis on the effect of impurities and electron trapping. We use a semi-analytical approach similar to Ref. [2, 3] to describe the vicinity of the shock. These shock solutions show good correspondence to simulation results initialized with density discontinu- ities with the fully kinetic, Eulerian Vlasov-Maxwell solver of Gkeyll[4]. We find that even a small amount of impurities can influence the shock properties signifi- cantly, including the reflected light ion fraction, which can change several orders of magnitude. We provide accurate analytical expressions for the reflected fractions of main ions and impu- rities, which illuminate the different behavior of hydrogen, depending on its role as main ion or impurity. The reflection of heavy impurities by a shock in a hydrogen plasma is vanishingly small, while shocks in heavy ion plasmas – with relevance to laser-based ion acceleration ex- periments – reflect most of the hydrogen impurity ions. When the electron distribution is flat in the trapped phase space regions due to the downstream potential oscillations, bifurcation of shock-like solutions is observed for low Mach-numbers. References [1] D. Haberberger et al., Nat. Phys. 8 95 (2012). [2] I. Pusztai et al., Plasma Phys. Control Fusion 60, 035004 (2018). [3] R. A. Cairns et al., Plasma Phys. Control Fusion 57, 044008 (2015). [4] J. Juno et al., J. Comput. Phys. 353, 110 (2018).

Speaker: Istvan Pusztai

14:00 P4.4005 Stability analysis of a periodic system of relativistic current filaments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4005.pdf Stability analysis of a periodic system of relativistic current filaments A. Vanthieghem1,2 , M. Lemoine1 , L. Gremillet3 1 Sorbonne Université, UPMC Univ Paris 6 et CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France 2 Sorbonne Universités, Institut Lagrange de Paris (ILP), 98 bis bd Arago, 75014 Paris, France 3 CEA, DAM, DIF, F-91297 Arpajon, France Homogeneous counterstreaming plasmas are 12 2 subject to the transverse filamentation (or 1.8 10 1.6 Weibel) instability that leads to the formation 1.4 of magnetically pinched current filaments. The 8 1.2 y [c/ Ωp ] nonlinear evolution of this instability is of prime 6 1 interest in astrophysics where it is held respon- 0.8 4 sible for generating the magnetic turbulence in 0.6 the precursor region of relativistic collisionless 2 0.4 0.2 shocks [1]. It also plays an important role in 0 0 high-intensity laser-plasma interactions in ac- 0 5 10 15 20 25 t [ Ω-1 ] p counting for the angular spread of the laser- Space-time evolution of an initially y-periodic accelerated particles [2]. chain of current filaments in a plasma composed In this presentation, we perform a linear sta- of two counterstreaming pair beams. The lat- bility analysis of a periodic system of relativis- ter drift along the x-axis, and are described by tic current filaments described by a relativistic Jüttner-Synge distributions of proper tempera- warm-fluid model. Using the Floquet theory, we ture T0 = me c2 and Lorentz factor γ0 = 10. Space compute the exact eigenmodes of the system, and time coordinates are normalized by the rela- and show that the dominant modes transit from tivistic plasma frequency Ω p associated with the coalescence-type to kink-type instabilities with peak density of a single electron beam . increasing nonlinearity and asymmetry between the plasma streams. Our theoretical predictions are supported by particle-in-cell simulations. In a strongly nonlinear symmetric configuration, the stationary state consists of a chain of Harris-type current sheets, for which we derive a new analytic expression for the relativistic kink instability. This formula closely matches the numer- ical results, and allows us to delimit the coalescence and kink-dominated parameter regions. References [1] M. Milosavljevic and E. Nakar, Astrophys. J. 641, 978 (2006) [2] A. Debayle, J.J. Honrubia, E. d’Humières and V.T. Tikhonchuk, Phys. Rev. E 82, 036405 (2010)

Speaker: Arno Vanthieghem

14:00 P4.4007 Efficiency of the X-mode anomalous absorption in the plasma filament associated with the two upper-hybrid-plasmon decay

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4007.pdf Efficiency of the X-mode anomalous absorption in the plasma filament associated with the two upper-hybrid-plasmon decay A. Altukhovb, V. Arkhipenkoa, A. Gurchenkob, E. Gusakovb, A. Popovb, L. Simonchika, P. Tretinnikov b, M. Usachonaka a Stepanov Institute of Physics of NAS of Belarus, Minsk, Belarus b Ioffe Institute, St-Petersburg, Russia As it was shown firstly at the Textor tokamak [1], the second harmonic X-mode heating experiments are accompanied by anomalous backscattering phenomena. The theoretical model proposed recently [2] explains the anomalous backscattering as a result of the two upper-hybrid (UH) plasmon parametric decay (TUHPD) instability possessing very low threshold due to trapping of nonlinearly excited plasmons in the vicinity of the density maximum that accompanies the magnetic island. The theory [2] also predicts substantial (up to 25%) anomalous absorption due to this process. To test an efficiency of the X-mode anomalous absorption associated with the TUHPD leading to excitation of the trapped UH waves the model experiment is performed in the laboratory plasma. The TUHPD occurs in a plasma filament produced by high-frequency discharge (27 MHz, 100 W) in long quartz tube with the inner diameter of 22 mm filled with argon (pressure about 1 Pa) oriented in the direction of the magnetic field. The tube passes through the waveguide (72 x 34 mm2) in parallel to the wide wall. Using the waveguide the X-mode microwave pulses (up to 200 W) at frequency of 2.35 GHz, substantially higher than the electron cyclotron resonance and UH values, are incident onto the plasma. By means of optical and microwave diagnostics the strong anomalous absorption of the microwave power is observed in the plasma at density higher than the UH resonance value for the frequency equal to half value of the pump frequency. The microwave power (incident, reflected, transmitted) is measured and efficiency of anomalous absorption due to the TUHPD is determined at the level of 80% in maximum and 45% in the steady state. The theoretical model of the two-UH-plasmon decay in strongly inhomogeneous plasma is developed demonstrating a huge growth of nonlinear coupling in this case. The localization, threshold and growth rate of the TUHPD instability is determined in agreement with experimental observations. Financial support of the RSF grant 16-12-10043 and BRFBR grant BRFBR F16R-095 is acknowledged. [1] S.K. Nielsen, M. Salewski, et al., Plasma Phys. Control. Fusion 55, 115003 (2013) [2] E.Z. Gusakov and A.Yu. Popov, Physics of Plasmas 23, 082503 (2016)

Speaker: Leanid Simonchik

14:00 P4.4008 Possibility of ion acceleration in ECR produced expanding plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4008.pdf Possibility of Ion Acceleration in ECR Produced Expanding Plasma A. Verma, A. Ganguli, D. Sahu, R. Narayanan and R. D. Tarey Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi, India 110016 Of the different mechanisms that have been used for ion acceleration for thruster application, helicon wave thrusters have gained considerable attention [1]. It is well known that in helicon thrusters, the main acceleration is given by a double layer that forms near the junction of the source chamber and an expansion chamber, in an axially converging-diverging magnetic field. It is noteworthy however, that in spite of their high efficiency in producing high density plasmas, ECR based ion thrusters have not received significant attention [2]. This may be due to the fact in the few studies conducted till now on ECR based thrusters it has not been possible to observe double layer formation. This paper revisits this problem using a somewhat different magnetic field configuration. The experimental system is very similar to that used for helicon thrusters. It consists of a long cylindrical vessel (dia. 85 mm, length 356 mm) that opens into another much larger diameter (~ 50 cm) expansion chamber. Permanent ring magnets have been employed for producing the magnetic field in the source chamber, and in the expansion chamber as well. Within the source chamber an ECR zone is formed, immediately followed by an on-axis magnetic null, beyond which the magnetic field exhibits converging-diverging behavior [3]. Argon plasma is produced using 300 Watts of microwave power (2.45 GHz) ≤ 0.1 mTorr. Typical measurements at 0.1mTorr, reveal evidence for strong bulk electron heating (Te ~ 40 eV) along with fairly high plasma density (n ~ 3.8×1011 cm-3). This is accompanied by very high plasma potentials (Vp ~ 250 V). Both, the high electron temperature and the plasma potential are quite unusual for ECR plasmas that are generated in similar configurations. The significance of the role of the magnetic field geometry in the present experiments can be gauged from the fact that n, Te, and Vp all peak in the vicinity of magnetic null, before decreasing smoothly along the axis (n ~ 3×1010 cm-3, Te ~ 10 eV and Vp ~ 100V typically ~ 35 cm away from null). These results indicate that the high axial plasma potentials in the present configuration can be exploited suitably for efficient ion acceleration. Further work along these lines is already underway. References: 1. C. Charles, J. Phys. D: Appl. Phys. 42, 163001 (2009). 2. Cannat et al. Phys. Plasmas 22, 053503 (2015). 3. A.Ganguli et al. Plasma Sources Sci. Technol. 25, 025026 (2016).

Speaker: Anshu Verma

14:00 P4.4009 (Ultra)cold ion-neutral collisions for new (astro)chemistry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4009.pdf (Ultra)cold ion-neutral collisions for new (astro)chemistry M. Hejduk1 , N. Coughlan1 , J. Toscano1 , L. Petralia1 , A. Tsikritea1 , J. Elworthy1 , H. McGhee1 T. P. Softley2 and B. R. Heazlewood1 1 PTCL, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom 2 University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom Our ultimate goal is to study low energy ion-neutral reactions on the threshold of the so called “quantum regime”, i.e. under conditions when the de Broglie wavelength of the particles is comparable to their dimensions. Furthermore, in order to reveal the full quantum nature of the studied reactions, it is desirable to have the reactants in defined (electronic, ro-vibrational) quantum states. Such demands on the reaction environment are not unnatural at all, as tempera- tures in pre-stellar cores regularly reach approximately 10 K [1] and emission nebulae can reach temperatures lower than 3 K of the microwave background radiation [2]. One way to achieve our objective is to store the ionic species in a cryogenic ion trap and inject very slow neutral particles into it. As the temperature of the ions has to be very low (a few Kelvin), they must be cooled sympathetically in a Coulomb crystal [3]. This would only decrease their kinetic energy, though, so buffer gas cooling has to be employed as well. The neutral reactants can be slowed down in Zeeman or Stark decelerators. Exactly this kind of equipment is being developed in our group. Internal temperatures of ionic species will reach < 10 K and the velocities of the neutral species will be as low as several tens of metres per second. The reaction products, including those trapped in local minima of potential energy surfaces, will be analysed by a time-of-flight mass spectrometer, by analysis of the Coulomb crystal’s fluorescence image, and by action spectroscopy. To our knowledge, this will be the first cryogenic Coulomb crystal device that incorporates neutral particle slowers with these analytical methods. Here we are going to present the current state of development and plans for the first measure- ments. References [1] A. Roy, Ph. André, P. Palmeirim et al., Astronomy & Astrophysics 562, A138 (2004) [2] R. Sahai and L. øA., The Astrophysical Journal Letters 487, L155 (1997) [3] B. R. Heazlewood and T. P. Softley, Annual Review of Physical Chemistry 66, 475 (2015)

Speaker: Michal Hejduk

14:00 P4.4010 Exploring astrophysical condition with ab initio kinetic PIC simulation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4010.pdf Exploring astrophysical condition with ab initio kinetic PIC simulation N. Shukla1 , J.Vieira1 , P. Muggli2 , G. Sarri3 , R. Fonseca1,4 and L. O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal 2 Max Planck Institute for Physics, Munich, Germany 3 Centre for Plasma Physics, School of Mathematics and Physics, Queen’s University of Belfast, Belfast BT7 1NN, United Kingdom 4 DCTI/ISCTE, Instituto Universitario de Lisboa, Lisbon, Portugal The fireball model allows for explaining the origin and amplification of magnetic fields in as- trophysical settings [1]. A relativistic fireball consists of a flow of electrons and positrons in an electronically quasi-neutral state. Interactions of these beams with the background plasma are believed to trigger microinstabilities responsible for the field growth. Very recently, fire- ball beams have been experimentally generated [2], thus providing a platform to explore such processes in the laboratory. In this work, we carried out a detailed numerical and theoretical study with multidimensional particle-in-cell (PIC) simulations performed with the PIC code Osiris [3]. The aim of our work is to determine the required laboratory conditions under which the fireball beam becomes un- stable. In this work, we show that the ratio between the density of the fireball and background plasma controls a transition between the current filamentation instability (CFI) and the compet- ing transverse two-stream instability. When the density ratio is higher than unity the CFI can grow as long as the beam expansion rate, caused by a finite emittance, is larger than the CFI growth rate. We find that the longitudinal energy spread, typical of plasma-based accelerated electron-positron fireball beams, plays a minor role in the growth of CFI. Finally, we investigate the role of the transverse offsets between the centroids of the electron and positron beam spatial distribution. We find that the CFI can also grow as long as the transverse offsets between the beam centroids are smaller than a fraction of the beam transverse dimensions. References [1] P. Meszaros, M. Rees, ApJ. 405, 278 (1993). A. Gruzinov and E. Waxman ApJ. 511, 852 (1999). M. V. Medvedev et al ApJ., 618, L75 (2004). [2] G. Sarri et al, Nat. Commun 6, 1 2015. [3] R. A. Fonseca et al, LNCS 2331, 342 (2002); R. A. Fonseca et al., PPCF 50, 124034 (2008).

Speaker: Nitin Shukla

14:00 P4.4011 Gas breakdown in a focused beam of powerful sub-THz gyrotron

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4011.pdf Gas breakdown in a focused beam of powerful sub-THz gyrotron A. Sidorov, A. Kuftin, M. Morozkin, V. Malygin, S. Razin, A. Tsvetkov, A. Fokin, A. Veselov, A. Vodopyanov, M. Glyavin Institute of Applied Physics, Nizhny Novgorod, Russia The results of experimental and theoretical investigations of gas breakdown thresholds in a focused beam of powerful sub-THz radiation are presented. The gas discharge, maintained by the powerful radiation of terahertz frequency band, is a new specific object of gas discharge physics. Its investigation became possible due to the creation of the powerful sources of THz radiation – gyrotrons [1]. Up to now, several works have already appeared which consider specific features of the development of these discharges in stationary gases and non-uniform gas flow [2-3]. In the paper [4] the results of breakdown in argon by 1kW CW radiation at 0.263 THz were presented. Due to the not so high power the breakdown was observed only for noble gases and in presence of strong preionization. This paper presents the experiments with pulsed gyrotron capable of generation 250 kW power at 0.25 THz frequency. The gyrotron wave beam was focused by means of quasi-optical mirrors into the spot with diameter less than 3 mm that provided intensity into the focal spot up to 3.5 MW/cm2. Achieved electrical field intensity was enough for gas breakdown into the range of pressure values of 1-1500 Torr for various gases (argon, krypton, nitrogen, air). The boundary values of field intensity for discharge existence were measured. Noble gases data was compared to the analytical model of Raizer and Vyskrebentsev [5] for monatomic gases. Data for air was compared with previous higher-frequency data. References [1] M.Yu. Glyavin, A.G. Luchinin, G.S. Nusinovich, J. Rodgers, D.G. Kashyn, C.A. Romero-Talamas, and R.Pu, Applied Physics Letters 101, 153503 (2012) [2] V.L. Bratman, V.G. Zorin, Yu.K. Kalynov, V.A. Koldanov, A.G. Litvak, S.V. Razin, A.V. Sidorov, and V.A. Skalyga, Physics of Plasmas 18, 083507(2011) [3] V.L. Bratman, S.V. Golubev, I.V. Izotov, Yu.K. Kalynov, V.A. Koldanov, A.G. Litvak, S.V. Razin, A.V. Sidorov, V.A. Skalyga, and V.G. Zorin, Physics of Plasmas 20, 123512 (2013) [4] A.V. Sidorov, S.V. Razin, A.I. Tsvetkov, A.P. Fokin, A.P. Veselov, S.V. Golubev, A.V. Vodopyanov, and M.Yu. Glyavin, Proceedings of Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May, 2017, 2600-2602 [5] A.I. VyskrebentsevYu.P. Raizer, Journal of Applied Mechanics and Technical Physics 14, 32–38 (1973)

Speaker: Alexander Sidorov

14:00 P4.4012 Mass to charge dependence of particle injection into DSA

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4012.pdf Mass to Charge Dependence of Particle Injection into DSA A. Hanusch1 , T. Liseykina1 , M. Malkov2 1 Institut für Physik, Universität Rostock, Germany 2 CASS and Department of Physics, University of California, San Diego, USA The high precision spectrometry of galactic cosmic rays (CR), e.g., the Pamela experiment [1], accurately determined an ≈0.1 difference between the rigidity spectral indices of protons and helium ions. Similar deviations have been indicated earlier by other experiments [2] and were confirmed by the recent high-fidelity AMS-02 measurements [3]. These findings may shed light on the long standing problem of CR origin. While the CR particles are believed to be accelerated in supernova remnant (SNR) shocks via diffusive shock acceleration (DSA), it is still not under- stood how different CR elements are extracted from the supernova environments and injected into the DSA. Comparing the spectra of accelerated particles with different mass-to-charge ra- tios is a powerful tool for studying the physics of particle injection. Moreover, the similarity of He/p, C/p, and O/p rigidity spectra demonstrated by AMS-02 has provided new evidence that injection is a mass-to-charge dependent process. In oder to investigate the elemental selectivity of the injection mechanism and to determine the injection efficiency of ion species with dif- ferent mass-to-charge (A/Z) ratio, we performed fully self-consistent hybrid simulations. Our results confirm the earlier theoretical predictions: the efficiency of injection depends on the shock Mach number (M) and its increase with A/Z saturates at a level that grows with M. More- over, our results show that for high A/Z the injection efficiency decreases. By convolving the time-dependent injection rates of p and He, obtained from the simulations, with a decreasing shock strength over the active life of SNRs, we generate the integrated SNR spectra for p and He. These spectra are consistent with the AMS-02 and Pamela data. In particular they correctly predict the decrease in p/He ratio with increasing rigidity at exactly the rate measured in the experiments for R > 10 GV. Only at lower rigidities, R . 10 GV, the difference between the data and our predictions becomes noticeable. Except for this deviation, which might be due to propagation effects or solar modulation, the suggested mechanism for A/Z-dependence of the injection fully explains the measured p/He ratio. References [1] O. Adriani, et al., Science 332, 69 (2011) [2] A.D. Panov, et al., Bul. Russian Academy of Sciences: Physics, 73, 564 (2009) [3] M. Aguilar, et al. (AMS Collaboration), Phys. Rev. Lett., 115, 251101 (2015)

Speaker: Adrian Hanusch

14:00 P4.4013 The reaction of O+ with HD at low temperatures

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4013.pdf The reaction of O+ with HD at low temperatures T. D. Tran1, A. Kovalenko1, S. Rednyk1, Š. Roučka1, R. Plašil1 and J. Glosík1 1 Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic The reaction of O+ with HD has two channels 𝑘OH O+ + HD → OH++ D, (1) 𝑘OD → OD++ H. (2) The total reaction rate coefficient is the sum of rate coefficients of both channels k = kOH + kOD reaction. k and the isotopic branching ratio kOH/k have been measured as a function of temperature using a 22-pole ion trap apparatus [1]. The apparatus allows measuring reaction rate coefficients in the temperature range 15 – 300 K. The systematic uncertainty of measurement is 20 %. First results are shown in the figure. Our measurements will be compared with previous studies, where the lowest measuring temperature is 93 K [2,3,4]. 1000 100 + OHD , OH + (a) (b) 3 O+ OH+ OD+, OH2+ 100 10 OD+, OH2+ T22PT = 25.9 K Ni(t) Ni(t) T22PT = 26.1 K OH+ [He] = 3.5·1013 cm–3 1 [He] = 3.4·1013 cm–3 10 [HD] = 3.5·1010 cm–3 [HD] = 4.2·1011 cm–3 OHD+, OH3+ k = (1.48 )·10–9 cm3s–1 k = (1.50 0.04)10–9 cm3s–1 O + kOH/k = 0.53  0.1 1 0 2 4 6 8 10 12 0 2 4 6 8 10 12 14 16 18 20 t (ms) t (ms) Figure: Example of time evolution of numbers of O+ ( ), OH+ ( ), OD+ and OH2+ ( ), OHD+ and OH3+ ( ) ions at low temperatures in the trap. Ions of the same mass cannot be distinguished from each other. Ions OHD+, OH3+ and other products OD2+, ODH2+ and H+ are not involved in fit model. (a) Measurement with high number density of HD. The rate of reaction is too fast to observe production of OH + and OD+. However, by fitting a decay of O+ we can get the total reaction rate coefficient k. (b) Measurement with low number density of HD. k and also kOH, kOD can be determined. Acknowledgments: We thank the Technical University of Chemnitz and the DFG for lending us the 22-pole ion trap instrument and professor Dieter Gerlich for discussion. This work is partly supported by GACR Grant No. 17-19459S and 17-18067S, by GAUK Grant No. 1584217 and 1168216. References [1] Gerlich, D., et al., J. Phys. Chem. A, 2013, 117(39), 10068-10075. [2] Dateo, C. E., & Clary, D. C., J. Chem. Soc. Faraday Trans. 2, 1989, 85(10), 1685-1696. [3] Sunderlin, L. S., et al., 1990, Chem. Phys. Lett., 167(3), 188-192. [4] Viggiano, A. A., et al., 1991, J. Chem. Phys., 95(11), 8120-8123.

Speaker: Thuy Dung Tran

14:00 P4.4014 Accessing the Nonlinear Physics of Astrophysical Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4014.pdf Accessing the Nonlinear Physics of Astrophysical Plasmas Mohamad Shalaby1,2 , Avery E. Broderick1,3 , Philip Chang4 , Christoph Pfrommer5 , Astrid Lamberts6 and Ewald Puchwein7 Astrophysical plasmas are ubiquitous and differ from laboratory plasmas in key aspects. They are typically cold kB T me c2 , collisionless, and usually contain relativistic sub-populations. To study the evolution of such plasmas, typically, it is necessary to employ a fully kinetic treatment of the plasmas, as described by Boltzmann equation coupled with Maxwell’s equations. -0.5 This can be accomplished via Particle-in-cell (PIC) -1.0 -1.5 algorithms, which combine Eulerian and Lagrangian -2.0 methods to efficiently solve for plasmas full evolution. -2.5 -3.0 Due to numerical heating in PIC algorithms, exploring -3.5 nonlinear and long term (e.g., millions of ω p−1 ) evolu- -4.0 2 tion is typically unreliable. However, the use of higher 0 order interpolation (up to 5th order spline) has been -2 shown to be a key in increasing the accuracy of the -4 coupling between the Eulerian and Lagrangian parts -6 0.5 1.0 1.5 2.0 2.5 3.0 3.5 of the algorithm and thus ensuring long term stability (without the need to resolve the Debye length in some instances) [1]. This greatly improves energy conservation while exactly conserving both the charge and the total momentum. I have developed a fully relativistic PIC codes (called SHARP), in 1D [1], 1D3V, 2D and 2D3V, where up to fifth order spline shape function are implemented. The computation cost of using SHARP codes are much lower than using higher resolution sim- ulations with typical (1st or 2nd order) interpolation to achieve comparable accuracy. Thus, SHARP codes enable the reliable explorations of the nonlinear evolution of astrophysical plas- mas. In my talk, I will present some results where these codes have been used to study the nonlinear evolution of tenuous beam-plasmas instabilities [2] . References [1] Shalaby, M., Broderick, A. E., Chang, P., et al. 2017, ApJ, 841, 52 [2] Broderick, A. E., Chang, P., & Pfrommer, C. 2012, ApJ, 752, 22 1 Perimeter Institute for Theoretical Physics, Waterloo, Canada. 2 University of Chicago, USA. 3 University of Wa- terloo, Canada. 4 University of Wisconsin-Milwaukee, USA. 5 Leibniz Institute for Astrophysics, Potsdam, Ger- many. 6 California Institute of Technology, USA. 7 University of Cambridge, UK.

Speaker: Mohamad Shalaby

14:00 P4.4015 Kappa distributions: Theory and applications in plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4015.pdf Kappa distributions: Theory and applications in plasmas G. Livadiotis Southwest Research Institute, San Antonio TX, USA Classical particle systems reside at thermal equilibrium with their velocity distribution function stabilized into a Maxwell distribution. On the contrary, collisionless and correlated particle systems, such as space and astrophysical plasmas, are characterized by kappa distributions or combinations thereof [1-3]. Understanding the statistical origin of kappa distributions [4] was the cornerstone of further theoretical developments and applications, which, among others, are the following: (i) Connection to zero-th law of thermodynamics [5]; (ii) Physical meaning of temperature [1,4,5]; (iii) Multi-particle description of kappa distributions [6]; (iv) Phase-space kappa distributions for Hamiltonians with non-zero potential [7,8]; (v) Sackur-Tetrode entropy for kappa distributions [1,5], (v) Generation of kappa distributions in plasmas [1,9], and (vii) Existence of a large-scale phase-space constant, about 12 orders larger than the one given by the Planck’s constant [10,11]. 1. Livadiotis, G., 2017, Kappa distributions: Theory and applications in plasmas, Elsevier, Netherlands-UK-US. 2. Livadiotis, G., 2015, Statistical background and properties of kappa distributions in space plasmas, J. Geophys. Res., 120, 1607–1619 (13pp). 3. Livadiotis, G., & McComas, D.J., 2013, Understanding kappa distributions: A toolbox for space science and astrophysics, Space Sci. Rev., 75, 183–214 (32pp). 4. Livadiotis, G., & McComas, D.J., 2009, Beyond kappa distributions: Exploiting Tsallis statistical mechanics in space plasmas, J. Geophys. Res., 114, A11105 (22pp). 5. Livadiotis, G., & McComas, D.J., 2010, Exploring transitions of space plasmas out of equilibrium, Astrophys. J., 714, 971 (17pp). 6. Livadiotis, G., & McComas, D.J., 2011, Invariant kappa distribution in space plasmas out of equilibrium, Astrophys. J., 741, 88 (28pp). 7. Livadiotis, G., 2015, Kappa distribution in the presence of a potential energy, J. Geophys. Res., 120, 880-903. 8. Livadiotis, G., 2018, Using kappa distributions to identify the potential energy, J Geophys Res., 123, doi: 10.1002/2017JA024978. 9. Livadiotis, G., Desai, M.I., & Wilson III, L.B., 2018, Generation of kappa distributions in solar wind at 1au, Astrophys. J., 853, 142 (15pp). 10. Livadiotis, G., & McComas, D.J., 2013, Evidence of large scale phase space quantization in plasmas, Entropy, 15, 1118-1132 (15pp). 11. Livadiotis, G., & Desai, M.I., 2016, Plasma-field coupling at small length scales in solar wind near 1au, Astrophys. J., 829, 88 (14pp).

Speaker: George Livadiotis

14:00 P4.4018 High current gasdynamic electron cyclotron resonance ion sources with gyrotron plasma heating

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4018.pdf High current gasdynamic electron cyclotron resonance ion sources with gyrotron plasma heating V.A. Skalyga, S.V. Golubev, I.V. Izotov, R.L. Lapin, S.V. Razin, R.A. Shaposhnikov, A.F. Bokhanov, M.Yu. Kazakov Federal Research Center Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russian Federation Fundamental research of a powerful millimeter wave gyrotron radiation interaction with an electron cyclotron resonance (ECR) discharge plasma confined in an open magnetic trap carried out at the Institute of Applied Physics of Russian Academy of Sciences (IAP RAS) have resulted in development of a new type of ECR ion sources – a gasdynamic ECR ion source. The key feature of the source is the high plasma density up to 1014 cm-3 combined with almost 100% ionization degree and electron mean energy in the range from tens to hundreds electronvolts. Such combination of the plasma parameters leads to a so-called quasi-gasdynamic confinement regime and allows production of very intense beams of protons either multicharged ions for different applications. At SMIS 37 experimental facility equipped with 37,5 or 75 GHz / 100 kW gyrotrons in a pulsed operation a possibility of ion beams formation with current up to 500 mA, current density at the level of 600 – 700 mA/cm2 in combination with low emittance (normalized RMS emittance below 0.1 π·mm·mrad) was demonstrated. The next step in the research is a transition to continuous wave (CW) operation. For this purpose, preliminary studies of plasma parameters were performed using a CW source with 24 GHz/5 kW gyrotron heating. To continue development of the CW gasdynamic ion source a new experimental facility is under construction at the IAP RAS. Future source will utilize 28 and 37,5 GHz gyrotron radiation for plasma heating. Overview of the obtained results and the status of the new source development will be presented. According to estimations, ion source output parameters would be enough for development on its basis of a D-D neutron generator with neutron flux density about 1010 – 1011 s-1cm-2. It is assumed that such neutron source could be perspective as a comparably compact device for boron neutron capture therapy studies. Presented work is being supported in frame of realization of Federal targeted program R&D in Priority Fields of the S&T Complex of Russia (2014-2020) contract #14.604.21.0195 (unique identification number RFMEFI60417X0195).

Speaker: V. A. Skalyga

14:00 P4.4019 Dependence of the Nonhelical Dynamo on Shear: Numerical Exploration of the Magnetic Shear-Current and Stochastic-alpha Effects

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4019.pdf Dependence of the Nonhelical Dynamo on Shear: Numerical Exploration of the Magnetic Shear-Current and Stochastic-α Effects A. Hankla1 , C. Fendt1 1 Max Planck Institute for Astronomy, Heidelberg, Germany Under certain conditions, a well-ionized plasma can generate its own magnetic field in what is known as a “dynamo”. The need for a theory to describe dynamo action is evident from e.g. the Earth (whose magnetic field would have decayed long ago if not for a dynamo); however, the standard “α effect” mechanism fails in systems that lack reflectional symmetry, for instance near the midplane of accretion disks around black holes. Two competing models attempt to fill this shortcoming: the “stochastic α” effect, relying on random fluctuations of this same α coefficient, and the “magnetic shear-current” effect, suggesting that the off-diagonal resistive term ηyx can be negative, hence providing a sort-of reverse diffusion of the field [1]. The goal of this work is to disentangle the contributions of these models by investigating the dependence of stress and magnetic energy production on a simple system’s degree of shear. Using unstratified shearing boxes, we investigate a range of shearing parameters q, defined such that the orbital velocity Ω ∼ r−q , from near rigid body (q = 0) to Keplerian (q = 1.5) rota- tion. Although many parameters behave according to predictions, an unexpected break occurs in others (e.g the ratio of Maxwell stress to magnetic energy) around q = 1.2. This effect is only present in “tall” boxes whose length in the z-direction is at least twice as long as the ra- dial length, supporting Ref. [2]’s hypothesis that the dynamo can only act when longer vertical modes are allowed. We investigate the transport coefficients to shed light on this break. Another as-yet unexplained feature of these dynamos is the periodic reversal of the toroidal magnetic field, similar to the sun’s 11-year cycle, which could explain the origin of knots in black hole jets [3]. We characterize the unstratified dynamo’s reversal as a function of shear (complementary to Ref. [4]’s analysis for stratified shearing boxes) to motivate future theoreti- cal work on the origin of the reversals within the context of the magnetic shear-current effect. References [1] J. Squire and A. Bhattacharjee, J. Plasma Phys. 82 (2016) [2] J. Shi, J. Stone, and C. Huang, MNRAS 456 (2016) [3] D. Stepanovs, C. Fendt, and S. Sheikhnezami, ApJ 796, 29 (2014) [4] O. Gressel and M. Pessah, ApJ 810, 59 (2015)

Speaker: A. Hankla

16:00 → 16:30 COFFEE

16:30 → 18:30 BPIF

Chair: A. Ravasio

Convener: A. Ravasio

16:30 I4.211 Dense Plasma Chemistry of Hydrocarbons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.211.pdf Dense Plasma Chemistry of Hydrocarbons D. Kraus1,2 1 Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany 2 Technische Universität Dresden, Dresden, Germany Carbon-hydrogen demixing and subsequent diamond precipitation has been predicted to strongly participate in shaping the internal structure and evolution of icy giant planets like Neptune and Uranus. The very same dense plasma chemistry is also a potential concern for CH plastic ablator materials in inertial confinement fusion (ICF) experiments where similar conditions are present during the first compression stage of the imploding capsule. Here, carbon-hydrogen demixing may enhance the hydrodynamic instabilities occurring in the following compression stages. First experiments applying dynamic compression and ultrafast in situ X-ray diffraction at SLAC’s Linac Coherent Light Source demonstrated diamond formation from polystyrene (CH) at 150 GPa and 5000 K [1]. Very recent experiments have now investigated the influence of oxygen, which is highly abundant in icy giant planets on the phase separation process. Compressing PET (C5H4O2) and PMMA (C5H8O2) we find again diamond formation at pressures above ~150 GPa and temperatures of several thousand kelvins, showing no strong effect due to the presence of oxygen. Thus, diamond precipitation deep inside icy giant planets seems very likely. Moreover, small-angle X-ray scattering (SAXS) was added to the platform, which determines an upper limit for the diamond particle size, while the width of the diffraction features provides a lower limit. We find that diamond particles of several nanometers in size are formed on a nanosecond timescale. Finally, spectrally resolved X-ray scattering is used to absolutely scale amorphous diffraction signals and additionally allows for determining the amount of carbon-hydrogen demixing inside the compressed samples even if no crystalline diamond is formed. This whole set of diagnostics provides unprecedented insights into the nanosecond kinetics of dense plasma chemistry. [1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017).

Speaker: Dominik Kraus

17:00 I4.212 Addressing the Inverse Problem Instability in Plasma Physics Modelling using Stochastic Machine Learning Optimization

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.212.pdf Addressing the Inverse Problem Instability in Plasma Physics Modelling using Stochastic Machine Learning Optimization Sam M. Vinko, M.F. Kasim, T. Galligan, J. Topp-Mugglestone, G. Gregori Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK Our understanding of the behaviour of matter in extreme conditions has greatly benefited from the advent of novel laser and free-electron laser facilities, and the growing availability of high-performance supercomputing. Large-scale plasma experiments are now commonly mod- elled via increasingly detailed simulations, where the agreement between experiment and sim- ulation enables the extraction of physical quantities and the understanding of novel underlying processes. However, simulations with large parameter spaces suffer from the inverse problem instability, where very similar simulated outputs can map back to very different sets of input pa- rameters. While this provides a fundamental problem for interpreting the results from integrated experiments, the effect is seldom comprehensively explored due to the intractably large num- ber of simulations required to fill the parameter space. Here we show how this problem can be addressed using stochastic machine learning optimization together with Markov Chain Monte Carlo techniques. We apply our approach to extract physical information from three common experimental diagnostics: x-ray emission spectroscopy, inelastic x-ray scattering and proton ra- diography. We find that all three suffer from inverse instabilities, rendering the extraction of physical information from some experimental measurements impossible even when excellent agreement with a simulation can be found. Our method provides a way to quantify the uncer- tainty due to the unstable nature of reverse physical models, and we describe an approach to experimental design that can mitigate its impact.

Speaker: Sam Vinko

17:30 O4.205 All-optical laser-based magnetic field generators: from nano- to picosecond laser regimes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.205.pdf All-optical laser-based magnetic field generators: from nano- to picosecond laser regimes J.J. Santos , Y. Abe , J. Apiñaniz , M. Bailly-Grandvaux , M. Ehret , 1 2 3 1,4 1,5 S. Fujioka , J.J. Honrubia , M. Huault , E. d’Humières , Ph. Korneev , 2 6 3 1 7 Y. Kochetkov , K.F.F. Law , S. Malko , A. Morace , M. Roth , 7 2 3 2 5 G. Schaumann , V. Stepanishchev , V.T. Tikhonchuk , L. Volpe 5 7 1 3 1 Uni. Bordeaux, CNRS, CEA, Centre Lasers Intenses et Applications, Talence, France 2 Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan 3 Centro de Láseres Pulsados, Salamanca, Spain 4 Univ. California San Diego, San Diego, USA 5 Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany 6 ETSI Aeronáutica y del Espacio, Universidad Politécnica de Madrid, Madrid, Spain 7 National Research Nuclear University MEPhI, Moscow, Russian Federation Our experiments, along with numerical and theoretical modelling, show and explain the generation of strong magnetic fields (B-fields), in the range of the kilotesla, using high-energy nanosecond or high-intensity sub-picosecond lasers interacting with solid targets of various curved geometries. Such capability paves the ground for novel magnetized high-energy density physics (HEDP) investigations, related to laser-generated sources of high-energy particles and their transport, to fusion energy production schemes and to laboratory astrophysics. Magnetic fields of nanosecond duration are generated in a coil connected to a nanosecond laser-driven diode supplying a quasi-stationary electric current. This scheme was successfully applied for magnetizing solid-density targets and improving the relativistic electron beam transport in those targets. It is readily usable for other HEDP applications. In the sub-picosecond regime, B-fields stem from supra-thermal electron ejection from the target or from laser-driven electron vortices. Data shows the presence of B-fields for more than 100 ps, a time scale much longer than the laser pulse duration. When confined within the target structure, these B-fields can be used for controlling electron and ion acceleration and guiding. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: João Jorge Santos

17:45 O4.206 High resolution measurement of the momentum-dependent plasmonic excitations of 1 Mbar matter

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.206.pdf High resolution measurement of the momentum-dependent plasmonic excitations of 1 Mbar matter T. R. Preston1, P. Sperling2,3, K. Appel1, B. Chen4, L. B. Fletcher3, S. H. Glenzer3, S. Göde1, Z. Konôpková1, H. J. Lee3, H. Marquardt5, E. E. McBride1, 3, B. Nagler3, M. 1 Nakatsutsumi , B. B. L. Witte2,3, and U. Zastrau1 1 European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany 2 Institut für Physik, Universität Rostock, 18051 Rostock, Germany 3 Stanford Linear Accelerator Center (SLAC), Menlo Park, CA 94025, USA 4 China Academy of Engineering Physics (CAEP), Mianyang, China 5 Bayerisches Geoinstitut, University of Bayreuth, 95440 Bayreuth, Germany The modelling of astrophysical objects such as the interiors of giant planets, low mass stars and brown dwarfs is heavily reliant on the understanding of matter at temperatures of a few eV and pressures around 1 Mbar. The creation and diagnosis of these plasmas is challenging requiring controlled laser shock compression in order to keep the temperature low and simultaneous probing through inelastic X-ray scattering. Seeded operation at the Linac Coherent Light Source (LCLS) [1] gives us access to ultrafast, bright, highly monochromatic X-ray probes allowing the determination of highly resolved dynamic structure factor data [2]. We present here repeatable measurements of the plasmon dispersion in Aluminium both at ambient conditions and at compressed conditions around 1 Mbar pressure, and make estimates of the pressure, density and temperature using X-ray diffraction and optical VISAR measurements. We compare the plasmon dispersion with that expected from density- functional-theory molecular-dynamics calculations and explore the validity of various models at temperatures below 1 eV. Finally, we look forward to future measurements at the European XFEL’s HED instrument. [1] S H Glenzer et al., J. Phys. B: At. Mol. Opt. Phys. 49, 092001 (2016), [2] L. Fletcher et al., Nature Photonics 9, 274 (2015).

Speaker: Thomas Robert Preston

18:00 O4.207 Design Studies of Ultra-High Hohlraum-Capsule Coupling Efficiency Experiments for the NIF

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.207.pdf Design Studies of Ultra-High Hohlraum-Capsule Coupling Efficiency Experiments for the NIF* P.A. Amendt1, M.A. Belyaev1, C.J. Cerjan1, D.D. Ho1, M.W. Sherlock1 and F. Tsung2 1 Lawrence Livermore National Laboratory, Livermore CA 94551 2 University of California, Los Angeles In indirect-drive inertial confinement fusion a high-Z cylindrical enclosure (or “hohlraum”) surrounds a low-Z capsule containing DT fuel. Laser beams irradiate the interior of the hohlraum through a pair of laser entrance holes, creating an x-ray radiation bath that compresses the fuel to ignition conditions. The coupling of laser light to the capsule is typically ~10%, resulting in ~200 kJ absorbed energy for the ~2 MJ-scale laser at the National Ignition Facility (NIF). A new hohlraum design has been found that can accommodate ~50% larger capsules for up to 3´ more capsule absorbed energy and ~30% coupling efficiency. This new design uses two truncated, conically-shaped hohlraum halves that join above the capsule equator to provide a large volume for fitting a larger (1.5 mm radius) capsule and facilitating laser beam propagation over the entire laser pulse duration. Integrated hohlraum simulations in 2-D show good control of x-ray drive asymmetry with peak radiation temperatures reaching 295 eV at 1.8 MJ of laser energy. The potential for nearly tripling the capsule absorbed energy translates into a similar increase in performance margin, thereby improving the prospects for achieving ignition on the NIF. Backscatter of the laser light at late time when the laser is at peak intensity and the hohlraum has filled with plasma is a common risk with indirect drive, but a simulation post-processor (LIP) used to estimate linear instability growth rates predicts benign levels. Further analysis of the potential for laser-plasma interactions in the nonlinear regime will be reported using particle-in-cell simulations with the OSIRIS [1] code, the laser beam propagation code PF3d [2] and the 2D Vlasov Fokker-Planck code K2 for modelling hot electron transport. [1] R.A. Fonseca, Plasma Phys. Cont. Fus., 50, 124034 (2008). [2] R.L. Berger et al., Phys. Rev. Lett. 75 (6), 1078 (1995). * Work performed under the auspices of U.S. Department of Energy by LLNL under Contract DE-AC52- 07NA27344 and supported by LDRD-17-ERD-119

Speaker: Peter Andrew Amendt

18:15 O4.208 Experimental progress of pulse shape integrated implosion on SGIII facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.208.pdf Experimental progress of pulse shape integrated implosion on SGIII facility Bolun Chen1, Tianxuan Huang1, Shiyang Zou2, Zhongjing Chen1, Wei Jiang1, Fengjun Ge2, Jiamin Yang1 1 Laser Fusion Research Centre, China Academic of Engineering Physics, Mianyang, China 2 Institute of Applied Physics and Computational Mathematics, Beijing, China The ShenGuang III(SGIII) laser facility was completed in 2015 which has 48 beams with wavelength λ =0.35 μm, at peak power 40-60TW. From 2016 pulse shaped implosion experiment was carried out on SGIII facility with gas filled cylindrical hohlraum. Implosion performance with DD filled capsule was investigated by varying the trough width. Several integrated implosion tuning platforms were implemented and several technical and engineering problems were emerged. Many efforts were engaged in the improvement of the capsule also the assembling arts of the hohlraum last year. In 2017, 2D backlit imaging technique was used for the measurement of the driven symmetry. Both of the backlit imploded thin shell and thick shell methods were performed. Symmetry tuning was demonstrated by varying the fraction of the power on the inner versus outer beams. The ratio of shell shape P2/P0 asymmetry to the cone fraction is coincided with the view-factor simulation. The pulse shaped integrated implosion was also demonstrated after the symmetry tuning by varying the power of picket pulse. The highest neutron yield 8.8E9 was obtained corresponding to nearly 30% YoC. In the presentation, we will introduce the recently experimental progress on SGIII facility. Treated as the substituted target of the cryogenic capsule, a good comprehension on the consequence of the recently experiments will be helpful for the cryogenic capsule implosion experiments which would be carried out in the next two years on SG-III facility.

Speaker: Bolun Chen

16:30 → 18:30 BSAP

Chair: M. Romé

Convener: M. Romé

16:30 I4.405 Overview of the Basic Plasma Science Facility: the physics of waves relevant to space, astrophysical and fusion plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.405.pdf Overview of the Basic Plasma Science Facility: the physics of waves relevant to space, astrophysical and fusion plasmas T.A. Carter, S. Dorfman, W. Gekelman, G. Morales, S. Tripathi, B. Van Compernolle, S. Vincena Dept. of Physics and Astronomy, UCLA The Basic Plasma Science Facility (BaPSF) at UCLA is a US national user facility for studies of fundamental processes in magnetized plasmas. The centerpiece of the facility is the Large Plasma Device (LAPD), a 20m long, magnetized linear plasma device [1]. This LAPD has been utilized to study a number of fundamental processes, including: collisionless shocks [2], dispersion and damping of kinetic and inertial Alfvén waves [3], flux ropes and magnetic recon- nection [4], three-wave interactions and parametric instabilities of Alfvén waves [5], turbulence and transport [6] and interactions of energetic ions and electrons with plasma waves [7]. A brief overview of research using the facility will be given, followed by a more detailed discussion of studies of the nonlinear physics of Alfvén waves [8]. Recent experiments have resulted in the first laboratory observation of the parametric instability of shear Alfvén waves. Shear waves with sufficiently high ω/Ωc,i (> 0.6) and above a threshold wave amplitude are observed to de- cay into co-propagating daughter waves; one a shear Alfvén wave and the other a low-frequency quasimode. The observed process is similar to the modulational decay instability. References [1] W. Gekelman, et al., Review of Scientific Instruments 87, 025105 (2016). [2] A.S. Bondarenko, et al., Nature Physics 13, 573 (2017). [3] C.A. Kletzing, et al., Phys. Rev. Lett. 104, 095001 (2010). [4] W. Gekelman, et al., Phys. Rev. Lett. 116, 235101 (2016). [5] G. Howes, et al., Phys. Rev. Lett. 109, 255001 (2012). [6] D.A. Schaffner, et al., Phys. Rev. Lett. 109, 135002 (2012). [7] B. Van Compernolle, et al., Phys. Rev. Lett. 114, 245002 (2015). [8] S. Dorfman and T.A. Carter, Phys. Rev. Lett. 116, 195002 (2016).

Speaker: Troy Carter

17:00 I4.406 Direct measurements of mm-wave beam scattering by field-aligned blobs in magnetically-confined plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.406.pdf Direct measurements of mm-wave beam scattering by field-aligned blobs in magnetically-confined plasmas O. Chellaï1 , S. Alberti1 , M. Baquero-Ruiz1 , I. Furno1 , T. Goodman1 , F. Manke1 , G. Plyushchev1 , L. Guidi2 , A. Koehn 2,3 , O. Maj2 , E. Poli2 , K. Hizanidis4 , L. Figini5 , D. Ricci5 and the TCV team1 1 Swiss Plasma Center, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland 2 Max Planck Institute for Plasma Physics, Garching, Germany 3 Institute of Interfacial Process Engineering and Plasma Technology, Stuttgart, Germany 4 National Technical University of Athens, Greece 5 Istituto di Fisica del Plasma, Consiglio Nazionale delle Ricerche, Milan, Italy In magnetically confined fusion devices, the use of EM radiations ranges from plasma di- agnostics to plasma heating, current drive and core confinement preservation. For large toka- maks such as ITER, numerical simulations and analytical studies suggest that, in the presence of plasma edge turbulence, the path length of the beam will be long enough to significantly broaden the EC-beam, which could lead to a loss of current drive efficiency and possibly pre- vents tearing modes stabilization at the expected power levels [1, 2]. We report first direct measurements of millimeter wave (mmw) beam scattering by plasma turbulence. The experiments are carried out in the basic plasma physics device TORPEX and the Tokamak à Configuration Variable (TCV) . The two devices are equipped with an exten- sive set of diagnostics, which provide an ideal environment to diagnose plasma turbulence and associated structures, such as blobs. A mmw-beam is injected from the top of the device and the power is measured at the bottom. We show that the measured plasma density fluctuations are the cause of fluctuations of the transmitted mmw-power. Conditional sampling is used to identify the effect of measured density structures. On TORPEX, electron density fluctuations are measured using an in-situ array of Langmuir probes. A full-wave model based on COM- SOL multiphysics is presented and compared to experiments [3]. Using the SOL turbulence simulations from the GBS turbulence code, comparison between the scattering effect on the mmw-beam using both COMSOL Multiphysics and the WKBeam code [2] are in progress in TCV. The results of the two codes as well as comparison with the experiments are discussed. References [1] C. Tsironis et al. Phys. Plasmas, vol. 16, p. 112510, 2009. [2] A. Snicker et al. Nucl. Fusion, vol. 58, p. 016002, 2018. [3] O. Chellaï et al., “Millimeter-wave beam scattering by field-aligned blobs in simple magnetized toroidal plas- mas,” Phys. Rev. Lett., vol. Accepted for publication, 2018.

Speaker: Oulfa Chellaï

17:30 I4.407 Fundamental tests with antihydrogen atoms based on advances in non-neutral plasma physics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.407.pdf Fundamental tests with antihydrogen atoms based on advances in non-neutral plasma physics J. Fajans, U.C. Berkeley, Berkeley CA USA Abstract: Antihydrogen can be synthesized and trapped by mixing positron and antiproton plasmas confined in superimposed Penning-Malmberg and minimum-B trap fields. Superb control of these two plasmas is necessary to trap antihydrogen. Recent advances in plasma physics have allowed CERN's ALPHA collaboration to increase our trapping rate by a factor of twenty, and have allowed us to trap as many as 1000 antihydrogen atoms simultaneously. The work on antihydrogen is motivated by the baryogenesis problem (the scarcity of antimatter in the University). We have measured the spin flip frequency of these antiatoms to 0.1%, and the charge of the antiatoms to 0.7ppb; both of these studies search for CPT violations. Recently, we were able to determine the 1s-2s transition energy by illuminating antiatoms held within a 243nm laser cavity. At an accuracy of 200ppt, this is, by some measures, approaching the most precise CPT tests, and tighter limits are expected shortly. We have also set crude bounds on the gravitational properties of these antiatoms (antimatter g limited by +/-100g), and are constructing a new apparatus designed to measure the antimatter g to 1%; this is a test of the weak equivalence principle. In this talk I will discuss some of the recent advances in plasma physics, as well as some of the results of our CPT and weak equivalence tests.

Speaker: Joel Fajans

18:00 O4.406 Overview of the status of the PAX/APEX pair plasma project

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.406.pdf Overview of the status of the PAX/APEX pair plasma project 1,2 1 1 1,3 1,4 1,3 H. Saitoh , U. Hergenhahn , J. Horn-Stanja , S. Nißl , T. Sunn Pedersen , E.V. Stenson , M. 3 3 3 5 6 6 Dickmann , C. Hugenschmidt , M. Singer , M.R. Stoneking , J.R. Danielson , C.M. Surko 1 Max-Planck Institute for Plasma Physics, Garching and Greifswald, Germany 2 The University of Tokyo, Kashiwa, Japan 3 Technische Universität München, Garching, Germany 4 Ernst-Moritz-Arndt-Universität, Greifswald, Germany 5 Lawrence University, Appleton, USA 6 University of California, San Diego, USA By combining recent progress in the fields of toroidal non-neutral plasmas and antimatter physics, we aim to create magnetically-confined electron-positron pair plasmas [1] in a dipole magnetic configuration [2]. Experimental verification of the pair plasma properties, such as remarkable stability [3] and wave propagation characteristics, is the final goal of the project. Ultimately, intense slow positrons from NEPOMUC (NEutron induced POsitron source MUniCh) [4] will be accumulated in PAX (Positron Accumulator eXperiment) by using the so-called buffer gas technique [5], and then transported to and confined in the levitated dipole trap APEX (A Positron Electron eXperiment) together with an equal number of electrons. Our key challenges include the accumulation of a large number of positrons in PAX, highly efficient transport of positrons from the NEPOMUC beamline into the closed dipole field lines of APEX, and stable and simultaneous trapping of positrons and electrons as plasmas therein. Based on beam characterization [6] and numerical orbit analysis, we have realized essentially lossless injection of positrons into a prototype dipole field trap created by a permanent magnet. After injection, we observed more than 1 s of long trapping of positrons in the dipole magnetic field. This was realized by carefully eliminating the asymmetry of the electric fields in the system and reducing the loss channel of positrons toward the magnet poles. Based on these initial results in the prototype dipole trap [7], we are conducting design and construction studies for a buffer gas type positron accumulator and a superconducting levitated dipole configuration for pair plasma confinement. This work is supported by the European Research Council (T. Sunn Pedersen, ERC-2016-ADG No.741322). [1] T. Sunn Pedersen et al., New J. Phys. 14, 035010 (2012). [2] U. Hergenhahn et al., AIP Conf. Procs. 1928, 020004 (2018). [3] P. Helander, Phys. Rev. Lett. 113, 135003 (2014). [4] C. Hugenschmidt et al., New J. Phys. 14, 055027 (2012). [5] J.R. Danielson et al., Rev. Mod. Phys. 87, 247 (2015). [6] J. Stanja et al., Nucl. Instr. Meth. Phys. Res. A 827, 52 (2016). [7] H. Saitoh et al., New J. Phys. 17, 103038 (2015).

Speaker: Haruhiko Saitoh

18:15 O4.407 Near-lossless positron injection into a dipole magnetic field

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.407.pdf Near-lossless positron injection into a dipole magnetic field E. V. Stenson1,2 , U. Hergenhahn1 , S. Nissl1,2 , J. Horn-Stanja1 , H. Saitoh1,3 , T. Sunn Pedersen1,4 , M. R. Stoneking5 , M. Singer2 , M. Dickmann2 , C. Hugenschmidt2 , J. R. Danielson6 , C. M. Surko6 1 Max Planck Institute for Plasma Physics, Garching & Greifswald, Germany 2 Technische Universität München, Garching, Germany 3 The University of Tokyo, Kashiwa, Japan 4 University of Greifswald, Greifswald, Germany 5 Lawrence University, Appleton, WI, U.S.A. 6 University of California, San Diego, La Jolla, CA, U.S.A. The nucleation and trapping of a small-Debye-length, electron-positron pair plasma in a toroidal device will enable laboratory studies of these systems, which are predicted to have novel properties significantly different from those of standard electron-ion plasmas — e.g., “re- markable stability” [1]. A key prerequisite is the development of a scheme that enables efficient injection of positrons from an external source, across flux surfaces, into the confinement region. Previously, the NEPOMUC (NEutron-induced POsitron source MUniCh) beam was injected with beam line 38% efficiency into the dipole field of a supported per- manent magnet and subsequently trapped [2]. Essen- tially lossless injection into the same device has now been demonstrated. This was accomplished by tailor- ExB plate ing positrons’ 3D guiding-center drift orbits via opti- mization of electrostatic potentials applied to various plates and wall segments, thereby producing localized particle transport via the E × B drift. Experimental re- magnet sults are in excellent agreement with numerical simu- lations (Fig. 1), enabling a comprehensive understand- ing of the process. This paves the way for upcoming experiments, in which dense pulses of positrons will be injected into the dipole field of a levitated coil. Figure 1: Simulated trajectories of a finite- References temperature positron bunch being loss- [1] P Helander. Phys. Rev. Lett., 113:135003, 2014. lessly drift-injected into a dipole trap. [2] H Saitoh, et al. New J. of Physics, 17(10):103038, 2015.

Speaker: Eve Virginia Stenson

16:30 → 17:30 LTDP

Chair: J.-S. Yoon

Convener: J.-S. Yoon

16:30 I4.309 DC microplasma arrays on silicon wafers

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.309.pdf DC microplasma arrays on silicon wafers R. Dussart1, R. Michaud1, S. Iseni1, O. Aubry1, A. Stolz1, S. Dzikowski2, V. Schulz-von der Gathen2, L.J. Overzet3, L. Pitchford4 1 GREMI, CNRS-University of Orleans, France 2 Experimental Physics II, Ruhr-Universität Bochum, Germany 3 PSAL, University of Texas at Dallas, Richardson, TX, USA 4 LAPLACE, CNRS – University Toulouse III, France Introduced in the mid 90’s, DC Micro Hollow Cathode Discharges (MHCD) have the remarkable property of operating at atmospheric pressure in a normal glow (non equilibrium) regime provided the cathode area is not fully utilized [1], [2]. MHCD on silicon platforms were first studied by J. G. Eden’s group [3]. Silicon processing initially developed for microelectronic devices offers many opportunities to design new, original and efficient devices to produce high density microplasmas. At GREMI lab, original microreactors were fabricated in a clean room facility using different process steps such as lithography, deposition, oxidation, etching… The device consists of two electrodes separated by a dielectric layer. The thermal silicon oxide layer separating the two electrodes is 8 µm thick and is etched to form microcavities having a diameter of typically 100 µm. Arrays of up to 1064 microplasmas using an etched silicon cathode could be completely ignited in different gases such as argon, helium or nitrogen [4]. Even if complete arrays could be successfully ignited, the device operation was unstable and produced many current spikes that significantly damaged the microcavities and led to device failure. The mechanisms responsible for this unstable operation and short lifetime were investigated [5]. In this paper, we will discuss the involved mechanisms and the different ways to enhance the stability and lifetime of the microdischarges. A 2D fluid model developed at LAPLACE was used to simulate a single microplasma in helium. Finally, a very stable operation of the microdischarge array was obtained. The ignition dynamics of the array was also studied versus pressure. [1] K.H. Schoenbach et al., Appl. Phys. Lett., 68 (1996) 13–15 [2] T. Dufour et al., Appl. Phys. Lett. 93 (2008) 71508 [3] J.G. Eden et al., J. Phys. D: Appl. Phys. 36 (2003) 2869–77 [4] M.K. Kulsreshath et al., J. Phys. D: Appl. Phys. 33 (2012) 285202 [5] V. Felix et al., PSST 25 (2016) 025021

Speaker: Remi Dussart

17:00 I4.310 From streamers to long lived species: dynamics of a surface barrier discharge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.310.pdf From streamers to long lived species: dynamics of a surface barrier discharge M. I. Hasan1, A. Dickenson1, A. Nikiforov2, C. Leys2, N. Britun3, J. L. Wlash1 1 Centre for Plasma Microbiology, Department of Electrical Engineering and Electronics, the University of Liverpool L69 3GJ, Liverpool, United Kingdom. 2 Department of Applied Physics, Ghent University, Sint-Pietersnieuwstraat 41, Gent 9000, Belgium. 3 Chimie des Interactions Plasma-Surface (ChIPS), CIRMAP, Université de Mons, 23 Place du Parc, B-7000 Mons, Belgium. In recent years, applications based on Surface Barrier Discharges (SBDs) have increased significantly. SBDs in such applications serve as a simple and low cost source of reactive chemical species under ambient conditions (atmospheric pressure and room temperature). Examples of applications where this type of discharges is being used include CO2 conversion, pollution abatement in water, and microbial decontamination [1]. Critically, in the SBD configuration, reactive species are not only generated, but transported beyond the discharge region through an induced flow of the background gas caused by Electrohydrodynamic (EHD) forces generated by the plasma [2]. For any given application it is necessary to understand the spatial distribution of the generated reactive species, which is a challenging task as the chemistry of the discharge is influenced by its induced flow [2]. In this work, a 2D multiscale experimentally-validated numerical model is used to identify the distribution of reactive species in space and time. The physics described by the model is verified through comparison with flow pattern measured using Particle Image Velocimetry (PIV). While the chemistry described in the model is verified by comparison of calculated densities of species to measured densities using Laser Induced Fluoresce (LIF) and Fourier Transform Infrared spectroscopy (FTIR). The comparison shows close agreement over a range of conditions and that the distribution of NO produced by the discharge is confined to the induced flow region above SBD. While this is not the case for several other species. References [1] M. Modic N. P. McLeod, J. M. Sutton, J. L. Walsh International Journal of Antimicrobial Agents 49 375– 378 (2017) [2] A. Dickenson, Y. Morabit, M. I. Hasan and J. L. Walsh Sci. Rep. 7, 14003 (2017) [3] M. I. Hasan and J. L. Walsh Appl. Phys. Lett 110, 134102 (2017).

Speaker: Mohammad I. Hasan

16:30 → 18:30 MCF

Chair: T. Eich

Convener: T. Eich

16:30 I4.116 Effect of magnetic perturbations for ELM control on divertor heat loads and detachment in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.116.pdf Effect of magnetic perturbations for ELM control on divertor heat loads and detachment in ASDEX Upgrade M.Faitsch, D.Brida, B.Sieglin, W.Suttrop, T.Lunt, T.Eich, M.Wischmeier, A.Herrmann, the ASDEX Upgrade Team1 and the Eurofusion MST1 Team2 Max-Planck-Institute for Plasma Physics, Boltzmannstr. 2, D-85748 Garching, Germany 1 See appendix of "A. Kallenbach 2017 Nucl. Fusion 57 102015" 2 See author list of "H. Meyer et al 2017 Nucl. Fusion 57 102014" The reduction of transient heat loads induced by edge localised modes (ELM) in H-Mode is fundamental to the success of ITER/DEMO. The application of 3D magnetic perturbation (MP) fields is studied as a method for ELM control and full ELM suppression in ASDEX Upgrade. These 3D fields lead to toroidal asymmetries of the heat load pattern in the divertor that cause further challenges for future devices. ASDEX Upgrade is equipped with a versatile set of MP coils and high resolution edge and target diagnostics to characterise the impact of MPs on diver- tor heat loads and the access to detachment. The heat flux in L- and H-Mode can be studied in ASDEX Upgrade, thanks to the flexible power supply, with slowly rotating MP fields, allowing the complete toroidal characterisation of the heat flux pattern. For a scan of various poloidal perturbation field spectra in low density discharges, a large toroidal variation is only observed in the so called resonant configuration which is foreseen for ITER for ELM control. When the profiles are toroidally averaged and the standard 1D Fit- Function for diffusive power spreading is applied, the same power fall-off length λq and divertor broadening S as in the non-perturbed reference case is found throughout the scan. With increasing density, while still being in attached conditions, the toroidal variation of the heat flux pattern is reduced. This is accredited to an increase of S. The toroidal peaking, the toroidal maximum divided by the mean value, decreases from 1.9 to 1.2 when increasing line averaged edge density from 0.8 to 1.8 ·1019 m−3 in L-Mode. Here, S increases from 0.3 to 1.2 mm and λq from 3.6 to 6.0 mm leading to an increase of the integral width λint - and thereby also a reduction of normalised peak heat flux - by a factor of two. By increasing the density even further, the toroidal peaking in the ITER relevant high recycling regime reaches about unity. On the other hand, no detriment effect on the access to detach- ment is observed. Hence, for ITER a problematic toroidal peaking of the inter-ELM heat flux is expected to be alleviated by operating with high scrape-off layer and/or divertor density and thereby a cold divertor. However, ELM filaments lock to the perturbation and may lead to en- hanced sputtering at distinct toroidal locations if no variation of the perturbation is applied.

Speaker: Michael Faitsch

17:00 I4.117 Correlation of the near SOL transport with plasma properties of the confined edge region in ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.117.pdf Correlation of the near SOL transport with plasma properties of the confined edge region in ASDEX Upgrade H J. Sun1, E. Wolfrum1, T. Eich1, B. Kurzan1, A. Kallenbach1, A. Scarabosio1, U. Stroth1,2 and the ASDEX Upgrade Team 1 Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany 2 Physik-Department E28, Technische Universität München, 85747 Garching, Germany Improvements to the Thomson Scattering edge system have enabled, for the first time in ASDEX Upgrade, the study of upstream SOL electron density (ne) and temperature (Te) profiles and thermal transport over a wide set of plasma parameters and regimes, which include H-, L-, and I- mode, as well as the high density limit (HDL). Results show that parallel transport in the near SOL region is always dominated by Spitzer-Harm conduction in both L-and H-mode, consistent with SOLPS modelling. The near SOL ne and Te profiles are found to be closely coupled across different plasma regimes and divertor conditions, with gradient ratio 1 ≤ 𝜂𝑒 ≤ 2. A study of H-L back transitions show that there is a bifurcation between H- and L-mode plasmas in near SOL perpendicular transport, at the same global parameters and heating power. An expression for the perpendicular thermal diffusivity, 𝜒 ⁄2 𝜒 𝜒 𝜒⫠ = 𝑐𝐿,𝐻 𝑛𝑒 −1 𝑇𝑒3 with 𝑐𝐻 �𝑐𝐿 ≈ 0.5, is derived from the wider database. Also the transition from L-mode to I-mode shows a change in perpendicular thermal transport. For H-mode plasmas under attached conditions, steep pedestal gradients and higher pedestal top values of both Te and pe, which are beneficial for plasma performance, appear to correlate with narrower SOLs, which are unfavourable for plasma exhaust. However, the same trend is not observed for fixed plasma current. Here, the pedestal Te gradients can vary by a factor of 2 while the SOL Te decay lengths do not change. This suggests that the pedestal-SOL correlation is a consequence of the pedestal and the SOL regions being influenced differently by the same global parameters rather than a direct dependence of one on the other. This offers the prospect of optimising the two regions separately. A good example is the increase of the pedestal top pressure by N seeding while no influence on the SOL Te decay lengths is observed. Across the database of H-mode plasmas, the SOL MHD ballooning parameter, αsep , increases almost linearly with separatrix density for 𝛼𝑠𝑠𝑠 <2, consistent with JET results. After 𝛼𝑠𝑠𝑠 reaches 2-2.5, it doesn’t vary with density which is consistent with the theoretically predicted onset of ballooning modes. A confinement degradation caused by these modes may be the mechanism for the HDL.

Speaker: Hongjuan Sun

17:30 O4.105 Physics of power loading on the gap edges of castellated plasma-facing components in fusion reactors

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.105.pdf Physics of power loading on the gap edges of castellated plasma-facing components in fusion reactors M. Komm1, J.P. Gunn2, R. Dejarnac1, R. Panek1, R.A. Pitts3, A. Podolnik1,4, S. Ratynskaia5 and P. Tolias5 1 Institute of Plasma Physics of the CAS, Za Slovankou 3, 182 00 Prague 8, Czech Republic 2 CEA, IRFM, F-13108 Saint-Paul-Lez-Durance, France 3 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France 4 Fac. Math & Phys., Charles University, V Holešovičkách 2, 180 00 Prague 8, Czech Republic 5 KTH Royal Institute of Technology, Space & Plasma Physics, SE-10044 Stockholm, Sweden In order to manage thermal stresses, actively cooled tokamak plasma-facing components (PFCs) in high heat flux areas must typically be divided or “castellated” into small units separated by gaps both in toroidal and poloidal directions. Heating of the edges introduced by this castellation is a serious, and, until recently, little studied complication for component power handling [1]. It will be critically important on ITER and imposes careful PFC shaping design to mitigate the consequences. In support of the ITER tungsten divertor target design and as an interpretive tool for experiments on several devices designed to study this problem, plasma interaction with castellated PFCs and the related role of sheath electric fields has been investigated by means of the SPICE 2D and 3D particle-in-cell codes. In addition to providing predictions of detailed ITER divertor power loading, this work substantially improves the general understanding of the processes occurring in the magnetized sheath which forms in the vicinity of the PFCs and is a key quantitative tool for validation of simpler ion orbit approaches which neglect the sheath electric field [1], but which are less computationally intensive when deployed for PFC design. These studies are being augmented by the investigation of thermionic emission from tungsten surfaces, including 3D effects relevant to localized hotspots, and providing in addition important constraints for the modelling of melt motion on PFCs subject to high energy transients. A number of interesting physics phenomena in the magnetized sheath affect the heat load distribution on gap edges. Inside toroidal gaps, depending on the magnetic field orientation, electrons and ions can either strike the same side (with the magnetically wetted side receiving all the heat load entering the gap), or opposite sides (with the heat load shared between the two sides of the gap) due to ion Larmor gyration and radial EB drift in the sheath. Dedicated PIC simulations have confirmed that the former is the dominant mechanism of the toroidal gap power loading for ITER plasma conditions, providing further confidence that ballistic ion orbit simulations can be used as a good approximation in the study of gap edge loading for component design. [1] J.P. Gunn et al., Nuclear Fusion 57 (2017) 046025

Speaker: Michael Komm

17:45 O4.106 Role of neoclassical mechanisms in the formation of a tokamak scrape-off layer

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.106.pdf Role of neoclassical mechanisms in the formation of a tokamak scrape-off layer V. Rozhansky1, E. Kaveeva1, I. Senichenkov1, E. Vekshina1 1 Peter the Great St.Petersburg Polytechnic University, St.Petersburg, Russia Understanding of the mechanisms responsible for the formation of tokamak scrape-off layer (SOL) is crucial for ITER as well as for future tokamak reactors. In particular it is necessary to understand inverse dependence of the SOL width on the plasma current observed on present day tokamaks. Grad B drift could be a candidate for a leading mechanism of SOL formation as was suggested by Goldston [1]. However, the radial ion flux caused by grad B drift should be considered together with the radial ion ExB drift as it was done in standard neoclassical theory for closed flux surfaces, and the resulting flux is determined by ion viscosity [2]. In the present paper role of neoclassical mechanisms in the formation of density and electron temperature fall-off lengths is analyzed. It is shown that neoclassical mechanisms can give SOL width of the order of ion Larmor radius multiplied by safety factor in accordance with the observed inverse current dependence. Radial transport is followed by flow of radial current which is short-circuited through the divertor plates. The analytics is supported by numerical modeling of edge plasma by SOLPS5.2 code [2] with the reduced anomalous transport coefficients in the SOL. These results are in agreement with the earlier modeling with reduced anomalous diffusion coefficient [3]. A possibility of contribution from blob (filament) transport to the SOL formation is also considered. It is shown that blob transport can also give inverse current dependence of the SOL with. [1] Goldston R J 2012 Nucl. Fusion 52 013009 [2] Rozhansky V, Kaveeva E, Senichenkov I, Vekshina E 2018 Plasma Phys. Control. Fusion 60 035001 [3] Meier E T, Goldston R J, Kaveeva E G, Makowski M A, Mordijck S, RozhanskyV A, Senichenkov I Yu, Voskoboynikov S P 2016 Plasma Phys. Control. Fusion 58 125012

Speaker: Vladimir Rozhansky

18:00 O4.107 SOLPS simulation of TCV divertor leg length studies

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.107.pdf SOLPS simulation of TCV divertor leg length studies M. Wensing1 , H. De Oliveira1 , B. P. Duval1 , O. Février1 , A. Fil2 , R. Maurizio1 , H. Reimerdes1 , C. Theiler1 , C. K. Tsui1,3 K. Verhaegh1,2 , M. Wischmeier4 , the EUROfusion MST1 team and the TCV team 1 EPFL - Swiss Plasma Center (SPC), Lausanne, Switzerland 2 University of York - Plasma Institute, York, United Kingdom 3 University of California San Diego (UCSD), San Diego, United States 4 Max-Planck-Institut für Plasmaphysik, Garching, Germany This contribution uses TCV experiments with varying divertor configurations to investigate the particle and heat cross-field transport within the scrape-off layer, which greatly determines the peak heat flux on the plasma-facing components. The proximity of expected peak heat fluxes to the material limits for ITER raises the necessity of obtaining a quantitative understanding of the mechanisms that determine the heat flux profiles on the divertor plates. Target heat flux profiles are often described by a truncated exponential profile with a decay length λ convoluted with a Gaussian of width S, which are interpreted as broadening due to diffusive transport upstream and in the divertor regions, respectively [1]. The TCV tokamak with its 16 independent poloidal shaping coils provides unique capabilities for studying the effect of divertor geometry on target heat flux profiles and large variations in divertor leg length Ldiv , flux expansion and flux flaring have been achieved. It is, in particular, found that an increase of Ldiv (~ factor 3.5) leads to a somewhat unexpected increase of λ , while having little effect on S [2]. The aim of this study is to reproduce the experimental findings quantitatively using the SOLPS code package. Sensitivity studies on spatially constant transport parameters were per- formed to match an experimentally well-diagnosed case. It is shown that diffusive transport without spatial dependence fails to reproduce the experimentally observed trends in λ and S, in agreement with earlier studies [3]. Different setups of transport profiles are investigated: in the first case the upstream cross-field transport increases as function of Ldiv , whereas in a second approach the cross-field transport in the divertor is chosen to be radially asymmetric. References [1] T. Eich, et al., Phys. Rev. Lett. 107, 215001 (2011) [2] R. Maurizio, et al., Nucl. Fusion 58, 016052 (2018) [3] A. Gallo, et al., Plasma Phys. Control. Fusion 60, 014007 (2018)

Speaker: Mirko Wensing

18:15 O4.108 Test of the Eich model for ELM energy densities in DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.108.pdf Test of the Eich model for ELM energy densities in DIII-D M. Knolker1, A. Bortolon2, T. Evans1, A.W. Leonard1, R. Nazikian2, H. Zohm3 1 General Atomics, San Diego, USA 2 PPPL, Princeton, USA 3 IPP, Munich, Germany A non-dimensional collisionality scan conducted on DIII-D confirms the model for ELM energy densities recently put forward by Eich [1], but also reveals key effects that may explain the large scatter typically observed about the scaling. The values of the peak parallel ELM energy density 𝜀∥ are found to be within 0.5 - 2 x the prediction of the Eich model, where 𝜀∥ is the maximum of the time-integrated heat flux during ELMs mapped onto the divertor. The experiment did not reveal an explicit pedestal-pressure dependence of 𝜀∥ as proposed in the model. The ratio of heating power to the power required to overcome the L- H-threshold is identified as a parameter determining the accuracy of the model, with discharges marginally above the threshold exceeding the prediction by up to a factor of two and showing the largest scatter in the database. Operation close to the L-H- threshold comes with low ELM frequency and large ELM heat loads. In general, the divertor peak heat flux is found to be slightly higher on the inner than on the outer divertor target. Using linear stability calculations, ELM energy densities are shown to be Figure 1 Inverse proportionality between linear mode number with the highest growth rate and peak parallel inversely proportional to the most unstable ELM energy density for type-I ELMy plasmas linear mode number 𝑛𝑚𝑎𝑥 before the ELM crash (figure 1). Low n peeling-ballooning modes come with large ELM sizes, especially if close to the L-H-threshold, the ITER operational space. Hence, our studies encourage further machine comparisons regarding low heating scenarios and influence of mode numbers on ELM energy densities. 1 This material is based upon work supported by the U.S. Department of Energy under Award Number(s) DE- AC05-00OR22725, DE-AC02-09CH11466, and DE-FC02-04ER54698. [1] T. Eich et al., Nuclear Materials and Energy 12 (2017) 84–90

Speaker: Matthias Knolker

17:30 → 18:30 MCF

Chair: B. Duval

Convener: B. Duval

17:30 I4.118 Impurity Transport Studies at Wendelstein 7-X by Means of X-ray Imaging Spectrometer Measurements

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I4.118.pdf Impurity Transport Studies at Wendelstein 7-X by Means of X-ray Imaging Spectrometer Measurements A. Langenberg1, N.A. Pablant2, A. Dinklage1, Th. Wegner1, P. Traverso3, O. Marchuk4, B.Geiger1, B. Buttenschön1, C. Brandt1, H. Thomsen1, M. Kubkowska5, A. Czarnecka5, S. Jabłoński5, U. Neuner1, N. Tamura6, J.L. Valesco7, J.A. Alonso7, A. Mollén1, D. Zhang1, R. Burhenn1, R.C. Wolf 1 and the W7-X team 1 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany 2 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 3 Auburn University, Auburn, Alabama, USA 4 Institut für Energie und Klimaforschung-IEK-4, Forschungszentrum Jülich, 52425 Jülich, Germany 5 Institute of Plasma Physics and Laser Microfusion, Hery 23 St. 01-497 Warsaw, Poland 6 National Institute for Fusion Science, 322-6, Oroshi-cho, Toki-City, Gifu 509-5292, Japan 7 Laboratorio Nacional de Fusión, Asociación EURATOM-CIEMAT, Madrid, Spain Due to non axis symmetric 3D magnetic fields, impurity transport in the hot plasma core in stellarators is fundamentally different to tokamaks. In view of reactor-like operation, understanding the impurity transport is a prerequisite for steady-state operation. These aspects motivate initial impurity transport studies in W7-X at previously - in optimized stellarators – unexplored, reactor-relevant collisionalities. New effects, like potential variations on flux- surfaces [1] or screening effects due to species dependent transport regimes [2] are examples for aspects which attracted recent interest. Spatio-temporal impurity emissivities were measured by the x-ray imaging spectrometers XICS [3] and HR-XIS [4], optimized to detect He-like impurity emission. These spectrometers provide measurements of the radial electric field [5] and also allow for a direct determination of diffusive and convective transport parameters D and v [6]. Therefore, impurity transport in various stellarator specific transport regimes can be studied. In this paper, a systematic parameter scan varying the electron cyclotron resonance (ECR) heating power and the electron density ne has been carried out. Furthermore, the specific settings of the power deposition reveal a significant impact on impurity confinement time, possibly driven by changes in the radial electric field at very low collisionalities – uniquely addressable in large stellarators like W7-X. Experimental findings are compared to neoclassical theory [7] and modeled with the 1D transport analysis code STRAHL. The study aims to reveal the impact of aspects entering stellarator optimization (e.g. ripples, magnetic mirrors) on the impurity fluxes. [1] J.M Garcia-Regana et al, Nucl. Fusion 57, 056004 (2017) [2] P. Helander et al., Phys. Rev. Lett. 118, 155002 (2017) [3] N.A. Pablant, M. Bitter, R. Burhenn et al. 41st EPS conference on Plasma Physics Berlin (2014) [4] G. Bertschinger, W. Biel, H. Jaegers, and O. Marchuk, Rev. Sci. Instrum. 75 3727 (2004) [5] N.A. Pablant, A. Langenberg, S. Satake et al. 43rd EPS conference on Plasma Physics Leuven (2016) [6] A. Langenberg, N.A. Pablant, O. Marchuk et al. Nucl. Fusion 57 086013 (2017) [7] A. Mollén, S. Newton, P. Helander et al. 21st Int. Stellarator Workshop, Kyoto, (2017) (invited)

Speaker: Andreas Langenberg

18:00 O4.109 Turbulence measurements and gyrokinetic validation at ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.109.pdf Turbulence measurements and gyrokinetic validation at ASDEX Upgrade S.J. Freethy1,2 , T. Happel1 , G.D. Conway1 , A. Creely2 , T. Görler1 , P. Hennequin3 ,C. Lechte 4 , J. Pinzon1,5 , D. Prisiazhniuk1,5 , U. Stroth1,5 , A.E. White2 and the ASDEX Upgrade Team1 1 Max Planck Institute for Plasma Physics, 85748 Garching, Germany 2 MIT Plasma Science and Fusion Center, Cambridge, MA, USA. 3 Laboratoire de Physique des Plasmas, Ecole Polytechnique, 91128, Palaiseau cedex, France 4 IGVP, Universit at Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany 5 Physik-Department E28, Technische Universität München, Garching, Germany Quantitative comparison of gyrokinetic (GK) models of plasma turbulence to experimental measurements of fluctuating quantities is essential to provide stringent tests of the theory. Re- cently, the development in the fidelity of GK simulations, new experimental diagnostics and ad- vanced synthetic diagnostics for qunatitative comparison, means that GK models can be tested more thoroughly than ever. At ASDEX Upgrade (AUG), using a recently developed 30 channel Correlation Electron Cyclotron Emission (CECE) radiometer, measurements of the fluctuation amplitude, δ Te⊥ , radial correlation length, Lr (Te ), and ne -Te cross-phase, αne Te , have been ob- tained simultaneously in an L-mode plasma and are quantitatively compared to non-linear ion- scale GK simulations in an extensive validation study [1]. Additionally, eddy tilt angles have been measured for the first time at AUG using Radial Correlation Doppler Reflectometry and are found to be different for ITG and TEM dominated turbulence [2]. The results are interpreted through the use of extensive full wave simulations and compared directly to theoretical values. Doppler Reflectometry (DR) was recently used in the AUG core plasma to measure the electron density k⊥ spectrum in the range 0.4 < k⊥ ρs < 3 [3]. Discrepancies between O and X mode measurements are found to be explained by a combination of non-linear saturation at low-k and an enhanced power response at high-k [4]. O-mode results are in reasonable agreement with GK simulations. Furthermore, measurements of the eddy dissipation time and perpendicular correlation length of ne fluctuations have been made using Poloidal Correlation Reflectome- try [5] and compared to GK values. Experiments were recently performed to bring together as many simultaneous, spatially overlapping turbulence measurements as possible for quantitative comparisons to non-linear GK simulations. The measurements and progress in their quantitative comparison to GK simulations will be discussed. References [1] S.J. Freethy et al. Phys. Plasmas, in preparation. [2] J.R. Pinzon et al. Phys. Rev. Lett., in preparation. [3] T. Happel et al. Plasma Phys. Control. Fusion, 59(054009), 2017. [4] J.R. Pinzon et al. Plasma Phys. Control. Fusion, 59(035005), 2017. [5] D. Prisiazhniuk et al. Plasma Phys. Control. Fusion, 59(025013), 2017.

Speaker: Simon James Freethy

18:15 O4.110 Transport theory of phase space zonal structures

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O4.110.pdf Transport theory of phase space zonal structures M. V. Falessi1 and F. Zonca1,2 1 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy, matteo.falessi@enea.it 2 Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, China ABSTRACT A set of equations is derived that describes the transport of particles and energy in a thermonuclear plasma on the energy confinement timescale. The equations thus derived allow to study collisional and turbulent transport self- consistently retaining the effect of magnetic field geometry without assuming any scale separation between fluctuations and the reference state. In a previous article [1], transport equations holding on the reference state lengthscale have been derived using the moment approach introduced in [2]. Furthermore it has been shown how this approach is not suitable for the description of smaller length-scales. In this work, this analysis is extended to micro- and meso-scales adopting the framework of phase space zonal structure theory [3, 4]. Previous results are recovered in the long wavelength limit and, in the general case, transport equations in the phase space for particles and energy are obtained that correctly take into account meso-scale structures. References [1] M. V. Falessi and F. Zonca. Gyrokinetic theory for particle and energy transport in fusion plasmas. Physics of Plasmas, 25(3):032306, 2018. [2] F. L. Hinton and R. D. Hazeltine. Theory of plasma transport in toroidal confinement systems. Reviews of Modern Physics, 48(2):239, 1976. [3] F. Zonca, L. Chen, S. Briguglio, G. Fogaccia, G. Vlad, and X. Wang. Nonlinear dynamics of phase space zonal structures and energetic particle physics in fusion plasmas. New Journal of Physics, 17(1):013052, 2015. [4] L. Chen and F. Zonca. Physics of alfvén waves and energetic particles in burning plasmas. Reviews of Modern Physics, 88(1):015008, 2016. 1

Speaker: Matteo Valerio Falessi

20:00 → 22:00 CONFERENCE DINNER

Friday, 6 July

09:00 → 10:10 PLENARY SESSION

T. Bell

Convener: T. Bell

09:00 I5.012 Collisional and collisionless shocks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.012.pdf Collisional and collisionless shocks D.D. Ryutov Lawrence Livermore National Laboratory, Livermore CA 94550, USA Shock waves are one of the most common plasma phenomena. They play a significant role in astrophysical and magnetospheric environments, as well as in laboratory plasmas. The classical collisional shocks usually connect two well-defined equilibrium states (those before and after the shock transition). Each of these equilibrium states is characterized by the thermodynamic parameters of density, temperature, and pressure, whose upstream and downstream values are related by the continuity of mass, momentum, and energy flux. In the collisionless plasmas, however, the initial state can be any of the much broader class of states as long as constrained only by the requirement of being micro-stable. To find a final state (which is micro-stable but, generally, non-Maxwellian) one now has to follow the evolution of the system through the whole transition, and a lot of universality is lost. Despite this important conceptual difference, there are also many similarities between the two types of shocks: i) a formation mechanism by the hydrodynamic overtaking, ii) an important role of the electron and ion mass disparity, iii) the presence of several sub-scales in the shock transition, and iv) the composition variation within the shock transition. These general features will be illustrated by examples from laboratory astrophysics, high-energy-density fusion experiments, and edge plasmas of toroidal devices. A special class of shock-like transitions in the form of double layers will also be discussed. Taken together, these phenomena reveal a fascinating interplay of hydrodynamics, statistical mechanics, and plasma physics. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52- 07NA27344.

Speaker: Dmitri D. Ryutov

09:35 I5.013 Active Control of Alfvén Eigenmodes in Fusion Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.013.pdf Active Control of Alfvén Eigenmodes in Fusion Plasmas M. Garcia-Munoz1, S. E. Sharapov2, E. Ascasibar3, A. Cappa3, L. Chen4, J. Galdon-Quiroga1, J. M. García-Regaña3, J. Gonzalez-Martin1, W. W. Heidbrink5, Ph. Lauber6, L. Sanchis-Sanchez1, P. Schneider6, J. Stober6, W. Suttrop6, Y. Todo7, M. A. Van Zeeland8, F. Zonca9 and the AUG and MST1 Teams 1 Dept. of Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, Sevilla, Spain, 2 CCFE, Culham Science Centre, Abingdon, UK, 3CIEMAT, Madrid, Spain, 4IFTS, Zhejiang University, Hangzhou, China, 5Dept. of Physics and Astronomy, University of California, Irvine, CA, USA, 6Max Planck Institut für Plasmaphysik, Garching, Germany, 7 National Institute for Fusion Science, Toki, Japan, 8General Atomics, San Diego, CA, USA, 9ENEA, Frascati, Italy Alfvén waves are magnetohydrodynamic fluctuations inherent to magnetized plasmas. Gradients in the energetic particles’ distribution determine the resonant wave-particle energy and momentum exchange. Burning plasmas in magnetically confined fusion devices are prone to develop Alfvén Eigenmodes (AEs) that, if allowed to grow unabated, can cause an important degradation of fusion performance through fast-ion redistribution. To obtain a self-maintained burning plasma, fusion-born alpha particles must, however, be well-confined. Recent breakthroughs in the diagnosis of the temporal evolution of the energetic particles’ phase-space have allowed the identification of wave-particle interactions that lead to a net fast-ion transport enabling the development of dedicated control techniques. Several external actuators have shown their potential to mitigate or even suppress the AE activity and associated fast-ion transport in tokamaks and stellarators. Most control techniques aim at modifying the background kinetic and current profiles. Recent experimental results have shown, however, that an active control of the fast-ion distribution, i.e. AE drive directly, can be a robust and promising technique towards future burning plasmas. Externally applied 3D fields and heating systems provide an excellent tool to tailor the fast-ion distribution in phase-space, thus modifying their drive/damping through local wave-particle interactions. Non-linear 3D hybrid kinetic-MHD simulations help to identify the wave-particle resonances responsible for the observed AE drive/transport improving our ability to develop robust control techniques for future burning plasmas. Recent experimental and modelling results from a worldwide effort focused on addressing this important problem will be presented. The prospects of each technique towards ITER will be discussed.

Speaker: Manuel Garcia-Munoz

10:10 → 10:40 COFFEE

10:40 → 12:40 BPIF

Chair: M. Nakatsutsumi

Convener: M. Nakatsutsumi

10:40 I5.213 Plasma optics: ion gratings for energy transfer in the picosecond regime

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.213.pdf Plasma optics: ion gratings for energy transfer in the picosecond regime L. Lancia1 , J.-R. Marquès1 , F. Amiranoff1 , R.L. Berger2 , M. Blecher3 , S. Bolaños1 , M. Chiaramello4 , J. Fuchs1 , T. Gangolf1,3 , A. Giribono5 , K. Glize6 , C. Riconda4 , S. Weber7 , O. Willi3 1 LULI, CNRS, École Polytechnique, CEA, Sorbonne Université, Palaiseau, France 2 Lawrence Livermore National Laboratory, Livermore, California 94550, USA 3 ILPP, Heinrich-Heine Universität Düsseldorf, 40225 Düsseldorf, Germany 4 LULI, Sorbonne Université, CNRS, École Polytechnique, CEA, Paris, France 5 Dip. SBAI, Università di Roma "La Sapienza", Via A. Scarpa 14, 00161 Rome, Italy 6 CEA, DAM, DIF, F-91297 Arpajon, France 7 Institute of Physics of the ASCR, ELI-Beamlines, 18221 Prague, Czech Republic. At the interface between laser-plasma physics and photonics "Plasma optics" aims at manip- ulating high intensity laser pulses by exploiting the optical properties of a plasma. Transient plasma structures (or plasma photonic crystals, or gratings) present a ultrahigh damage thresh- old that overcomes the limit of traditional solid-state optics and makes it possible to manipulate and control ultra-short intense laser pulses[1]. Two kinds of gratings can be produced in a plasma by the beating of two transverse electro- magnetic waves (laser beams). According to the nature of the particle motion, whether electron (Raman) or ion (Brillouin) plasma waves, the properties of these structures differ in terms of lifetime and light manipulation capabilities. The possibility to generate ion plasma gratings and induce a controlled energy transfer is by now well established [2]. At laser intensities as high as 1015 − 1016 W.cm−2 the characteristic time-scales for the setup of these non-linear ion-like waves can easily attain a few hundred femtoseconds and their lifetime can last several picoseconds. We will review the progress in the realization and optimization of an ion grating (Stimulated Brillouin Scattering) based amplifier, discuss the main limits that affect the energy transfer. We will present recent results in the case of counter-propagating as well as co-propagating, sub-picosecond beams at the same wavelength. We will discuss the role of laser and plasma parameters in the interaction geometries. References [1] P. Michel et al., Phys. Rev. Lett. 113, 205001 (2014); D.Turnbull et al., Phys. Rev. Lett. 116, 205001 (2016); G. Lehmann et al., Phys. Rev. Lett. 116, 225002 (2016); [2] L. Lancia et al., Phys. Rev. Lett. 104, 025001 (2010); 116, 075001 (2016); M. Chiaramello, et al., Phys. Plasmas 23, 072103 (2016).

Speaker: Livia Lancia

11:10 I5.214 Novel Mechanism of Magnetic Field generation in a finite beam Plasma System

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.214.pdf Novel mechanism of Magnetic field generation in a finite beam plasma system Amita Das1 , Atul Kumar1 , Chandrasekhar Shukla1 , Ratan Kumar Bera1 , Deepa Verma1 , Devshree Mandal1 , Ayushi Vashistha1 , Bhavesh Patel1 , Predhiman Kaw1 , Y. Hayashi2 , K. Tanaka3 , G. Ravindra Kumar4 and Amit Lad4 1 Institute for Plasma Research, Bhat Gandhinagar, India 2 Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 Japan 3 Extreme Laser Infrastructure-Nuclear Physics 30 Reactorului, PO Box MG-6, Bucharest Magurele 077125 Romania 4 Tata Institute for Fundamental Research 1 Homi Bhabha Road, Mumbai 400005, India When an energetic electron beam propagates in a plasma it produces return shielding currents from background electrons. The combination of forward and return shielding currents are con- ventionally believed to be unstable to the Weibel instability which generates magnetic field at the electron skin depth scales. We have demonstrated by Particle - In - Cell (PIC) as well as fluid simulations, laser plasma experiments and analytic theory that a hitherto unknown instability (distinct from both Weibel and Kelvin Helmholtz ) is excited in the beam plasma system where the beam has a finite transverse size. This instability is responsible for the generation of mag- netic fields at scales comparable to the transverse beam dimension which can be much longer than the electron skin depth scale. This counter-intuitive result arises due to radiative leakage associated with finite beam boundaries which is absent in the infinite and/or periodic systems considered in all earlier simulations.

Speaker: Amita Das

11:40 O5.201 A wireless solenoïd generated from laser plasma interaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.201.pdf A wireless solenoïd generated from laser­plasma interaction R.Nuter1, P. Korneev2, I. Thiele3 and V.T. Tikhonchuk1 1 Université Bordeaux, CNRS, CEA, UMR 5107, 33405 Talence, FRANCE 2 National Research Nuclear University 'MEPHi' Moscow, 115409 RUSSIA 3 Chalmers University of Technology, Departement of Physics, SE­41296 Göteborg, SWEDEN Generating a quasi­static magnetic field from the laser­plasma interaction gives rise to many theoretical[1­4] and experimental studies[5­6]. Two approaches are considered : one consists in designing the target in such way that the interaction with laser generates an azimutal current [7], another one consists in transfering angular momentum from the laser to the electrons by considering adapted laser polarization or structured laser spatial shape. Here we will present a numerical study in which a strongly focused radially polarized laser beam carrying an orbital angular momentum transfers angular rotation to the plasma electron in such way that a static magnetic field is generated. The numerical simulations performed with the 3D Particle In Cell code OCEAN show that the generated quasi­static magnetic field can be controlled with the laser characteristics : pulse duration, angular momentum and focal spot. Longitudinal view of magnetic field Transversal coordinate Longitudinal coordinate 1­ V.I. Berezhiani et al., Physical Review E, 55:995 (1997) 2­ R. Hertel, J. of magnetism and magnetic materials, 303 : L1 (2006) 3­N. Naseri et al, Physics of plasmas, 17:083109 (2010) 4­ S. Ali et al, Physical Review Letters, 105:035001 (2010) 5­Z. Najmundin et al., Physical Review Letters, 87:215004 (2001) 6­ J.Deschamps et al., Physical Review Letters, 25:1330 (1970) 7­ Ph. Korneev et al., New Journal of physics, 19:033023 (2017)

Speaker: Rachel Nuter

11:55 O5.202 Experimental evidence of radiation reaction effects in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.202.pdf Experimental evidence of radiation reaction effects in the collision of a high-intensity laser pulse with a laser-wakefield accelerated electron beam J. M. Cole1, K. T. Behm2, E. Gerstmayr1*, T. G. Blackburn3, J. C. Wood1, C. D. Baird4, M. J. Duff5, C. Harvey3, A. Ilderton3,6, A. S. Joglekar2,7, K. Krushelnick2, S. Kuschel8, M. Marklund3, P. McKenna5, C. D. Murphy4, K. Põder1, C. P. Ridgers4, G. M. Samarin9, G. Sarri9, D. R. Symes10, A. G. R. Thomas2,11, J. Warwick9, M. Zepf8,9,12, Z. Najmudin1, S. P. D. Mangles1 1 The John Adams Institute for Accelerator Science, Imperial College London, London, UK 2 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan, USA 3 Department of Physics, Chalmers University of Technology, Gothenburg, Sweden 4 York Plasma Institute, Department of Physics, University of York, York, UK 5 SUPA Department of Physics, University of Strathclyde, Glasgow, UK 6 Centre for Mathematical Sciences, Plymouth University, UK 7 University of California, Los Angeles, Los Angeles, California, USA 8 Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, Jena, Germany 9 School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, UK 10 Central Laser Facility, Rutherford Appleton Laboratory, Didcot, UK 11 Physics Department, Lancaster University, Bailrigg, Lancaster, UK 12 Helmholtz Institut Jena, Jena, Germany *e.gerstmayr15@imperial.ac.uk We present experimental evidence of radiation reaction in the collision of a highly relativistic electron beam generated by laser-wakefield acceleration (e > 500 MeV) with an intense laser pulse (a0 > 10). This was recently published in [1]. We measure the electron and g-ray spectra from inverse Compton scattering simultaneously to infer the conditions at the point of interaction independently. The energy loss in the electron spectrum after the collision and the g-ray signal are correlated, consistent with a quantum description of radiation reaction. The generated g-ray spectrum reaches a critical energy ecrit > 30 MeV, being the highest g-ray energy from an all-optical inverse Compton scattering scheme reported so far [2,3,4]. [1] J. M. Cole et al., Physical Review X 8, 011020 (2018) [2] K. Ta Phuoc et al., Nature Photonics 6, 308 (2012) [3] N. D. Powers et al., Nature Photonics 8, 28 (2014) [4] G. Sarri et al., Physical Review Letters 113, 1 (2014)

Speaker: Elias Gerstmayr

12:10 O5.203 Prospects for producing XUV bursts by laser-plasma interactions in the regime of relativistic electronic spring

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.203.pdf Prospects for producing XUV bursts by laser-plasma interactions in the regime of relativistic electronic spring A. Gonoskov1,2,3, T. Blackburn1, M. Blanco4, M.T. Flores-Arias4, B. Svedung Wettervik1, M. Marklund1 1 Chalmers University of Technology, SE-41296 Gothenburg, Sweden 2 Institute of Applied Physics, RAS, Nizhny Novgorod 603950, Russia 3 Lobachevsky State University of Nizhni Novgorod, Nizhny Novgorod 603950, Russia 4 Universidade de Santiago de Compostela, Campus Vida, Santiago de Compostela, Spain High-intensity lasers provide an opportunity to drive controllable, relativistic plasma dynamics through the irradiation of solids. In this way, the laser energy can be converted into extreme ultraviolet (XUV) radiation with tailored properties such as high brightness, ultra-short duration and tunable polarization. In the regime of relativistic electronic spring (RES), the irradiated plasma acts as a spring, repeatedly accumulating and releasing the incident energy in the form of XUV bursts within every optical cycle. These bursts can be a hundred times higher in intensity as compared to the incident radiation. This manifests a distinct difference from the relativistic oscillating mirror (ROM) regime, which implies subcycle phase variations without the change of amplitude. In our study, we analyse the prospects of using the RES regime for creating laser-based sources of tailored XUV pulses. We use the theoretical principles proposed in [1] to develop a theory of the process applicable to an arbitrary density profile, laser pulse shape and polarization [2]. The theory indicates that there are clear possibilities for tuning the ellipticity of the generated XUV bursts by adjusting the laser polarization and other interaction parameters [3]. We also demonstrate that the efficient generation of XUV bursts is achievable, and even enhanced, by the density gradients that naturally emerge in laser-solid interactions due to the effect of finite contrast [4]. Finally, we assess the possibility of using the generated XUV busts for driving wake-fields in solids [5]. References: [1] A. Gonoskov et al. Phys. Rev. E 84, 046403 (2011) [2] A. Gonoskov Phys. of Plasmas 25, 013108 (2018) [3] M. Blanco, M. T. Flores-Arias and A. Gonoskov, arXiv:1706.04785 (2017) [4] T. G. Blackburn, A. A. Gonoskov and M. Marklund, arXiv:1701.07268 (2017) [5] B. Svedung Wettervik, A. Gonoskov, M. Marklund, Phys. of Plasmas 25, 013107 (2018)

Speaker: Arkady Gonoskov

12:25 O5.204 Relativisitic Flying Mirror in the Ultra-high Intensity Regime

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.204.pdf Relativisitic Flying Mirror in the Ultra-high Intensity Regime J. K. Koga1 , S. V. Bulanov1,2 , T. Zh. Esirkepov1 , M. Kando1 , S. S. Bulanov3 , A. S. Pirozhkov1 , A. Bierwage4 , P. Valenta2,5 1 National Institutes for Quantum and Radiological Science and Technology, Kizugawa, Japan 2 ELI BEAMLINES, Dolní Břežany, Czech Republic 3 Lawrence Berkeley National Laboratory, Berkeley, USA 4 National Institutes for Quantum and Radiological Science and Technology, Rokkasho, Japan 5 Czech Technical University in Prague, Prague, Czech Republic There is the need for high brillance γ-ray sources for fundamental physics applications. Rel- ativistic flying mirrors generated by ultra-high intensity laser pulses (driver) propagating in plasma have been used to upshift and focus counter-propagating laser pulses (source) via the double Doppler effect (see [1] and cited references). Up to now the source laser pulse has been of sufficiently low intensity so as to not significantly perturb the mirror. We have shown in particle-in-cell (PIC) simulations that in the case where the source pulse is of high intensity the boosted harmonics can be generated[2]. In this paper we investigate this using 2D and 3D PIC simulations where two counter-propagating laser pulses of high intensity, one focusing and one de-focusing, collide. We will present our considerations for using relativistic flying mirrors towards achieving high flux γ-ray sources. References [1] S. V. Bulanov, T. Zh. Esirkepov, M. Kando, A. S. Pirozhkov and N. N. Rosanov, Phys. Usp. 56, 429 (2013) [2] J. K. Koga, S. V. Bulanov, T. Zh. Esirkepov, M. Kando, S. S. Bulanov and A. S. Pirozhkov, submitted to Plasma Phys. Control. Fusion (2018)

Speaker: James K. Koga

10:40 → 12:40 BSAP/MCF

Chair: E. Solano

Convener: E. Solano

10:40 I5.J601 Simulating tokamak edge instabilities: advances and challenges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.J601.pdf Simulating tokamak edge instabilities: advances and challenges M. Hoelzl1, G.T.A. Huijsmans2,3, F. Orain1, F.J. Artola4, S. Pamela5, F. Liu2,6, D. van Vugt3, S. Futatani7, M. Becoulet2, A. Cathey1, K. Lackner1, S. Günter1, MST1 Team*, ASDEX Upgrade Team1 1 Max Planck Institute for Plasma Physics, Garching, Germany 2CEA, IRFM, 13108 Saint- Paul-Lez-Durance, France 3Eindhoven University of Technology, Eindhoven, The Netherlands 4Aix-Marseille University, 13397 Marseille Cedex 20, France 5CCFE, Culham Science Centre, UK 6Université Côte d’Azur, 06108 Nice Cedex 02, France 7 Barcelona Supercomputing Center, Barcelona, Spain *H. Meyer et al, Nucl. Fusion 57,102014 (2017) Large scale magneto-hydrodynamic (MHD) instabilities are of common interest in astrophysical, space and fusion plasmas. In all these research fields, the progress in non- linear MHD simulations has significantly increased the understanding of the observed phenomena. This talk is devoted to the recent progress in non-linear MHD simulation for tokamak plasmas. After giving an overview of the most important instabilities in tokamak plasmas and introducing the JOREK non-linear MHD code used for our studies, we focus on so-called edge localized modes (ELMs). Such instabilities lead to a periodic expulsion of energy and particles from the plasma. Uncontrolled ELMs are expected to considerably deteriorate the life-time of divertor components in ITER. It is shown how simulations contribute in the effort of pushing forward the fundamental understanding of ELM physics. Based on recent experimental and simulation advances, the most important aspects of ELM physics are reviewed. This includes precursor modes, filament formation, field stochastization, impurity transport, and heat loads onto machine structures. An overview is also given of ELM control including natural ELM free regimes, and techniques for ELM pacing, mitigation and suppression. It will be shown that quantitative agreement of simulations is achieved with many key experimental observations for ELMs and ELM control. Simulations allow to perform complementary investigations to the experimental approaches, and are successively developing the predictive capabilities to establish robust operational scenarios for future fusion devices. Open challenges will also be addressed.

Speaker: Matthias Hoelzl

11:10 I5.J602 First direct observation of whistler waves driven by relativistic electrons in a toroidally-confined laboratory plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.J602.pdf First direct observation of whistler waves driven by relativistic electrons in a toroidally-confined laboratory plasma D.A. Spong1, W.W. Heidbrink2, C. Paz-Soldan3, X.D. Du2, K.E. Thome3, M.A. Van Zeeland3 1 Oak Ridge National Laboratory, Oak Ridge, USA 2 University of California, Irvine, USA 3 General Atomics, San Diego, USA Whistlers are dispersive electromagnetic waves that can be driven unstable by energetic electrons in both space and laboratory plasmas. They are unstable in the outer radiation belts of planetary atmospheres, where they are known as chorus waves. Perpendicular scattering of energetic electrons by whistlers contributes to the aurora. The first detection (in 1894!) was generated by lightning. In the present experiment, a confined population of ~ 10 MeV “runaway” electrons drives whistlers unstable in the DIII-D tokamak (Fig. 1). The detected 100-200 MHz waves are in the band between the ion cyclotron and lower hybrid frequencies and satisfy the cold-plasma dispersion relation, with the expected dependencies on magnetic field and density. Whistler activity is correlated with the intensity of hard x-rays produced by the runaways. Fluctuations occur in discrete frequency bands, and not a continuum as would be expected from plane wave analysis, suggesting the important role of toroidicity. An MHD model including the bounded/periodic nature of the plasma identifies multiple eigenmode branches. For a toroidal mode number n = 10, the predicted frequencies and spacing are similar to observations. The instabilities are stabilized with increasing magnetic field, as expected from the anomalous Doppler resonance. The whistler amplitudes show intermittent time variations. Predator-prey cycles with electron cyclotron emission (ECE) signals are observed, which can be interpreted as wave-induced pitch angle scattering of moderate energy electrons. Such nonlinear dynamics are supported by quasi-linear simulations indicating that electrons are scattered both by whistlers and high frequency magnetized plasma waves. The whistler wave predominantly scatters the high energy electrons, while the magnetized plasma wave scatters the low energy electrons, abruptly enhancing the ECE signal. If whistlers that pitch-angle scatter runaways are excited in future devices, the enhanced runaway dissipation could reduce the likelihood of runaway-electron induced damage. Work supported by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA27344, DE- FG02-07ER54917, DE-SC00-16268, and DE-AC05-00OR22725. Figure 1. Whistler waves detected by a magnetic probe. The time evolution of the dominant toroidal magnetic field is indicated by the dashed line; the density is nearly constant in this discharge. The frequency exhibits the expected linear dependence on magnetic field. The modes are more easily destabilized at lower magnetic field, probably because the electron energy is higher. The banded, discrete nature of the observed modes is evident.

Speaker: William Heidbrink

11:40 O5.J601 The tearing instability in relativistic magnetohydrodynamics

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J601.pdf The tearing instability in relativistic magnetohydrodynamics L. Del Zanna1,2,3 , E. Papini1,2 , S. Landi1,2 , M. Bugli4 , N. Bucciantini2,1,3 1 Dipartimento di Fisica e Astronomia, Università di Firenze, Firenze, Italy 2 INAF - Osservatorio Astrofisico di Arcetri, Firenze, Italy 3 INFN - Sezione di Firenze, Firenze, Italy 4 CEA-Saclay, Paris, France Magnetic energy dissipation in relativistic plasmas is a crucial process operating in many en- vironments typical of high-energy astrophysics, such as pulsar winds and nebulae, magnetars, and magnetized disks around black holes. In many cases such dissipation is required to be of explosive type, given that flaring activity is often observed in such objects, in the form of sudden releases of gamma rays. Here we discuss the role of the aspect ratio of the reconnecting current sheet, which, as for classic and Hall magnetohydrodynamics (MHD), when sufficiently small is known to lead to a very rapid evolution of the spontaneous tearing instability and to explo- sive secondary reconnection events (super-tearing or plasmoid instability). Multi-dimensional simulations of resistive, relativistic MHD are presented for various magnetizations and plasma betas, and 2-D results show a quasi-universal evolution, occurring on the ideal (relativistic) Alfvén time. Extension to the 3-D case and possible applications to the physics of magnetars and pulsar wind nebulae are briefly discussed.

Speaker: Luca Del Zanna

11:55 O5.J602 Nonlinear ballooning flux tubes in tokamak geometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J602.pdf Nonlinear ballooning flux tubes in tokamak geometry C.J. Ham1, S.C. Cowley2, H.W. Wilson,1,3 1 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 2 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford, UK 3 York Plasma Institute, Department of Physics, University of York, Heslington, York UK The nonlinear phase of MHD ballooning modes determines whether they are essentially benign or disruptive. Disruptive or hard limits are produced by ballooning modes across magnetic confinement fusion, for example; as ELMs, some tokamak disruptions [1], and perhaps the LHD Core Density Collapse [2]. This work improves our understanding of how these instabilities develop and might allow us to design plasma profiles such that hard limits are avoided and so improve machine availability and performance. A nonlinear theory for ballooning flux tubes in large aspect ratio toroidal geometry has been developed [3] which shows that linearly ballooning stable profiles can be unstable to finite amplitude displacements, i.e. they are metastable. We now use the generalized Archimedes' principle developed in [3] to study the nonlinear phase of ballooning flux tubes in realistic tokamak equilibria. We see that saturated filamentary ballooning states are available even when the profile is linearly stable. We qualitatively compare the saturated amplitude of these states to those seen experimentally, for example on KSTAR [4]. We also investigate if this model is applicable Figure 1: Elliptical (orange) flux tube to type II ELMs which are thought to be purely sliding along (blue) surface S parting surrounding (black) field lines. The tube’s ballooning in character [5]. displacement is larger on the outboard side This model focuses on the saturation of the ideal of the flux surfaces – the tube balloons. The magnetic shear (s = rq′/q) causes the twist MHD ballooning flux tubes which is likely to occur and narrowing of the tube on the inside. on a fast time scale. However, once this occurs we may see the flux tube break off due to magnetic reconnection and we assess the likely location of this reconnection site. [1] E D Fredrickson et al Phys. Plasmas 3 (1996) 2620 [2] S Ohdachi et al Nuclear Fusion 57 (2017) 066042 [3] C J Ham et al Phys Rev. Lett. 116 (2016) 235001 [4] G S Yun et al Phys Rev. Lett. 107 (2012) 045004 [5] S Saarelma et al Plasma Phys. Control Fusion 51 (2009) 035001

Speaker: Christopher Ham

12:10 O5.J603 Simulations of bremsstrahlung and synchrotron radiation from runaway electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J603.pdf Simulations of bremsstrahlung and synchrotron radiation from runaway electrons M. Hoppe, O. Embréus, P. Svensson, L. Unnerfelt, T. Fülöp Department of Physics, Chalmers University of Technology, Göteborg 412 96, Sweden The main method for diagnosing runaway electrons in tokamak experiments is to measure the radiation they emit. Both the bremsstrahlung (BR) [1, 2] and synchrotron radiation (SR) [3, 4] emission from runaways is strongly dependent on particle energy, pitch angle and position, and thus provide valuable insight into runaway electron dynamics. In this contribution we present recent developments of the Synchrotron-detecting Orbit Following Toolkit (SOFT) [5], which has previously been used to study SR images and spectra [5, 6]. Specifically we present the implementation of BR and the polarization of SR in SOFT, and analyze the effects of first-order corrections to the guiding-center motion. Due to the strong anisotropy of both BR and SR, the camera images from both types of radiation depend strongly, and in a similar way, on the runaway pitch-angle and radial distribu- tions [6]. The amount of emitted SR however increases with energy, while it decreases for BR, thus causing different parts of the momentum-space distribution function to dominate emission of each type, effectively allowing different parts of momentum-space to be analyzed. Another technique suggested for acquiring sufficient data to unambiguously infer both the dominant energy and pitch angle of the runaways is to measure the polarization components of SR. We consider its usefulness as a diagnostic technique as well as its implementation in SOFT. The high energy of runaway electrons is associated with large guiding-center drift orbits which shift guiding-centers away from magnetic flux surfaces and hence modify spatial dis- tribution of runaways. The high energy is however also associated with perturbations to the particles’ gyro-motion, which will change the gyro-averaged angular distribution of radiation emitted by runaways and which must also be considered in a consistent treatment. We estimate the relative importance of these effects from a radiation-detection point-of-view and show that they must both be included in a model based on first order guiding-center theory. References [1] Y. Peysson et al., Rev. Sci. Instrum. 70, 3987 (1999). [2] C. Paz-Soldan et al., Phys. Rev. Lett. 118, 255002 (2017). [3] K. H. Finken et al., Nucl. Fusion 30, 859 (1990). [4] R. J. Zhou et al., Phys. Plasmas 21, 063302 (2014). [5] M. Hoppe et al., Nucl. Fusion 58, 026032 (2018). [6] M. Hoppe et al., Accepted for publication in Nucl. Fusion (2018).

Speaker: Mathias Hoppe

12:25 O5.J604 Tokamak Plasma Self-driven Current Generation in the Presence of Turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.J604.pdf Turbulence W. X. Wang1 , E. Startsev1 , S. Ethier1 , J. Chen1 , C. H. Ma1 , T. S. Hahm2 , M. G. Yoo2 1 Princeton Plasma Physics Laboratory, Princeton, USA 2 Seoul National University, Seoul, Korea Plasma self-generated current (e.g., the bootstrap current) contributes to the generation of poloidal magnetic field for plasma confinement in tokamaks, and also strongly affects key MHD instabilities. It is found that plasma turbulence may strongly influence self-driven current gen- eration. This could have a radical impact on various aspects of tokamak physics. Our simulation study employs a global gyrokinetic model coupling self-consistent neoclassical and turbulent dynamics with focus on mean electron current. Distinct phases in electron current generation are illustrated in our initial value simulation. In the early phase before turbulence develops, the electron bootstrap current is established in a time scale of a few electron collision times, which closely agrees with the neoclassical prediction. The second phase follows when turbu- lence begins to saturate, during which turbulent fluctuations are found to strongly affect electron current. The profile structure, amplitude and phase space structures of electron current density are all significantly modified relative to the neoclassical bootstrap current by the presence of turbulence. Both electron parallel acceleration and parallel residual stress drive due to turbu- lence are shown to play important roles in turbulence-induced current generation. The former can change the total plasma self-generated current though turbulence-induced momentum ex- change between electrons and ions, and the latter merely modifies the current density profile while keeping the total current unchanged. The current density profile is modified in a way that correlates with the fluctuation intensity gradient through its effect on k -symmetry breaking in fluctuation spectrum. Turbulence is shown to reduce (enhance) plasma self-generated current in low (high) collisionality regime, and the reduction of total electron current relative to the neoclassical bootstrap current increases as collisionality decreases. The implication of this re- sult to the fully non-inductive current operation in steady state burning plasma regime could be important and should be investigated. Finally, a significant non-inductive current is observed in flat pressure region, which is a nonlocal effect and results from turbulence-spreading-induced current diffusion. Work supported by U.S. DOE Contract DE-AC02-09-CH11466.

Speaker: Weixing Wang

10:40 → 12:40 LTDP

Chair: V. Guerra

Convener: V. Guerra

10:40 I5.311 Electron-CO excitation cross sections for plasma modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.311.pdf Electron-CO excitation cross sections for plasma modelling A. Laricchiuta, L.D. Pietanza, M. Capitelli, G. Colonna PLASMI Lab NANOTEC CNR Bari (Italy) The plasma activation of CO2 in different plasma regimes is nowadays attracting large in- terest in the scientific community, representing a promising new-concept technology for the conversion of anthropogenic CO2 emissions. The non-equilibrium conditions met in plasmas could, in fact, selectively promote reactive channels leading to efficient dissociation and, in turn, to the formation of CO. The detailed description of the vibrational and electronic state kinetics within the state-to-state approach can considerably contribute to the understanding of the collisional mechanisms that critically determines the conversion efficiency [1, 2, 3, 4]. The electron-impact induced disso- ciative and non-dissociative excita- 20.0 excitation cross section tions for dipole-allowed transitions in 15.0 [10-18 cm2] CO molecule are here reconsidered 10.0 in the framework of the similarity approach [5] for the derivation of 5.0 vibrationally-specific dynamical data. 0.0 0 1 2 3 4 5 6 7 8 9 10 In Fig. 1 the (X1 Σ+ , υ 00 ) → (A1 Π, υ 0 ) final vibrational level υ � cross sections, obtained optimizing the 1 + 00 1 0 similarity function parameters for the Figure 1: Cross sections for (X Σ , υ = 0) →(A Π, υ ) total excitation cross section from the excitations in e-CO collisions (solid line) at E=30 eV, compared with experiments (close circles) [6] (open dia- υ 00 = 0 level, are compared with experi- monds) [7] and BE f theoretical results (dashed line) [6]. mental and theoretical results [6, 7]. The effect of non-adiabatic vibronic coupling in the excitations to the B1 Σ+ -D01 Σ+ Rydberg-valence complex, is also investigated. References [1] M. Capitelli, G. Colonna, G. D’Ammando and L.D. Pietanza, Plasma Sources Sci. Technol. 26 055009 (2017) [2] A. Bogaerts, W. Wang, A. Berthelot and V. Guerra, Plasma Sources Sci. Technol. 25 055016 (2016) [3] L.D. Pietanza, G. Colonna and M. Capitelli, Plasma Sources Sci. Technol. 26 125007 (2017) [4] L.D. Pietanza, G. Colonna and M. Capitelli, J. Plasma Phys. 83 6 (2017) [5] S. Adamson, V. Astapenko, M. Deminskii, A. Eletskii, B. Potapkin, L. Sukhanov, A. Zaitsevskii, Chem. Phys. Lett. 436 308 (2007) [6] H. Kato, H. Kawahara, M. Hoshino, H. Tanaka, M.J. Brunger, Y.-K. Kim, J. Chem. Phys. 126 064307 (2007) [7] M.J. Mumma, E.J. Stone and E.C. Zipf, J. Chem. Phys. 54 2627 (1971)

Speaker: Annarita Laricchiuta

11:10 I5.312 Kinetic mechanisms in air plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.312.pdf Kinetic mechanisms in air plasmas C. D. Pintassilgo1,2, V. Guerra1 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal 2 Dep. de Engenharia Física, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal This work presents a comprehensive modelling study on the most important kinetic mechanisms that take place in air plasmas at low pressures (p ~1 Torr). Within this purpose we adopt three different experimental situations in synthetic dry air (N2-20%O2): (i) single DC pulsed plasmas; (ii) their afterglows and (iii) repetitively DC pulsed discharges, each of them produced in a cylindrical tube with inner radius of 1 cm, considering pulse durations of the order of a few milliseconds, as reported in [1, 2]. Our simulations for the pulsed discharge are based on the numerical solutions of the electron Boltzmann equation coupled to the system of time-dependent rate-balance equations which incorporates the kinetics of the most populated heavy (neutral and ionic) species produced in an air mixture including the vibrationally excited states of ground state molecular nitrogen of molecular nitrogen N2(X 1∑g+,v) [3]. The afterglow regime is described by the temporal relaxation of all heavy species, discarding the role of electron impact collisions [4]. Modelling simulations show that the production of N(4S) and O(3P) atoms, as well as NO(X) molecules is governed by an important interplay between mechanisms N2(X, v ≥ 13) + O → NO(X) + N(4S) and NO(X) + N(4S) →N2(X, v~3) + O for pulse durations longer than 1 ms, with an important contribution from N(2D) + O2 → NO(X) + O and N2(A) + O → NO(X) + N(2D) reactions for shorter times. These predictions include the important interdependence between most of the reaction rate coefficients and the gas temperature, namely in what concerns the highly exothermic process NO(X) + N(4S) →N2(X, v~3) + O (~2.45 eV), by solving at the same time the gas thermal balance equation. This work was partially supported by the Portuguese FCT Fundação para a Ciência e a Tecnologia, under Project UID/FIS/50010/2013. [1] A. Rousseau, A. Dantier, L. Gatilova, Y. Ionikh, J. Röpcke, Y.Tolmachev Plasma Sources Sci. Technol. 14 (2005) 70 [2] Y. Ionikh, A. V. Meshchanov, J. Röpcke , A. Rousseau 322 (2006) Chem. Phys. 411–22 [3] C.D. Pintassilgo, O. Guaitella, A. Rousseau Plasma Sources Sci. Technol. 18 (2009) 025005 [4] C.D. Pintassilgo, V. Guerra, O. Guaitella and A. Rousseau Plasma Sources Sci. Technol. 19 (2010) 055001

Speaker: Carlos Daniel Pintassilgo

11:40 O5.301 Magnetohydrodynamic and knudsen flow simulation of low pressure plasma phenomena using a cloud-based numerical simulation platform

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.301.pdf Vibrational excitation kinetics of CO2 in a pulsed glow discharge studied by FTIR and Raman spectroscopy B.L.M. Klarenaar , A.S. Morillo-Candas , M. Grofulović , M.C.M. van de Sanden , 1 3 4 1,2 O. Guaitella , R. Engeln 3 1 Eindhoven University of Technology, Eindhoven, The Netherlands 1 2 Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands 3 Ecole Polytechnique, Univ. Paris Sud-11, UPMC, CNRS, Palaiseau, France 4 Instituto Superior Técnico, Universidade de Lisboa, Portugal The intermittency property of renewable energy provides a great challenge when the share of renewable energy sources increases. E.g. solar energy is only produced during the day, while the electrical energy demand at night rarely drops below 50% of daytime demand. Due to the intermittent nature of renewable energy sources production and demand do not always coincide. To overcome this problem, renewable energy should be temporally stored, e.g. by producing energy-dense hydrocarbon fuels, or solar fuels, from CO2. In this process, efficient reduction of CO2 to CO is a key step. This dissociation step is believed to be most efficient when selectively exciting the asymmetric-stretch vibration of CO2 [1]. We study the vibrational dynamics of CO2 by performing in situ Fourier Transform Infrared (FTIR) spectroscopy [2], as well as rotational Raman spectroscopy [3] on a pulsed glow discharge. For the analysis of the FTIR data we developed an algorithm to calculate and fit the transmittance spectra for CO2 and CO mixtures. Some of the fit parameters are the rotational temperature, Trot, the temperature of the fermi-resonant symmetric stretch mode and bending mode of CO2, T1,2, and the temperature of the asymmetric mode, T3. The algorithm uses the HITEMP-2010 database. Time and spatially-resolved rotational Raman measurements are used to study the assumption made in the FTIR analysis, i.e. no temperature variations along the line-of-sight. No significant changes of Trot along the longitudinal axis of the reactor where found, while the values measured for different time points during the plasma duty cycle correspond well to IR transmittance fits. [1] V.D. Rusanov, A.A. Fridman, G.V. Sholin, Usp. Fiz. Nauk, 134, 6 (1981). [2] B.L.M. Klarenaar, R. Engeln, D.C.M. van den Bekerom, M.C.M. van de Sanden, A.S. Morillo-Candas, and O. Guaitella, Plasma Sources Sci. Technol., 26, 115008 (2017) [3] B.L.M. Klarenaar, et al., (submitted to Plasma Sources Sci. Technol.)

Speaker: P. Zikan

11:55 O5.302 Self--consistent modeling of Discharge: the role of superelastic collisions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.302.pdf Self–consistent modeling of Discharge: the role of superelastic collisions G. Colonna PLASMI Lab NANOTEC CNR Bari (Italy) To determine the rate coefficients of electron-induced processes the Boltzmann equation for free electrons must be solved to calculate the electron energy distribution function (eedf). Inte- grating the cross sections over the eedf, the rates of electron induced processes are calculated. The most advanced approach consists in coupling self–consistently the Boltzmann equation, with the state-to-state kinetics, determining at the same time the eedf and the level distribu- tion, accounting for their mutual interaction. To simplify the calculation, under the assump- tion that eedf relaxes much faster than the gas composition, the rate coefficients can be related only to the local electric field (local field approximation, LFA). However, LFA cannot consider the contribution of the superelastic collisions in the electron kinetics. In participating to the Round Robin [1] activity for the verification of different plasma kinetic codes, strong effects of superelastic collisions on the plasma prop- !2 erties have been observed, when a self– 1014 P = t e t/t0 P0 t0 Ar* consistent coupling of free electron and level 1011 P0 = 10 W particle density [cm-3] cm3 kinetics has been considered. It is well known t0 = 10 3 s 108 e- that superelastic collisions are very important 105 in the post-discharge. In the present work we Ar* e- 102 have observed that they are effective also in 10–1 the presence of high electric field, as shown in 10–10 10–8 10–6 10–4 10–2 100 time [s] the figure, where the density of free electrons and argon metastable are reported when su- Figure 1: Electron and argon metastable densities perelastic collisions are neglected or included with (continuous lines) and without (dashed lines) superelastic collisions in the Boltzmann equation. in the Boltzmann equation. When superelas- tic collisions are considered in the electron ki- netics, some plateaux appear in the eedf [2, 3], which completely change the rates of electron induced processes. These rates depends not only on the electric field, but also on the level pop- ulation and on the plasma composition, affecting the time evolution of species densities. References [1] L. Pitchford et al.: Plasma chemistry round robin, GT1.00063, 70th Annual GEC, 2017. [2] G. Colonna, A. D’Angola (Ed), Plasma Modeling: Methods and Applications, IOP (2017) [3] M: Capitelli et. al, Fundamental Aspects of Plasma Chemical-Physics: Kinetics (2016)

Speaker: Gianpiero Colonna

12:10 O5.303 Waterless fracturing for shale gas/oil production using plasma blasting

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.303.pdf Waterless fracturing for shale gas/oil production using plasma blasting BongJu Lee1, Yongwook Shin1, Boahn Jang2, and Kangryul Hur3 1 Handong Global University, Pohang, Korea, 37554 2 Kangwon National University, Chuncheon, Korea, 24341 3 POSTECH, Pohang, Korea, 37673 When extremely high voltage electricity is applied to metal electrodes, electrical energy in an arc discharge is then dissipated through the medium around the electrodes in nanoseconds or microseconds. The sudden temperature in the zone immediately adjoining the electrode increase produces a gas/plasma bubble, which causes an explosive volume increase, which in turn generates a very strong shock and pressure wave to transport energy to wall– this is the phenomenon known as plasma blasting. We have developed a plasma blasting fracking method that uses a liquid hydrocarbon (LHC) instead of water as the medium for transporting energy and registered into an US patent. The pressure of this shockwave reaches up to 3,500 bar with the 60% energy of hydraulic fracturing, and propagates through the medium of the wellbore and makes a crack in the shale layer. As a result, it is possible to collect shale gas using less than 10% of the LHC used by the existing LHC fracturing method. We believe that its method is able to save drilling cost because of lower viscosity and density of LHC compared to water, which results in the longer effective fracture length than that of hydraulic fracturing. This technology can minimize energy usage and substantially reduce the amount of potentially dangerous fluids being used; these results in advantages such as reducing costs, more effective production, minimizing the environmental impact, and preventing the depletion of water resources. We have obtained below results in a laboratory and will show them. 1. A wall of wellbore was kept while plasma blasting 2. Cracks by the plasma blasting showed the similar shape and direction with ones by the hydraulic fracturing 3. When the discharge plasma energy is increased, both main cracks and sub cracks with differences in extensity were observed 4. Multiple blasting experiments showed the extension of cracks, namely possible to have the desired effective fracturing lengths 5. Verified that proppants can be transported into cracks 6. Computer simulation to perform the parametric study for a plasma blasting

Speaker: Bong Ju Lee

12:25 O5.304 Simulation of electron interactions with liquid water and processes related to sub-nanosecond electrical breakdown

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.304.pdf Simulation of electron interactions with liquid water and processes related to sub-nanosecond electrical breakdown P. Bílek1 , M. Šimek2 , T. Hoder1 , Z. Bonaventura1 1 Department of Physical Electronics, Faculty of Science, Masaryk University, Brno, Czechia 2 Department of Pulse Plasma Systems, Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic Initiation of electric discharge in dielectric liquids such as water can be caused either by formation of gaseous bubbles (when the system is driven by high-voltage waveforms of mi- crosecond duration) or due to creation of cavitation voids in case of very-steep high-voltage pulses with sub-nanosecond rise times. Presence of these deformations prolong mean-free path of electrons, which can then gain enough energy for excitation/ionization/dissociation of water molecules. We propose to use Geant4-DNA [1, 2] toolkit for studies of elementary processes related to interaction of accelerated electrons with liquid water. The Geant4-DNA provides a complete set of models describing the step-by-step physical electromagnetic interactions of electrons with liquid water. These models describe both the cross sections and the final states of the physical interactions, with a full description of the interaction products, taking into account the molecular structure of liquid water. Geant4-DNA electron models for the calculation of ion- ization and excitation cross sections are based on the Emfietzoglou model [3] of the dielectric function of liquid water. The dielectric function approach is currently the state-of-the-art tech- nique for modeling the energy-loss of low-energy electrons in the condensed phase [4]. The aim of our work will be to study elementary processes related to interaction of electrons with liquid water. Basic parameters such as stopping distance and electron bremsstrahlung spectra will be determined for given voltage pulse conditions and confronted with experimental data aquired in point-plane electrode geometry [5, 6]. This research has been supported by the Czech Science Foundation research project 18-04676S. References [1] M.A. Bernal, M.C. Bordage, J.M.C. Brown, M. Davídková, E. Delage, Z. El Bitar, S.A. Enger, Z. Francis, S. Guatelli, V.N. Ivanchenko and others, Physica Medica: European Journal of Medical Physics 31, 8 (2015) [2] S. Incerti, A. Ivanchenko, M. Karamitros, A. Mantero, P. Moretto, H.N. Tran, B. Mascialino, C. Champion, V.N. Ivanchenko, M.A. Bernal and others, Medical physics 37, 9 (2005) [3] D. Emfietzoglou Radiat. Phys. Chem., 66, 373 (2003). [4] Emfietzoglou et al., Int. J. Radiat. Biol., 88, 22 (2012). [5] M. Šimek, B. Pongrác, M. Člupek, V. Babický and P. Lukeš, Book of Contributed Papers of 15th International Symposium on High Pressure Low Temperature Plasma Chemistry (HAKONE XV) p. 405-407 (2016) [6] M. Šimek, B. Pongrác, V. Babický, M. Člupek and P. Lukeš, Plasma Sources Science and Technology 26, 7 (2017).

Speaker: Petr Bilek

10:40 → 12:40 MCF

Chair: G. Ericsson

Convener: G. Ericsson

10:40 I5.119 Simulation and analysis of fast ion dynamics in a JT-60SA tokamak plasma subject to pressure- and current-driven instabilities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.119.pdf Simulation and analysis of fast ion dynamics in a JT-60SA tokamak plasma subject to pressure- and current-driven instabilities A. Bierwage, N. Aiba, A. Matsuyama, K. Shinohara, M. Yagi National Institutes for Quantum and Radiological Science and Technology (QST), Rokkasho Fusion Institute and Naka Fusion Institute, Japan The resistive MHD-PIC hybrid code MEGA has recently been used to study the ramp-up phase of a high-β plasma in the JT-60SA tokamak as predicted by integrated simulations [1]. Here, we analyze the effects of MHD and fast-ion-driven instabilities observed in the MEGA simulations. The fast ions originate from powerful negative-ion-based neutral beams (N-NB), which are deposited off-axis and have energies up to 500 keV. Effects of E × B drifts and magnetic perturbations with long wavelengths (low toroidal mode numbers n < 5) are examined. We report new results on the behavior of fast ions in the presence of reconnecting instabilities, whose magnetic perturbations evolve slowly compared to the fast ion motion. This was moti- vated by the possibility that off-axis N-NB injection in JT-60SA may produce nonmonotonic current and pressure profiles, whose gradients may destabilize multiple kink-tearing modes and cause minor internal disruptions. When such reconnecting instabilities develop in our simula- tions, we observe a flattening in the density profiles across the inner half of the plasma, both in the bulk and the fast ion components. When the underlying dynamics are examined using orbit- based resonance analysis combined with Poincarè maps, one can see that the flattening of the fast ion density profile cannot be explained with the formation and growth of magnetic islands, which influence only particles that closely follow magnetic lines of force. In contrast, in the case of fast particles that are subject to significant magnetic drifts — such as our energetic beam ions during current ramp-up [1], or relativistic electrons [2] — the radial redistribution is connected with the formation of resonant islands in canonical toroidal angular momentum space. These orbit islands have different existence conditions and, when projected into real space, they can be located in a different region of the plasma than the magnetic islands. The insights won in this study may be used for the development of reduced models that will allow to incorporate the effects of MHD activity into integrated codes. The ability to simulate the complex interplay of processes such as MHD activity, fast ion transport, current drive, torque and heating using integrated codes is necessary for shedding light on feedback loops that may exist on multiple spatio-temporal scales, and for reliably predicting their effects in experiments. [1] Bierwage et al., Plasma Phys. Control. Fusion 59 (2017) 125008. [2] de Rover et al., Phys. Plasmas 3 (1996) 4468; Matsuyama et al., Nucl. Fusion 54 (2014) 123007.

Speaker: Andreas Bierwage

11:10 I5.120 Fast-ion edge resonant transport layer induced by externally applied 3D fields in the ASDEX upgrade tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.120.pdf Fast-Ion Edge Resonant Transport Layer Induced by Externally Applied 3D Fields in the ASDEX Upgrade Tokamak L. Sanchis1*, M. Garcia-Munoz1, A. Snicker2, J. Galdon-Quiroga1, D. A. Ryan3, M. Nocente4, J. F. Rivero-Rodriguez1, L. Chen5, F. Zonca5,6,W. Suttrop7, E. Viezzer1, M. A. Van Zeeland8, D. Zarzoso9, ASDEX Upgrade and EUROfusion MST1§ Teams 1 Dept. of Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, 41012, Spain; 2Dept. of Applied Physics, Aalto University, FI- 00076, Aalto, Finland; 3CCFE, Culham Science Centre, OX14 3DB, Abingdon, UK; 4Universita degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126, Milano, Italy; 5IFTS, Zhejiang University, 310027, Hangzhou, China; 6ENEA C. R,. 65-00044, Frascati, Italy; 7Max Planck Institut für Plasmaphysik, Boltzmannstrasse 2, 85748, Garching, Germany; 8General Atomics, CA 92186-5608, San Diego, USA; 9Laboratoire PIIM, Aix-Marseille Université, France *Email: lsanchis@us.es Externally applied 3D fields are routinely used in present tokamaks to mitigate or even suppress ELMs [1]. Symmetry breaking 3D fields can, however, cause significant fast- ion losses threatening the integrity of future large devices. The impact of externally applied 3D fields on the ELM stability depends strongly on the poloidal spectra of the applied perturbative fields [2]. Recent experiments in the ASDEX Upgrade tokamak have revealed the existence of an Edge Resonant Transport Layer (ERTL) responsible for the fast-ion losses observed in the presence of externally applied 3D fields. The amplitude and velocity-space distribution of the measured fast-ion losses depends on the 3D field poloidal spectrum, the magnetic background helicity (q95) and the plasma collisionality. 100 Full orbit simulations carried out with the ωpol/ωtor ERTL 1.11 1.2 1.37 1.425 90 2 1.55 2.25 1.6 ASCOT code using the plasma response 2 80 calculated with MARS-F reproduce a strong 1 (a.u.) 70 correlation of fast-ion losses with the 3D fields’ E (keV) 1.11 1.425 1.37 60 0 poloidal spectra showing also that toroidal 1.55 1.6 2.25 2 50 sideband harmonics can modify significantly the −1 40 overall fast-ion losses. The plasma response can 1.711 30 ASCOT reduce or amplify the resonant fast-ion transport. −2 1. 1.3 2.25 1.55 #33143 Δφ =40º UL Separatrix Externally applied 3D fields induce a variation in 1.95 2 2.05 2.1 2.15 the particle toroidal canonical momentum (δPφ) Fig 1. structuresRin(m) the presence of a Δϕ =40º UL that is maximized around the separatrix due to magnetic perturbation configuration overlapped with the overlapping of a large number of linear and matching orbital resonances (ω /ω ). Black-blue pol tor areas represent outwards transport while yellow-white nonlinear resonances between the perturbative means inwards transport. fields and the particle orbital frequencies. Figure 1 shows the fast-ion as a function of particle energy and initial position in the presence of an externally applied 3D field caused by the ELM mitigation coils in AUG with a differential phase between the upper and the lower set of coils of ΔϕUL=40º. The fast-ion ERTL depends strongly on the particle pitch-angle, but not significantly on the particle energy suggesting that similar resonances may also exist for thermal ions and thus shedding some light on the physics underlying the thermal density pump-out commonly observed with externally applied 3D fields. The implications of the results presented here for the fast-ion confinement in ITER with externally applied 3D fields will be discussed. [1] T. E. Evans et al, Nature Physics, 2 419 (2006) [2] R. Nazikian et al, Physical Review Letters, 114 105002 (2015) § H.Meyer et al, Nucl. Fusion 57 102014 (2017)

Speaker: Lucía Sanchis-Sanchez

11:40 O5.101 Collective Thomson Scattering on Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.101.pdf Collective Thomson Scattering on Wendelstein 7-X I. Abramovic1,2, D. Moseev2, M. Salewski3, M. Stejner3, A. Pavone2, T. Stange2, F. Leipold3, S. Nielsen3, J. Svensson2, N. J. Lopes Cardozo1, H. P. Laqua2, R. C. Wolf2, and W7-X Team 1 Eindhoven University of Technology, Eindhoven, The Netherlands 2 Max-Planck-Institute for Plasma Physics, Greifswald, Germany 3 Technical University of Denmark, Kgs. Lyngby, Denmark Wendelstein 7-X (W7-X), the World's first so-called "optimized" stellarator, came into operation in 2016. The experiment is set out to show that the optimization has led to a fusion device with a confinement at least as good as in its competitor the tokamak. Plasma diagnostics play a crucial role in this endeavor. Here we present the work on the theory of an important diagnostic, collective Thomson scattering (CTS), which has been successfully brought into operation in the last experimental campaign [1]. CTS is a powerful microwave diagnostic, capable of measuring a number of plasma parameters such as: ion temperature, plasma composition, drift velocities, and fast ion population. The scattering is collective when the wavelength of the incident radiation os comparable to the Debye length. The incident radiation interacts with the fluctuations in the plasma and gives rise to a scattered wave which is picked up by a heterodyne receiver. What is finally obtained is a spectrum typically centered at the frequency of the incident wave. Spectra have been obtained from which the temperature is inferred by the use of a purpose-built forward model (eCTS) [2] and a Bayesian framework (Minerva) [3] which enables the inference of the parameter values from the data [4]. The forward model is further developed to enable the measurement of the radial electric field. We present the novel developments of the theory which were necessary in order to accommodate the inference of this parameter from the measured spectra. The theory is extended to non-axisymmetric plasmas and the results of a feasibility study of radial electric field measurements by CTS are presented. References [1] M. Stejner, et al., First collective Thomson scattering results from Wendelstein 7-X, talk EC20, (2018) [2] I. Abramovic, et al., Forward Modelling of Collective Thomson Scattering for Wendelstein 7-X Plasmas, submitted to CPC (2017) [3] J. Svensson, et al., Modelling of JET Diagnostics Using Bayesian Graphical Models, Contributions to Plasma Physics 51 (2-3) (2011) [4] I. Abramovic, et al., Collective Thomson scattering data analysis for Wendelstein 7 – X, JINST, (2017)

Speaker: Ivana Abramovic

11:55 O5.102 Losses of fusion products due to fishbones on JET and predictions for burning plasmas.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.102.pdf Losses of fusion products due to fishbones on JET and predictions for burning plasmas. M. Fitzgerald, J. Buchanan, S. E. Sharapov, V. G. Kiptily, M. Sertoli, G. Szepesi, J. Boom, R. Akers, D. King, and JET contributors* EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK Fishbones are ubiquitous in high performance JET plasma and are typically considered benign. However, in recent high-performance hybrid experiments, sporadic and explosive fishbones have been observed which correlate with decreases in performance and main chamber hotspots. Additionally, recent unambiguous measurements obtained with a 2D scintillator probe and fast acquisition show coherent losses of fusion product protons and tritons due to these explosive fishbones [1]. This is particularly of note due to the velocities of fusion products being much too large to resonate with the fishbone. Using careful MHD marker constrained EFIT reconstructions, we can show that the orbits of the lost fast fusion products are due to barely trapped/confined Figure 1: HALO predictions of TRANSP fusion product particles being ejected by the mode. Modelling numbers in equilibrium (left) and with the fishbone (right). Calculated losses are completely due to FLR the fishbone as a conventional n=1 MHD effects. internal kink oscillation we use HAGIS and the newly developed HALO (HAgis LOcust) code to confirm the non-resonant losses of fusion products. In the HAGIS drift calculations, the energy content of those losses is insufficient to explain the observed hotspots, however full-orbit HALO calculations show that a combination of magnetic-moment scattering, and wall proximity cause fishbones to produce a 25% loss of D-D fusion products at the experimentally observed location of the hotspot (Figure 1). A breakdown in magnetic moment conservation leads to a rapid diffusion in pitch-angle space. Extrapolations to JET DT and ITER will be presented that show the implications for alpha particle losses due to this previously neglected FLR mechanism for fishbone induced losses. Losses of this type on ITER are expected to be substantially less than 1% [1] V. G. Kiptily et al. Nucl. Fusion, vol. 58, no. 1, p. 14003, Jan. 2018. * See the author list of “X. Litaudon et al. 2017 Nucl. Fusion 57 102001”

Speaker: Michael Fitzgerald

12:10 O5.103 A quantitative comparison between confined fast ion data and models from radio frequency heating experiments with the three ion scenarios at JET

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.103.pdf A quantitative comparison between confined fast ion data and models from radio frequency heating experiments with the three ion scenarios at JET M. Nocente1, Ye. O. Kazakov2, V.G. Kiptily3, T. Craciunescu4, J. Eriksson5, L. Giacomelli1, G. Gorini1, C. Hellesen5, E. Lerche2, M. Mantsinen6, J. Ongena2, S. Sharapov3, M. Tardocchi1, D. Van Eester2 and JET Contributors* 1 Dipartimento di Fisica and Istituto di Fisica del Plasma, Milano, Italy 2 Laboratory for Plasma Physics, LPP-ERM/KMS, TEC Partner, Brussels, Belgium 3 Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, UK 4 National Institute for Laser, Plasma and Radiation Physics, Bucharest, Romania 5 Department of Physics, Uppsala University, Uppsala, Sweden 6 Barcelona Super Computing Centre and ICREA, Barcelona, Spain *See the author list of X. Litaudon et al 2017 Nucl. Fusion 57 102001 Electronic mail: massimo.nocente@mib.infn.it Ion cyclotron resonance heating (ICRH) by radio frequency waves is a commonly adopted tool to tailor the plasma discharge and boost the fusion performance. A recent breakthrough in this field has been the theoretical discovery [1] and subsequent experimental demonstration [2] that radio frequency power can be more efficiently absorbed by exploiting the favorable polarization properties of the wave electric field in vicinity of the left handed cut-off layer compared to conventional minority heating. This is possible in the so called 3 ion scenarios, where the plasma mixture is carefully adjusted so that two majority species, say hydrogen and deuterium, define the propagation properties of the wave, while a third species, at typical concentrations of few percents or less, absorbs the power with virtually 100% efficiency. Experiments at JET on the 3 ion scenarios have so far focused on D and 3He acceleration and have provided unambiguous qualitative evidence of the acceleration of fast ions to the MeV range. This ranges from the excitation of Alfvén eigenmodes to the observation of a rich gamma-ray emission from a variety of nuclear reactions between MeV range fast ions and 9Be impurities in the plasma (see figure 1). In this work, we present a quantitative study of confined fast ion data from 3 ion scenario experiments at JET and a comparison with predictions from advanced radio frequency codes that solve the wave propagation in the plasma and calculate the distribution function of the fast ions by means of a Monte Carlo kick operator. Synthetic diagnostics are used as means to bridge the gap between simulations of the fast ion phase space and indirect experimental data on the nuclear emission spectra from 3 ion plasmas. Although the enhancement of ICRH in the 3 ion scheme compared to minority heating is unambiguous, we find that data suggest mean fast ion energies which are significantly lower than predictions. Possible additional physics effects that might be needed to reconcile simulations and the experimental findings, such as the role of Alfven eigenmodes in effectively ejecting the most energetic ions or the super-adiabaticity of the fast ions as they get progressively accelerated by the wave electric field, are discussed. Figure 1. Gamma-ray spectrum from reactions between fast 3He ions and 9Be impurities in 3 ion ICRH experiments at JET. A detailed analysis of the complex gamma-ray spectrum born in these reactions resolves the individual contributions to the emission, which are used to determine the 3He ion energies for comparison with models. [1] Ye.O. Kazakov et al., Nucl. Fusion 55, 032001 (2015) [2] Ye.O. Kazakov et al., Nature Physics 13, 973 (2017)

Speaker: Massimo Nocente

12:25 O5.104 Component wise DT fusion yield extrapolation with neutron spectrometry

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/O5.104.pdf Component wise DT fusion yield extrapolation with neutron spectrometry A. Sahlberg1 , C. Hellesen1 , J. Eriksson1 , S. Conroy1 , G. Ericsson1 , L. Garzotti2 , D. King2 and JET Contributors∗ 1 Dept. of Physics and astronomy, Uppsala University, Sweden 2 CCFE, Culham Science Centre, Abingdon, Oxfordshire, UK As part of the preparation for ITER, a second Deuterium-Tritium campaign (DTE2) is planned at JET. To this end, methods for quickly and robustly predicting fusion yields of DT plasmas are sought. This paper investigates how neutron emission spectroscopy can predict equivalent DT fusion power of a deuterium discharge. The energy spectrum of the emitted neutrons has three major components (thermonuclear, beam-target, RF-target) which scale differently when going from a DD to a DT plasma. For each reaction component, a DD to DT scale-up factor can be calculated as the ratio between the DT and DD reaction rates. The scale-up factors depend on the cross sections, the energy distributions of the plasma ion species as well as the assumed fuel ion ratio nt /nd . From the component scale-up factors the total neutron rate scale-up factor can be calculated if the relative intensities of the neutron rate components are known. These can be estimated from the neutron energy spectrum, which is here measured with the time-of-flight spectrometer TO- FOR. The component scale-up factors are calculated using an ion temperature, either measured with charge exchange recombination spectroscopy or estimated from the neutron spectrum, along with a beam-ion distribution obtained from slowing down calculations. This method for identifying and separating the neutron reaction components and scaling them up from DD to DT has been applied to several JET pulses and compared to both earlier DT shots at JET (from the 1997 campaign DTE1) and DT extrapolations made with the transport codes JINTRAC and TRANSP. The comparisons with TRANSP fall within error bars while comparisons with JINTRAC differ by around 15-25%. The reason for this discrepancy is under investigation. Predicted DT fusion yields fall in line with comparable shots from DTE1. The current record baseline and hybrid discharges are both predicted to reach 6-7 MW of fusion power. The above results indicate that this method is useful for making quick and robust predictions for future DT pulses. ∗ See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001"

Speaker: Arne Sahlberg

12:40 → 14:00 LUNCH

14:00 → 16:00 POSTER SESSION

Mánes Exhibition Hall: MCF P5.1x, BSAP P5.4x
Mánes Multifunctional Hall: BPIF P5.2x, LTDP P5.3x

14:00 P5.1001 Development of Faraday-cup-based Fast Ion Loss Detector in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1001.pdf Development of Faraday-cup-based Fast Ion Loss Detector in Wendelstein 7-X K. Ogawa1, 2, M. Isobe1, 2, M. Osakabe1, 2, S. Bozhenkov3, S. Äkäslompolo3, C. Killer3, R. C. Wolf3, and the W7-X team 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 2 SOKENDAI (The Graduate University for Advanced Studies), Toki, Japan 3 Max-Planck-Institute for Plasma Physics, Greifswald, Germany A study on fast-ion losses due to magnetic field ripples and fast-ion-driven magnetohydrodynamic (MHD) modes is important in terms of view of research on fusion-born alpha losses in fusion devices. To understand fast-ion loss in Wendelstein 7-X (W7-X) plasmas, installation of fast-ion loss diagnostics for W7-X has been planned. For the Op1.2b campaign, the prototype Faraday-cup-based fast-ion loss detector (FILD) has been designed as joint cooperative project between National Institute for Fusion Science and Max Planck Institute for Plasma Physics. The Faraday-cup-based FILD is relatively cost-effective in construction compared with a scintillator-type FILD. The FILD is capable of providing the flux, pitch angle, and Larmor radius of escaping fast ions simultaneously, providing the clear understanding on fast-ion losses induced by MHD mode as well as non-axisymmetric magnetic field ripples. A Lorentz orbit code (LORBIT code and ASCOT code) has been used to find a position suitable for detection of escaping beam ions. It is found that the sufficient beam-ion flux on the head position of the multi-purpose manipulator (MPM) is expected. Therefore, we decided to install the prototype FILD head using the MPM. The detector is mainly composed of a molybdenum head having a set of two apertures restrict the orbits of fast ions that can enter the probe and eight Faraday films as a charge collector. The size and the position of those apertures are decided using the grid calculation program. Faraday film is a thin film of aluminum vapor deposited onto one side of the quartz substrate. The thickness of the films is approximately 0.2 μm. Electric current from each Faraday film will be carried to the low input impedance current amplifier (I-76, NF Corporation) and an isolation amplifier. The signal level of the FILD predicted by the ASCOT code is up to 0.5 μA, which is comparable with that of a FILD in the Compact Helical System (CHS).

Speaker: Kunihiro Ogawa

14:00 P5.1002 Edge density profile and turbulence measurements with an alkali beam diagnostic on Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1002.pdf Edge density profile and turbulence measurements with an alkali beam diagnostic on Wendelstein 7-X M. Vécsei1 , G. Anda1 , O. Asztalos2 , D. Dunai1 , S. Hegedűs1 , M. Otte3 , G. I. Pokol2 , B. Tál1 , S. Zoletnik1 and the W7-X team3 1 Department of Plasma Physics, Wigner Research Centre for Physics, Budapest, Hungary 2 Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest, Hungary 3 Max-Planck-Institute for Plasma Physics, Greifswald, Germany The Alkali Beam Emission Spectroscopy (A-BES) system is a recently installed diagnostic instrument at the Wendelstein 7-X stellarator. In comparison to the conventional Lithium-based BES (Li-BES) systems, the shorter lifetime of the relevant excited state of the Na atoms fa- cilitates a more localized analysis of the density profiles. This is a major advantage for the analysis of transport processes at the plasma edge, especially at the steep gradients expected at the banana-shaped cross section of the W7-X plasma. The diagnostic consists of a 60 keV Sodium atomic beam injector [1] which can provide about 1 mA ion equivalent neutral current in a ∼ 2 cm FWHM beam. The beam emission is observed from the poloidal direction with a high-etendue 40 channel optical system, where each channel collects light from a 4 × 0.5 cm (toroidal × radial) area of the beam. The light is detected by an Avalanche Photodiode (APD) system with 2 MHz sampling rate. Despite the 500 kHz analogue bandwidth the system has a peak signal-to-noise ratio up to 50, enabling the study of fast transients and turbulence. In addition to the CII background radiation, a considerable amount of light is also generated by Sodium gas originating from the beam neutraliser. The latter has a significant contribution to the detected light profiles inside the SOL. Resolving this necessitates the implementation of high-frequency modulation (chopping) of the atomic beam. A-BES has been operational since December, 2017. The experimental data have been utilized for the reconstruction of electron density profiles near the LCFS of the plasma. The results imply A-BES to be robust, even at a time resolution of a few 10µs. The detected light profiles show evidence for turbulent transport at the location of the beam. Notably, there is also a clear indication of the presence of a magnetic island, according to expectations. The results have been compared with the available experimental data of various plasma diagnostic tools. References [1] Anda, G., Dunai, D., Lampert, M., Krizsanóczi, T., et al., Review of Scientific Instruments, 89(1), 013503 (2018).

Speaker: Miklos Vecsei

14:00 P5.1003 Application of Doppler backscattering for Alfven mode investigation on the Globus-M tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1003.pdf Application of Doppler backscattering for Alfvén mode investigation on the Globus-M tokamak V.V. Bulanin1, V.K. Gusev2, G.S. Kurskiev2, V.B. Minaev2, M.I. Patrov2, A.V. Petrov1, M.A. Petrov1, Yu.V. Petrov2 N.V. Sakharov2, P.B. Shchegolev2, V.V. Solokha2, A.Yu. Telnova2, S.Yu. Tolstyakov2, A.Yu. Yashin1. 1 Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia 2 Ioffe Institute, St. Petersburg, Russia The Doppler backscattering method (DBS) was first employed as a tool for the investigation of Alfvén modes in the inner regions of a tokamak. The experiments were carried out on the spherical tokamak Globus-M in conditions where previously the toroidal Alfvén eigenmodes (TAE) were recorded using a Mirnov probe array [1]. The version of multifrequency DBS diagnostics was used to record simultaneously microwave backscattering on four major radii. Quadrature detection multifrequency scheme and the specifics of the use of the DBS method on the spherical tokamak under a large pitch angle and magnetic shear are described in detail in Ref. [2]. The cut-off positions of incident microwave radiation covered a range of normalized small radius from ρ = 0.5 to 0.75. The experiments were carried out in the deuterium plasma on Globus-M with NBI heating under the following discharge parameters: Ip = 250 kA, ne < 5×1019 m–3, and BT = 0.5 T. The Alfvén modes were manifested as oscillations of the poloidal plasma velocity, which was determined by the DBS diagnostics. The spectra of the velocity oscillations reproduce the magnetic-field fluctuation’s spectra with great accuracy. The most probable reason for the occurrence of the velocity oscillations is the ExB drift in the alternating electric field of the Alfvén wave. Based on this assumption, the absolute amplitudes of the radial electric field and the magnetic field of the Alfvén modes were estimated in the region of their existence. The multi-frequency DBS approach has made it possible to determine the areas of the development of Alfvén oscillations with different mode numbers. The data obtained in the experiment were used to identify the Alfvén modes in the Globus-M tokamak [3]. References: [1] Petrov Yu. V. et al. 2015 J. PLASMA PHYS 81 515810601 [2] Yashin A.Y. et al. 2015 JINST 10 P10023 [3] Petrov Yu. V. et al. 2018 this conference

Speaker: Viktor Bulanin

14:00 P5.1004 Characterization of MPPC coupled organic scintillator for RFP SXR spectra detection

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1004.pdf Characterization of MPPC coupled organic scintillator for RFP SXR spectra detection. A.Fassina, P.Franz Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy The detailed characterization of electron distribution function in RFPs is crucial in order to understand energy transfer between particle and magnetic field and to better understand the dynamo mechanism. SXR emission spectra is in principle able to return line-integrated informations on the electron energy distribution with a time resolution high enough (ms order) to discriminate different phases between Dynamo Reconnection Events (DRE); in order to do so, SXR detectors have to be operated in Pulse Height Analysis mode. This work present a characterization of organic scintillators coupled to MPPC (Multi Pixel Photon Counters) in terms of noise, energy cutoff, time response and recovery and linearity in an energy range of 1-10 keV. The scintillators (Scionix EL256) are manufactured in 3x3x50 mm rods with reflective coating, and they are coupled on the small side to a 1x1 and to a 3x3 mm Hamamatsu MPPC detector. The expected performances in the measurement of RFP plasma spectra in different plasma conditions is briefly discussed.

Speaker: Alessandro Fassina

14:00 P5.1005 Simulation and experimental test research on hydrogen/deuterium-α visible spectra diagnosis based on hL-2A tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1005.pdf Simulation and Experimental Test Research on Hydrogen/Deuterium-α Visible Spectra Diagnosis Based on HL-2A Tokamak J. Wu1, L.M.Yao1, P.Chen1, H.Wen1, M.T.Zou1, Y.J.Chen1, W.Zhang1, J.T.Shen1 1 School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China As a priority diagnosis in the tokamak fusion device, the hydrogen-α and visible spectroscopy could measure the distribution of impurities and hydrogen/deuterium densities in the divertor and scraping of layers. In the divertor and scraping layer area, firstly, because the divertor and the wall regions’ strong light reflection, directly and accurately measure the region of impurities (helium, carbon, tungsten, etc.) and hydrogen/deuterium distribution becomes difficult. Secondly, the strong magnetic field leads to the existence of Zeeman splitting in the visible spectrum of this region, and the magnetic field is different in edge locations, results in Zeeman splitting different. Based on this, the hydrogen-α and visible spectrum diagnosis system of HL-2A were established. The visible emission spectra were measured and fitted by simulation and experimental researches. The Zeeman Effect was used to distinguish the reflected light information at different positions, thereby accurately impurities, hydrogen/deuterium in the divertor and scraping layer could be obtained for spatial and temporal distribution. It is important to study the steady-state operation of the fusion device ITER and CFETR by measuring the correlation result under different experimental discharge conditions, carrying out the constraint mode conversion, the fuel cycle, the impurity and the plasma interaction researches. The author would thank Dr. Manfred for the discussion of the test work on JET and design work for the ITER using Zeeman paten to resolve the reflection light error on edge Dα diagnostics.

Speaker: Jing Wu

14:00 P5.1006 A new diagnostic on HL-2A tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1006.pdf Development and First Result of Phase Contrast Imaging Diagnostic on HL-2A tokamak Y.Yu1,M.Xu2,S.B.Gong1,2,L.Nie2,T.Lan1,R.Ke2,Y.F.Wu1,2,B.D.Yuan1,2,D.Guo2,T.Long2,H. J.Wang1,S.F.Mao1,M.Y.Ye1,X.R.Duan2 and HL-2A team 1 School of Physics, University of Science and Technology of China, 230026, Hefei, China 2 Southwestern Institute of Physics, P. O. Box 432, 610041, Chengdu, China We report the development of Phase Contrast Imaging (PCI) diagnostic on HL-2A tokamak, together with first experimental results. This diagnostic is to measure the phase shift of a CO2 laser probe when it passes through plasma. This system is designed to diagnose plasma density fluctuations with the maximum wavenumber of 15 cm-1. The designed wavenumber resolution is 2cm-1, and the time resolution can reach 0.2 μs. The broad kρs ranges from 0.2 to 3. The signal series in different PCI channels show a pronounced modulation of incident laser beam by the sound wave. The conversion relationship between the chord integral plasma density fluctuation and the signal intensity is 2.3×1013 m-2/mV, indicating a high sensitivity. First experimental results show the ability for turbulence investigation.

Speaker: Yi Yu

14:00 P5.1007 A new diagnostic on EAST tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1007.pdf Design of Ultra-fast Charge eXchange Recombination Spectroscopy diagnostic on EAST tokamak M.Y.Ye1, Yi Yu1, Yinyin Li2, Shifeng Mao1, Bo Lyu2 1 School of Physics, University of Science and Technology of China, 230026, Hefei, China 2 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China A four-testing-channel Ultra-Fast Charge eXchange Recombination Spectroscopy (UF-CXRS) diagnostic is under developing on the EAST tokamak and a 128-channel upgraded one will be combined with the existing 128-channel Beam Emission Spectroscopy to diagnose plasma pressure. This diagnostic is based on the active charge exchange to measure ion temperature with a time resolution at the order of 1 μs and a spatial resolution of 1 cm. The main component design and selection together with simulations and test results are presented in this report. The theoretical estimation of the emission photon flux which can reach the detector of UF-CXRS system has been carried out, proving the feasibility of the whole design.

Speaker: Mingyou Ye

14:00 P5.1008 Development of webcam-based near-infrared thermography in support of high temperature heat pipe experiments on Magnum PSI

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1008.pdf Development of webcam-based near-infrared thermography in support of high temperature heat pipe experiments on Magnum PSI S. A. Silburn1, G. F. Matthews1, T. W. Morgan2, R. E. Nygren3, and the Magnum PSI Team2 1 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 2 DIFFER, De Zaale 20, 5612 AJ Eindhoven, Netherlands 3 Sandia National Laboratories, Albuquerque NM 87185, USA Recent experiments on Magnum-PSI exposed a lithium-filled heat pipe to a hydrogen plasma beam to demonstrate the potential of radiatively cooled, high temperature heat pipes as Figure 1: Temperature image of a heat pipe (side view) under plasma load modular, replaceable in Magnum-PSI, obtained with webcam-based thermography. The plasma beam is impinging horizontally from the right of the image. plasma facing components. Monitoring the temperature distribution over the full 20cm length of the pipe was a crucial element of the experiment, requiring wide field-of-view infrared thermography diagnostics able to operate in the confined space and high magnetic field in the bore of the Magnum-PSI superconducting magnet. Here we present the development of a near-infrared (NIR) thermography system based on commercial high-resolution webcams (1920x1080 pixels) for this purpose. By removing the webcams’ internal NIR blocking filter and replacing it with an external bandpass filter of λ = 1.07µm, FWHM = 10nm, the cameras are sensitive for thermography over the temperature range ~500 - 1900℃ (for emissivity ε = 0.4). The voice coil motor auto-focus mechanism was removed from the webcams to enable operation in high magnetic fields, which was successfully demonstrated at up to 1T. A laboratory black body source was used for absolute calibration, after characterisation of the camera response curve shape in visible light. Python software for low frequency data acquisition (~1.25Hz) has been developed and provides live calibrated images, temperature plotting and the ability to issue simple temperature-based alarm signals over a serial port for overheating protection. Two of these cameras were used in the Magnum PSI heat pipe experiments, with an example image from one camera shown in figure 1. We will present details of the diagnostic development; calibration & data analysis methods, and example results from this experiment.

Speaker: Scott Alan Silburn

14:00 P5.1011 Effects of misaligning the probe beam and magnetic field in Doppler backscattering measurements

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1011.pdf Effects of misaligning the probe beam and magnetic field in Doppler backscattering measurements V.H. Chen1,2 , F.I. Parra1,2 , J.C. Hillesheim2 1 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3NP, UK 2 CCFE, Culham Science Centre, Abingdon OX14 3DB, UK. The Doppler Backscattering (DBS) microwave diagnostic enables the non-perturbative char- acterisation of density fluctuations (1 . k⊥ ρi . 10) and flows, both at the edge and the core of the plasma. The large magnetic pitch angle (up to 35◦ , compared to 15◦ in standard tokamaks like JET) and the time-varying magnetic equilibrium make the use of DBS in spherical toka- maks challenging. Due to spatial variation, it is not possible to simultaneously achieve align- ment between the probe beam and electric field for all launch frequencies. This misalignment, which affects the backscattered signal, can be empirically optimised with 2D beam steering [1]. However, empirical optimisation is inefficient, requiring repeated pulses with different diag- nostic settings, and may not always be possible. Hence, it is important to develop a model to quantitatively account for the effect of the misalignment on the backscattered signal, avoiding the need to optimise empirically. We used beam tracing [2] and the reciprocity theorem to derive an analytic model for the backscattered power and its dependence on the mismatch angle. Unlike previous work on reci- procity [3], our model works for both the O-mode and X-mode in tokamak geometry. Our more general model can be implemented numerically, allowing the misalignment of DBS measure- ments to be accounted for. The results are compared to scans of the toroidal launch angle from MAST data. With insight from our model, we also assessed the measurement capabilities for the planned MAST-U DBS system. Acknowledgements This work has been funded by the RCUK Energy Programme [grant number EP/P012450/1]. In order to obtain further information on the data and models underlying this work, please contact PublicationsManager@ukaea.uk. V.H. Chen’s DPhil is funded by a National Science Scholarship from A*STAR, Singapore. References [1] J.C. Hillesheim, N.A. Crocker, W.A. Peebles, H. Meyer, A. Meakins, A.R. Field, D. Dunai, M. Carr, N. Hawkes, and MAST Team, Nuclear Fusion 55 (7), 073024 (2015) [2] E. Poli, A.G. Peeters, and G.V. Pereverzev, Computer Physics Communications 136 (1-2), 90-104 (2001). [3] E.Z. Gusakov, and A.V. Surkov, Plasma Physics and Controlled Fusion, 46 (7), 1143 (2004).

Speaker: Valerian Hongjie Chen

14:00 P5.1012 Effects of magnetic topology on axisymmetric divertors

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1012.pdf Effects of magnetic topology on axisymmetric divertors Halima Ali1, Alkesh Punjabi1, and Allen Boozer2 1 Hampton University, Hampton, VA 23668, USA 2 Columbia University, New York, NY 10227, USA The effects of the magnetic topology on the size and structure of points of intersection of magnetic flux tubes is studied. Two distinct magnetic topologies are investigated: the open- unbounded and the closed-compact. Open-unbounded magnetic topology is generically represented by the simple map [A. Punjabi, A. Verma, and A. Boozer, Phys. Rev. Lett. 69, 3322 (1992)] and the closed-compact topology represented by the symmetric quartic map [M. Jones et al, Phys. Plasmas 16, 042511 (2009)]. Identical magnetic perturbation is applied in both topologies and field lines are given an artificial radial spiraling velocity. How the loss time, the size, and the structure of the intersection points scale with the spiraling velocity is studied and compared for both topologies; and from this comparison the effects of topology on the axisymmetric divertor are evaluated. This work is supported by the US DOE grants DE-FG02-01ER54624 and DE-FG02-04ER54793 to Hampton University. This research used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-05CH11231.

Speaker: Halima Ali

14:00 P5.1013 On the effects of kinetic minority ions on transport in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1013.pdf On the effects of kinetic minority ions on transport in Wendelstein 7-X F. Schluck1 , M. Rack1 , D. Reiter1 , and Y. Feng2 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Max-Planck-Institute für Plasmaphysik, 17491 Greifswald / 85748 Garching, Germany Three-dimensional transport modeling in the plasma edge region and in divertors is chal- lenged, amongst others, by the typical hybrid kinetic–fluid character of multi-phase flows. In most of the current edge plasma codes all ion components are typically described in a fluid approximation. However, particularly for minority components, the life span of some of these ions compared to local collisional relaxation times can be too short to meet the fluid constraint. The three-dimensional edge transport code package EMC3-EIRENE [1,2] provides a unique hybrid fluid–kinetic solution approach within a single, largely monolithic Monte-Carlo descrip- tion. Hence, it is particularly well suited for an integrated hybrid treatment of the various neutral and minority ion components in a (fluid) bath of electrons and main ions. Recent results [3] have already highlighted significant ballistic effects when treating He+ ions kinetically, in He–He+ –He2+ edge plasma conditions typical for early limiter Wendelstein 7-X helium discharges. For the investigated conditions it turned out that the primary source of singly charged helium is ionization of He, rather than recombination of He2+ . This is distinct from approximations made in earlier 2D edge plasma simulations in which all He ion charge states were treated with continuum approximations and strong mutual coupling assumptions (e.g. a common temperature for all ion components). We extend the rudimentary kinetic ion treatment within EIRENE with important features, e.g. drift effects and pitch-angle scattering. With this enhancement, we revisit previous investi- gations on helium operation in Wendelstein 7-X, as well as expand the impurity species study with hydrogenic and carbon ions. Although we presently focus on stellarator physics, the ex- panded kinetic ion transport strongly coupled to the neutral gas component can analogously be applied to tokamak studies. We draw conclusions on transport features, and plasma profiles and give an outlook on how the full three-dimensional EMC3-EIRENE code package is being further developed into a useful and predictive tool for impurity studies for ITER. References [1] Y. Feng, et al., Journal of Nuclear Materials 266-269, 812-818 (1999) [2] D. Reiter, et al., Journal of Nuclear Materials 220, 987-992 (1995) [3] M. Rack, et al., Nuclear Fusion 57, 056011 (2017)

Speaker: Friedrich Schluck

14:00 P5.1014 Neutral sampling vs. particle-identity conservation in a coupled fluid-kinetic Monte-Carlo code environment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1014.pdf Neutral sampling vs. particle-identity conservation in a coupled fluid-kinetic Monte-Carlo code environment M. Rack1 , D. Reiter1 , Y. Feng2 and H. Frerichs3 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany 2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald / 85748 Garching, Germany 3 Department of Engineering Physics, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Since early 1990s the magnetic confined fusion community utilises coupled code environ- ments for a self-consistent description of plasma flow and neutral gas transport in the edge region of toroidal fusion devices [1]. Usually, the plasma is treated with a fluid approach and the neutral gas transport requires a kinetic consideration. In two dimensions the plasma solu- tion is often calculated with implicit discretization schemes (cf. B2, EDGE2D, SOLEDGE-2D), whereas the neutral gas distribution is acquired via a Monte-Carlo technique to solve the lin- earized Boltzmann equation (cf. EIRENE, Degas 2). Consequently, the origin of neutrals is sampled from a distribution which adds numerical noise to the simulation result. Especially in large divertor tokamak geometries, noise effects are difficult to separate from physically driven instabilities [2]. Therefore, various noise cancellation techniques such as “correlated sampling” have been implemented to overcome this problem [3]. In contrast, plasma solutions for three-dimensional geometries are usually calculated based on a diffusion-advection Monte-Carlo technique that solves the fluid equation after transforma- tion to Fokker-Planck form (cf. EMC3 [4]). This can be understood as a particle-like treatment of fluid parcels in the transport code. In other words, the particle-identity can be conserved in the interface between the fluid and kinetic code. In the code package used here (EMC3-EIRENE), neutral sampling is the default option; however, particle-identity conservation may bring an ad- vantage to the numerical stability. Internally, EMC3 already uses a very strict particle-identity conserving scheme, which is one reason for the strength of EMC3 compared to other approaches for three-dimensional fluid solvers. In this contribution, we describe the currently developed particle-identity conserving interface and compare it to the sampling approach. References [1] D. Reiter. Journal of Nuclear Materials, 196-198, 80 (1992). [2] V. Kotov. Physics of Plasmas, 24 (4), 042511 (2017). [3] D. Stotler et al. Contributions to Plasma Physics, 40 (3-4), 221 (2000). [4] Y. Feng et al. Journal of Nuclear Materials, 266-269, 812 (1999).

Speaker: Michael Rack

14:00 P5.1015 Speed-up of SOLPS-ITER code for tokamak edge modeling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1015.pdf Speed-up of SOLPS-ITER code for tokamak edge modeling E. Kaveeva1, V. Rozhansky1, I. Senichenkov1, I. Veselova1, S. Voskoboynikov1, X. Bonnin2, D. Coster3 1 Peter the Great St.Petersburg Polytechnic University, St.Petersburg, Russia 2 ITER Organization, St Paul Lez Durance Cedex, France 3 Max-Planck Institut für Plasmaphysik, EURATOM Association, Garching, Germany Understanding of edge plasma performance and divertor exhaust is crucial for operation of ITER and other tokamaks. Traditionally this is done by transport codes like SOLPS and others, based on Braginskii model for parallel transport, experimentally based description of anomalous transport and Monte-Carlo model for neutral transport. In the early versions of SOLPS self-consistent electric fields, drifts and currents were ignored. These effects were introduced into the version which is known as SOLPS5.0 [1]. The physics of the edge plasma with drifts is treated much better by the new version, however one has to pay price by slower convergence of the code. Later modifications - SOLPS5.2 [2] and its upgrade by the ITER Organization to form a new package, SOLPS-ITER [3] still exhibit slow convergence. Account of drifts and currents dramatically decreases the accessible time step for the integration of time dependent equations of the code. Running the code with sophisticated EIRENE Monte-Carlo model for neutrals and large number of fluid equations for multiple ion species makes the computation time unacceptably long. In the present paper the mechanisms leading to the time step limitations in SOLPS-ITER are analyzed as well as the ways to relax these limitations. The numerical instability driven by drifts is associated with poloidal redistribution of particles inside the separatrix by ExB drift in combination with modification of the radial electric field by diamagnetic currents. It can be overcome by implementation of one of two algorithms. The first method uses artificial slowing down of poloidal density and temperatures redistribution. In the second method equations are modified to get faster convergence to a solution close to the true one, which then is used as an initial approximation for convergence to the true solution. Application of these schemes decreases the time of convergence for a steady state solution by more than an order of magnitude. Ways to improve convergence by introducing artificial particle sources and artificial rise of time derivatives are also suggested. [1] Rozhansky V. et al., Nucl. Fusion 41 (2001) 387 [2] Rozhansky et al., Nucl. Fusion 49 (2009) 025007 [3] S. Wiesen et al., J. Nucl. Mater.463 (2015) 480

Speaker: Elizaveta Kaveeva

14:00 P5.1016 Potential formation in front of a floating, planar, electron emitting electrode studied by particle in cell simulations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1016.pdf Potential formation in front of a floating, planar, electron emitting electrode studied by particle in cell simulations T. Gyergyek1,2, J. Kovačič2, J. P. Gunn3, I. Gomez2, M. Mozetič2 1 University of Ljubljana, Faculty of electrical engineering, Ljubljana, Slovenia 2 Jožef Stefan Institute, Ljubljana, Slovenia 3 CEA, IRM, F-13108 Saint-Paul-Lez-Durance, France The study of electron emitting surfaces is of great importance for plasma physics. Understanding the potential formation in front of an electron emitting solid surface in contact with a plasma is important for various applications – from emissive probes to implications in the field of fusion. For instance the divertor in ITER is expected to reach such high temperatures that it could become strongly emissive [1]. In this work potential formation in front of a planar, floating, electron emitting electrode is investigated using a 1d3v particle in cell code BIT1 [2]. Plasma is created by volume ionization in the entire space between two planar electrodes. The right electrode is at zero (reference) potential, while the left electrode is floating and emits electrons. It is assumed that the flux of emitted electrons is a given quantity. This corresponds to Richardson emission from a hot metal electrode. The distribution function of the emitted electrons is assumed to be a drifting Maxwellian. Effects of drift velocity, temperature and flux of emitted electrons on the potential profile are studied. As those three parameters are varied transitions between monotonic, space charge limited and inverted sheath [3] are observed. The drift velocity of emitted electrons turns out to be a rather important parameter. References 1) J. P. Gunn et al, Nucl. Fusion, 57, 046025 (2017). 2) D. Tskhakaya and R. Schneider, J. Comp. Phys. 225, 829 (2007). 3) M. D. Campanell, Phys. Rev E, 88, 033103 (2013). Acknowledgements This work has been partially supported by the grant P2-0073 of the Slovenian research agency and partially by the grant BI-FR/CEA/17-19-002.

Speaker: Tomaz Gyergyek

14:00 P5.1017 Advanced homogenization techniques in a tokamak plasma medium with ellipsoidal blobs: Mathematical treatment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1017.pdf Advanced homogenization techniques in a tokamak plasma medium with ellipsoidal blobs: Mathematical treatment F.Bairaktaris1 , K. Hizanidis1 , P.Papagiannis1 , A.K.Ram2 1 National Technical University of Athens, Athens, Greece 2 Massachussets Institute of Technology, Boston,MA, USA Homogenization of a dielectric mixture is not a new concept, as it dates back to 1996 [1] for plasma mediums. All previous models that have been made have significant limitations. The most basic existing model ignores the shape of the blobs [1], while the more advanced ones fall short of correct predictions if the wavelength of the incoming beam is not much greater than the radius of the insert dielectric. We present a new formalism, tailored for magnetized plasmas which makes use of quantities that are known under Fourier transformations, such as Green’s function and electric fields. This leads to a valid equation for any wavelength and blob (insert) size, which will need no modification if the filling ratio exceeds 50% (current formalisms need to invert the definitions of ambient plasma medium and blob in order to be valid). Finally, the equation can in turn be integrated in the Fourier space and then solved numerically to give the components of the dielectric tensor of the composite plasma medium. Results are only dependent upon (but not limited by) blob size, and there are no restrictions on wavelength magnitude. References [1] A. Sihvola, Homogenization of a dielectric mixture with anisotropic spheres in anisotropic background , Lund University (1996) [2] T.G Mackay, A. Lakhtakia, Modern analytical electromagnetic homogenization, Morgan & Claypool Pub- lishers (2015)

Speaker: Fotis Bairaktaris

14:00 P5.1018 VUV spectroscopy measurements on WEST first plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1018.pdf VUV spectroscopy measurements on WEST first plasmas C. Desgranges1, R. Guirlet1 ,O. Meyer1, J.L. Schwob2, S. Vartanian1 and the WEST team 1 CEA, IRFM, 13108 St-Paul-Lez-Durance, France 2 Racah Institute of Physics, The Hebrew University, 91904 Jerusalem, Israel The WEST machine aims at testing actively cooled full W monoblock Plasma Facing Units under long plasma discharge, with thermal loads of the same magnitude as those expected for ITER. For the first operation phase, copper plasma facing components were directly tungsten coated and carbonaceous components were coated with a molybdenum sublayer covered by a tungsten layer. Ten seconds stable L-mode X-point plasma discharges were routinely performed, including up to 2.5 MW LHCD. During the first plasmas, some runaway electron control issues were the cause of plasma contamination by wall material. The VUV spectroscopy measurements characterising this contamination are reported in this paper. WEST as well as Tore Supra, is equipped with two VUV spectrometers providing plasma impurity measurements. To perform tungsten spectroscopy measurements, various spectral ranges were selected. The spectral feature around 5 nm wavelength has been observed and allowed to show that the tungsten content increased on a pulse-to-pulse basis correlated with the LHCD power ramp-up. It showed also that in the same phase of the campaign, the core electron temperature was increased from 300 eV to more than 2 keV (as confirmed by the ECE electron temperature measurements). Operational limitations due to the tungsten content increase were also observed in some occasions and induced a modification of the plasma control strategy. Higher tungsten ionization stages (W38+-W45+) have been observed in the 11.5-15.5 nm wavelength range consistently with AUG observations [1] In the same time, in view of a more effective impurity monitoring, a thorough line identification of the VUV spectra has been performed: Copper and Molybdenum line brightnesses have been identified and studied by comparing them with the sources deduced from the visible spectroscopy diagnostics. Copper is correlated with the LH power while Molybdenum is due to runaway electron damages on tungsten coated plasma facing components. The latter cause might explain also why carbon, which was completely absent from the spectra at the beginning, appeared later in the campaign. [1] T. Pütterich et al. 2008 Plasma Phys. Control. Fusion 50 085016

Speaker: C. Desgranges

14:00 P5.1019 Sheath modelling for IShTAR ICRF antenna

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1019.pdf Sheath modelling for IShTAR ICRF antenna M. Usoltceva1,2,3,*, R. Ochoukov2, W. Tierens2, K. Crombé1,4, A. Kostic1,2, S. Heuraux3, E. Faudot3, J-M. Noterdaeme1,2 and the IShTAR team 1 Department of Applied Physics, Gent University, 9000 Gent, Belgium 2 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 3 Université de Lorraine, 54506 Vandœuvre-lès-Nancy, France 4 LPP-ERM-KMS, TEC partner, 1000 Brussels, Belgium Plasma heating with Ion Cyclotron Range of Frequency (ICRF) waves is one of the crucial systems of hot plasma devices. It is important to not only increase the effectivity of such a system, but to avoid destructive effects on plasma and plasma facing components. Among those effects it is known that in the proximity of the antenna limiters increased DC potentials are formed, causing particle and heat loads to rise significantly during the ICRF system operation. A study of the relevant sheath physics is performed on a dedicated linear device IShTAR [1] in conditions similar to the tokamak SOL. A combined experimental-numerical method is used to obtain the DC plasma potentials in the SOL plasma near the limiters of the IShTAR ICRF antenna. The experimental part consists of 3D magnetic field mapping in a broad region in front of the antenna. An array of B-dot probes on a movable manipulator is used to measure components of the RF magnetic field. The resulting experimental field map is compared to calculations performed in COMSOL software to validate the accuracy of the model. The COMSOL model includes precise geometrical representation of the experimental device. The parallel electric field in the region in front of the antenna between the antenna limiters, which is hard to be measured experimentally, is calculated in the COMSOL model. The plasma is simulated as a material with numerically assigned cold dielectric tensor. Fast and slow components of the wave are decoupled and studied separately. SSWICH-SW [2] is used as a final step of the procedure to obtain the rectified potentials on the limiters from the input parallel electric field from the COMSOL IShTAR model. A density profile in the SOL region is measured in the argon plasma discharge on IShTAR. The calculated DC potential can be compared to experimental measurements and can be studied for different plasma parameters and ICRF antenna regimes. [1] K. Crombé et al., 26th IAEA Fusion Energy Conference (2016) [2] L. Colas et al., Phys. Plasmas 19, 092505 (2012)

Speaker: Mariia Usoltceva

14:00 P5.1020 Dynamics of detachment in TCV with N2 seeding and flux expansion

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1020.pdf Dynamics of detachment in TCV with N2 seeding and flux expansion O. Février1, C. Theiler1, C. K. Tsui3,1, K. Verhaegh2,1, J.A. Boedo3, B. Duval1, B. Labit1, B. Lipschultz2, R. Maurizio1, H. Reimerdes1, the TCV Teama and the EUROfusion MST1 Teamb 1 EPFL-SPC, CH-1015 Lausanne, Switzerland, 2 York Plasma Institute, University of York, Heslington, York, YO10 5DQ, UK, 3 University of California-San Diego, La Jolla, California 92093, USA As the operation of future devices will require target heat fluxes of less than 10-20 MW/m2, finding ways of dissipating the power is a critical issue. This can be achieved by operating in a detached regime where a drop of the target ion flux is attributed to the onset of parallel momentum losses. To further understand this process in the TCV open divertor, we investigate detachment in a lower single-null X-Divertor geometry in range of flux expansions of 2 to 20, approaching detachment through nitrogen seeding at fixed integrated core density (25% or 45% of the Greenwald limit) or integrated core density ramps (from 30% to about 70% of the Greenwald limit) in L–Mode plasmas. We particularly focus on the relation between the roll-over of the target ion flux, the development of a parallel pressure gradient along the divertor leg and the evolution of the upstream profiles. The plasma profiles at the outboard midplane reveal a saturation, and eventually a roll-over of the upstream pressure. In the density ramp experiments, the development of a pressure drop of about 70% between the outer midplane and the target, as measured by a fast reciprocating probe and a set of wall-embedded Langmuir probes, is well-correlated with the roll-over of the target ion flux, indicating a possible role of parallel momentum losses. Preliminary analysis of the evolution of the pressure drop for N2 seeded discharges indicates a much weaker pressure drop than in the density ramp experiments. The above results will be interpreted using an extended two-point model with momentum and radiation losses and a one-dimensional fluid model. We will also present the first results of detachment experiments in TCV double-null configurations that aim to investigate a possible role of coupling between inner and outer legs in the detachment process. a See the author list of S. Coda et al, 2017 Nucl. Fusion 57 102011 b See the author list of H. Meyer et al 2017 Nucl. Fusion 57 102014

Speaker: Olivier Février

14:00 P5.1021 Understanding tungsten divertor sourcing, SOL transport, and its impact on core impurity accumulation in DIII-D high performance discharges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1021.pdf Understanding tungsten divertor sourcing, SOL transport, and its impact on core impurity accumulation in DIII-D high performance discharges * D.M. Thomas1, T. Abrams1, J. Barton2, J.A. Boedo3, A.R. Briesemeister4, D. Buchenhauer2, I. Bykov3, C.P. Chrobak1, R. Ding5, D. Donovan6, J.D. Elder7, B.A. Grierson8, H.Y Guo1, J. Guterl4, E.M Hollmann3, C.J. Lasnier9, A.W. Leonard1, M.A. Makowski9, A.G. McLean9, R. Nygren2, T.W. Petrie1, D.L. Rudakov3, P.C. Stangeby7, E.A. Unterberg4, B. Victor9, W.R. Wampler2, H.Q. Wang4, J.G. Watkins2, M. Zach4 1 General Atomics, General Atomics, San Diego, CA, USA 2 Sandia National Laboratory, Albuquerque, NM, USA 3 University of California San Diego, San Diego, CA, USA 4 Oak Ridge National Laboratory, Oak Ridge, TN, USA 5 Oak Ridge Associated Universities, Oak Ridge, TN, USA 6 University of Tennessee, Knoxville, TN, USA 7 University of Toronto, Toronto, ON, Canada 8 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 9 Lawrence Livermore National Laboratory, Livermore, CA, USA The DIII-D metal rings campaign demonstrated the ability to run high performance plasmas with tungsten at the outer divertor strike point and provided detailed information on W sourcing and transport from the divertor in a mixed material environment. Using two isotopically distinct toroidal rings of W-coated metal inserts, advanced tokamak (AT) discharges (PAUX=14 MW, H98 =1.5-1.6, βN =3.6-3.7) show performance similar to all-C divertor discharges, with low core W concentrations (few 10-5) for the case of central ECH and rapid ELMs (fELM~200 Hz). W impurities transported to the midplane, measured by collector probes inserted in the far SOL, predominantly originate from the outer strike point (OSP) region rather than from a W source positioned in the far SOL. Conversely, for discharges with larger, less frequent ELMs (fELM~60 Hz) the W impurities are shown to transport equally from the OSP and far-SOL regions. Direct measurement of gross W sputtering shows peak source rates during Type-I ELMs of 1-2x10E16 /cm2/s, many times the inter-ELM rate (1-2x 10E15 /cm2/s). Detailed analysis shows that C impurity and D fuel ions contribute equally to W divertor sourcing during ELMs, in contrast to the JET-ILW where D ions are the main contributor, or to the inter-ELM case on DIII-D where C dominates the W sputtering. In addition, ELM-resolved measurements of W sourcing for differing BT directions reveal the peak W erosion rate during large ELMs shifts radially due to a combination of drift effects and ELM wetted area. For L-mode experiments, OEDGE modeling suggests that measured asymmetries in the collected W may be explained by a W buildup in the SOL at the crown of the plasma, driven by the parallel grad-Ti force. __________________________ * This work was performed in part under the auspices of the U.S. Department of Energy by General Atomics under DE-FC02-04ER54698, DE-FG02-07ER54917, DE-AC05-00OR22725, DE-AC04-94AL85000, DE-AC02- 09CH11466, DE-AC52-07N27344, and DE-AC05-00OR23100.

Speaker: Dan M. Thomas

14:00 P5.1022 Experimental study of sheath heat transmission factors by thermocouples and triple probe in DiPS-2

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1022.pdf Experimental study of sheath heat transmission factors by thermocouples and triple probe in DiPS-2 S.J. Jeong1, M.-K. Bae1, I.J. Kang1, H.T. Oh1, I.S. Park1, S.H. Lee1, K.-S. Chung1 1 Department of Electrical Engineering, Hanyang University, Seoul, South of Korea Accurate prediction of heat flux is important because the lifetime of fusion reactor could be determined by the damage of various PFC’s due to the high heat flux. The measurement of heat flux relies on determination of sheath heat transmission factor ( 𝛾𝑠 ). Besides infrared measurement, thermocouple have provided reliable data for heat flux measurements [1, 2]. Plasma was generated in a linear device, called Divertor Plasma Simulator-2 (DiPS-2), with the following conditions: plasma density (ne) ~ 1017 cm-3 and electron temperature (Te) ~ 1 - 15 eV with argon, where plasma is flowing into a chamber, called DiSC (Dust interaction with Surfaces Chamber). Thermocouples and a triple probe were used to measure the heat flux toward the tungsten target in DiSC, which was operated with discharge current = 10 – 40 A, plasma density (ne) ~ 1016 – 1017 cm-3 and electron temperature (Te) ~ 1 – 15 eV. Based upon a simple sheath theory, a theoretical sheath heat transmission coefficient can be estimated as approximately 6-7 in pure argon plasma [3, 4]. To deduce the sheath heat transmission factor experimentally, three thermocouples were embedded directly into the tungsten target with thickness of 20 mm. Each thermocouple is located at 18 mm, 13 mm, and 3 mm from target surface, respectively. Theoretical heat flux estimated at DiSC center is about 30.76 kW/m2. Heat flux have been deduced by thermocouples in utilizing a simple heat conduction equation, 𝑞𝑇𝐶 = −𝑘(𝑇1 − 𝑇0 )/(𝑥1 − 𝑥0 ) , where T, 𝑥 are thermocouple temperature and position of thermocouple. Triple probe measured the electron temperature and ion saturation current. From these measurements, sheath heat transmission factor is obtained from 𝛾𝑠 = 𝑞𝑇𝐶 ⁄𝑘𝑇𝑒 Γ . Experimental values of sheath heat transmission factors in argon plasma have been compared with theoretical values. To expand the case of pure plasma to the impure plasma, we have generated He + Ar/N2 plasmas. By varying the pressure ratio of additional gas (Ar, N2), effect of impurity in sheath heat transmission factor was also investigated. [1] H. Matssura et al, Contrib. Plasma Phys. 54 (2014) 285. [2] D. Donovan et al, J. Nucl. Mater. 438 (2013) S467. [3] S. Marsen et al, J. Nucl. Mater. 438 (2013) S393. [4] J. Marki et al, J. Nucl. Mater. 363 (2007) 382.

Speaker: Seo Jin Jeong

14:00 P5.1023 Particles simulations of RMP fields effects in the COMPASS tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1023.pdf Particles simulations of RMP fields effects in the COMPASS tokamak F. Jaulmes1, S.Y.F. Cats2, T. Markovic1, E. Westerhof2, H.J. de Blank2, J. Urban1, and the COMPASS team 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 FOM-DIFFER Dutch Institute For Fundamental Energy Research, Eindhoven, The Netherlands The use of Resonant Magnetic Perturbation (RMP) coils has extensively been demonstrated as an experimental technique for mitigating or suppressing large edge localized modes (ELMs) in a number of tokamaks. In this work, we introduce a newly developed extension of the EBdyna_go code (introduced in [1]) that was designed to resolve the full-orbit of charged particles, in a collisionless manner. The new version of the code allows to study motions in the 3D perturbed fields generated by RMPs. The model has been applied on the COMPASS tokamak, comparing it with its extensive RMP campaign experimental database [2]. We took advantage of the diagnostics of the tokamak in order to assess the experimental effect of the RMP on the overall edge plasma conditions (density, temperature, current and rotation) and on the ELM activity. Detailed integrated transport modelling with the METIS code [3] has been used so that the latest experimental data can be wrapped up by self-consistent simulations and the pedestal data can be used in the RMP modelling described in this contribution. Our analysis focuses on comparing the effect on the particle transport and losses of the vacuum solution (using a Biot-Savart solver) and of a more elaborate solution that includes the plasma response to the perturbed field, calculated with the resistive MHD code MARS- F [4]. We present insights on the effect of the RMPs on the induced change on the pedestal momentum, the pedestal temperature as well as the impurity content in the edge region. [1] - Jaulmes F., Westerhof E. and de Blank H.J. 2014 Nucl. Fusion 54 104013 [2] - Markovic T. et al 2016 Nucl. Fusion 56 092010 [3] - Artaud J.F. et al. 2010 Nucl. Fusion 50, 043001 [4] – Liu Y., et al. 2000 Phys. Plasmas 7, 3681

Speaker: Fabien Jaulmes

14:00 P5.1024 Ground state population of sputtered tungsten atoms by peak emission analysis in PSI-2 argon plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1024.pdf Ground state population of sputtered tungsten atoms by peak emission analysis in PSI-2 argon plasmas S. Ertmer1 , O. Marchuk1 , A. Pospieszczyk1 , A. Kreter1 , S. Brezinsek1 1 Forschungszentrum Jülich GmbH - Institut für Energie- und Klimaforschung - Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany Tungsten (W) is one of the most promising materials for plasma-facing components (PFCs) in future fusion reactor [1]. The lifetime of W divertor PFCs will finally be determined by the erosion. The initial level population of sputtered W atoms from PFCs is of big interested for interpretation of spectroscopic data used for the estimation of gross erosion rates. Monoener- getic ion beam experiments with different metals (e.g. Fe) suggest a ground level population of released atoms of over 95 % [2] - Sputtering experiments in the tokamak TEXTOR with W PFCs exposed to a hot edge plasma (Te > 30 eV) lead to the assumption of a local thermal equi- librium in the fivefold ground term 5 D and the 7 D3 level with an effective temperature TW of 0.1 to 0.3 eV of physically sputtered W atoms by energetic Carbon ions at surface temperatu- res (Tsurf ) of more than 720 K [3]. To investigate the level population in more detail, we exposed a W sample (1.3×1.3 cm2 ; Tsurf = 300 K) to an argon plasma in the linear plasma device PSI-2 (Te ≈ 2 eV). We measu- red with an imaging spectrometer the line emission of several neutral tungsten (W I) transitions with a high spatial resolution of 50 µm over the first few mm penetration depth in front of the target. The axial distance of the peak of emission d x from target surface is approximately proportional to the velocity of the sputtered atoms vatom times the lifetime of the upper energy level τ [4]. This lifetime is equal to the reciprocal sum of the Einstein coefficients A and vatom is transfered due to the ion collisions during sputtering to the sputtered atoms. The axial peak position of the investigated ground state transition at 498.26 nm (7 F1 →5 D0 ) is consistent with the expected velocity and the Einstein coefficient. Whereas the lines at 484.38 nm and 424.43 nm, whose upper levels are not mainly fed by the 5 D0 level, peak further away from the target than expected. This experimental data shows that W is sputtered primarily in the ground level by a monoenergetic Ar ion beam for an impact energies between 100 and 200 eV, if the W sample is at room temperature. The other levels of the ground term are in this experi- mental condition populated subsequently of the plasma. References [1] S. Brezinsek et al. J. Nucl. Mater. 55 (2015) 063021 [2] A. P. Yalin et al. Applied optics 44 (2005) 6496 [3] I Beigman et al. Plasma Phys. Control. Fusion 49 (2007) 1833 [4] O. Marchuk et al. J. Phys. B: At. Mol. Opt. Phys 51 (2018) 025702

Speaker: Stephan Ertmer

14:00 P5.1025 Type-I ELM energy density measurements in the COMPASS divertor using a new system of probes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1025.pdf Type-I ELM energy density measurements in the COMPASS divertor using a new system of probes J. Adamek1, J. Seidl1, J. Horacek1, M. Komm1, T. Eich2, R. Panek1, J. Cavalier1,3, A. Devitre4, M. Peterka1, P. Vondracek1,5, J. Stöckel1, D. Sestak1, O. Grover1,6, P. Bilkova1, P. Böhm1, J. Varju1, A. Havranek1,7, V. Weinzettl1, J. Lovell8,9, M. Dimitrova1, K. Mitosinkova1,5, R. Dejarnac1, M. Hron1, The COMPASS Team1 and The EUROfusion MST1 Team10 1 Institute of Plasma Physics of the CAS, Prague, Czech Republic 2 Max-Planck-Institut für Plasmaphysik, Garching, Germany 3 Institut Jean Lamour IJL, Université de Lorraine, Vandoeuvre-lčs-Nancy, France 4 Faculté des sciences et techniques, Université de Lorraine, Vandoeuvre-lès-Nancy, France 5 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 6 Faculty of Nuclear Physics and Engineering, Czech Technical University in Prague, Prague, Czech Republic 7 Faculty of Electrical Engineering, Czech Technical University in Prague, Prague, Czech Republic 8 Department of Physics, Durham University, Durham,United Kingdom 9 Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, Oxon, United Kingdom 10 See the author list of Meyer H. et al 2017 Nucl. Fusion 57 102014 A new system of probes [1] was recently installed in the divertor of the COMPASS tokamak in order to investigate the electron temperature Te and the parallel heat flux q|| with high spatial and temporal resolution. The set of probes, with spatial resolution ~3.5 mm, consists of two arrays of rooftop-shaped Langmuir probes (LPs) used to measure the floating potential and the ion saturation current density and one array of ball-pen probes (BPPs) used to measure the plasma potential. The floating BPPs and LPs yield the electron temperature Te [2]. In combination with ion saturation current measurements from LPs we also obtain the parallel heat flux q|| with microsecond temporal resolution. The ELM energy density || is calculated as the integral of the parallel heat flux over the duration of a single ELM event. The Type-I ELM energy density was studied during a set of NBI-assisted ELMy H-mode discharges. The resulting peak values of || in the range of 10-40 kJ/m2 [1] are in good agreement with the predictions of model [3] and experimental data from JET, AUG and MAST [3]. [1] J. Adamek et al. Nucl. Fusion 57 (2017) 116017. [2] J. Adamek et al. Rev. Sci. Instrum. 87 (2016) 043510. [3] T. Eich et al. Nuclear Materials and Energy 12 (2017) 84–90.

Speaker: Jiri Adamek

14:00 P5.1026 Gyrofluid simulations of tokamak edge plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1026.pdf Gyrofluid Simulations of Tokamak Edge Plasmas A. Dempsey1 , H. Leggate1 , M. M. Turner1 1 Dublin City University, Dublin 9, Ireland Filaments are field aligned structures that are known to form in the scrape-off-layer (SOL) in tokamaks. These structures are composed of hot electrons and ions. They can constitute a non- negligible thermal and particle flux on the first wall. As such the propagation of these structures to the first wall is problematic. All unnecessary heat loading of structural components must be avoided to prolong the lifetime of a fusion device. In order to arrive at an optimal design for a next-generation machine it is advantageous to predict wall fluxes so that thermal loading and tritium retention can be modelled. One approach to predicting such fluxes in plasmas is to rely on simulation. However depending on which kinetic equation, closure and approximations are used some physics can be lost. For instance, finite Larmor radius effects are often lost. The approach described herein is to use a gyrofluid model. Gyrofluid models incorporate higher order finite Larmor radius effects more naturally that other fluid models. The gyrofluid model used in this study is briefly introduced [1] and initial progress towards solving it using BOUT++ [2] is presented. The focus of this simulation is on filament dynamics as modified by finite Larmor radius (FLR) effects. Of particular interest are filament-background interactions and filament propagation near the SOL. Figure 1: Filament density plots exhibiting typical radial propagation. References [1] Bruce Scott and Juri Smirnov, “Energetic consistency and momentum conservation in the gyrokinetic descrip- tion of tokamak plasmas”, Physics of Plasmas, vol. 17, no. 11, aug 2010. [2] B. D. Dudson, M. V. Umansky, X. Q. Xu, P. B. Snyder, and H. R. Wilson, “BOUT++: A framework for parallel plasma fluid simulations”, Computer Physics Communications, vol. 180, no. 9, pp. 1467–1480, 2009. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement No 633053 The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Speaker: Adam Dempsey

14:00 P5.1027 Edge plasma conditioning comparison between He/H discharges on W7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1027.pdf Edge plasma conditioning comparison between He/H discharges on W7-X E.H. Wang1, S. Brezinsek1, Y.L. Wei2, M. Krychowiak3, O. Ford3, K. Hammond3, L. Rudischhauser3, V. Winters4, Y. Liang1, S. Sereda1, O. Neubauer1, and W7-X team3 1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), Jülich, Germany 2 Southwestern Institute of Physics, Chengdu, China 3 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 4 University of Wisconsin-Madison, Madison WI, USA Edge plasma conditioning is one of the key issues for achieving high performance plasmas in fusion devices. The processes occurring on the wall, properties of plasma edge and the main plasmas has a strong nonlinear connection. The interaction of the edge plasma with the plasma facing components (PFCs) is determined by plasma density, temperature, flows, power fluxes and neutral fluxes. Physical and chemical sputtering is the main process in the plasma-wall interaction [1]. The gross erosion rates owing to physical and chemical sputtering processes have been investigated extensively by optical emission spectroscopy on TEXTOR [2], ASDEX-Upgrade [3], JET [4], and DIII-D [5]. Wendelstein 7-X (W7-X) is a large superconducting stellarator, which has an island divertor system for particle and energy exhaust. In W7-X operation phase 1.2a (OP1.2a), ten test divertor units (TDU) made of graphite without water cooling have been installed. The main heating method is electron cyclotron resonance heating (ECRH) with maximum input power 8.5MW. In order to study the divertor plasma conditioning, one Czerny-Turner spectrometer with high spectral resolution has been installed, which has 25 fiber input on I port and K port, respectively. Here, we report on the initial studies of edge plasma conditioning comparison between He/H discharges on divertor region. The fraction of chemical and physical sputtering at divertor plates as well as the dissociation chain of released hydrocarbons under typical edge plasma conditions has been studied. Comparison of carbon source and transport characteristics in divertor plasma in He/H discharges has been reported. References [1] G. Federici, et al., Nucl. Fusion 41 (2001) 1967-2137 [2] S. Brezinsek, et al., J. Nucl. Mat. 363-365 (2007) 1119-1128 [3] M. Zarrabian, et al., Physica Scripta. T91 (2001) 43-47 [4] S. Brezinsek, et al., J. Nucl. Mat. 337-339 (2005) 1058-1063 [5] R. C. Isler, et al., Phys. Plasmas 8 (2001) 4470-4482

Speaker: Erhui Wang

14:00 P5.1028 Role of the radiation opacity in divertor plasma detachment

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1028.pdf Role of the radiation opacity in divertor plasma detachment A.A. Pshenov1,2, A.S. Kukushkin1,2, S.I. Krasheninnikov3, E.D. Marenkov2 1 NRC “Kurchatov Institute”, Moscow, Russian Federation 2 National Research Nuclear University MEPhI, Moscow, Russian Federation 3 University of California San Diego, San Diego, USA Transition to the detached divertor regime that allows lowering the peak heat loads to the divertor targets in an ITER size tokamak-reactor to the tolerable level of 5-10 MW/m2 [1] is closely connected to the onset of the volumetric recombination process [2], which in turn requires low temperature Te ~ 1 eV and high density ne ~ 1021 m-3. Plasma in such conditions is opaque to the Lyman lines of the hydrogen isotopes [3] and radiation transport becomes an important part of the problem [4]. Radiation trapping results in both a reduction of the hydrogen “ionization cost” and a noticeable anisotropy of the heat fluxes associated with the photon transport inside the hydrogen recycling region [5]. Moreover, changes in the excited level populations modify the hydrogen ionization/recombination rates significantly and can even impose a stiff relation between the neutral and ion densities if the local thermal equilibrium (LTE) is reached. Almost all studies conducted with 2D edge plasma transport codes presume that the edge plasma is fully transparent for the line radiation of both hydrogen and impurities. Self-consistent modelling of radiation trapping and its influence on the plasma parameters have been performed once in [6] for ITER divertor plasma with fixed power entering the scrape-off layer. It was shown that in spite of the significant changes in the divertor plasma profiles, the control parameters (such as the peak heat loads, the neutral pressure in the divertor, the impurity concentration at the separatrix, etc.) remain largely unaffected. (At least in the interval of the neutral pressure inside the divertor volume studied in this paper.) This, along with the extreme computational demands for such a self-consisted radiation transport treatment, served as an “excuse” to neglect radiation transport in further studies. Therefore, up to now, no in-depth study of the influence that the hydrogen line radiation opacity may have on divertor plasma detachment has been reported. In this work we test the radiation transport block of the SOLPS code package [6] by comparing its results with the exact 1D slab solution of the Biberman-Holstein equation [7]. We study also the divertor plasma detachment process for a DIII-D-sized tokamak for two limiting cases of the plasma fully transparent and completely opaque for the Lyman lines of hydrogen by self-consistent modeling that accounts for hydrogen line radiation transport. We analyze the impact of the opacity on the divertor plasma parameters, on the global detachment threshold (i.e. the rollover of the total plasma flux to the divertor targets) and on transition to detachment inside specific flux tubes. References 1. Loarte A. et al., Nucl. Fusion 47 (2007) S203–S263. 2. Krasheninnikov S.I. et al., Phys. Plasmas 23 (2016) 055602. 3. Terry J.L. et al., Phys. Plasmas 5 (1998) 1759–1766. 4. Reiter D. et al., J. Nucl. Mater. 313-316 (2003) 845–851. 5. Marenkov E. et al., Contrib. to Plasma Phys. (2018) currently in press 6. Kotov V. et al., Contrib. to Plasma Phys. 46 (2006) 635–642. 7. Sdvizhenskii P.A. et al., Contrib. to Plasma Phys. 56 (2016) 669–674.

Speaker: Andrey Alekseevich Pshenov

14:00 P5.1029 Enhancement of Helium Exhaust During Application of Resonant Magnetic Perturbation Fields at DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1029.pdf Enhancement of Helium Exhaust During Application of Resonant Magnetic Perturbation Fields at DIII-D* E. Hinson1, H. Frerichs1, O. Schmitz1, G. McKee1, Z. Yan1, C. Collins2, C. Paz-Soldan2, M. Wade2, T.E. Evans2, T. Abrams2, D. Thomas2, B. C. Lyons2, B. Grierson3, I. Bykov4, R.A. Moyer4, E.A. Unterberg5 1 University of Wisconsin-Madison, Madison, United States 2 General Atomics, San Diego, United States 3 Princeton Plasma Physics Laboratory, Princeton, United States 4 University of California at San Diego, San Diego, United States 5 Oak Ridge National Laboratory, Oak Ridge, United States Resonant magnetic perturbation (RMP) fields used to suppress Edge Localized Modes (ELMs) in high confinement (H-mode) tokamak plasmas are found to lead to strong enhancement of global helium exhaust, as measured by the effective He particle confinement time τp*He, in recent experiments at DIII-D. In ELM-suppressed H-modes, τp*He was reduced by 40% compared to unsuppressed discharges, and τp*He/τE where τE is energy confinement time, was reduced by between 10-20%. These first-time findings are important for ITER, where application of RMP fields is planned for ELM control, as they suggest RMP fields can replace the impurity exhaust produced by the ELM events. Improved helium exhaust was obtained for ITER-shaped plasmas at DIII-D using argon frosted divertor cryo-panels for active pumping of He injected in short test pulses into a deuterium plasma. A multiple-reservoir particle balance model was used for analysis of the experimental data. In both the plasma edge and core reservoirs, midplane He density measurements from charge-exchange spectroscopy show reduced magnitudes and faster decay times during ELM suppression, suggesting faster outward transport and/or reduced He back-fueling after recycling. Increased He-I and He-II emission in the Scrape-off Layer (SOL) and increased neutral He pressure in the pumping plenum show that more He is retained in the SOL and neutral reservoirs, which is important for effective removal of He from the entire plasma. EMC3-EIRENE fluid plasma edge and kinetic neutral transport modeling of comparable scenarios, in addition to the experimental measurements, suggests two mechanisms behind the beneficial enhancement of helium exhaust. First, reduced parallel temperature gradients due to magnetic field stochastization in the vicinity of the separatrix can increase the friction force acting on impurities relative to the thermal force, which enhances outward transport in the region of the perturbed magnetic field. Second, the evolution of helical lobes, which connect the separatrix region to the divertor via a helical magnetic footprint, yields increased He neutral pressure due to increased divertor plasma plugging. Both effects are being analyzed with dedicated EMC3-EIRENE modeling including plasma response from M3D-C1 extended MHD code, which defines the level of magnetic field stochastization at the separatrix. *Work supported by US DOE DE-FC02-04ER54698, DE-SC0013911, DE-FG02-07ER54917, DE- AC52-07NA27344, DE-AC05-06OR23100, DE-AC05-00OR22725, DE-AC04-94AL85000, DE- AC02-09CH11466

Speaker: Edward Thomas Hinson

14:00 P5.1030 L-mode heat flux scaling at tokamaks JET, EAST and COMPASS at vertical and horizontal divertors

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1030.pdf L-mode heat flux scaling at tokamaks JET, EAST and COMPASS at vertical and horizontal divertors J. Horacek1 , J. Adamek1 , J. Seidl1 , P. Vondracek1,2 , M. Komm1 , K. Jirakova1 , R. Panek1 , Ch. Guillemaut3 , A. Jardin4,5 , G. Deng6,7,8 , X. Gao6,7 , L. Wang6,7,9 , R. Ding6 , G. Matthews10 , M.E.F.M. Mostafa11 , K.M. Camacho12 , MST1 Contributors and JET Contributors∗ 1 Institute of Plasma Physics of the CAS, Za Slovankou 3, Prague, 18000, Czech Republic 2 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 3 Instituto de Plasmas e Fusao Nuclear, IST, Universidade Lisboa, Portugal 4 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 5 Institute of Nuclear Physics, Polish Academy of Sciences, PL-31-342, Krakow, Poland 6 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China 7 University of Science and Technology of China, Hefei 230026, China 8 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA 9 School of Physics and Optoelectronic Technology, Dalian University of Technology, China 10 Culham Centre for Fusion Energy, Culham Science Centre, Abingdon, OX14 3DB, UK 11 University of Carlos III Madrid, Leganes, Spain 12 Universite de Lorraine, Nancy, France ∗ See the author list of X. Litaudon et al 2017 Nucl. Fusion 57 102001 Established scalings of divertor target power decay length are based on infra-red thermog- raphy (IR) which cannot access the JET vertical targets. This paper presents experiments in tokamaks JET, EAST and COMPASS, aiming at enlarging the span in scaling parameters and in case of JET for configurations with the strike points at ITER-relevant location - the vertical divertor targets. We analyzed hundreds of Langmuir+ball-pen probe divertor profiles, described omp principally by the plasma radial decay length 1 mm< λq <15 mm. The data set contains omp L-mode, 2.5< q95 <8, 1.7< ne [1019 m−3 ] <9 and plasma current 0.15< Ip [MA] <3. λq with errors below 50% are only taken into account; especially some of the JET inner target profiles are removed due to magnetic shadowing. Cross-checking with IR camera shows difference, however, within the error bars. Previously published scaling seems consistent with those new divertor probe data from JET, COMPASS and EAST at both bottom horizontal and outer verti- cal targets. This is probably because the edge plasma density is nearby the inner/outer divertor symmetry point. We look for a new scaling taking into account all these aspects.

Speaker: Jan Horacek

14:00 P5.1031 Geodesic Acoustic Mode Driven by Energetic Particles with bump-on-tail distribution

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1031.pdf Geodesic Acoustic Mode Driven by Energetic Particles with bump-on-tail distribution Haijun Ren1 and Hao Wang2 1 CAS Key Laboratory of Geospace Environment and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, P. R. China 2 National Institute for Fusion Science, Toki 509-5292, Japan Energetic-particle-driven geodesic acoustic mode (EGAM) is analytically investigated by adopting the bump-on-tail distribution for energetic particles (EPs), which is created by the fact that the charge exchange time (τcx ) is sufficiently shorter than the slowing down time (τsl ). The equilibrium distribution of EPs is proportional to (E 3/2 + Ec )τs −1 , where E is the kinetic 3/2 energy of EPs and Ec is the critical one. For τs = 0, the distribution is reduced to the slowing- down model. The dispersion relation is derived in the use of gyro-kinetic equations. The ratio of critical energy kHz 70 Ec to the inertial energy E0 is generally considered 60 to be less than unit for theoretical study, while in 50 Frequency 40 Growth rate the realistic experiments or relative simulation, the 30 Frequency (MEGA) Growth rate (MEGA) = 20.4/3 ratio can be up to 0.35, leading to remarkable ef- 20 s 10 fects. Similar to the slowing-down model, there are 0 three branches of EGAM. We concentrate only on 0.0 0.2 0.4 0.6 the unstable branch. Following relative simulation and experimental work, we specifically considered Figure 1: The real frequency (solid curve) two cases: τsl /τcx = 3.4 and τsl /τcx = 20.4. The and growth rate (dashed one) versus the pitch pitch angle is shown to significantly enhance the angle for τs = 20.4/3. The density ratio εh = growth rate and meanwhile, the real frequency is 0.3 is adopted. The major radius R0 = 3.9m dramatically decreased with increasing pitch angle. is used as done in the simulation [1]. In the The excitation of high-frequency EGAM is found, right part, the MEGA simulation dates are and this is consistent with both the experiment and cited from Fig. 10 in Ref. [1]. the simulation. References [1] H. Wang et al, Phys. Plasmas 22, 092507 (2015). [2] G. Fu, Phys. Rev. Letts. 101, 185002 (2018). [3] N. Winsor, J. L. Johnson and J. M. Dawson, Phys. Fluids 11, 2448 (1968).

Speaker: Haijun Ren

14:00 P5.1032 Kink Mode Study in EAST High βP Plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1032.pdf Kink Mode Study in EAST High 𝜷𝑷 Plasma Liqing Xu, Yi Yuan, Wei Shen and Liqun Hu Institute of plasma physics, CAS (ASIPP) Two types of kink modes, fishbone and long-lived mode are experimentally and numerically studied at EAST tokamak. In high 𝛽$ plasma, sawtooth instability was replaced by a saturated 1/1 internal kink mode which either manifests itself as a periodical burst energetic ion related fishbone or as a long-lived mode which is associated to the core safety factor at 𝑞& ~1. The present of those1/1 internal modes are beneficial to the sustainment of hybrid scenario with extended regions of low-magnetic shear profile and 𝑞& ~1, because of that they can expel high- Z impurity and can make flux pumping. The mechanism responsible for the flux pumping caused by kink mode was numerically in nonlinear 3D magnetohydrodynamic simulations using the M3D code. Furthermore, M3D+K code hybrid simulation shows a good agreement to the fishbone activity in EAST. Sawtooth crash replaced by 1/1 dominated helical mode and bursting of many toroidal harmonics (n=2 to n=7) in hybrid scenario are also confirmed by M3D simulation. Figure 1. Long-lived mode in EAST low-magnetic shear profile and q& ~1 hybrid plasma.

Speaker: Liqing Xu

14:00 P5.1033 Tearing mode seeding by externally provided resonant magnetic perturbations in the presence of Neoclassical Toroidal Viscosity

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1033.pdf Tearing mode seeding by externally provided resonant magnetic perturbations in the presence of Neoclassical Toroidal Viscosity D. Meshcheriakov1 , M. Hoelzl1 , V. Igochine1 , S. Fietz1 , V. Bandaru1 , F. Orain2 , S. Günter1 , H. Zohm1, ASDEX Upgrade Team and MST1 Team∗ 1 Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching b. M., Germany 2 Centre de Physique Théorique, Ecole Polytechnique, CNRS, F-91128 Palaiseau Cedex, France ∗ See author list of MST1 Team in H. Meyer et al, Nucl. Fusion 57,102014 (2017) The (Neoclassical) Tearing Mode is a plasma instability leading to the formation of the mag- netic islands causing degradation of plasma confinement and even disruptions. These modes are marginally stable in the large present day devices and develop once being seeded by a suf- ficiently large perturbation. Non-axisymmetric external magnetic perturbation (MP) fields arise in every tokamak e.g. due to the imperfections in the external coils positions. Additionally many tokamaks, like ASDEX Upgrade (AUG), are equipped with, so-called, Resonant Magnetic Per- turbation coils which produce a perturbation field for the control of Edge Localized Modes and other magnetohydrodynamical (MHD) instabilities. The previous results [1] of numerical simulations of the tearing mode onset with the toroidal, two fluids, non-linear MHD code JOREK [2] showed good qualitative agreement with the ex- perimental observations. The scan in the simulation parameters also included a set of parameters chosen to be as close as possible to one of the low collisionality L-mode plasma discharges with externally applied MP fields from ASDEX Upgrade [3]. Despite the good qualitative agreement, a higher amplitude of the perturbation field was required in order to get the mode penetration. The slow down of plasma rotation in the simulation was also not as efficient as in the experiment. This can partly be explained by the absence of the Neocalssical Toroidal Viscosity (NTV) in the code, which provides additional torque to the plasma in the presence of the non-axisymmetric magnetic field. In the present work, we show results of simulations with an input closer to re- alistic parameters and identify the threshold for mode penetration in several parameters like perturbation amplitude and rotation velocity. Additionally, we show the implementation of an NTV model in the JOREK code together with first results based on this extension. References [1] D. Meshcheriakov et al., proc. 44nd EPS conf. plasm. phys. P5.139, (2017). [2] G. Huysmans and O. Czarny, Nuclear Fusion 47, (2007). [3] S. Fietz et al., proc. 42nd EPS conf. plasm. phys. P1.123, (2015).

Speaker: Dmytro Meshcheriakov

14:00 P5.1034 Island bundle diverter configuration for quasi-axisymmetric stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1034.pdf Island bundle diverter configuration for quasi-axisymmetric stellarator S. Okamura1, H. Liu2, A. Shimizu1, M. Isobe1, Y. Xu2 1 National Institute for Fusion Science, Toki, Japan 2 Institute of Fusion Science, Southwest Jiaotong University, Chengdu, People’s Republic of China National Institute for Fusion Science, Japan and Southwest Jiaotong University, China are making collaboration in a joint project NSJP for constructing a new stellarator CFQS in China. The device design concept is based on the quasi-axisymmetric advanced stellarator. As well as good performances of confinement properties of core region, the magnetic configuration of the peripheral region is very important because the diverter performance is crucial for the successful achievement of the future reactor design. For the present stellarator experiments, two leading concepts for the divertor are well known, namely, the intrinsic helical diverter, represented by LHD in Japan, and the island diverter represented by W7-X in Germany. For the new stellarator CFQS, we propose a new diverter concept of “Island Bundle Diver- tor (IBD)”. Since the diverter magnetic configuration of IBD is constructed with magnetic island structure, there is a similarity between IBD and the island diverter in W7-X. However the essential difference is a very large size of the islands surrounding the core region, which clearly define two separate confinement regions of core confinement and divertor region (Fig.1). These two regions are facing with each other through a clearly defined magnetic separatrix. Divertor field line tracing pattern shown in Fig. 2 is similar to the tokamak divertor and the connection length of field lines between the separatrix and the divertor wall is long enough (without exceptional short lines) for the good divertor performance. Fig. 2 Divertor tracing with vacuum Fig. 1 Magnetic surfaces of Island Bundle chamber wall in blue Divertor

Speaker: Shoichi Okamura

14:00 P5.1035 Influence of energetic ions on magnetic island

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1035.pdf Influence of toroidal rotation on magnetic islands in tokamaks Huishan Cai1, Jintao Cao2 1 University of Science and Technology of China, Hefei, China 2 Institute of Physics, Beijing, China The dynamics of magnetic islands including toroidal rotation in tokamaks is studied. It is found that the contribution of toroidal rotation to the dynamics of magnetic islands is mainly through the coupling of magnetic curvature with pressure and density. In the presence of toroidal rotation, pressure and density are poloidal asymmetric. Then, their coupling with magnetic curvature provides a perpendicular current, and a corresponding return parallel current is induced to affect the dynamics of magnetic islands. It is found that the effect of toroidal rotation depends on its magnitude, rather than the shear. It also depends on the relative magnitude of the island propagation frequency to sound frequency. When the Mach number is large enough, the effect of toroidal rotation is stabilizing and dramatic, and overcomes the contribution of polarization current, namely the onset threshold of NTMs increases. Further, it is also suggested that the toroidal rotation plays an important role in the stability of small scale magnetic islands. References: (1) Huishan Cai, Jintao Cao, "Influence of toroidal rotation on tearing modes", Nucl. Fusion 57, 056006(2017) (2)Huishan Cai, Jintao Cao, "Influence of toroidal rotation on magnetic islands in tokamaks", Nucl. Fusion 58, 036008(2018)

Speaker: Huishan Cai

14:00 P5.1036 Non-linear MHD simulations of the plasma instabilities by pellet injection in LHD plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1036.pdf Non-linear MHD simulations of the plasma instabilities by pellet injection in LHD plasma Shimpei Futatani1 and Yasuhiro Suzuki2,3 1 Department of Physics, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain 2 National Institute for Fusion Science (NIFS), 322-6 Oroshi-cho, Toki 509-5292, Japan 3 Tha Graduate University for Advanced Studies (SOKENDAI), 322-6 Oroshi-cho, Toki 509-5292, Japan The pellet injection is an experimentally proven method of plasma refueling in tokamaks [1,2] and stellarators plasmas [3]. The pellet injection into the plasma is also used for plasma control, i.e. ELM (Edge Localized Mode) mitigation for tokamaks by means of the excitation of the Magnetohydrodynamic (MHD) activities via pellet injection. However, the plasma instabilities which are inimical phenomena via pellet injection are problems that have come into focus simultaneously. It is crucial to identify the complex physics mechanism between the plasma stability and the pellet ablation physics with non-linear MHD analysis. In this work, the global MHD dynamics of the Large Helical Device (LHD), which is a large superconducting Heliotron in Japan, has been analyzed with MIPS code [4] which solves the full MHD equations coupled with the pellet ablation model. The pellet ablation model which is based on neutral gas shielding model has been implemented in MIPS. The two important features are reflected in the implementation of the model into MIPS code in a similar manner with JOREK [5,6]. The first feature is that the pellet is modelled as a localized adiabatic time-varying density source. The pellet density source is toroidally and poloidally localized. The second feature is that the pellet moves at fixed speed and the direction. Initial MIPS-Pellet runs for non-linear MHD dynamics have been performed. The modelled LHD plasma has the edge electron pressure (p e) of 1 kPa and pe of the core region is 7.8 kPa. The electron temperature (Te) at the edge is 0.4 keV and the core is 2.1 keV. The results of the pellet size dependence in the LHD plasmas show that the pellet penetration depth ranges for 0.5-0.7 m according to the pellet size which is scanned for 1.0x10 21D, 1.5x1021D and 2.0x10 21D particles in a pellet. The simulation result is reasonably comparable values with the experiment observation [7]. The transport of the pellet cloud in the whole plasma domain in a time scale of the pellet ablation which is typically 400-600s has been observed. The performance of the parallel computing has been analyzed using MareNostrum IV which is the most powerful supercomputer in Barcelona, Spain. The numerical resolution of the simulation domain for the test case is 128x128x256. The number of cores has been varied for 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384 cores. The speed of the MPI computing increases linearly according to the number of cores until 4096 cores. A detailed analysis and an optimization will be carried out as a future work. References: [1] L. Baylor et al., Physi. Plasmas 12, 056103 (2005). [2] P.T. Lang et al., Nucl. Fusion 41 1107 (2001). [3] R. Sakamoto et al., Nucl. Fusion 44, 624 (2004). [4] K. Ichiguchi et al., Nucl. Fusion 55, 073023 (2015). [5] G.T.A. Huysmans and O. Czarny, Nucl. Fusion 47, 659 (2007). [6] S. Futatani et al., Nucl. Fusion 54, 073008 (2014). [7] T. Bando et al., Physics of Plasmas 25, 012507 (2018).

Speaker: Shimpei Futatani

14:00 P5.1037 Preliminary analysis of breakdown and startup conditions for the first plasma of HL-2M

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1037.pdf Preliminary analysis of breakdown and startup conditions for the first plasma of HL-2M J.X.Li, J.H.Zhang, X.M.Song, G.Y.Zheng, R.Ma, Y.D.Pan Southwestern Institute of Physics, Chengdu, China HL-2M is a new tokamak under construction in SWIP. In order to achieve the first plasma on HL-2M successfully, the initial discharge breakdown and start-up conditions are analyzed according to the engineering and physical goals of HL-2M, and the self-consistent initial discharge parameters are designed. In this paper, we will introduce the design of the equilibrium configuration, the compensation of the magnetic field generated by the eddy currents in the vacuum vessel and the plasma breakdown conditions for the discharge in detail. Finally, a self- consistent initial plasma discharge parameters are designed. In this paper, the limiter equilibrium configuration for the initial discharge of HL-2M is designed by EFIT. And then the divertor configurations with a low elongation are explored to further optimize the plasma discharge control technology on HL-2M. Since the vacuum vessel of HL-2M is designed to be conductive in the toroidal direction, the eddy current induced in vacuum vessel before and after the breakdown of the plasma will produces a strong vertical magnetic field in the plasma region. The vertical field destroy the pure (regardless of eddy current effects) null magnetic field configuration, which is too bad to the plasma breakdown and plasma current ramp-up. Therefore, this paper will explore the compensation of the magnetic field generated by the eddy current, and then design a self- consistent null-field configuration and give the initial plasma discharge parameters. A preliminary estimation of the volt-second consumption in the plasma discharge process is made based on the Ejima's coefficient and Spitzer's resistance method. Refer to the plasma startup design on EAST and KSTAR by J.A. Leuer, the self-consistent initial plasma discharge waveform among the plasma current, the PF coil current and the CS coil current are designed. At the same time, the additional currents that compensate for the magnetic field generated by the eddy currents are considered in the evolution of these waveforms. This work was supported by National Nature Science Foundation (Grant Nos. 11505050, 11575056, 11775071) and Chinese ITER Plan Project Foundation (Grant Nos. 2015GB105001, 2015GB105004)

Speaker: Jiaxian Li

14:00 P5.1038 Twenty-one years establishing ECCD stabilization of NTMs in DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1038.pdf Twenty-One Years Establishing ECCD Stabilization of NTMs in DIII-D* R.J. La Haye1 for the DIII-D Team 1 General Atomics, PO Box 85608, San Diego, California 92186-5608, USA Since the seminal predictions [1] in 1997 of how narrow radially localized electron cyclotron current drive could stabilize neoclassical tearing modes (NTMs) by replacing the “missing” bootstrap current in an island, DIII-D has been at the forefront of experimental validation. The previous commencement of 110 GHz gyrotron installation on DIII-D enabled this. The first complete stabilization (following ASDEX-Upgrade) of an NTM Fig. 1. Cross-sections of ITER and of a DIII-D ITER (m/n=3/2) using two gyrotrons injecting 1 Baseline Scenario discharge showing the launch of MW was achieved in 2000. The most rays (170 GHz 1*fce and 110 GHz 2*fce respectively) to drive co-ECCD at q=2. recent DIII-D experiments are in a low- torque ITER baseline scenario and mimic the ITER geometry for ECCD aligned to the q=2 surface as shown in Figure 1. Initially there was no real-time capability for ECCD alignment on a rational surface; the development of alignment progressed from fixed mirrors with mirror angle or toroidal field changed shot-to-shot, to closed-loop control of the entire plasma major radius and thus island location or control of toroidal field and thus ECCD location, to moving the mirrors during a discharge [2]. The subsequent increase in the numbers of gyrotrons (and thus EC power) and the real-time mirror control to keep the ECCD “scalpel” on a given q=m/n surface allows tests of simultaneous preemption/avoidance of both 3/2 and 2/1 modes in the IBS in DIII-D. Real-time logics for gyrotron power management progressed from applying after a saturated mode, to always-on CW for preemption of the mode, to turning on with detection of a growing mode. Comparison of CW to standby ECCD to “catch” a growing mode to “subdue” it with return to standby is under yet further development as ITER will need to keep the average EC power for NTM stabilization at a minimum in order to maximize Q. *Work supported by the US DOE under DE-FC02-04ER54698. [1] C.C. Hegna and J.D. Callen, Phys. Plasmas 4, 2940 (1997), H. Zohm, Phys. Plasmas 4, 3433 (1997), F. Perkins, R. Harvey, M. Makowski, and M. Rosenbluth, 24th EPS Conf. on PPCF, Berchtesgaden, 1997, 1017. [2] E. Kolemen, A.S. Welander, R.J. La Haye, et al., Nucl. Fusion 54, 073020 (2014).

Speaker: Robert John La Haye

14:00 P5.1039 Double tearing modes in the presence of anti-symmetric shear flow

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1039.pdf Double tearing modes in the presence of anti-symmetric shear flow L. Wei1, M.J. Nemati1, Z.X. Wang1 1 Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian 116024, China The linear properties of both even and odd double tearing modes (DTMs) in the presence of plasma shear flow are studied based on a reduced resistive MHD model in slab geometry. It is found that for the symmetric shear flow, the linear growth rate of even eigenmode of DTM is almost independent of the strength of shear flow, while the odd eigenmode decreases with the shear flow strength. However, for anti-symmetric shear flow, the linear growth rates of even (odd) eigenmode of DTM decrease (increase) with increasing the strength of shear flow. Moreover, in the small wavenumber regime, the growth rate of the even eigenmode is larger than that of the odd eigenmode, while the growth rates of two kinds of eigen states coalesce with each other (the same growth rate and opposite frequencies) when the wavenumber exceeds a critical value Kc. It is demonstrated that Kc decreases with decreasing resistivity for a fixed separation between two resonant surfaces Xs, while decreasing Xs raises the critical value of Kc for a fixed shear velocity. In the nonlinear regime for a low value of resistivity, it is observed that the formation of plasmoids changes gradually, by increasing the strength of anti-symmetric shear flow.

Speaker: L. Wei

14:00 P5.1040 Computational modeling of quasi-single helicity states in an RFP

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1040.pdf Computational modeling of quasi-single helicity states in an RFP A.S. Ware and C. Miele University of Montana, Missoula, Montana, USA This work explores the impact of boundary shaping on access into and out of quasi-single helicity states in reverse-field-pinch (RFP) plasmas. Experiments have shown that RFP plasmas can self-organize to a quasi-single helicity (QSH) equilibrium with a helical axis [1, 2]. These states have improved confinement and lower magnetic turbulence levels compared to a standard RFP plasma which has multiple helicities in the magnetic spectrum. The VMEC code can obtain similar equilibria with a helical axis and a symmetric boundary [3]. These equilibria all have circular, or nearly-circular cross-sections. In this work we analyze the VMEC input parameters that control access to QSH states and test the impact of 2D-shaping of the boundary on RFP equilibria. Particular attention is paid to the impact that shaping has on access to quasi-single helicity states. The effect of increasing elongation and triangularity are tested systematically. Increased elongation results in lower plasma current for the same safety factor profile a nd a larger radial excursion of the helical axis in a QHS state. Optimization of the boundary coeffi- cients targeting an increased radial excursion of the helical axis is undertaken. Results will be presented. References [1] D.F. Escande, et al., Phys. Rev. Lett. 85, 1662 (2000) [2] L. Marrelli, L., et al. Phys. Plasmas 9, 2868 (2002) [3] J.D. Hanson, et al., Nucl. Fusion 53, 083016 (2013)

Speaker: Andrew Ware

14:00 P5.1041 Fast ion effects on the magnetic islands in a tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1041.pdf Fast ion effects on the magnetic islands in a tokamak V. Y. Savin1, 2, S. V. Konovalov1 1 National Research Center «Kurchatov institute», Moscow, Russian Federation 2 National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russian Federation It is known that the presence of helical perturbations that violate the axial symmetry of the magnetic field of a tokamak leads to the formation of magnetic islands with a width ∆𝑚 ~√𝐵̃, as well as to a change in the drift trajectories of charged particles, coupled with their radial redistribution and/or additional losses. In this case, according to [1], the drift trajectories of fast ions, characterized by a significant deviation from the magnetic surfaces, λ, are more stable to helical perturbations of the magnetic field than magnetic surfaces. In turn, the perturbation of the drift motion of fast ions leads to the appearance of a helical current perturbation capable of both facilitating and preventing the growth of the magnetic island. In the present paper, we consider both the case λ>Δm [2], when the helical current perturbation is due to the compensating electron drift, 𝑉𝐸 ~[𝐸̃ × 𝑩], and the inverse, λ

Speaker: Vyacheslav Savin

14:00 P5.1042 Investigating the effect of neoclassical tearing modes on fast ions in ASDEX Upgrade: measurements and modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1042.pdf Investigating the effect of neoclassical tearing modes on fast ions in ASDEX Upgrade: measurements and modelling A. S. Jacobsen1 , B. Geiger1 , R. J. Akers2 , J. Buchanan2 , K. G. McClements2 , A. Snicker3 , V. Igochine1 , M. Salewski4 , M. Dunne1 , E. Poli1 , P. A. Schneider1 , G. Tardini1 , A. Jansen van Vuuren1 , M. Weiland1 the ASDEX Upgrade team and the EUROfusion MST1 team∗ 1 Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany 2 CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom 3 Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland 4 Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark Neoclassical tearing modes (NTMs) are pressure-driven MHD instabilities which degrade the plasma performance and can lead to disruptions. They form at rational surfaces, typically ap- pearing in plasmas with high βN values, and have been observed to be responsible for fast-ion losses[1, 2, 3]. Here we present first measurements of the internal redistribution of neutral beam injected fast ions caused by NTMs in ASDEX Upgrade, as inferred from tomographic recon- structions and radial profiles of fast-ion Dα spectroscopy. Depending on its size and amplitude, the NTM can cause a significant reduction of the fast-ion density. Neoclassical simulations using an axisymmetric transport code have been performed, considering the NTM-induced modifica- tion of plasma profiles, but not the structure of the magnetic perturbation itself. In this case the simulated fast-ion transport is not sufficient to explain the observations and additional anoma- lous diffusion is needed. This is especially the case for (m, n) = (2, 1) NTMs, where m and n refer to the poloidal and toroidal mode numbers, respectively. To carry out more sophisticated simulations, considering the 3D magnetic structure of the NTMs, we describe the perturbation analytically, add it to the axisymmetric equilibrium and feed it into the full-orbit Monte Carlo fast-ion codes LOCUST[4] and ASCOT[5]. The resulting predicted fast-ion redistribution is presented and compared with the experimental results. References [1] H. E. Mynick, Physics of Fluids B 5, 1471 (1993) [2] M. García-Muñoz et al., Nuclear Fusion 47, L10-L15 (2007) [3] E. Poli et al., Physics of Plasmas 15, 032501 (2008) [4] R. J. Akers et al., 39th EPS Conference & Int. Congress on Plasma Physics, P5.088 (2012) [5] T. Kurki-Suonio et al., Nuclear Fusion 49, 095001 (2009) ∗ See author list of "H. Meyer et al 2017 Nucl. Fusion 57 102014"

Speaker: Asger Schou Jacobsen

14:00 P5.1043 Status of parametric equilibrium reconstructions for Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1043.pdf Status of Parametric Equilibrium Reconstructions for Wendelstein 7-X J.C. Schmitt , S.A. Lazerson , J. Geiger , J. Schilling , and the W7-X Team 1 2 3 3 1 Auburn University, Auburn, AL, U.S.A 2 Princeton Plasma Physics Laboratory, Princeton, NJ, U.S.A. 3 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany The reconstruction of the plasma equilibrium is a vital tool for toroidal fusion experiments to help understand plasma performance and interpret diagnostic signals. The procedure involves solving the MHD equilibrium, computing synthetic diagnostic signals based on that equilibrium, and comparing these signals to measured signals. The parameters that describe the equilibrium are adjusted to find a best-fit of the measured and synthetic signals. Information gained from the reconstruction includes details about the shape of the plasma, the location of the plasma edge, and profile information regarding the plasma pressure, current, and individual plasma species (e.g. T , N , T , N ). These inferred e e i i profiles are used to interpret diagnostic information and are used for further analyses. The constraints for the reconstructions of plasmas at Wendelstein 7-X (W-7X) include magnetic diagnostics (‘segmented’ and ‘complete’ Rogowski coils, diamagnetic and compensated flux loops, saddle coils, field coil currents), Thomson Scattering, interferometry, electron cyclotron emission, soft x-ray arrays and x-ray imaging crystal spectroscopy. Treatments of edge constraints related to the edge rotational transform and divertor location are also presented. The MHD equilibrium solution is provided by VMEC, which assumes solution with nested, closed flux surface. The contribution summarizes a benchmarking of the three equilibrium reconstruction codes that use VMEC: V3FIT (approximate quasi-Newton with 1 SVD), STELLOPT (modified Levenberg-Marquardt, and others), and MINERVA (a 2 Bayesian modelling framework). Furthermore, the current status and future plans for equilibrium reconstructions for W-7X are shown and discussed. 1 J. D. Hanson, S. P. Hirshman, S. F. Knowlton, L. L. Lao, E. A. Lazarus, and J. M. Shields, Nucl. Fusion 49, 075031 (2009). 2 J. Svensson and A. Werner, 2007 IEEE International Symposium on Intelligent Signal Processing, 2007, pp. 1-6.

Speaker: John C. Schmitt

14:00 P5.1044 3D Equilibrium Reconstruction with Islands

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1044.pdf 3D Equilibrium Reconstruction with Islands M. Cianciosa1, S.P. Hirshman1, S.K. Seal1, M.W. Shafer1 1 Oak Ridge National Laboratory, Oakridge TN, United States There are many situations where the nested flux surface topology of fusion plasmas break. When resonant magnetic perturbations (RMP) for edge localized mode control are applied nested magnetic surfaces can tear resulting in magnetic islands. During disruptions, equilibrium surfaces can break down to the point of stochastic field lines. The normal operation of tokamaks and advanced stellarators break the nested surfaces at the last closed flux surface to control the exhaustion of hot plasma. Equilibrium reconstruction has played an important role in determining unknown quantities and setting the basis for advanced modeling. To understand scenarios like these, it is critical to be able to reconstruct equilibria with arbitrary topologies. 1 2 Until recently, 3D reconstruction using V3FIT , which is based on VMEC , has been limited to plasmas with closed nested flux surfaces. V3FIT has been extended to include 3 SIESTA as an equilibrium solver allowing for non-nested or stochastic magnetic topologies. Using a VMEC equilibrium as background coordinates, SIESTA tears the nested magnetic surfaces by applying resonant magnetic perturbations. Reconstruction determines the strength of these magnetic perturbations along with other equilibrium quantities by matching synthetic signals to physical measurements. Experiments show that measured temperature profiles flatten inside magnetic islands. Using this signal information the first ever reconstruction of a non-nested equilibrium 4 topology was performed on the DIII-D experiment . This presentation will highlight the methods used to reconstruct non-nested topologies and show preliminary results of 5 reconstructing island diverter cases using the new free boundary SIESTA . References [1] J.D. Hanson, et al., Nucl. Fusion, 49, 075031 (2009) [2] S.P. Hirshman, et al., Physics of Fluids, 26, 3553 (1983) [3] S.P. Hirshman, et al., Physics of Plasmas, 18, 062504 (2011) [4] M. Cianciosa, et al., Plasma Physic Control. Fusion, In Press (2018) [5] H. Peraza-Rodriguez, et al., Physics of Plasmas, 24, 082516 (2017)

Speaker: Mark Cianciosa

14:00 P5.1045 Kinetic Effects on Resistive Tearing Mode and Drift Tearing Mode

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1045.pdf Kinetic Efects on Resistive Tearing Mooee ane Drift Tearing Mooee Wenlu Zhang1,2, Hao Shi2,1, Hongying Feng1,2 1 Institute of Physics, Chinese Academy of Science 2 University of Science and Technology of China The kinetic efectt on ttability of retittive tearing mode are invettigated by global timulationt in cylindrical geometry uting Gyrokinetic Toroidal Code(GTC). The fuid timulation of retittive tearing mode agreet well with theory prediction. Kinetic efectt are found to reduce the growth rate of the tearing mode and the radial width of mode ttructure. The drift-tearing mode it obtained when contidering dentity gradient, which hat the frequency of the diamagnetic drift frequency. The decreate of growth rate due to the diamagnetic drift motion it obterved, which agreet well with the derivation of theory. Betidet, the radial mode width of the drift tearing mode it wider.

Speaker: Hao Shi

14:00 P5.1046 Non-inductive current start-up and ramp-up by X-wave ECCD in fusion tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1046.pdf Non-inductive current start-up and ramp-up by X-wave ECCD in fusion tokamaks Takashi Maekawa, Masaki Uchida and Hitoshi Tanaka Graduate School of Energy Science, Kyoto University, Kyoto, Japan Some improvement in engineering of tokamak reactors would be possible, if a hot plasma with Te up to a few keV and Ip up to a few hundred kilo amperes could be non-inductively built up prior to inductive current ramp-up to a full current for fusion ignition and burning. From the view point of reactor engineering, electron cyclotron (EC) heating and current drive (ECH/ECCD) is attractive for the non-inductive build up. In a startup discharge, toroidal plasma current is initially low and all the plasma would be in open fields. As the current develops by ECH, a small closed flux surface would appear and then the current inside the surface would develop by ECCD. Eventually the discharge would develop into the tokamak stage, where whole the plasma is contained in large closed flux surfaces, and the plasma is heated with the current ramp-up by ECCD, and finally the goal of hot plasma buildup would be accomplished. It has been shown that oblique X-waves are useful for ECH/ECCD for every stage of the discharge and it was suggested that an injection power of Prf~4 MW could build up a hot plasma with the toroidal plasma current of Ip~200kA, ne~1.2x1019m-3, Te~2keV, a=1 m and R0=5.1m in ITER [1]. As the electron temperature Te increases into keV range, however, plasma conductivity becomes very high and the return current driven by the self-induction voltage from EC driven current would hamper the current ramp-up. Here we study the current ramp-up for an ITER case using a current circuit model for the ECCD driven current and the return current. The circuit equation is coupled with the ECCD efficiency equation [2] and the ITERL-97P energy confinement scaling [3]. Numerical study for various cases elucidates key points for efficient current ramp-up in keV range plasmas. [1] T. Maekawa, M. Uchida and H. Tanaka, Nucl. Fusion 58 (2018) 016037. [2] C.F.F. Karney and N.J. Fisch, Phys. Fluids, 29 (1986)180. [3] S.M. Kaye and ITER Confinement Database Working Group Nucl. Fusion 37(1997) 1303.

Speaker: Takashi Maekawa

14:00 P5.1047 Application of three-ion species ICRH scenarios for ITER operation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1047.pdf Application of three-ion species ICRH scenarios for ITER operation Ye.O. Kazakov1, M. Schneider2, J. Ongena1, R. Bilato3, J.M. Faustin4, E. Lerche1, D. Van Eester1 and J.C. Wright5 1 Laboratory for Plasma Physics, LPP-ERM/KMS, Brussels, Belgium 2 ITER Organization, Route de Vinon-sur-Verdon, St. Paul-lez-Durance Cedex, France 3 Max-Planck-Institut für Plasmaphysik, Garching, Germany 4 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 5 Plasma Science and Fusion Center, MIT, Cambridge, USA E-mail: kazakov@chalmers.se The application of heating and current drive scenarios, including ion cyclotron resonance heating (ICRH), has been recently reassessed for each of the four operational stages in the revised ITER schedule [1]. Recently, it has been shown that a small amount of minority particles injected into a two- ion plasma mixture can very efficiently absorb (nearly all) of the deposited RF power [2]. The application of these so-called three-ion species ICRH scenarios can be further extended to using impurity ions as part of the plasma mix or as resonant ions, as well as using beam ions as resonant species [3]. In this contribution, we give an overview of various three-ion ICRH scenarios that hold promise for ITER operations and also highlight their possible applications beyond heating. 1) Heating full-field H plasmas, including impurities with (Z/A)imp < 1/2 such as 9Be, 40Ar and 22Ne, with 4He as absorbing species (f ≈ 40 MHz) in the non-active phase. Since (Z/A)imp < (Z/A)4He < (Z/A)H, the optimal 4He concentration for plasma heating depends strongly on the amount of intrinsic 9Be impurities. In H-9Be plasmas, wave absorption by the 4He ions at very small concentrations is maximized at n9Be/ne ≈ 2%. Additional injection of Ar or 22Ne impurities with a similar (Z/A)imp as for 9 Be has been proposed for further optimizing wave polarization and depositing ICRH power to 4He minority ions [4]. 2) Heating H-4He plasmas with 3He as absorbing species in the non-active phase. This scenario relies on adding ~5–15% of 4He ions into H plasma, and a tiny amount of 3He ions (< 1%) to absorb RF power. For full-field ITER operation, central 3He heating is achieved at f ≈ 54 MHz. The advantages of this scheme in ITER include: i) more ICRH power is available at this frequency than at f ≈ 40 MHz [5]; ii) reduction of the L-H power threshold by ~20% in H-4He mixtures (w.r.t. H plasma) was reported in JET-ILW [6]. The lack of an efficient IC scenario at half-field ITER hydrogen plasmas also led to the proposal to apply off-axis 3He heating in H-4He plasmas at 3T and 3.3T [4]. Note that off-axis 3He heating in equivalent H-D plasmas has been recently successfully shown in AUG experiments [7]. 3) Bulk ion heating in D-T plasmas with 9Be as absorbing species. The T-(9Be)-D heating scheme can be exploited to enhance off-axis RF power absorption by 9Be impurities in full-field D-T plasmas in ITER at f ≈ 40 MHz. Due to their higher mass, 9Be ions will effectively deposit absorbed RF power to bulk D and T ions via Coulomb collisions, a feature particularly attractive for a fusion reactor. This ICRH scenario is applicable for D:T=50:50 plasmas without the need to inject extra ions into the plasma (an intrinsic concentration n9Be/ne < 1% would be sufficient). Central plasma heating with 9Be impurities requires somewhat lower RF frequencies, f ≈ 38 MHz. Whether the ITER ICRH system can operate at this frequency without too strong power degradation still needs to be assessed. 4) Using NBI ions as resonant species for ICRH heating of mixture plasmas. Efficient ICRH heating of H-D plasmas with the fast injected deuterium NBI ions as resonant ‘third’ species was recently demonstrated on JET [3]. Those ions in the beam distribution that have a Doppler-shifted cyclotron resonance close to the ion-ion hybrid layer resonate with the excited fast wave and absorb RF power. The ITER NBI heating system foresees injection of H and D neutrals at energies 0.87 MeV and 1 MeV, respectively. This allows to exploit NBI+ICRH synergies using the 4He-(HNBI)-H heating scenario in 4He-H plasmas [8]. In a similar way, deuterium NBI absorption can be further enhanced using the T-(DNBI)-D scenario to contribute to efficient heating of D-T plasmas in ITER. [1] M. Schneider et al., Proc. 44th EPS Conf. on Plasma Physics, P5.153 (2017) [2] Ye.O. Kazakov et al., Nature Physics 13, 973-978 (2017) [3] J. Ongena et al., EPJ Web Conf. 157, 02006 (2017) [4] M. Schneider et al., EPJ Web Conf. 157, 03046 (2017) [5] P.U. Lamalle et al., AIP Conf. Proc. 1187, 265 (2009) [6] J. Hillesheim et al., Proc. 26th IAEA Fusion Energy Conference, EX/5-2 (2016) [7] A. Kappatou et al., this conference [8] R. Bilato et al., this conference

Speaker: Yevgen Kazakov

14:00 P5.1048 First LHCD experiments in WEST

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1048.pdf First LHCD experiments in WEST M. Goniche, A. Ekedahl, J.-F. Artaud, C. Bourdelle, L. Delpech, N. Fedorczak, J. Garcia, J.P. Gunn, Y. Peysson and the WEST Team CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. The WEST tokamak has achieved X-point plasmas in lower single null configuration with plasma current up to IP = 0.8 MA, magnetic field BT = 3.7 T and q95 ~ 3 [1]. WEST is the first and only full W-device relying on only radiofrequency systems for heating and current drive. This paper presents the first lower hybrid current drive (LHCD) experiments performed in WEST with the two launchers designed for coupling 6-7 MW power in view of long pulse operation at high density (ne = 6-7×1019 m-3) [2]. The experiments presented here were carried out in low density plasmas (ne = 1.7-2.2×1019 m-3) with up to 2.4 MW coupled LHCD power. Several plasma equilibria were tested aiming at minimising the reflection coefficient (RC) of the LHCD power. As expected, it was found that RC was sensitive to the radial outer gap (ROG), which was generally different for the waveguides rows above and below the mid- plane. The average RC was typically 5-10% for ROG = 3 cm and ~ 30% for ROG = 6 cm. Langmuir probes installed in a poloidal limiter showed very low electron densities, < 1×1018 m-3 at 15 mm in front of the poloidal limiter, indicating that the density at the launchers was near or below the LH cut-off density (at f = 3.7 GHz). This was consistent with the high RC values measured. The main focus of the experiments was thus to find reproducible plasma equilibria giving sufficiently low RC (< 20%) over the whole launchers. Once adequate plasma equilibrium had been found, maximum 2.4 MW LHCD power was coupled to the plasma (and 2.3 MW for 2 s). As the LHCD power was increased, loop voltage dropped from 1.2 V to 0.4 V, the central electron temperature exceeded 2 keV and bremsstrahlung measurements in the hard X-ray range (40-200 keV) gave evidence of an increasing fast electron population. The radiated power fraction in the plasma bulk decreased as the LHCD power increased, from PRad,bulk/PTot ~ 80% down to 45%. The time evolution of the radiated power followed that of the W-signal from VUV spectroscopy, suggesting that W contributes to the radiated power. Simulations with the METIS code are used to check the overall coherency between radiation, loop voltage, plasma composition, etc. [1] E. Nardon et al., this conference [2] C. Bourdelle et al., Nucl. Fusion 55 (2015) 063017

Speaker: Annika Charlotte Ekedahl

14:00 P5.1049 High field side LHCD in DIII-D: physics demonstration of reactor relevant current drive

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1049.pdf High field side LHCD in DIII-D: physics demonstration of reactor relevant current drive G.M. Wallace , P.T. Bonoli , S. Shiraiwa , S.J. Wukitch , J. Doody , R. Leccacorvi , R. 1 1 1 1 1 1 Vieira , W. Helou , C. Holcomb , J. Ferron , R.I. Pinsker 1 2 3 4 4 1 MIT Plasma Science and Fusion Center, Cambridge, MA USA 2 CEA, IRFM, F-13108 St-Paul-Lez-Durance, France 3 Lawrence Livermore National Laboratory, Livermore, CA USA 4 General Atomics, La Jolla, CA USA Calculations show that high field side (HFS) launch of lower hybrid range of frequencies (LHRF) power represents an integrated solution that both improves core wave physics (high current drive efficiency at proper location) and mitigates plasma material interaction (PMI)/coupling issues [1] . To demonstrate the benefits associated with HFS LHCD (wave coupling, propagation, absorption, and current drive efficiency), a conceptual HFS LHCD system has been developed for DIII-D, which represents the first fully developed HFS LHRF system design for an operating tokamak. Using existing DIII-D discharges, we have identified high performance scenarios with excellent wave penetration, single pass absorption and high off-axis current drive efficiency (r/a~0.6-0.8, FWHM of r/a=0.2 and driven current up to ~0.21 MA/MW). The DIII-D antenna design utilizes proven launching technology (slotted waveguide, multijunction) while remaining within established power density limits. The performance of the antenna was simulated by ALOHA [2] and 3D MFEM [3] and shows low reflected power for a range of plasma conditions. From an operational perspective, launcher placement on the HFS has potential issues: reduction of inner wall gap and launcher material compatibility. The former was investigated through a scan of the plasma-HFS wall gap. Little or no impact of these plasma shape changes was found on discharge confinement or stability. Data on material compatibility from a molybdenum/carbon mockup antenna installed on the HFS wall of DIII-D will be presented. Work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using User Facility DIII-D, under Award Number DE-FC02-04ER54698 and by US DoE Contract No. DE-FC02- 01ER54648 under a Scientific Discovery through Advanced Computing Initiative. [1] P.T. Bonoli et al, 26th FEC IAEA TH/5-1 (2016). [2] J. Hillairet, et al, Fusion Engineering and Design 84, 953-955 (2009). [3] S. Shiraiwa et al, EPJ Web of Conferences 157, 03048 (2017).

Speaker: Gregory Wallace

14:00 P5.1050 Integrated modelling of ITER scenarios with D-T Mix control

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1050.pdf Integrated modelling of ITER scenarios with D-T Mix control A.R. Polevoi1, A. Loarte1, S.Yu. Medvedev2, E. Fable3, A.Yu. Dnestrovskiy4, E.A. Belli5, M. Hosokawa1, A.A. Ivanov2, F. Köchl 6, A. Kuyanov4 1 ITER Organization, Route de Vinon-sur-Verdon, 13067 St Paul Lez Durance, France 2 Keldysh Institute of Applied Mathematics, Miusskaya 4, 125047 Moscow, Russia 3 Max-Planck Inst. für Plasmaphysik, Boltzmanstraße 2, D-85748 Garching, Germany 4 NRC "Kurchatov Institute", Kurchatov sq. 1, 123098 Moscow, Russia 5 General Atomics, PO Box 85608, San Diego,CA 92186-5608,USA 6 Atominstitut, Technische Universität Wien, Stadionallee 2, 1020 Vienna, Austria An analysis of D and T fuelling requirements for DT mix control for ITER H-mode plasmas is presented in this paper. This includes the use of pellet injection for core plasma fuelling and ELM pacing, and gas fuelling for edge density and divertor power load control, consistent with the ITER fuelling and pumping systems capabilities. The simulations are carried out by 1.5D core transport modelling with separate treatment of D and T ions with the ASTRA suite of codes with boundary conditions and particle sources from gas puffing derived from scalings based on SOLPS simulations. The width and height of the pedestal evaluated by the EPED1+SOLPS scaling prediction which are compared with direct simulations of the pedestal stability limits by the KINX code. In this way the effect of the impact of core pressure from self-consistent core simulations with TGLF on the pedestal height is included. The ITER simulations have been carried out with GLF and TGLF transport models for the range of currents and densities foreseen to be required to develop the ITER baseline q95 = 3 scenario from low field 5 MA/1.8T, 7.5 MA/2.65T to high field operation 15 MA/5.3 T Q = 10 for DT plasmas with varying T levels in a wide range of plasma densities. In most plasma conditions, penetration of recycled neutrals is found to be very limited so that pellet fuelling is an efficient tool to control the DT mix with a timescale determined by the relaxation of the D and T profiles. TGLF modelling predicts highly stiff temperature profiles for ITER plasmas with T′~ const, rather than LT~ const and more robust access to high Q conditions than previously evaluated with GLF23. A factor that also contributes to this H-mode access robustness is the rapid decrease of the fast particle energy associated with fast D ions from NBI and alpha particles in the low density phase which slow down as the density increases thus providing additional heating to the plasma to keep it in H- mode as the density increases in the core. This increase is predicted to occur on a faster timescale by TGLF than by GLF23.

Speaker: Alexei R. Polevoi

14:00 P5.1051 Fast wave experiments at LAPD in support of fusion

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1051.pdf Fast wave experiments at LAPD in support of fusion B. Van Compernolle1, M. Martin1, T. A. Carter1, W. Gekelman1, P. Pribyl1, D. Van Eester2, K. Crombe3, R. Perkins4, C. Lau5, E. Martin5, J. Caughman5, S.K.P. Tripathi1, S. Vincena1 1 University of California, Los Angeles, United States, 2 LPP, Royal Military Academy, Brussels, Belgium, 3 Ghent University, Ghent, Belgium, 4 Princeton Plasma Physics Laboratory, Princeton, United States, 5 Oak Ridge National Laboratory, United States Recent work on ICRF physics at the Large Plasma Device (LAPD) at UCLA has focused on deleterious near-feld antenna efects, such as RF rectifcation, sputtering, convective cells and power lost to the plasma edge. Plasma parameters in LAPD are similar to the scrape-of layer of current fusion devices. The machine has a 17 m long, 60 cm diameter magnetized plasma column with typical plasma parameters ne ~ 1012 – 1013 cm-3, Te ~ 1 – 10 eV and B0 ~ 1000 G. A new high-power (~150 kW) RF system and fast wave antenna have been developed for LAPD, enabling the generation of large amplitude fast waves. Evidence of rectifed RF sheaths is seen in large increases (~ 10 Te) in the plasma potential on feld lines connected to the antenna, and in copper deposition on plasma facing components due to sputtering at the antenna. The rectifed potential scales linearly with antenna current. The rectifed RF sheaths set up convective cells of local E x B flows, measured indirectly by potential measurements, and measured directly with Mach probes. At high antenna powers substantial modifcations of the density profle were observed after the RF antenna is powered up. The density rearrangement is asymmetric with a decrease in plasma density near the top of the antenna and an increase near the bottom. The plasma density profle initially exhibits transient low frequency oscillations (~10 kHz) and settles into a quasi- steady state profle for the remainder of the RF pulse. RF antenna current is constant during the pulse. In preliminary experiments at low antenna powers, the parasitic coupling to slow waves in the low density region in front of the antenna is being studied. Detailed wave feld measurements show coupling to both the short wavelength slow wave and the long wavelength fast wave if the density at the antenna is low enough. Coupling to lower hybrid waves was demonstrated for a range of normalized frequencies, from 1 < f / fci < 30. M. J. Martin et al, Phys. Rev. Lett. 119, 205002 (2017) Supported by NSF/DOE at BaPSF

Speaker: Bart Van Compernolle

14:00 P5.1052 Full-wave simulation of mode-converted electron Bernstein waves at very low magnetic field in the SCR-1 Stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1052.pdf Full-wave simulation of mode-converted electron Bernstein waves at very low magnetic field in the SCR-1 Stellarator R. Solano-Piedra1 , A. Köhn2 , V.I. Vargas1 , E. Meneses3 , D. Jiménez 3 , A. Garro-Vargas3 , F. Coto-Vílchez1 M.A. Rojas-Quesada1 , D. López-Rodríguez1 , J. Sánchez-Castro1 , J. Asenjo1 and J. Mora1 1 Plasma Laboratory for Fusion Energy and Applications, Instituto Tecnológico de Costa Rica, Cartago, P.O.Box 159-7050, Costa Rica. 2 IGVP, University of Stuttgart, Germany. 3 Advanced Computing Laboratory, Costa Rica National High Technology Center, CENAT, San José, Costa Rica SCR-1 is a 2-field period small modular Stellarator (R = 247.7 mm, R/a = 6.2, ιa = 0.264) with a very low magnetic field (< B >= 41.99 mT) and an ECR heating frequency of 2.45 GHz (5 kW). Few studies on conversion of electrostatic Bernstein waves under these conditions have been performed in Stellarators [1, 2]. This work presents the results of converting electrostatic Bernstein waves in the SCR-1 Stellarator using the full wave code IPF-FDMC [3], taking the 3D magnetic field obtained by VMEC code as input and the experimental electron density pro- file obtained using a Langmuir probe. New microwave heating scenarios that take the SCR-1’s vacuum vessel into account in order to improve the O-X conversion due to reflection of the in- coming radiation from the ECRH system are presented. The results indicate a single pass O-X mode conversion is around 3%. The possible location of a microwave antenna and its character- istics for proper function in SCR-1 stellarator are explained. Additionally, the improvements in BS-SOLCTRA code (Biot-Savart Solver for Compute and Trace Magnetic Fields) are shown. This code was developed by our research group to calculate 3D magnetic fields and display the magnetic surfaces in SCR-1. The road to convert it into a parallel and high-performance com- puting platform for tracing particles in SCR-1 is shown. Finally, the results of the comparison of the flux surfaces measured with an electron beam and fluorescent rod, with computed flux surfaces by means of BS-SOLCTRA code are shown. Similarly, the designs of the magnetic diagnostics (Rogowski, Voltage Loops and Mirnov) and the bolometer that will be installed in SCR-1 are presented. References [1] Y. Podoba et al, Physical Review Letters. 98, 25 (2007). [2] R. Ikeda et al, Physics of Plasmas, 15 , 7, (2008). [3] A. Köhn et al, Plasma Physics and Controlled Fusion 55, 1 (2013).

Speaker: Ricardo Solano Piedra

14:00 P5.1053 Effects of pellets and impurity injection on runaway control experiments on FTU

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1053.pdf Effects of pellets and impurity injection on runaway control experiments on FTU A.Romano1, G. Apruzzese1, F.Bombarda1, L.Boncagni1, P. Buratti1, D.Carnevale2, S. Ceccuzzi1, F. Cordella1, C. Di Troia1, G. Ferrò2, L.Gabellieri1, E. Giovannozzi1, M. Gospodarczyk2, G. Ramogida1, S. Sibio1, B.Tilia1, O. Tudisco1 and the FTU team* 1 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy 2 Dip. di Ing. Civile ed Informatica, Università di Roma “Tor Vergata”, Italy *See G. Pucella et al., Nucl. Fusion 57 102004 (2017) Generation of runaway (RE) beams following disruptions is a serious concern in tokamak devices. FTU is conducting an extensive program aimed at controlling and mitigating the purposely generated RE beams (natural and induced disruptions) [1, 2]. During the last experimental campaign different mitigation techniques have been tested, which involved injection of impurity gas (Neon), of multiple Deuterium pellets (1-2⋅1020 atoms), and of Laser Blow Off metal impurities (Tungsten, Molybdenum, Iron and Zirconium). The injections have been performed both during the plasma current flat top with seed REs embedded in a hot plasma and after current quench with current mainly carried by REs. The experimental results point to a complex picture where MHD effects, impurity transport and radiation, temperature and density variation all play different roles depending on the target plasma condition. As far as the LBO is concerned, the element providing the most useful information was Fe. Injections during the plasma current flat-top in RE discharges show up in the spectroscopic diagnostics, bolometry and Soft X-ray. The signal time correlations appear to be related to the amount of RE electrons in the plasma, qualitatively estimated from the ratio of the (neutron+gamma)/neutron signals. Pellets injected during this phase caused an increase of plasma density; the effects on the RE beams were analyzed. LBO injections performed on the RE beam formed after the current quench do not produce any effects on any diagnostics nor on the beam itself, possibly because of the very low electron temperatures. Deuterium pellets injected into a RE beam display complex behaviors. When injected in the early phase of the beam the pellet is ablated but ionization does not take place, presumably because the background plasma is too cold; the electron density surprisingly diminishes in this case. When the pellets are injected a later time into a warmer plasma and a less energetic RE beam, they are ionized increasing the electron density. [1] D. Carnevale, et al., Runaway Electron Beam Control, EPS 2018. [2] B Esposito et al 2017 Plasma Phys. Control. Fusion 59 014044.

Speaker: Afra Romano

14:00 P5.1054 Vertical stability margin studies on TCV: experiments and modelling

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1054.pdf Vertical stability margin studies on TCV: experiments and modelling F. Villone1, R. Ambrosino1, V.P. Loschiavo1, S. Coda2, TCV and EUROFusion MST1* teams 1 Consorzio CREATE, DIETI, Università degli Studi di Napoli Federico II, Italy 2 Swiss Plasma Center, EPFL, Lausanne, Switzerland *See the author list H. Meyer et al 2017 Nucl. Fusion 57 102014 The stabilization of the vertical position in future fusion devices (e.g. DEMO [1]) is particularly challenging, due to a number of reasons. First of all, the high fusion performances required of the plasma call for a relatively high elongation [2], which in turn increases the vertical instability growth rate. Secondly, toroidally conducting structures providing most of the passive stabilization (typically the vessel) are very far from the plasma, since massive blankets are required to shield and collect neutrons produced by fusion reactions. The electric power needed for stabilization is one of the key drivers in the design of a new device. This quantity depends critically on the so-called stability margin [3], which is a fundamental indication on the passive stability properties of a given configuration. During the recent experimental campaign carried out on TCV in the frame of the EUROFusion Medium Size Tokamak Task Force, dedicated experiments have been carried out, aimed at extensively studying the minimum achievable stability margin beyond which stability is lost. The results achieved, reported in the present paper, allow us in particular to experimentally validate the modelling approach used for the design of future devices. The experimental strategy is based on arranging a plasma configuration exhibiting a slowly decreasing stability margin, e.g. thanks to a slow ramp in elongation during a shot. The plasma is subject to repetitive perturbations (ELMs) during the configuration ramp. The instant at which the feedback controller is not able to stabilize the plasma any longer corresponds to the limit value of the stability margin, which depends on the feedback controller and the perturbation under analysis. Since the stability margin cannot be directly measured, a specific modelling activity is carried out with the CREATE_L model [4], which can provide indications on passive and active stabilization even beyond the calculation of the stability margin. [1] R. Wenninger et al 2015 Nucl. Fusion 55 063003 [2] C.M. Greenfield et al 1997 Nucl. Fusion 37 1215 [3] A. Portone 2005 Nucl. Fusion 45 926 [4] R. Albanese and F. Villone 1998 Nucl. Fusion 38 723

Speaker: Vincenzo Paolo Loschiavo

14:00 P5.1055 Integrated software environment for numerical modeling of experiments on tokamaks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1055.pdf Integrated software environment for numerical modeling of experiments on tokamaks D.Yu. Sychugov1, I.V. Zotov1, S.Yu. Solov’ev1, L.I. Vysotsky1,V.E. Lukash2, R.R. Khayrutdinov2, A.D. Sadykov3 1 Faculty of CMC, Lomonosov Moscow State University, 119991 Moscow, Russia 2 National Research Centre “Kurchatov Institute”, 123182 Moscow, Russia 3 Institute of Atomic Energy of NNC RK, 071100 Kurchatov, Kazahstan Nowadays, several hundred of numerical codes have been created and successfully operated within the framework of research program of Controlled Fusion, simulating all the most important processes in the plasma. The most important problem today is the creation of an integrated software environment on their basis capable of designing of Tokamak installations and supporting of experiments on them. The creation of such an environment implies the development of software that is equally convenient for calculators, experimenters and engineers. The development of such software includes the construction of developed informational and computational portals that allow using locally stored numerical codes and simulation systems remotely via a standard Web-browser. Recently appeared Web-programming systems, Internet technologies and new computer protocols provide the necessary basic tools for creating such informational-computational portals. We’ve developed a new open access computing resource nfusion.cs.msu.ru, which includes modules for calculating the equilibrium, vertical stability, evolution and transport of plasma, as well as simulation systems for magnetic plasma diagnostics [1-5]. These modules are integrated into a unified software environment that allows the numerical support on tokamak installations. The resource allows you to access the calculation modules stored on the server via the Internet, perform an automated data exchange between the modules, and print out the results of calculations in the form of files, pictures, graphs and tables. The resource supports the work of several users located in different places simultaneously and has a system of information support in two languages (Russian, English). This work was carried out with the support from the RFBR (grants No. 17-07-00544-a, 17-07-00883-a). References [1]. Sadykov A.D., Sychugov D.Yu., Shapovalov G.V., Chektybaev B.Zh., Skakov M.K. and Gasilov N.A. 2015 Nuclear Fusion, 55, N. 4, 55043017. [2]. Belov A.G., Zotov I.V., Sychugov D.Yu. 2012 SCET2012 - Spring World Congress on Engineering and Technology (Xi’an, China, 2012), pp 278-280 (http://www.scirp.org). [3]. Zotov I.V., Belov A.G. 2014 Problems of Atomic Science and Technology. Ser. Thermonuclear Fusion, 37, No. 1, pp.97-102. [4]. Khayrutdinov R.R., Lukash V.E. 2010 Problems of Atomic Science and Technology. Ser. Thermonuclear Fusion, 33, No. 3, pp.50-54. [5]. Sadykov A.D., Shapovalov G.V., Chectybaev B., Sychugov D.Yu., Gasilov N.A. 2013 Problems of Atomic Science and Technology. Ser. Thermonuclear Fusion, 36, No. 4, pp.94-101.

Speaker: D. Yu. Sychugov

14:00 P5.1056 Predictive integrated modelling for the preparation of the advanced operation scenarios in KSTAR

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1056.pdf Predictive integrated modelling for the preparation of the advanced operation scenarios in KSTAR H.-S. Kim1, Y.-M. Jeon1, S.W. Yoon1, J.Y. Kim1, Y.-S. Na2, Y.-K. Oh1, J.-F. Artaud3, F. Koechl4,5 1 National Fusion Research Institute, Daejeon, Republic of Korea 2 Department of Nuclear Engineering, Seoul National University, Seoul, Republic of Korea 3 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 4 Fusion@ӦAW, TU Wien, Atominstitut, Vienna, Austria 5 CCFE, Culham Science Centre, Abingdon, United Kingdom One of the mission goals of KSTAR project is to operate in the regime of long pulse (>10τR, ~300 s) and high performance (βN>3.0) [1,2]. In order to meet the mission and the objectives of the KSTAR tokamak, the hybrid and the advanced tokamak regime will be explored. In this way, an activity of predictive simulation study is essential to propose a practical guide before experiments are carried out. In this work, we have two purposes; one is the evaluation of the absorbed heating power and the driven current associated with KSTAR H/CD upgrade plan[3] on various plasma conditions, and the other is the feasibility study of the advanced operation scenario. We mainly consider totally 18 MW of external heating power with two H/CD systems such NBI and ECH. KSTAR NBI system will equips six beam sources manageable up to totally 12 MW. Two of them, 4 MW, will be capable to be injected to off- axis. KSTAR ECH system will equips four 105/140 GHz gyrotrons manageable up to totally 4 MW and two 170 GHz gyrotrons up to totally 2 MW. Based on the H/CD system specifications, the database applicable to design the operation scenario is built by evaluating each H/CD system on various plasma operation conditions. Secondly, the practical guide of external H/CD mix scenarios, the appropriate scheme of the combination of NBI beam lines, and the launching conditions of ECH system are suggested to achieve advanced operation regimes. Finally, the advanced operation scenarios are suggested for KSTAR. The suggested operation scenarios are simulated and extrapolated based on the existing high performance discharges operated in relatively low heating power in KSTAR. Also, the corresponding specific q profiles are also presented here to evaluate the reliability in the view of the physics based manner. The reliable results from our work could become a useful database for exploring the advanced regime of KSTAR discharges in the near future. Reference [1] Kwon M. et al 2011 Nucl. Fusion 51 094006, [2] Na Y-S. et al 2009 Nucl. Fusion 49 115018 [3] Wang S-J. et al 2018 KSTAR Conference (Muju, Republic of Korea)

Speaker: Hyun-Seok Kim

14:00 P5.1057 Study on Optimal Configuration of a Tokamak Fusion System with Coupled Analysis of Tokamak Plasma and a Radiation Transport

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1057.pdf Study on Optimal Configuration of a Tokamak Fusion System with Coupled Analysis of Tokamak Plasma and a Radiation Transport B. G. Hong Chonbuk National University, 567 Baekje-daero, Jeonju-si, Jeollabuk-do, Korea 54896 New simulation method which couples a conventional tokamak plasma analysis and a radiation transport analysis is developed. This simulation can incorporate both plasma physics and engineering constraints on a tokamak fusion system self-consistently. Using this simulation, we found not only plasma performance and system parameters, but also the optimal radial build of the tokamak fusion system with the plasma physics and engineering constraints moderately extrapolated from the constraints adopted in the design of International Thermonuclear Experimental Reactor (ITER). In a low-aspect-ratio configuration, the minimum major radius to produce a given fusion power was determined by the shielding requirements and the magnetic field at the toroidal field (TF) coil. With a confinement enhancement factor H = 1.3, Q > 10 was possible for fusion power greater than 1,000 MW with an aspect ratio of A = 1.5; however, Q > 10 was possible for fusion power greater than 2,000 MW with an aspect ratio of A = 2.0. In a normal aspect ratio configuration, configuration with only an outboard breeding blanket does not satisfy requirement on tritium self-sufficiency. The optimum system size to produce a given fusion power is determined by the requirements on the shielding, tritium breeding and the magnetic field at the toroidal field (TF) coil. With a confinement enhancement factor H = 1.3, Q > 30 was possible for fusion power greater than 2,000 MW with an aspect ratio of A = 3.0; however, Q > 30 was impossible with an aspect ratio of A = 4.0. The tritium breeding capability of a low-aspect-ratio tokamak exhibited better performance since the number of fusion neutrons that contributed to tritium breeding were larger than the case with a larger aspect ratio tokamak.

Speaker: B. G. Hong

14:00 P5.1058 Merging/Compression start-up in ST40: Comparison between the first experimental results and numerical model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1058.pdf Merging/Compression start-up in ST40: Comparison between the first experimental results and numerical model P.F. Buxton1 , O. Asunta1 , M.P. Gryaznevich1 , B Huang1 , S. McNamara1 , J.M. Wood1 1 Tokamak Energy Ltd., 120A Olympic Avenue, Milton Park OX14 4SA, UK Tokamak Energy Ltd. is presently commissioning ST40 [1], a relatively small (R = 0.4 m) spherical tokamak which has been designed to operate with a high toroidal field (BT ∼ 3 T) and high current density (I p ∼ 2 MA). The aim of this commissioning has been to test all sub- systems and to integrate them into the Plasma Control System (PCS). During this phase ST40 operated with a toroidal field of 0.7 T at R = 0.4 m (Irod = 1.38 MA) and have achieved a plasma current of I p ∼ 300 kA. Start-up in ST40 uses a technique called Merging/Compression which involves [2, 3]: in- ductively forming plasma around two internal poloidal field coils, when the current within the internal poloidal coils is close to zero the two plasma rings are attracted towards each other and merge, and through magnetic reconnection ∼ 5% of the poloidal flux is converted into thermal energy. To manage forces within ST40 the vacuum vessel is relatively thick, consequently, substantial eddy currents (up to 700 kA) are induced into the vessel during Merging/Compression start- up. This adds two complications: firstly, it makes magnetic reconstruction more challenging and secondly, the eddy currents have a large impact on the Merging/Compression technique - therefore they must be accounted for when designing Merging/Compression start-up scenarios. In this presentation both of these issues are discussed and addressed. During this commissioning phase ST40 had the following magnetic diagnostics: 5 Rogowski coils, 36 flux loops and 70 poloidal field pickup probes, and we have developed and tested a new magnetic reconstruction code in which the vessel is approximated by the 20 longest lived eigenmode excitations and the plasma is approximated by a set of orthogonal basis functions. Later, this code will be integrated into the PCS to allow real-time control of the plasma current, plasma current centroid position (RI p and ZI p ) and plasma shape. We have included the effects of these eddy currents in our predictive modeling of the Merging/Compression start-up technique, and find good agreement with experimental results. References [1] M.P. Gryaznevich, ST Path to Fusion: First Results from ST40, EPS (2018) [2] P.F. Buxton, M.P. Gryaznevich, Merging compression start-up predictions for ST40, Fus. Eng. Des. (2017) [3] M.P. Gryaznevich, A. Sykes, Merging-compression formation of high temperature tokamak, Nuc. Fus. (2017)

Speaker: Peter Francis Buxton

14:00 P5.1059 Simulating the plasma startup scenario in the Alborz tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1059.pdf Simulating the plasma startup scenario in the Alborz tokamak M. Ghasemi1, H. Sadeghi1, D. Iraji1, R. Amrollahi1 1 Fusion Laboratory, Amirkabir University of Technology, Tehran, Iran Abstract The Alborz tokamak program was started from 2012 at Amirkabir university of technology – Iran. This device has been assembled recently and now the discharge tests are in the process of getting started. The startup process in tokamak machines presents unique challenges due to their characteristics. In the present study, a series of simulations are carried out in Alborz tokamak to improve the startup to test whether the proposed startup scenarios are feasible and appropriate. For this important goal, the power supply modification and its influence on discharge are considered and investigated in this work.

Speaker: Maryam Sadat Ghasemi

14:00 P5.1061 Poloidal 2D scans to investigate potential and density profiles in the TJ-II stellarator using Heavy ion beam probe diagnostic

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1061.pdf July 2 – 6, 2018 Prague, Czech Republic Poloidal 2D scans to investigate potential and density profiles in the TJ-II stellarator using Heavy ion beam probe diagnostic R. Sharma1a, P. O. Khabanov2,6, A.V. Melnikov2,4, N.K. Kharchev2 , E. Sánchez1, A. Chmyga3, G.N. Deshko3, L.G. Eliseev2, C. Hidalgo1, S.M. Khrebtov3, A.D. Komarov3, A.S. Kozachek3, L.I. Krupnik3, J. Lopez1, G. Martin1, A. Malaquias1a, B van Milligen1, A. Molinero1, J.L. de Pablos1, I. Pastor1, M.V. Ufimtsev5, V.N. Zenin3 and the TJ-II team 1a IPFN, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa, Portugal. 1 Fusion National Laboratory, CIEMAT, 28040, Madrid, Spain 2 National Research Centre ‘Kurchatov Institute’, 123182, Moscow, Russia 3 Institute of Plasma Physics, NSC KIPT, 611108, Kharkov, Ukraine 4 National Research Nuclear University MEPhI, 115409, Moscow, Russia 5 Moscow State University, 119991, Moscow, Russia 6 Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Russia Recent simulations have shown that in the plasma regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the largest fluctuations of density and plasma potential form narrow bandlike structures on the magnetic surfaces [1]. In addition, flux-surface variations of electrostatic potential can have a significant impact on high-Z impurities radial fluxes [2]. Heavy Ion Beam Probe (HIBP) set up has been used to experimentally characterize these 2-D structures of plasma fluctuations in the TJ-II stellarator mapped by varying the energy of the Cs+ probing beam. Experiments were carried out in low-density (0.4 x 1019 m-3) ECRH plasmas characterized by peaked and hollow electron temperature and density profiles respectively. This unique experiment allows the investigation of 2D poloidal contour map for plasma potential and the RMS fluctuation in potential and density from high to low field side for the plasma volume under examination [Fig. 1]. The 2D poloidal scan indicates the local maximum of potential (fig1 left) to be slightly shifted upwards from the center of vacuum magnetic flux surface, which coincides with the local maximum in RMS potential(fig1 Right). Also, there is a visible up-down poloidal asymmetry of RMS potential fluctuations for both LFS and HFS in the range of 5-10 V. Similar contour plots were also investigated for RMS fluctuation in density. It should be noted that there exist an uncertainty in the HIBP measurements for ρ > ±0.8 due to low plasma density in periphery. The 2-D characterization of plasma potential and fluctuations covering the whole TJ-II plasma cross-section will be performed in the near future. 48 890 46 885 45 846 43 807 -5 42 768 40 -5 729 690 38 651 37 612 35 34 y (cm) 573 y (cm) 534 32 495 30 456 29 417 -10 27 -10 378 26 339 24 300 22 261 21 222 19 183 18 144 16 105 -15 -15 -30 -25 -20 -15 -30 -25 -20 -15 x (cm) x (cm) Fig1: The 2D poloidal mapping of mean potential (left) and RMS potential fluctuations (right) for the plasma volume scanned (units in volts) [1] P. Xanthopoulos et al., Physical Review X 6 (2016) 021033 [2] J.M. García-Regaña, et al., Nucl. Fusion 57 (2017) 056004 Corresponding author: Ridhima Sharma Email: rsharma@ipfn.ist.utl.pt

Speaker: Ridhima Sharma

14:00 P5.1062 Poloidal asymmetry of perpendicular velocity of the density fluctuations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1062.pdf Fast ion confinement study by NB blips in the LHD deuterium plasma Taleo Nishitani1, Kunihiro Ogawa1,2, Sadayoshi Murakami3, Neng Pu2, Hiroki Kawase2, Mitsutaka Isobe1,2, Masaki Osakabe1,2, and the LHD Experiment Group 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 2 The Graduate University for Advanced Studies, Toki- 509-5292, Japan 3 Kyoto University, Kyoto 615-8520, Japan The confinement of neutral beam (NB)-injected fast ions has been investigated by neutron emission rate response to the short pulse NB injection called “NB-blip” at the Large Helical Device (LHD). This method is widely used in tokamaks with deuterium plasma operation, however, this is the first time application to the large size helical systems. Generally, neutron intensity decay time after the NB blip is analysed by a 0-dimensional fast ion slowing down model, where differences of the beam deposition profile for each shot is not taken into account. We have developed a neutron emission rate calculation code FBURN based on the classical slowing down model, which is taking into account of not only the beam deposition profile but also other plasma parameter profiles such as the electron density and the electron temperature, and time evolutions of those parameters. The confinement of NB-injected fast ions is investigated by the discrepancies between measured and calculated neutron emission decay time τn after the NB blip and between measured and calculated maximum neutron emission rate Sn during the NB blip. The former is reflected by the collisional diffusion mainly and the later is reflected by the collision-less diffusion and prompt loss mainly. The Large Helical Device (LHD) has five NB injectors. NBI#1, #2, and #3 are tangential direction injectors with typical energy is 180 keV. NBI#4 and #5 are perpendicular direction injectors with typical energies are 60 keV and 80 keV, respectively. In this experiment, NBI#1, #2, #3, and #4 each with the pulse width of 40 ms are injected into different configuration plasmas with various electron densities. It is found that the diffusion coefficient of NB-injected fast ion evaluated from τn is 1-3 m2/s for perpendicular injections and 0.3 m2/s or smaller for tangential injections, and the diffusion coefficient evaluated from Sn is 2-5 m2/s for perpendicular injections and 1.5 m2/s or smaller for tangential injections. Also, the diffusion coefficient increases as the plasma axis is shifted outward.

Speaker: Laure Vermare

14:00 P5.1063 Intrinsic impurity composition in helium and hydrogen discharges in Wendelstein 7-X

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1063.pdf Intrinsic impurity composition in helium and hydrogen discharges in Wendelstein 7-X B. Buttenschön, D. Zhang, Th. Wegner, R. Burhenn, and the W7-X Team Max Planck Institute for Plasma Physics, Greifswald, Germany Intrinsic impurities in fusion devices serve as an indicator for thermally overloaded in- vessel components, but also constitute an important energy loss channel entering the global energy balance of the confned plasma. In the Wendelstein 7-X stellarator (W7-X), the impurity composition is constantly monitored by means of the High Efciency XUV Overview Spectrometer (HEXOS) system. The intensity calibration of the instrument, available over large parts of the covered wavelength range, allows, combined with transport codes such as STRAHL, to estimate the concentration of selected impurities. The transport coefcients employed in the calculations are obtained from the evaluation of laser blow-of eeperiments that have been performed in various discharge scenarios. The intrinsic impurity composition (with C and O being the main impurities) and their concentrations are evaluated for W7-X discharges in helium and hydrogen, which showed a signifcant diference in overall plasma performance. In addition, the daily and the long- term impurity concentration evolution are evaluated particularly with regard to the planned wall boronization in the upcoming operation phase.

Speaker: Birger Buttenschön

14:00 P5.1064 The EUROfusion JET-ILW global confinement database

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1064.pdf The EUROfusion JET-ILW global confinement database M. Maslov1, M. Romanelli1 and JET contributors* 1 UKAEA, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK * See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″ In 2009-2011 so-called ITER-like wall was installed on JET tokamak, with beryllium limiters and tungsten divertor. Change of the plasma facing materials from carbon to metallic had a significant effect on plasma operations and confinement. Achieving steady plasma performance has become more challenging due to impurity accumulation [1], which has put additional constraints on the available operational space. Confinement in scenarios with low Ploss/PLH<2 was found to be worse with respect to similar scenarios in JET C-wall, due to degraded confinement in the pedestal [2]. This contribution summarises the recent work done under the EUROfusion JET confinement database project. The project encompasses the systematic collection and study of the JET 0-D data as well as sharing with interested parties such as the international H-mode confinement database. The work is presently focussed on the JET-ILW data which has not been included into the international multimachine database until now. Virtually all steady state type I ELMy H-mode plasmas achieved in the JET-ILW period so far were included in the dataset, with all the standard engineering parameters and measured quantities. The database is in progress of being converted to the IMAS (ITER Integrated Modelling & Analysis Suite [3]) format and will be made available to the EUROfusion Research Units and collaborators. The database is under continuous development and expansion of the dataset with new pulses is anticipated, including the future TT and DT operations. For the presently available data a study of the global energy confinement scaling with various parameters will be shown in this work together with comparison to the widely used HIPB98(y,2) scaling. The domain of existence of JET-ILW confinement database will be compared with the JET-C one. Effect of the parameters which are not included into the H98 scaling will also be discussed, such as divertor configuration, gas fuelling, SOL density and neutral gas pressure outside the plasma. [1] G. Matthews et al, “Plasma operation with an all metal first-wall: Comparison of an ITER-like wall with a carbon wall in JET”, Journal of Nuclear Materials, Volume 438, Supplement, July 2013, S2-S10 [2] M.N.A. Beurskens et al, “Global and pedestal confinement in JET with a Be/W metallic wall” Nucl. Fusion 54 (2014) 043001 [3] S.D Pinches et al, 44th EPS Conference on Plasma Physics (Belfast, Ireland), P4.155 http://ocs.ciemat.es/EPS2017PAP/pdf/P4.155.pdf

Speaker: Mikhail Maslov

14:00 P5.1065 Insight into turbulent transport via measurements of the plasma flow

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1065.pdf Insight into turbulent transport via measurements of the plasma flow R. M. McDermott1, A. Lebschy1,2, C. Angioni1, I. Erofeev1, E. Fable1, W. Hornsby1, A. Medvedeva1,2, D. Prisiazhniuk1,2, U. Stroth1,2, E. Viezzer3 and the ADEX Upgrade Team [1] Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany [2] Physik-Department E28, Technische Universität München, Garching, Germany [3]Dept. of Atomic, Molecular and Nuclear Physics, University of Seville The core charge exchange recombination spectroscopy (CXRS) systems on ASDEX Upgrade (AUG) now provide a very high accuracy measurement of the impurity (B, N) poloidal rotation in the plasma core (upol,Z). This diagnostic has been used to assemble a database of upol,Z measurements that covers a wide range of plasma parameters. In the edge (ρϕ>0.7) upol,Z is electron-diamagnetic directed, consistent with neoclassical (NC) theory. However, in the plasma core (0.2 0.8). Second, the core intrinsic toroidal rotation reverses concomitant with the peaking of the electron density, which is indicative of trapped electron modes (TEM) also in the plasma core. Next, at the point of both maximum rotation reversal and density peaking, ion-directed turbulent phase velocities are observed in the plasma edge supporting the idea that the turbulence change from TEM to ITG occurs first in this region and then propagates inward. Lastly, the core toroidal rotation reverses again as the electron density profile flattens, indicating ITG turbulence also in the core. These experimental observations show a connection between the dominant residual stress mechanisms and the electron density profile. This is inline with the results of new, non- linear, radially global, turbulence simulations of AUG Ohmic plasmas, which quantitatively reproduce the measured, hollow, rotation gradients and show that the shape of the simulated residual stress and intrinsic flow is strongly determined by the second derivative of the density profile.

Speaker: Rachael Marie McDermott

14:00 P5.1066 Density dependence of heat pulse transport property in LHD

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1066.pdf Density dependence of heat pulse transport property in LHD T. Kobayashi1 , K. Ida1 , S. Inagaki2,3 , T. Tokuzawa1 , H. Tsuchiya1 , N. Tamura1 , H. Igami1 , Y. Yoshimura1 , S.-I. Itoh3,2,4 and K. Itoh5,1,3 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan 2 Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan 3 Research Center for Plasma Turbulence, Kyushu University, Kasuga, Japan 4 Department of Innovative Energy Science and Engineering, Graduate School of Engineering, Chubu University, Kasugai, Japan 5 Institute of Science and Technology Research, Chubu University, Kasugai, Japan Understanding of cross-field thermal transport in magnetically confined plasmas is regarded as a key issue for realization of thermonuclear fusion reactor. It is well-known that electron ther- mal transport in axially heated plasmas cannot be modeled by the classical diffusion transport model with a single scalar diffusive coefficient. Recently, emergence of hystereses in the flux- gradient relation was discovered [1, 2], involving rapid responses of turbulence intensity and turbulent transport to heating. A model that can describe the transport hysteresis was developed [3]. Empirically the transport hysteresis is known to emerge in low density plasmas. However, systematic density scans have not yet been performed. In this study, we performed the modulation electron cyclotron resonance heating (MECH) experiment in order to analyze the transport hysteresis in the electron thermal transport in LHD. The MECH frequency and the peak-to-peak amplitude were set to 23 Hz and ∼ 700 kW, re- spectively. The target plasmas were sustained with two nearly balanced neutral beam heating systems. Electron density was scanned from 0.6 × 1019 m−3 to 2.3 × 1019 m−3 with a small step ∼ 0.3 × 1019 m−3 , in order to discuss the density dependence of the transport hysteresis. Re- sponse in the electron temperature was measured with a multi-channel electron cyclotron emis- sion radiometer system. At low density plasmas, the transport hysteresis appeared. The hystere- sis width became smaller as the density is increased. Above a threshold density, 1.5 × 1019 m−3 , the hysteresis width became less than the noise level. References [1] S. Inagaki et al Nucl. Fusion 53 113006 (2013) [2] T. Kobayashi et al Nucl. Fusion 57 076013 (2017) [3] S.-I. Itoh and K. Itoh Sci. Rep. 2 860 (2012)

Speaker: Tatsuya Kobayashi

14:00 P5.1067 Resonance overlap and non-linear velocity spread in Hamiltonian beam-plasma systems

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1067.pdf Resonance overlap and non-linear velocity spread in Hamiltonian beam-plasma systems N. Carlevaro1,2 , G. Montani1,3 , F. Zonca1,4 1 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy 2 LTCalcoli Srl, Via Bergamo 60, 23807 Merate (LC), Italy 3 Physics Department, “Sapienza” University of Rome, P.le Aldo Moro 5, 00185 Roma (Italy) 4 Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, China We analyze in some detail the properties of the beam-plasma instability [1, 2, 3] with respect to both the morphology of the linear dispersion relation, and the non-linear behavior of the particle velocity spread. First, we investigate non-perturbative effects in the dispersion relation, charac- terizing the linear growth rates and the frequency shift with respect to the plasma frequency where the perturbative inverse Landau damping expression breaks down. Then, we discuss the behavior of the non-linear velocity spread as function of the linear growth rate. We introduce three basic criteria to estimate the non-linear velocity spread, and demonstrate that only the full change of the particle velocity profile is really predictive of resonance overlap. Finally, we dis- cuss aspects of the mode saturation level in the case of a broad fluctuation spectrum [4] and, by the help of an analytical toy model, we illuminate the mechanism responsible for higher satura- tion intensity with suitable overlapping resonances with respect to the case of single resonance with an isolated mode. ** Work carried out within the framework of EUROfusion as Enabling Research Projects: NLED (AWP15-ENR-01-ENEA-03) and NAT (AWP17-ENR-MFE-MPG-01) ** References [1] L. Chen, F. Zonca, Rev. Mod. Phys. 88, 015008 (2016) [2] N. Carlevaro, M.V. Falessi, G. Montani, F. Zonca, J. Plasma Phys. 81, 495810515 (2015) [3] T.M. O’Neil, J.H. Winfrey, J.H. Malmberg, Phys. Fluids 14, 1204 (1971) [4] N. Carlevaro, A.V. Milovanov, M.V. Falessi, G. Montani, D. Terzani, F. Zonca, Entropy 18, 143 (2016)

Speaker: Nakia Carlevaro

14:00 P5.1068 Dynamics and transport in the W7-X Scrape-Off-Layer measured by reciprocating probes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1068.pdf Dynamics and transport in the W7-X Scrape-Off-Layer measured by reciprocating probes C. Killer1 and the W7-X team1 1 Max-Planck-Institut fuer Plasmaphysik, Greifswald, Germany Wendelstein 7-X (W7-X) is an optimised stellarator employing an island divertor. In this con- cept, large, low rational magnetic islands form the three-dimensional heat and particle exhaust to the divertor. Understanding the plasma properties and dynamics especially within the islands is essential for the assessment of parallel and perpendicular heat and particle transport in the edge of W7-X and therefore crucial for both sustaining high performance plasmas as well as ensuring safe divertor operation. One major and established diagnostic approach for Scrape-Off-Layer (SOL) measurements is the use of reciprocating probes. At W7-X, a versatile carrier system for probe heads, the Multi- Purpose Manipulator (MPM), is installed at the outboard mid-plane. From the plasma vessel wall, it can perform fast plunges through the SOL (including the island chain) up to the last closed flux surface. Using the MPM with a dedicated probe head for fluctuation studies con- taining a poloidal array of 22 Langmuir pins and a Mach probe for parallel and perpendicular flows, we obtained radial profiles of plasma density, electron temperature, plasma flows and electric fields. These measurements allow us to infer properties relevant for divertor operation, such as the plasma pressure driving the parallel flow to the divertors or the SOL width which is defined by the ratio of parallel and perpendicular transport and is related to the strike line properties on the divertor. Exploiting in addition the poloidal probe array gives insight into the poloidal dynamics and propagation of turbulent fluctuations in plasma density and poloidal electric field and the associated perpendicular fluctuation-induced transport. A particular focus of this contribution is on the peculiarities of the island divertor concept. First data analysis from the 2017 operation phase OP1.2a suggests a high sensitivity of plasma pa- rameters in the islands (e.g. density, temperature, flow, electric field) to subtle changes in the edge magnetic field topology. Typical plasma parameters obtained using the MPM are electron temperatures up to 100 eV, densities up to 1 · 1019 m−3 and electric fields up to 20 kV/m. The dependency of SOL plasma profiles and the associated gradient-driven turbulent transport is observed to display a strong scaling with central heating power and core plasma density.

Speaker: Carsten Killer

14:00 P5.1069 Filament statistics with imaging techniques and comparison with langmuir probes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1069.pdf Filament statistics with imaging techniques and comparison with langmuir probes T. Farley1,2, F. Militello1, N.R. Walkden1, J. Harrison1, S.S. Silburn1, J.W. Bradley2 1) CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 2) Department of Electrical Engineering and Electronics, University of Liverpool, L69 3GJ, UK The dynamics of plasma filaments govern the transport of particles in the scrape-off layer (SOL) of tokamak plasmas [D’Ippolito et. al., PoP, 2011] and thus scrape off layer density profiles. A technique has been developed which maps the light emission in fast visible camera images to a midplane grid of field line emission, using camera registration and magnetic equilibrium information. Emission along field lines is used as a proxy for plasma density, facilitating the identification and tracking of SOL plasma filaments. This pseudo-inversion filament analysis technique is described in detail and benchmarked against synthetic camera data in new paper [T Farley et. al., RSI, 2018 (in preparation)]. Here the technique is applied to L-mode fast camera data from the MAST tokamak. Considering individual field lines from within 2D field line emission maps, we construct pseudo-Langmuir probes. These probes are used to calculate probability density functions (PDFs) and time averaged radial profiles and perform conditional averaging and other related statistical techniques. The statistics of the filaments’ properties are interpreted using the theoretical ergodic framework described in [F. Militello & J.T. Omotani, PPCF, 2016] in order to better understand how time averaged filament dynamics produce SOL density profiles. Toroidal filament separation is found to be exponentially distributed, indicating toroidally uniform, independent generation of filaments with no toroidal mode number. Filament waiting times are also seen to be exponentially distributed, indicating filament generation is a Poisson process in agreement with Langmuir probe time series measurements. These findings provide important validation of assumptions in the ergodic framework and give insight into the physics of the filaments. Finally, the statistics measured with the pseudo-Langmuir probe technique are compared directly with Langmuir probe measurements made in similar discharges and with results from the full 2D pseudo-inversion technique.

Speaker: Tom Farley

14:00 P5.1070 Influence of the collisionality and the safety factor on the transport in the Globus-M spherical tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1070.pdf Influence of the collisionality and the safety factor on the transport in the Globus-M spherical tokamak A.Yu. Telnova1, G.S. Kurskiev1, N.N. Bakharev1, V.K. Gusev1, E.O. Kiselev1, N.A. Khromov1, D.M. Larionova1, M.M. Larionova1, V.B. Minaev1, I.V. Miroshnikov1, M.I. Patrov1, Yu.V. Petrov1, N.V. Sakharov1, A.D. Sladkomedova1, P.B. Shchegolev1, V.V. Solokha1, V.A. Tokarev1, S.Yu. Tolstyakov1 1 Ioffe Institute, St. Petersburg, RF The presentation is devoted to analysis of the thermal energy confinement in Globus-M [1]. Globus-M was a spherical tokamak with the major radius R=0.36 m, minor radius a=0.24 m, the ranges of operational current and toroidal magnetic field were Ip=100-250 kA and BT=0.3-0.5 T correspondingly. The aim of the research was to identify the thermal insulation efficiency in a compact spherical device in terms of the electron and ion diffusion coefficients for different discharge conditions. The experimentally measured electron and ion temperature profiles as well as more accurate estimations of the NBI absorbed power allowed us to provide increased accuracy of the transport modelling using ASTRA code [2]. It was found that both BT and IP increase had a strong effect on the electron and ion heat diffusivities (χe and χi respectively). The comparison of χi with neoclassical theory was performed and the role of the collisionality (ν*) and safety factor (q) on the transport was analyzed. The influence of the q=1 resonant surface presence on the plasma performance was studied. The NBI at the current ramp-up phase permitted distinguishing the relatively long phase with inversed q profile, while minimum value of q (qmin) in the plasma core was more than one (AT-like q profile). Such modes can be characterized by improved core confinement and are usually accompanied by formation of the internal transport barriers (ITB). The ITB formation is also relevant for the pure ohmic heated plasma. References [1] Gusev V. K. et al, 1999 Tech. Phys. 44 1054. [2] Pereverzev G. and Yushmanov P. N., 2002, Max-Plank IPP Report 5/98.

Speaker: Anna Telnova

14:00 P5.1071 Lagrangian Coherent Structures in magnetized plasmas: Particle transport in a time dependent magnetic configuration

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1071.pdf Lagrangian Coherent Structures in magnetized plasmas: Particle transport in a time dependent magnetic configuration D. Grasso1 , G. Di Giannatale2 , M.V. Falessi3 , F. Pegoraro4 ,T.J. Schep5 1 ISC - CNR and Politecnico di Torino, Dip. Energia C.so Duca degli Abruzzi 24, Torino. Italy 2 IGI - CNR, Corso Stati Uniti 4, Padova, Italy 3 ENEA, C. R. Frascati, Via E. Fermi 45, Frascati, Italy 4 Dip. Fisica E. Fermi, Pisa University, largo Pontecorvo 3, Pisa, Italy 5 Dep. Applied Physics, Eindhoven Univ. of Technology, 5600MB Eindhoven, The Netherlands The understanding of transport phenomena in low-collisionality, magnetized plasmas is one of the most challenging tasks in the investigation of both laboratory and space plasmas due to their generally non-diffusive nature. In recent years the concept of Lagrangian Coherent Struc- tures (LCS) has been introduced by G. Haller in the context of transport processes in complex fluid flows [1]. LCS are a generalization of the dynamical structures observed in autonomous and periodic systems to temporally aperiodic flows. Therefore, they separate the flow domain into macro-regions inside which fast mixing phenomena take place. Over the finite time span which characterizes the LCS these macro-regions do not exchange fluid elements and thus act as transport barriers. In two recent works [2, 3] we apply this conceptual framework to the study of particle transport in a magnetized plasma. Futhermore we introduce a simplified model that allows us to consider explicitly a magnetic configuration evolving in time on timescales comparable to the particle transit time through the configuration. This analysis requires that a system that is aperiodic in time is investigated. In this case the Poincaré map technique can- not be applied and LCSs remain the only viable tool. By means of a numerical procedure we investigate the LCSs in the case of a magnetic configuration with two island chains that are gen- erated by magnetic reconnection and evolve nonlinearly in time. The comparison with previous results [4, 5], obtained by assuming a fixed magnetic field configuration, allows us to explore the dependence of transport barriers on the particle velocity. References [1] G Haller. Annual Review of Fluid Mechanics, 47:137–162, 2015. [2] G Di Giannatale, MV Falessi, D Grasso, F Pegoraro, and TJ Schep. submitted to Physics of Plasmas. [3] G Di Giannatale, MV Falessi, D Grasso, F Pegoraro, and TJ Schep. submitted to Physics of Plasmas. [4] G Rubino, D Borgogno, M Veranda, D Bonfiglio, S Cappello, and D Grasso. submitted to Plasma Physics and Controlled Fusion, 57(8):085004, 2015. [5] MV Falessi, F Pegoraro, and TJ Schep. Journal of Plasma Physics, 81(05):495810505, 2015.

Speaker: Daniela Grasso

14:00 P5.1072 Study of the transport coefficient dependence on the heating power in self-organized plasma in the T-10 tokamak

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1072.pdf Study of the transport coefficient dependence on the heating power in self-organized plasma in the T-10 tokamak N.V. Kasyanova1,2, K.A. Razumova1, A.A. Borschegovskij1, M.M. Dremin1, N.A. Kirneva1,3, S.V. Krylov1, T.B. Myalton1, G.E. Notkin1, Yu.D. Pavlov1, D.V. Ryzhakov1, D.V. Sarychev1, D.S. Sergeev1, M.V. Chukanov1 1 National Research Center “Kurchatov Institute”, Moscow, Russia 2 Moscow Institute of Physics and Technology, Dolgoprudny, Russia 3 National Research Nuclear University MEPhI, Moscow, Russia Effect of the energy confinement enhancement during impurity gas puffing in the T-10 tokamak is studied. Experiments were carried out with Ne and He puffing in various regimes with ohmic heating (OH) and on- and off-axis ECR heating (Ipl=230 kA, Bz= 1.9 - 2.3 T, ne=1.5-4x1019 m-3, PECRH=0.45-1.3 MW). It was shown that in both OH and ECRH regimes the stored energy first increased with growth of the radiation losses in the plasma edge due to the impurity gas puffing and then it reached a saturation level Wsat. It is found that for on-axis ECRH deposited in a narrow area in the center of the plasma the energy saturation level depends only on ECRH power and doesn't depend on the kind of impurity. In this work, the explanation of the observed effect from a plasma self-organization position is offered. This approach assumes that the plasma pressure profile is self-consistent. Relaxation of the pressure profile distorted by external impact is described by the energy balance equation obtained in [1]. In this equation the transport coefficient χ can be written as follows: χ = θ(χ0+χ1). The first term χ0 corresponds to the undistorted self-consistent pressure profile, the second term χ1(Γ1) depends on the radial heat flux Γ1 disturbing the pressure profile. During impurity gas puffing the radiation losses in the plasma periphery increase resulting in decrease of the radial heat flux Γ1, hence the transport coefficient χ in the plasma edge reduces until it reaches the minimum value χ0. As a result the stored energy of plasma increases and reaches the saturation level. The value χ0 doesn't depend on the heating power and can be determined from the energy saturation level Wsat. The value χ1 is obtained from dependence of the stored energy on the power of OH and ECR heating. The dependence of Wsat on plasma parameters is defined by the coefficient θ ~ p0β0/qL. [1] K.S. Dyabilin and K.A. Razumova. Nucl. Fusion 55 (2015) 053023

Speaker: Nadezhda Kasyanova

14:00 P5.1074 Gyrokinetic theory of toroidal Alfvén eigenmode nonlinear saturation via ion Compton scattering

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1074.pdf Gyrokinetic theory of toroidal Alfvén eigenmode nonlinear saturation via ion Compton scattering Z. Qiu1 , L. Chen1,2 and F. Zonca3,1 1 Inst. Fusion Theory and Simulation, Zhejiang Univ., Hangzhou 310027, P.R.C. 2 Dept. Physics and Astronomy, Univ. of California, Irvine CA 92697-4575, U.S.A. 3 ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Frascati (Roma), Italy Shear Alfvén wave instabilities such as toroidal Alfvén eigenmode (TAE) [1] are expected to play important roles in magnetic confinement fusion devices as energetic particles (EPs) contribute significantly to the total power density [2, 3]. TAE can be driven unstable by EPs, and in turn, induce EP transport and degrade overall plasma confinement. In this work, the TAE frequency cascading via ion Compton scattering and saturation due to enhanced coupling to SAW continuum, originally investigated in Ref. [4] in the long wavelength MHD limit, is extended to the burning plasma relevant short wavelength regime [3]. The equa- tion describing a test TAE nonlinear evolution due to interacting with the bath of background TAEs is derived using gyrokinetic theory, which is then applied to deriving the wave-kinetic equation for the TAE spectrum evolution in the continuum limit. The wave-kinetic equation is solved to obtain the saturation spectrum of TAE, yielding an overall fluctuation level lower than the estimation by drift kinetic theory [4], as a consequence of the enhanced nonlinear couplings in the short wavelength limit [5]. The bulk ion heating rate from nonlinear ion Landau damp- ing is also calculated. Our theory also shows that, for TAE saturation in the parameter range of practical interest, several processes with comparable scattering cross sections can be equally important. References [1] C. Z. Cheng, L. Chen and M. S. Chance, Ann. Phys. 161, 21, (1985). [2] M. Rosenbluth and P. Rutherford, Phys. Rev. Lett. 34, 1428 (1975). [3] L. Chen and F. Zonca, Rev. Mod. Phys. 88, 015008, (2016). [4] T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266, (1995). [5] Z. Qiu, L. Chen and F. Zonca, Nuclear Fusion 57, 056017, (2017).

Speaker: Zhiyong Qiu

14:00 P5.1075 Fast isotope mixing in Ion Temperature Gradient driven turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1075.pdf Fast isotope mixing in Ion Temperature Gradient driven turbulence J. Citrin1 , C. Bourdelle2 , Y. Camenen3 , M. Marin1 , F.J. Casson4 , F. Koechl5 , M. Maslov4 and JET Contributors6 1 DIFFER - Dutch Institute for Fundamental Energy Research, Eindhoven, the Netherlands 2 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France 3 CNRS, Aix-Marseille Univ., PIIM UMR7345, Marseille, France 4 CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK 5 ÖAW/ATI, Atominstitut, TU Wien, 1020 Vienna, Austria 6 See the author list of X. Litaudon et al 2017 Nucl. Fusion 57 102001 Recent multiple-isotope experiments at JET have found evidence for ion particle transport co- efficients larger than electron particle transport coefficients [1]. We apply GKW [2] nonlinear and QuaLiKiz [3] quasilinear modelling to show the consistency with expectations of particle transport in the Ion-Temperature-Gradient (ITG) driven regime. The effect is explained through the dependency of particle transport coefficients on the wave-particle resonance condition [4]. In spite of the disparity in particle transport coefficient magnitude, ambipolarity is maintained by large inward ion convective pinches being compensated by the large outward diffusion. In multiple-ion experiments, the ambipolarity condition can be matched by the summation of mul- tiple ion fluxes, providing for additional freedom where the large ion transport coefficients can then provide fast ion mixing. We illustrate these ramifications for multiple-isotope transport through JETTO [5, 6] integrated modelling with QuaLiKiz, through numerical experiments based on a well modelled JET-ILW baseline discharge [7]. The large ion particle transport co- efficients implies that the ion density profiles are uncorrelated to the corresponding ion source, allowing peaked isotope density profiles even in the absence of core source. Furthermore, the relaxation time of the individual ion profiles in a mixed system can be significantly faster than the total density profile relaxation time which is constrained by the electrons. This leads to fast isotope mixing and fast impurity transport in ITG regimes. In Trapped-Electron-Mode (TEM) turbulence, the situation is the inverse: ion particle turbulent transport coefficients are smaller than their electron counterpart. References [1] M. Maslov et al., to be submitted to Nucl. Fusion; M. Marin et al., this conference. [2] A. Peeters et al., 2009 Computer Physics Communications 180 12. [3] C Bourdelle et al. 2016 Plasma Phys. Control. Fusion 58 014036. [4] C. Bourdelle, Y. Camenen, J. Citrin, M. Mirin et al., to be submitted to Nucl. Fusion. [5] G. Cenacchi, A. Taroni, JETTO: A free-boundary plasma transport code, JET-IR (1988). [6] M. Romanelli et al. 2014 Plasma and Fusion Research Volume 9, 3403023. [7] J Citrin et al., 2017 Plasma Phys. Control. Fusion 59 12.

Speaker: Jonathan Citrin

14:00 P5.1077 Quasi-continuous low frequency edge fluctuations in the W7-X stellarator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1077.pdf Quasi-continuous low frequency edge fluctuations in the W7-X stellarator G. A. Wurden1, S. Bozhenkov2, C. Brandt2, B. Buttenschoen2, M. Endler2, S. Freundt2, K. Hammond2, M. Hirsch2, U. Hoefel2, G. Kocsis3, P. Kornejew2, M. Krychowiak2, S. Lazerson4, K. Rahbarnia2, L. Rudischhauser2, T. Szepesi3, V. Winters5, and the W7-X Team 1 Los Alamos National Laboratory, Los Alamos, USA 2 Max Planck Institute for Plasma Physics, Greifswald, Germany 3 Wigner Research Centre for Physics, Budapest, Hungary 4 Princeton Plasma Physics Laboratory, Princeton, USA 5 University of Wisconsin, Madison, USA We have observed quasi-continuous low frequency (150-400 Hz) n=0 edge oscillations via multiple diagnostics in Wendelstein 7-X for some magnetic configurations. These events appear to originate at mid-radius, losing energy outwards to the walls, while a weak cold wave propagates towards the core. They are characterized by easily observable decreases in plasma kinetic energy (via diamagnetic loops) and simultaneous large (∆I/I = 300%) transient plasma current increases, albeit on a small net plasma current (<1kA). Core and edge responses occurs after the initial (~1-3%) global energy drop on each event. Fast cameras and segmented Rogowski diagnostics show an overall m=0 edge brightening, while electron cyclotron emission show an electron temperature fluctuation inversion point at mid-to-outer-radii. Using fiber filterscopes at multiple toroidal locations, the n=0 nature of the edge response (H-alpha, Carbon-III emission) is determined. Langmuir probes in the divertor show an edge density increase with each burst. These events are especially visible in so-called “high iota” discharges, when iota-bar is nearly 1 in the core, rising to 5/4 at the edge. Their magnitude is larger with higher input power, and their frequency is increased at higher plasma density. Their associated sawtooth-like energy loss, integrated over one energy confinement time, accounts for ~30% of the total energy loss.

Speaker: Glen Anthony Wurden

14:00 P5.1078 Experimental separation of core transport and edge pedestal isotope dependencies by variation of the plasma shape

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1078.pdf Experimental separation of ore transport and edge pedestal isotope dependen ies by variation of the plasma shape P. A. S hneider1 , C. Angioni1 , M. Cavedon1 , M. G. Dunne1 , P. Hennequin2 , B. Kurzan1 , R. M. M Dermott1 , F. Ryter1 , M. Willensdorfer1 and the ASDEX Upgrade Team1 1 Max-Plan k-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Gar hing, Germany 2 Laboratoire de Physique des Plasmas, E ole Polyte hnique, Fran e The mass dependen e of energy onnement in fusion plasmas is still not fully under- stood. One of the main reasons is the di ulty of making dire t omparison studies. Often the ause for this di ulty is multiple dierent me hanisms inuen ing onne- ment. A variety of these me hanisms depending on the hydrogen isotope mass have been reported on in the past [14℄. If not separated properly, understanding one of these me h- anisms always relies on a urate knowledge of the others. In this ontribution we present a possibility to separate the inuen e of the ore transport and the edge pedestal on onnement. In H-mode plasmas there are two major ontributions whi h determine the energy onnement. The heat and parti le transport in the ore and the stability of the edge transport barrier. Both are largely independent, so for transport studies the pedestal top an be in good approximation regarded as boundary ondition. However, in experiments with dierent isotopes, here hydrogen and deuterium, the assumption of the pedestal as boundary ondition does not hold anymore. The reason for this is a strong degradation of the pedestal in hydrogen ompared to deuterium for similar heat and parti le uxes. To re over the quality of a boundary ondition the pedestal top values need to be mat hed for omparable sour e terms. This an be a hieved by utilizing the ee t the plasma triangularity has on the edge transport barrier. We will present a variation of the shape between plasmas in hydrogen and deuterium with mat hed edge onnement - meaning same pedestal top values for the same ion and ele tron heat uxes as well as gas pu levels. The pedestal is then found to be lose to peeling-ballooning stability for both isotopes. In the ore the plasma shows similar transport properties when the heat uxes are mat hed despite the dierent isotopes. Impli ations for the understanding of isotope dependen ies are dis ussed. [1℄ BUSTOS, A. et al., Physi s of Plasmas 22 (2015) 012305. [2℄ SCHNEIDER, P. A. et al., Nu lear Fusion 57 (2017) 66003. [3℄ GARCIA, J. et al., Plasma Physi s and Controlled Fusion 59 (2017) 14023. [4℄ LAGGNER, F. M. et al., Physi s of Plasmas 24 (2017) 56105.

Speaker: Philip A. Schneider

14:00 P5.1079 Initial Results on Impact of Background Hydrogen Isotope on Impurity Behavior in the EC-heated LHD plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1079.pdf Initial Results on Impact of Background Hydrogen Isotope on Impurity Behavior in the EC-heated LHD plasmas N. Tamura1, 2, C. Suzuki1, K. Mukai1, 2, H. Funaba1, M. Yoshinuma1, 2, K. Ida1, 2, T. Fornal3, A. Czarnecka3, M. Kubkowska3 and LHD Experiment Group1 1 National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan, 2 The Graduate University for Advanced Studies (SOKENDAI), Toki, Japan, 3 Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland A first assessment of the impact of background hydrogen isotope on the impurity behavior in EC-heated plasmas of the LHD has been performed. In the case of Hydrogen (H) plasmas, no impurity accumulation has been observed up to 3.2 x 1019 m-3 as a line-averaged electron density nebar with 2.1 MW ECH. The plasma was generally terminated as intended. On the other hand, in the case of Deuterium (D) plasmas under the similar condition, the nebar of 3.0 x 1019 m-3 with 1.7 MW ECH, a plasma radiation suddenly started to increase, and then the plasma was finally collapsed. During this event, there is no external fueling. This is a clear indication of the occurrence of impurity accumulation, which can be also supported by the temporal behavior of the intensity of line emissions from highly-ionized impurities externally introduced into the core plasmas. As shown in Fig. 1, the decay time of the Li-like intensity from the Vanadium impurity ion, which was introduced into the core plasma by the TESPEL method [1], in such high-density D plasma more than doubled (0.848 s à 1.812 s), as compared to that in the similar-density H plasma. And, in comparison with the H plasma, the rise time (time required to reach maximum) of the Vanadium Li-like intensity in the D plasma is also increased. In general, the rise and decay time of the line emission from the highly-ionized impurity reflect mainly the diffusivity and convection velocity, respectively. Therefore, the experimental result clearly indicates that such high-density D plasma has a lower impurity diffusivity and larger impurity inward convection velocity, as compared with the H Fig. 1 Temporal evolution of Vanadium Li-like integrated plasma under the similar condition. counts measured with a VUV spectrometer. [1] S. Sudo and N. Tamura, Rev. Sci. Instrum. 83 023503 (2012). *This work is supported by a Grant-in-Aid for Young Scientists from a Toray scientific foundation and a Grant-in-Aid for Scientific Research (B) (Nos. 15H03759, and 15H04234) from Japan Society for the Promotion of Science and a budgetary Grant-in-Aid (ULHH007, ULHH012) of the National Institute for Fusion Science.

Speaker: Naoki Tamura

14:00 P5.1080 Dissipative trapped-electron modes inWendelstein 7-X and other configurations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1080.pdf Dissipative trapped-electron modes in Wendelstein 7-X and other configurations J.H.E. Proll1 , P. Xanthopoulos2 , P. Helander 2 1 Eindhoven University of Technology, Eindhoven, The Netherlands 2 Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17489 Greifswald, Germany In neoclassically optimised stellarators like Wendelstein 7-X (W7-X) or the Helically Symmet- ric Experiment (HSX), turbulent transport is expected to be the dominant transport channel at outer radii of the plasma. Research in stellarator turbulent transport and the underlying insta- bilities has thus gained momentum in the recent years. So far, most research was focussed on electrostatic collisionless instabilities such as ion-temperature-gradient modes (ITG) [1, 2] and trapped-electron modes (TEM). It was found analytically that quasi-isodynamic configurations with the maximum-J property are stable to density-gradient-driven TEM in large regions of pa- rameter space [3]. In these configurations, all trapped particles precess in the direction opposite to the propagation of drift waves. Thanks to the lack of resonance, electrons have a stabilis- ing influence, which leads to the absence of TEM. In linear numerical simulations using the GENE code [4] it was shown that also Wendelstein 7-X, which is only approximately quasi- isodynamic, benefits from enhanced TEM stability [5]. Very recently it was shown that this enhanced stability also persists nonlinearly [6]. With the completion of Wendelstein 7-X we are now in the position to test the theory also experimentally and to compare the numerical simula- tions against turbulence measurements. However, before meaningful comparisons can be made, we need to include collisions in the simulations since the experimentally accessible plasma conditions call for a collisional treatment. From a theoretical viewpoint, we expect collisions to significantly affect TEMs in a stellarator, due to scattering of particles across the trapping boundary. Here we present how collisions affect the microinstabilities—TEMs in particular— and how the effect differs in various 3D magnetic geometries. References [1] G.G. Plunk, et al., Phys. Plasmas 21, 032112 (2014). [2] M. Nunami, et al., Phys. Plasmas 20, 092307 (2013). [3] J.H.E. Proll, et al., Phys. Rev. Lett. 108, 245002 (2012). [4] F. Jenko, et al., Phys. Plasmas 7, 1904 (2000). [5] J.H.E. Proll, et al., Phys. Plasmas 20 122506 (2013). [6] J.H.E. Proll, et al., to be published

Speaker: Josefine Henriette Elise Proll

14:00 P5.1081 Parallel SOL transport regime in tokamak COMPASS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1081.pdf Parallel SOL transport regime in tokamak COMPASS K. Jirakova1,2 , J. Seidl1 , J. Adamek1 , P. Bilkova1 , J. Cavalier 1 , J. Horacek1 , M. Komm1 1 Institute of Plasma Physics, Czech Academy of Sciences, Prague 2 Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Prague The topic of parallel SOL transport regimes is of great interest for future fusion devices, as the detached or partially detached regimes allow to reduce heat fluxes incident on the diver- tor targets by dissipating a substantial part of the energy carried by plasma particles. Tokamak COMPASS is well suited for SOL transport studies, possessing an advanced system of diag- nostics such as a divertor probe array capable of measuring heat fluxes with high temporal resolution [1]. However, due to its short connection length (R ≈ 3 m) and open divertor con- figuration, it is not clear which transport regime tokamak COMPASS operates in. This study addresses the question based on an analysis of electron temperature profiles. Using the vertical and horizontal reciprocating probe, the divertor probe array, and the High Resolution Thomson Scattering diagnostics, electron temperature profiles are measured at three poloidal locations: the plasma top, the outer midplane, and the divertor. Position of the separa- trix, whose accurate knowledge is crucial for the analysis, is discussed in depth. The resulting profiles are compared in the view of the two-point model [2], providing an estimate of par- allel temperature gradient and plasma collisionality. By processing the database of tokamak COMPASS discharges, a scan over plasma parameters such as plasma current or line-averaged density is performed, yielding operational space in which partial detachment plays a role. COMPASS Scrape-Off Layer is shown to be typically in the sheath-limited regime or in the transition region between the sheath-limited and conduction-limited regimes. This has im- plications on the behavior of both the upstream and downstream temperatures. While in the conduction-limited regime the upstream separatrix temperature is expected to be largely insen- sitive to plasma conditions [2] [3], in the sheath-limited regime it decreases with increasing plasma density. Since at low collisionalities the downstream temperature closely follows the upstream one, a significant drop of target temperatures at high density, observed on COMPASS in [4], must be treated with great care before it can be considered as a sign of detachment. References [1] J. Adamek et al, Nuclear Fusion 57 116017 (2017) [2] P. C. Stangeby, The Plasma Boundary of Magnetic Fusion Devices, IOP Publishing Ltd, 2000, section 5.2 [3] G. D. Porter et al, Physics of Plasmas 5, 1410 (1998) [4] M. Komm et al, 45th Conference on Plasma Physics (2018)

Speaker: Katerina Jirakova

14:00 P5.1082 Turbulent fluctuations of plasma injected in open magnetic trap from independent UHF source

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1082.pdf ! " # ! ! "# $% &' ' $ ( & ) $ & ) ) ' ' * +, & , - .,,, " / ( ' ' $ & 0' *123/ & ' 0' & ' & & *45 / ) ! & & 6 & 123 & 7 8 & 123 ) & ) & && ! & ) ) & & ' ' 3 ) && & & ) ! 9 & & 123 ' ' ' * 6 & 123 ' & ) %, - :, / & $' & & 45 & 123 *%:,, #2 ;., (/ ( & ' ' ' & ' ' &' ' ' && 6 &< ' 6 ) 6 =. & 123 ' & ( ' && ' ' &&

Speaker: Sulkhan Nanobashvili

14:00 P5.1083 Inter-ELM power losses and their dependence on pedestal parameters in JET-C and JET-ILW H-mode plasmas.

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1083.pdf

Speaker: Anthony Robert Field

14:00 P5.1084 Ion cyclotron emission properties in NBI-heated TUMAN-3M plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1084.pdf Ion cyclotron emission properties in NBI-heated TUMAN-3M plasma L.G. Askinazi, G.I.Abdullina, A.A. Belokurov, V.A. Kornev, S.V. Krikunov, S.V. Lebedev, D.V. Razumenko, A.I. Smirnov, A.S. Tukachinsky, N.A. Zhubr Ioffe Institute, St. Petersburg, Russian Federation Ion cyclotron emission (ICE) in routinely registered in many tokamaks. It was recently observed in the TUMAN-3M tokamak [1, 2] in ohmically and neutral beam injection (NBI)- heated regimes in D and H plasma. This presentation describes some characteristic features of NBI-induced ICE observed in TUMAN-3M, with emphasis on spectral structure of the emission. In contrast to many other observations, ICE frequency ωICE in the TUMAN-3M NBI scenario corresponds to a core location of a radiating body, close to the plasma center. In NBI-heated plasma, ICE generation is usually explained by the presence of fast particles (beam ions or fusion charged products) with high transversal kinetic energy. In the TUMAN- 3M, high energy charged fusion products are not confined due to the low toroidal field (BT=1 T) and small size (R/a = 0.55 m / 0.25 m) of the tokamak and could not effectively excite ICE. NBI in the TUMAN-3M is performed in co-current tangential direction; as a result the fast ions with high transversal energy are born predominantly in the plasma periphery and then move to the core plasma along drift trajectories. Among these trajectories, a class of potato- like ones features the strong deviation from magnetic surface. This kind of trajectories looks beneficial for central ICE generation, as they have long vertical part located close to plasma center; particle drifting along this vertical part spends a longer time in a region of constant toroidal field, i.e. constant ωICE. Thus, these particles could be a possible candidate for central NBI ICE excitation in the TUMAN-3M. This model reproduces qualitatively well other important features of NBI ICE observed in the deuterium plasma in TUMAN-3M, such as frequency line splitting (fine structure) and ICE frequency dependence on beam energy. The former is explained by the presence of different energy components (1/2E0, 1/3E0 etc ) in the beam, in addition to main energy E0; the latter ensues from (a weak) dependence of location of vertical part of the trajectory on the fast ion’s energy. Experimental study of the ICE was supported by Russian Science Foundation (Project # 16-12-10285). Modeling of the fast ion trajectories was supported by Ioffe Institute. References 1. Lebedev S.V. et al, EPJ Web of Conferences 149, 03010 (2017), https://doi.org/10.1051/epjconf/201714903010 2. L.G.Askinazi et al, 15th IAEA TM on Energetic Particles in Magnetic Confinement Systems, 5-8 Sept. 2017, Princeton, P2. https://nucleus.iaea.org/sites/fusionportal/Shared%20Documents/EP%2017th/BoA.pdf

Speaker: Leonid Askinazi

14:00 P5.1085 Toroidal momentum maintenance and transport in simulations of nonlinear turbulent convection in tokamak core plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1085.pdf Toroidal momentum maintenance and transport in simulations of nonlinear turbulent convection in tokamak core plasmas V.P. Pastukhov, D.V. Smirnov NRC "Kurchatov Institute", Moscow, Russian Federation The paper continues our previous theoretical study and simulations of low-frequency turbulence and the associated cross-field anomalous transport processes in tokamak core plasmas [1-3]. The main goal of the paper is simulation of toroidal momentum transport in the presence of self-consistent nonlinear turbulent plasma convection. Contrary to many other studies our simulations are based on adiabatically-reduced MHD-like plasma dynamic model in which the toroidal plasma flows are the natural parts of the nonlinear turbulent plasma convection [1, 2]. We assume that magnetic field in tokamaks is axi-symmetric with nested magnetic flux surfaces. As a result, there are inherent conservation laws for the toroidal momentum and the dynamic vorticity in this model. Code CONTRA-C developed in a frame of simplified cylindrical model for tokamaks was used for this series of simulations. Temporal evolution and radial profiles of plasma potential, toroidal momentum density, and dynamic vorticity in presence of different torque sources are simulated and analyzed. We consider torque sources those correspond to neutral beam injection, various symmetry breaking mechanisms, as well as to momentum and vorticity exchange between plasma core and SOL region at the external boundary of simulation domain. Special attention is paid to regimes in which conditions for ITB formation near the major rational surfaces could be satisfied [3]. References [1] V.P. Pastukhov, N.V. Chudin and D.V. Smirnov, Plasma Phys. and Controlled Fusion 53, 054015 (2011) [2] V.P. Pastukhov and D.V. Smirnov, Plasma Phys. Reports 42, 307 (2016) [3] V.P. Pastukhov and D.V. Smirnov, Proceedings of 44th EPS Conference on Plasma Physics, report P2.173 (http://ocs.ciemat.es/EPS2017PAP/pdf/P2.173.pdf)

Speaker: Vladimir Pastukhov

14:00 P5.1086 Determining the electron transport mechanisms from direct heat flux reconstructions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1086.pdf Determining the electron transport mechanisms from direct heat flux reconstructions M. van Berkel1,2 , T. Kobayashi3 , G. Vandersteen2 , H.J. Zwart4 , H. Igami3 , S. Kubo3 , N. Tamura3 , M.R. de Baar1,4 , and the LHD Experiment Group 1 Dutch Institute For Fundamental Energy Research (DIFFER), PO Box 6336, 5600HH Eindhoven, The Netherlands 2 Vrije Universiteit Brussel (VUB), ELEC, Pleinlaan 2, 1050 Brussels, Belgium 3 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki-city, Gifu, 509-5292, Japan 4 Eindhoven University of Technology, ME, PO Box 513, 5600MB Eindhoven, The Netherlands Confinement in fusion devices is largely determined by the transport mechanisms in electron transport, LHD discharge #111121 at ; = 0:47 16 harmonic reconstruction which is generally described by the heat equation 14 polynomial reconstruction ∂ 12 time (ne Te (ρ,t)) = ∇ρ (−qe (ρ,t)) + p (ρ,t) , (1) qe =ne [keVm/s] 10 ∂t 8 where Te (ρ,t) is the electron temperature, ρ the nor- 6 malized radius, ne the electron density, and p (ρ,t) the 4 heating power density. The heat flux qe dependencies 2 2 2.5 3 3.5 !r; Te [keV/-] on the diffusivity χe , convective velocity Ve , critical gradients, power dependence, etc., is crucial in under- Figure 1: Experimentally determined standing what drives transport. However, as the heat relative heat flux qe as a consequence flux cannot be directly measured and qe is a time and of a block-wave power modulation. space-dependent quantity, we must identify qe implicitly. The standard approach is to pre-define the heat flux dependencies [1]. Therefore, standard forms such as qe = −ne χe ∇ρ Te − neVe Te are used to identify the heat flux. Casting the heat flux in a specific dependence allows the esti- mation of the time invariant quantities χe and Ve . However, it also poses a danger as we made an assumption of the heat flux structure. We propose an alternative approach by combining the heat flux reconstruction in [2] and advanced frequency domain signal processing techniques to directly estimate the heat flux qe [3]. The experimental result is shown in Fig. 1, which can be used to estimate, e.g., diffusion coefficient χe via the slopes [3]. References [1] M. van Berkel, et al., Phys. Plasmas 21, 112507, 2014. [2] S. Inagaki, et al., Nucl. Fusion, pp. 113006, 2013. [3] M. van Berkel, T. Kobayashi, et al., (submitted to) Plasma Phys. Control. Fusion, 2018.

Speaker: Matthijs van Berkel

14:00 P5.1087 Quantitative study of kinetic ballooning mode theory in magnetically confined toroidal plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1087.pdf Quantitative study of kinetic ballooning mode theory in magnetically confined toroidal plasmas K. Aleynikova1,2 , A. Zocco1 , P. Xanthopoulos1 , P. Helander1 1 1Max-Planck-Institut für Plasmaphysik, EURATOM Association, Greifswald, Germany 2 Moscow Institute of Physics and Technology, Dolgoprudny, Russian Federation Kinetic ballooning modes (KBMs) are investigated by means of analytical theory and linear electromagnetic gyrokinetic (GK) numerical simulations in a magnetically confined toroidal plasma. A physics-based ordering for beta (the ratio of kinetic to magnetic plasma pressure) with small asymptotic parameters is found. This allows us to derive several simplified limits of previously known theory [1] and to identify regimes where quantitative agreement between theory and numerical simulations can be achieved. For the axisymmetric case, in simple s-alpha geometry, it is found that, for large pressure gradients, the growth rate and frequencies computed by the gyrokinetic codes GS2 and GENE show excellent agreement with those evaluated by using, in the quadratic forms, a diamagnetic modification of ideal MHD. This is true only if geometric drifts are kept consistent with the equilibrium pressure gradient. In the stellarator Wendelstein 7-X (W7-X), we find a finite-beta stabilization of the ion- temperature-gradient (ITG) and trapped particle (TEM) modes, as well as KBM destabiliza- tion. The results are compared to a generic tokamak case. For large pressure gradients in W7-X geometry the KBM frequencies agree with the analytical prediction of the diamagnetic modi- fication of ideal magnetohydrodynamic (MHD) limit already verified for the tokamak [2]. The KBM destabilization thresholds are predicted for different W7-X configurations. We discuss the relation of these thresholds with the ideal MHD stability properties of the corresponding equilibria. References [1] W.M. Tang, J.W. Connor, and R. J. Hastie, Nucl. Fusion 20, 1439 (1980) [2] K. Aleynikova and A. Zocco, Physics of Plasmas 24, 092106 (2017)

Speaker: Ksenia Aleynikova

14:00 P5.1088 Heat and particle transport simulation in COMPASS and T-10 with Canonical Profile Transport Model

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1088.pdf Heat and particle transport simulation in COMPASS and T-10 with Canonical Profile Transport Model A.V. Danilov1, Yu.N. Dnestrovskij1, A.V. Melnikov1, S.V. Cherkasov1, L.G. Eliseev1, A.Yu. Dnestrovskij1, S.E. Lysenko1, G.F. Subbotin1, V.A. Vershkov1, J. Havlíček 2, J. Urban2, J. Stöckel2, P. Bílková2, P. Böhm2, M. Šos2, M. Hron2, M. Komm2, R. Pánek2 1 NRC ‘Kurchatov Institute’, 123182 Kurchatov Sq. 1, Moscow, Russia 2 Institute of Plasma Physics of the CAS, 18200 Prague 8, Czech Republic The remarkable property of tokamak plasma to maintain the shape of some parameters profiles (e.g. the electron pressure, electron temperature, toroidal rotation velocity) under different external influences has been discussed since early eighties [1, 2]. This effect is considered as manifestation of plasma self-organization and corresponding normalized profiles are called as stiff. The quantitative measure of the profiles stiffness appeared as a factor standing in front of the difference between the normalized gradient of temperature (or pressure) and the critical gradient in expressions for heat or particle fluxes in the Canonical Profile Transport Model (CPTM) [3]. The report presents the CPTM simulation results using the ASTRA code for L-mode plasmas of the circular limiter tokamak T-10 and D-shaped diverted plasmas of COMPASS. On top of that, Ohmic and NBI heated H-mode in COMPASS was modeled. The H-mode simulation was performed by means of “forgetting factors”, suppressing heat and particle fluxes, caused by profile stiffness, inside the edge transport barrier [4]. Modeled electron temperature and density profiles are consistent with the measured ones with RMS deviations within the range of experimental accuracy: 10-15%. Calculations demonstrate quite similar density profiles for Ohmic and NBI heated H- mode plasmas in COMPASS and higher electron temperature pedestal for NBI heated H- mode in agreement with measurements. The results of L-mode simulation in COMPASS were compared with those obtained for T-10. For both tokamaks the simulation results met measurements, but stiffness coefficients in the particle transport equation for T-10 proved to be about two times less than these for COMPASS. [1] Coppi B., Plasma Phys. Control. Fusion, 1980, 5, 261 [2] Kadomtsev B.B., Sov. J. Plasma Phys., 1987, 13, 443 [3] Dnestrovskij Yu.N., Pereverzev G.V., Plasma Phys. Control. Fusion, 1988, 30, 1417 [4] Dnestrovskij Yu.N., Self-Organization of Hot Plasmas, Springer, 2015

Speaker: Alexander Danilov

14:00 P5.1089 Collisionless damping of geodesic acoustic modes with a finite inverse aspect ratio

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1089.pdf Collisionless damping of geodesic acoustic modes with a finite inverse aspect ratio J. Seol1, K. C. Shaing2 1 National Fusion Research Institute, Daejeon, Republic of Korea 2 National Cheng Kung University, Tainan, Taiwan In this study, the theory of geodesic acoustic modes is extended to the tokamak plasmas with a finite inverse aspect ratio. Using the drift kinetic equation, we investigate the collisionless damping rate of geodesic acoustic mode both analytically and numerically. The damping rate is reduced as the inverse aspect ratio increases.

Speaker: JaeChun Seol

14:00 P5.1090 BSTING: modifying the BOUT++ framework for fluid simulations of turbulence in non-axisymmetric geometries

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1090.pdf BSTING: modifying the BOUT++ framework for fluid simulations of turbulence in non-axisymmetric geometries B Shanahan1, B Dudson2, P Hill2, and P Helander1 1 Max-Planck Institute für Plasmaphysik, Teilinstitut Greifswald, Germany 2 York Plasma Institute, Department of Physics, University of York, UK It is becoming increasingly important to simulate plasma turbulence in non- axisymmetric configurations, especially in the edge where turbulence could become the dominant transport process. The high collisionality of tokamak and stellarator edge plasmas facilitates a fluid approach to turbulence simulations. While there are several fluid turbulence codes for tokamak geometries, previous attempts to develop such a simulation framework for stellarators have been unsuccessful. The recent implementation of the Flux Coordinate Independent (FCI) [1] method for parallel derivatives in BOUT++ [2] has allowed for simulations in nonaxisymmetric geometries [3,4]. Here we present the most recent results for the BSTING project, which seeks to modify the BOUT++ framework to Simulate Turbulence In Non-axisymmetric Geometries. To allow for fully three dimensional turbulence simulations, the metric tensor components in BOUT++ have been extended to vary in three dimensions. Following this extensive modification, we present the results of several tests to ensure the accuracy and stability of the framework have been maintained. Of particular importance are the tests of the parallel derivatives and the associated parallel boundary conditions. These methods have been examined qualitatively by tracing non-axisymmetric flux surfaces and quantitatively via the Method of Manufactured Solutions [5], the results of which will be presented. A fully three dimensional framework provides a very flexible test bed, and therefore several new features to exploit this flexibility will be presented here: modifications to the Zoidberg grid generator which allow for Wendelstein 7-X geometries and a newly- implemented FCI curvilinear coordinate system are discussed in detail. Finally, initial investigation of plasma filaments in non-axisymmetric geometries using an isothermal model which evolves electron density, vorticity, electromagnetic potential and parallel momentum is presented. The implications of these simulations for future experiments will be explored. [1] F Hariri and M Ottaviani, Computer Physics Communications, 184(11):2419 – 2429, 2013. [2] B Dudson et al., Computer Physics Communications, 180: 1467-1480 [3] P Hill, B Shanahan and B Dudson, Computer Physics Communications, 213: 9-18, 2016 [4] B Shanahan et al., Journal of Physics: Conference Series 775 012012, 2016. [5] P J Roache, Journal of Fluids Engineering 124 4, 2002.

Speaker: Brendan Shanahan

14:00 P5.1091 Strong safety-factor (q) profile dependence of the linear electromagnetic stabilizing effect and its role in the internal transport barrier formation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1091.pdf Strong safety-factor (q) profile dependence of the linear electromagnetic stabilizing effect and its role in the internal transport barrier formation J.Y. Kim and H.S. Han National Fusion Research Institute, Daejeon 34133, Korea A well-known feature of the internal transport barrier (ITB) is that its formation condition strongly depends on the safety-factor (q) profile. For example, up to now most ITBs (except the hot-ions, super-shot, PEP modes) were obtained only in some specific q-profiles with the reverse or weak- positive shear. The threshold beta for the ITB formation also appears to have a substantial difference, depending on the magnitude of q-min, even with nearly the same magnetic shear (as can be seen from comparison between the optimized-shear [1] and hybrid [2] modes). While numerous theoretical models have been proposed for the ITB trigger mechanism [3], the physics origin of this strong q-profile dependence is still not so clear. Here, as an effort to find a possible model we present a re-assessment of the linear electromagnetic effect on the toroidal ion temperature gradient (ITG) mode, which is widely believed to be the main background turbulence in high temperature core plasmas where the ITB is formed. Noting that the linear electromagnetic stabilization of the toroidal ITG, which arises from the coupling with the shear-Alfven ballooning branch, becomes stronger as plasma beta approaches the ballooning threshold [4], a similar q- profile dependence is first expected between the ITB formation (through the ITG stabilization) and the ballooning threshold. With the well-known ballooning threshold property, which becomes smaller as q increase or magnetic shear (s) decreases through the reduction of the field-line bending force, it is then shown that a strong q-profile dependence can arise in the ITB formation condition. Furthermore, in this case the ITB formation is found to occur through not only the increase of ITG threshold but also the reduction of profile stiffness. With the stabilization of the ITG, the kinetic ballooning mode can be then excited and an estimate is given on its effect in relation to the further development of the ITB. In addition, the effect of trapped elections, which can reduce the electromagnetic stabilization degree, is briefly estimated by using a non-local code in the 1-D ballooning space, which was upgraded from our previous one in Ref. 4 to include trapped electrons. [1] C. Gormezano et al., 1997 Proc. 16th Int. Conf. on Fusion Energy vol I (Montreal: IAEA) p 487 [2] O. Gruber et al., Phys. Rev. Lett. 83, 1787 (1999). [3] for example, see J. Citrin et al., Nucl. Fusion 54, 023008 (2014). [4] J.Y. Kim et al., Phys. Fluids B 5, 4030 (1993).

Speaker: Jinyong Kim

14:00 P5.1092 Enhancement of zonal flow drive through equilibrium shear flows

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1092.pdf Enhancement of zonal flow drive through equilibrium shear flows T. Ullmann1 , B. Schmid1 , P. Manz2 , M. Ramisch1 1 University of Stuttgart, IGVP, Pfaffenwaldring 31, 70569 Stuttgart, Germany 2 Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2 , 85748 Garching, Germany Turbulence generated zonal flows (ZFs) are known to be part of regulating turbulent transport and, therefore, are suspected to be involved in spontaneous transitions from low to high con- finement regimes in toroidal fusion plasmas. ZFs are driven by radial gradients of the turbulent Reynolds stress (RS) he vθ ver i which de facto measures the tilt of vortices. Therefore, equilibrium shear flows can constitute a seed flow for initially tilting vortices, initiating the ZF drive and stimulating its self-amplification. In this contribution the dependence of the RS on the background flow shearing rates is inves- tigated experimentally. To this end, the poloidal E×B background flow in the stellarator TJ-K is controlled via plasma biasing. A ring shaped electrode is positioned in the plasma and set on a positive potential with respect to the vacuum vessel. The current drawn from the plasma changes the equilibrium plasma potential profiles and therefore imposes strong E×B back- ground flows. This application even allows to equalize the pressure driven E×B background flow and, thus, to minimize flow shear. The plasma potential φ (r), from which the shearing rate i.e. Ω = (RB0 )2 B−1 ∂r (RBθ )−1 ∂r φ is deduced [1], is measured with a radially moving emis- sive probe. For measurements of the poloidal RS distribution and related radial gradients, a specifically designed poloidal Langmuir probe array is employed, which consists of 128 probes with 32 tips each of four adjecent flux surfaces, measuring potential fluctuations. This way, the approximate flux surface averaged RS, the RS drive, and even zonal potential structures is anal- ysed with respect to background flow shear experimentally. Varying the bias voltages from 0 to 50V the shearing rates increase from negative to positive values in the kHz range. With the shear approaching zero also the RS vanishes. At this point the ZF power has a local minimum. The ZF power behaves similar to the RS and RS drive. Shear induced changes in the RS are considered a consequence of a modification in the non- linear wave coupling process, in which the amount of coupling modes is reduced as to increase efficiency in the energy transfer into the zonal flow [2]. This paradigm is tested by means of bispectral analysis carried out on the measured RS data. References [1] Burrell et al., PPCF 40, 1585 (1998). [2] Ö. D. Gürcan, PRL 109, 155006 (2012).

Speaker: Til Ullmann

14:00 P5.1093 Plasma rotation and low-Z impurity transport across sawteeth in TCV

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1093.pdf Plasma rotation and low-Z impurity transport across sawteeth in TCV B.P. Duval, C. Marini, A. Karpushov, Y. Andrebe, O. Sauter and the TCV teama Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC) CH-1015 Lausanne, Switzerland The local particle and heat transport increase across sawteeth (ST) crashes in a tokamak plasma is well documented. Although plasma momentum transport, often estimated from radially resolved plasma rotation, is often modelled as a continuous process that depends on the plasma parameters and their gradients, MHD has long been shown to strongly affect TCV’s experimental profile, and that in many other machines. For similar conditions (plasma shape density and temperature) the rotation profile gradient outside the ST-mixing radius was seen to be reasonably constant whereas the average profile is flattened inside, with what appeared to be a co-plasma current core-weighted additional component, and this for a wide range of plasma currents. In the experiments reported in this paper, the natural ST period (~2ms) was lengthened by precision X2 ECCD deposition close to the q=1 surface stabilising the ST to obtain regular ST periods in the range of 8-40ms. A diagnostic neutral beam system based CXRS system measured the Carbon intrinsic impurity rotation profiles, in the absence of a perturbing external torque, with a 2ms temporal resolution. Acquisition was synchronised to the ST crashes where conditional resampling was then particularly appropriate to decrease the measured rotation profile uncertainties. The ST event was found to reset the rotation profile to similar values independently of the ST period with the whole rotation profile then increasing at similar rates after each crash so that the pre-ST profile peaks with increasing ST period. The behaviour of the ion temperature and Carbon impurity density measured during the ST crash is also presented showing that this low-Z impurity is preferentially evacuated from the plasma core, compared to the Deuterium working gas. Together, these measurements underline how a description and prediction of plasma rotation and impurity transport must include the effect of ST and, most probably, all other strong MHD activity. a See the author list of S. Coda et al, 2017 Nucl. Fusion 57 102011

Speaker: Basil Duval

14:00 P5.1094 Edge instabilities across the L-H transition and in H-mode of ASDEX Upgrade

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1094.pdf Edge instabilities across the L-H transition and in H-mode of ASDEX Upgrade L. Gil1, C. Silva1, T. Happel2, G. Birkenmeier2, G.D. Conway2, L. Guimarãis1, P. Hennequin3, V. Nikolaeva1, F. Mink2, D. Prisiazhniuk2, T. Pütterich2, J. Santos1, E. Seliunin1, A. Silva1, U. Stroth2, J. Vicente1, E. Wolfrum2, the ASDEX Upgrade Team and the EUROfusion MST1 Teama 1 Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Lisboa, PT 2 Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany 3 Laboratoire de Physique des Plasmas, École Polytechnique, 91128 Palaiseau, France The H-mode is currently the preferable operational regime for a fusion reactor but the physics of the L-H transition and confinement enhancement is not yet fully understood. Turbulence suppression is responsible for the formation of the edge pedestal, whose growth is believed to be limited by the onset of instabilities. The L-H transition in ASDEX Upgrade (AUG) is often accompanied by the appearance of edge coherent [1] or quasi-coherent modes (QCMs) [2] in density fluctuations. QCMs have also been detected in other devices [e.g. 3-4], including during ELM cycles. The underlying instabilities of these modes are mostly an open question, despite their relevance for understanding edge transport and pedestal physics. Slow power ramp shots at different densities have been conducted in AUG to study edge instabilities across the L-H transition and in H-mode, including the intermediate I-phase. Reflectometers are the main diagnostics used in this work, with emphasis on the frequency modulated continuous wave reflectometer, which has the unique capability of providing simultaneous measurements on the high-field side (HFS) and low-field side (LFS). It was operated either in fixed frequency to measure density fluctuations at several radial positions or in broadband sweeping mode to measure density profiles. The existence of edge coherent and quasi-coherent modes with frequencies ranging from ~40 to 140 kHz and a complex time evolution after the L-H transition is observed. Their type and behavior is different for the low and high density branches of the L-H power threshold. At low density, the modes are coherent and have an up-chirping frequency with a multi-peak structure. They are observed at the LFS and HFS and also feature a radial magnetic field component, with dominant toroidal mode numbers from -3 to -9, where the negative sign indicates propagation in the electron diamagnetic direction in the lab frame. In the high density shots, the mode is quasi-coherent, with a down-chirping frequency and a broad peak structure. It is observed in the density fluctuations but does not appear in the magnetic coil signals. At medium density, near the minimum L-H power threshold, both types of modes are observed: first the one with magnetic component and then the one without. There is a period of alternation between the two types, which suggests different instabilities come into play. These modes may play an important role in the H-mode pedestal structure, stability and confinement. Their characteristics and relation to the inter-ELM modes will be discussed. [1] A. Medvedeva et al., PPCF 59, 125014 (2017) [3] H.Q. Wang et al, PRL 112, 185004 (2014) [2] S. da Graça et al, EPS Plasma Physics (2013) [4] A. Diallo et al, NF 55, 053003 (2015) a See the author list of Meyer et al 2017 Nucl. Fusion 57 102014.

Speaker: Luís Gil

14:00 P5.1096 Theory-based scaling of energy confinement time for future reactor design

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1096.pdf Theory-based Scaling of Energy Confinement Time for Future Reactor Design* J.M. Park1, G. Staebler2, P.B. Snyder2, C.C. Petty2, D.L. Green1, K.J. Law1 1 Oak Ridge National Laboratory, Oak Ridge, TN, USA 2 General Atomics, PO Box 85608, San Diego, CA, USA A theory-based scaling of thermal energy confinement time has been derived based on TGLF and EPED in burning plasma conditions for future reactor design. The simulation dataset consists of a massive number of predictive IPS-FASTRAN [1] simulations, self-consistent with core transport (TGLF), edge pedestal (EPED), alpha heating, and MHD equilibrium (EFIT). The DAKOTA-enabled Integrated Plasma Simulator (IPS) framework generates the multi-dimensional parametric scan with random sampling of major radius (4 < R < 8 m), aspect ratio (2.5 < R/a < 3.5), elongation (1.5 < k < 2.0), triangularity (0.3 < d < 0.6), toroidal magnetic field (4 < BT < 8 T), plasma current (3.5 < q95 < 8.5), line average density (0.6 < ne /nGW < 1), and heating power (20 < Pinj < 150 MW). Each IPS-FASTRAN simulation in the scan is largely theory-based except a model specification of the heating and plasma current profiles. A Gaussian form of the heating profile is employed with the ratio of electron and ion heating as an additional scan parameter (0.0 < Pe/Pi < 1.0) to take into account difference in the heating and current drive actuators such as neutral beam injection and RF heating. The model current profile is a combination of the bootstrap current in the edge pedestal determined by EPED and the core current profile parameterized to make variation of minimum q (qmin), the minimum q location (rqmin), and the average magnetic shear (q0-qmin) in the core. For the ITER baseline H-mode type current profile with q0~1.0, the TGLF/EPED energy confinement time scales as tTGLF/EPED = 0.098 Ip0.80 BT0.28 ne0.42 P-0.71 R2.1 k0.81 e0.90, in a dimensionally homogenous form, showing ~ +/-10% difference from the ITER H-mode confinement scaling of the multi-machine experimental database [2] for the data set generated in burning plasma condtion. The exponent of the log-linear scaling expression reveals different dependency on the engineering variables, for example stronger dependency on BT. Substantial improvement of energy confinement time is predicted for the broader current profile, tTGLF/EPED ~ (1+0.45rqmin1.2), identifying an optimization path to AT steady- state reactor. An example of the system code application will be presented. [1] Park et al, Phys. Plasmas 25, 012506 (2018) [2] McDonald et al, Nucl. Fusion 47, 147 (2007) *This work was supported in part by US Department of Energy under DE-AC05-00OR22725, DE-FC02- 04ER54698, DE-FG02-95ER54309, and DE-SC0012656

Speaker: J. M. Park

14:00 P5.1098 Zonal flow - drift wave interactions in 2D 2-fluid ITG

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1098.pdf Zonal Flow — Drift Wave Interactions in 2D 2-Fluid ITG P.G. Ivanov1,3 , A.A. Schekochihin1,2 , A.R. Field4 1 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, 1 Keble Rd, Oxford OX1 3NP, UK 2 Merton College, Oxford OX1 4JD, UK 3 St John’s College, Oxford OX1 3JP, UK 4 EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, UK It is believed that most of the heat transport in tokamak plasmas is caused by turbulence. Numerical simulations have shown that turbulence in tokamaks is regulated by the interaction of 3 different phenomena — shear of the mean plasma flow, zonal flows (ZF) and drift waves (DW) [1, 2]. The latter represent wave-like fluctuations in the plasma, driven by gradients in the background plasma parameters — density, temperature, etc. Zonal flows are Larmor-scale shear flows in the poloidal direction (around the smaller radius of the torus), which are generated nonlinearly by the drift-wave turbulence itself. We aim to find an analytical description of the nonlinear interaction of ZFs and DWs and the phenomena resulting thereafter — the Dimits shift [1] and the recently discovered state dominated by coherent structures [3]. Our equations are obtained by taking density and temper- ature moments of the electrostatic gyrokinetic equation in an appropriate cold ion limit (Ti → 0) 2 ρ 2 . The resulting system of two PDEs and large collisionality expansion νi ω ∼ ω∗ ∼ νi k⊥ i is shown to exhibit both a linear ion-temperature-gradient instability, driven by a background magnetic field and temperature gradients, a nonlinear (secondary) instability towards the de- velopment of strong zonal flows, as well as the break-up of the ZF-dominated state (tertiary instability). We present analytical results on both the linear and nonlinear behaviour of the sys- tem, together with numerical validations. References [1] A.M. Dimits et al, Nuclear Fusion 40, 3Y (2000) [2] B.N. Rogers, W. Dorland, M. Kotschenreuther, Physical Review Letters 85, 25 (2000) [3] F. van Wyk et al, Journal of Plasma Physics, 82, 6 (2017)

Speaker: Plamen Ivanov

14:00 P5.1099 Integrated core-pedestal modeling with the AToM framework

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1099.pdf Integrated core-pedestal modeling with the AToM framework∗ J. Candy1 , E. Belli1 , D. Green3 , C. Holland2 , O. Meneghini1 , J.M. Park3 , S. Smith1 and the AToM team. 1 GeneralAtomics, San Diego, CA 2 Universityof California at San Diego, San Diego, CA 3 Oak Ridge National Laboratory, Oak Ridge, TN In this presentation we will report on two novel integrated simulation capabilities of the Ad- CORE TR PED vanced Tokamak Modeling (AToM) framework. The original AToM0 SciDAC-3 project was a 3- year effort that concluded in 2017. For the pe- riod 2017-2022, a new 5-year AToM SciDAC-4 project has begun. First, we give an overview of coupled core-pedestal integrated simulations, with application to DIII-D plasmas. These sim- ulations take into account the strong interplay between core turbulent-plus-collisional trans- port, pedestal structure, current profile and plasma equilibrium. Integrated modeling work- flows capable of calculating the steady-state self-consistent solution to this strongly-coupled problem have been developed and implemented Experimental data Successive workflow iterations in AToM via the OMFIT-TGYRO [1] and the Pedestal density input to the workflow IPS-FASTRAN [2] workflows. Here, kinetic plasma equilibrium is computed by EFIT using profile data from the transport solver and kinetic bootstrap current from the neoclassical module. Given an EFIT equilibrium, core profiles are evolved by the transport solver by combining col- lisional and turbulent fluxes to maintain balance with heating and fueling sources. The updated value of the global plasma pressure is passed to EPED to obtain the self-consistent pedestal structure. For the OMFIT-TGYRO-TGLF-NEO workflow (see plot), the scheme is iterated to convergence in a few iterations and is independent of initial profiles. By using only the elec- tron density at the top of the pedestal as an input, profiles are calculated from magnetic axis to separatrix – in good agreement with experiment (DIII-D 153523, 3745ms). Second, we will review a key subcomponent of these coupled core-pedestal simulations: the time-dependent (i.e, mulitple time-slice) kinetic EFIT reconstruction. Here, a self-consistent kinetic neoclas- sical bootstrap current calculation with NEO is coupled to the EFIT equilibrium solve. This ensures the highest-accuracy calculation of the bootstrap current and consistent plasma equilib- rium across the entire plasma profile. ∗ Work supported by US DOE under DE-SC0017992. References [1] O. Meneghini, S.P. Smith, P.B. Snyder, G.M. Staebler, J. Candy and E.A. Belli, Nucl. Fusion 57, 0866034 (2017) [2] J.M. Park, J.R. Ferron, C.T. Holcomb, et al, Phys. Plasmas 25, 012506 (2018)

Speaker: Jeff Candy

14:00 P5.1100 Properties of ion temperature gradient mode in tokamak plasmas with inverted density profiles

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1100.pdf Properties of ion temperature gradient mode in tokamak plasmas with inverted density profiles Huarong Du1, Zhengxiong Wang2, Yuhong Xu1 1 Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China 2 Key Laboratory of Materials Modification by Beams of the Ministry of Education, School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024, China The ion temperature gradient (ITG) mode in tokamak plasmas with inverted density profiles are numerically investigated with the gyrokinetic integral eigenmode equation. From comprehensive local parametric scans, we obtain stability diagrams for ITG mode and trapped electron mode (TEM) in terms of density and temperature gradient scale lengths [1]. In addition, deviations are found on the ITG threshold from an early analytic theory in sheared slab geometry with the adiabatic electron response [2]. Results show that, for the inverted density profile, there exists a normalized threshold temperature gradient above which the ITG mode and TEM are either separately or simultaneously unstable [3]. Besides, the trapped electrons are observed to stabilize the ITG mode with typical scale length k i  1 , which is different from the conventional ITG mode in the long wavelength region. The critical ion temperature gradient R / LTic of the ITG mode for negative R / Ln ( Ln  n / n ) is somewhat higher (lower) than that for positive R / Ln in the moderate (steep) density gradient region. Moreover, the effects of different physics elements (such as safety factor, temperature ratio, magnetic shear, and toroidicity) have also been studied. [1] Huarong Du, Zheng-Xiong Wang, et al., Phys. Plasmas 21, 052101(2014). [2] T. S. Hahm and W. M. Tang, Phys. Fluids B 1, 1185 (1989). [3] Huarong Du, Hogun Jhang, T. S. Hahm, et al., Phys. Plasmas 24, 122501(2017).

Speaker: Huarong Du

14:00 P5.1101 Studies of role of inter-ELM pedestal instabilities on pedestal structure and ELM onset in DIII-D

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1101.pdf Studies of role of inter-ELM pedestal instabilities on pedestal structure and ELM onset in DIII-D A. Diallo1, J. Dominski1, F. Laggner2, K. Barada3, L. Zeng3, M. Brookman4, M. Knolker1, M. Austin5, G. Canal6, B. Grierson1, E. Kolemen2, G. McKee7 1 Princeton Plasma Physics Laboratory, Princeton, NJ, USA: 2Princeton University, Princeton, NJ, USA: 3UCLA, Los-Angeles, CA, USA: 4General Atomics, San Diego, CA USA: 5University of Texas, Austin, USA: 6Plasma Physics Laboratory, Institute of Physics, University of São Paulo, Brazil: 7University of Wisconsin, Madison, WI, USA Experiments have been performed on DIII-D to study the role of inter-ELM pedestal instabilities on both the pedestal structure and the onset of ELMs. In these experiments, we scanned the NBI torque, puffed gas in the edge as well as varied the edge ECH heating to study the impact of these actuators on the inter-ELM pedestal modes. We observe a transition from a regime dominated at the beginning of the inter-ELM period by a single mode located near q=5 which expands to a more balanced organization between this mode and two secondary modes located near the q=6 surface just before the ELM onset. These additional modes can couple energy from the pedestal into the separatrix, providing a channel for the expulsion of energy and particles in the form of an ELM. More specifically, a large majority of energy losses from the pedestal is thought to occur between ELMs [1]. The key players in this energy loss are instabilities localized in the pedestal such as kinetic ballooning modes (KBM), electron temperature gradient (ETG), microtearing modes (MTM), ion temperature gradient (ITG), etc. Many experiments have reported inter-ELM pedestal modes (JET[2], C-Mod[3], DIII-D[4], AUG[5], EAST[6], and HL-2A[7]) that are correlated with saturation of the pedestal gradients prior to the ELM onset. Recent gyrokinetic calculations (GENE) have identified the pedestal modes on DIII-D to be consistent with microtearing modes [9]. Here, we study the pedestal evolution between ELMs to investigate the ELM onset mechanism. In addition, we report on pedestal experiments where we extract the dynamics of the most dominant modes localized in the pedestal during multiple inter-ELM periods and the effects of the various actuators on these modes. This work was performed under US DoE contract DE-AC02-09CH11466, DE-FC02-04ER5469, DE-FG02-08ER54984 and DE-FC02-04ER54698. [1] A. Loarte ,et.al., Nucl. Fusion 54 (2014) 033007; [2] Perez et al., NF 2004; [3] Diallo et al. PRL 2014; [4] Diallo et al., PoP 22, 056111 (2015); [5] Laggner et al., PPCF 2016; [7] Gao et al., NF 2015; [8] Zhong et al., PPCF 2016. [9] M. Kotschenreuther et al., US-TTF 2017 “Fundamental considerations of gyrokinetic pedestal transport”

Speaker: Ahmed Diallo

14:00 P5.1102 On the mechanism of the plasma fuelling in JET experiment with external gas puff

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1102.pdf On the mechanism of the plasma fuelling in JET experiment with external gas puff. Yu.F.Baranov1, A.Salmi2, T.Tala2, G.Corrigan1, D.Harting1, F.J.Casson1, F.Koechl1, E.Militello Asp1, V.Parail1and JET Contributors* 1 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK 2 VTT, P.O. Box 1000, FI-02044 VTT, Espoo, Finland Scenario development for ITER requires an understanding of the mechanism of the plasma fuelling with external particle source. Experiments on plasma fuelling with modulated gas puff have been done on JET [1] to clarify details of the particle penetration into the plasma core. The modulation caused a periodic variation of the plasma parameters in the scrape off layer (SOL), divertor and the plasma core, which have been measured by numerous JET diagnostics. An evolution of the plasma parameters has been modelled with the JINTRAC code [2]. The modelling results have been compared with the experimental data. The plasma fuelling in the experiment was provided by a constant source from the NBI system, and modulated gas puff from the top of the plasma chamber [1]. The level of the puff was relatively small, and it did not change the global plasma confinement significantly. The experiments have been done in D and H plasmas. Qualitatively, the observations were similar in both gases. The density variation caused by the modulated gas puff were observed propagating from the plasma periphery to the core. The modulation footprint was seen in the plasma SOL and divertor. The integrated suite of core and SOL/divertor transport codes JINTRAC [2] has been used to self-consistently model the plasma evolution during modulated gas puff. The suite couples JETTO/SANCO, a 1.5D core transport solver that includes impurities, with EDGE2D/EIRENE, a 2D SOL/edge multi-fluid solver that includes plasma interactions with the JET Be wall and W divertor. Transport properties in the core were assumed to be governed by a combination of the neoclassical and Bohm/gyro-Bohm model with anomalous particle pinch. The boundary conditions were deduced from EDGE2D calculations. The accuracy of the predictive modelling of the plasma temperature and density was tested against free parameters used in the model. Good agreement between measured and modelled plasma parameters in the core, SOL and divertor has been found, including density evolution, saturation ion current and ion flux in the divertor. The modelling revealed the relationship between the variation of the gas puff rate, plasma density in SOL/core and the neutral particle flux through the separatrix. The modelling results showed that the modulated core plasma fuelling is defined by the boundary conditions on the separatix rather than by the neutral particle flux from the gas puff through the separatrix. This conclusion is valid for both H and D gases and it does not depend on the choice of the model describing the transport, provided that the evolution of the plasma parameters is consistent with experimental observation. [1] A.Salmi et al., “Investigation of gas fuelling characteristics in JET experiments”, EPS 2017 [2] M.Romanelli et al., “JINTRAC: A System of Codes for Integrated Simulation of Tokamak Scenarios”, Plasma and Fusion Research, 9, 3403023 (2014) *See the author list of “X. Litaudon et al 2017 Nucl. Fusion 57 102001″

Speaker: Yu. F. Baranov

14:00 P5.1103 Helicon wave experiments with steep magnetic field gradient devices Mini-RT and Mini-RT/L

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1103.pdf Helicon wave experiments with steep magnetic field gradient devices Mini-RT and Mini-RT/L Y. Ogawa1, T. Takemoto1, T. Sueyoshi1, C. Kawai1, J. Morikawa1 1 Graduate School of Frontier Sciences, the University of Tokyo, Kashiwa, 277-8568, Japan To explore high beta plasmas on the internal coil device Mini-RT (B ~ 0.01T) with the dipole magnetic configuration, the Electron Cyclotron Wave (f =2.45GHz) has been applied and the plasma density of 1017 m-3 (about two times higher than the cut-off density) has been achieved. In addition, the mode conversion to the Electron Bernstein Wave has been observed by direct measurement of wave propagation in plasmas[1]. Now we have conducted helicon wave experiments in the Mini-RT device, since helicon wave might be an attractive candidate to produce higher density plasmas in the low magnetic field devices. Compared with other linear and torus devices, the Mini-RT has slightly unique characteristics; i.e., the magnetic field by the dipole configuration has a steeper gradient, plasma radius is relatively large ( a = 15 ~ 20 cm) and a filling pressure is limited at low level ( 0.01 ~ 0.05 Pa). In addition, only a saddle type antenna can be installed at the outer surface of the plasma column. The mode conversion condition to Trivelpiece-Gould wave from helicon one is calculated with the FDTD code. At present, preliminary experimental results show that the plasma density of less than 1016 m-3 has been achieved in the Mini-RT device. Since the steep gradient configuration of the magnetic field in the Mini-RT device is quite different from other devices, a new linear device Mini-RT/L with a divergent magnetic field has been fabricated, in order to study excitation, propagation and absorption of the helicon wave in the steep magnetic field gradient configuration. In the Mini-RT/L experiments, as the helicon wave power is increased up to 3 kW, the plasma density of 4x1017 m-3 has been achieved. As the magnetic field has been raised, the plasma density has become the maximum value around 40 G. This characteristics seems to be similar to that observed by F.F. Chen[2]. Since the wave index is calculated to be 10 ~ 30 m-1, the corresponding phase velocity is roughly equal to the thermal velocity of electron with the temperature of a few tens eV. This would suggest the possibility of Landau damping of the helicon wave. [1] K. Uchijima, T. Takemoto, J. Morikawa and Y. Ogawa, Plasma Phys. Contr. Fusion, 57, 065003 (12pp) (2015). [2] F.F.Chen, et.al., Plasma Phys. Contr. Fusion, 39, A411-A420 (1997).

Speaker: Y. Ogawa

14:00 P5.1104 Magnetic compression at General Fusion - experiment and simulation with neutral fluid

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1104.pdf Magnetic compression at General Fusion - experiment and simulation with neutral fluid Carl Dunlea1,2, Ivan Khalzov2, Stephen Howard2, Wade Zawalski2, Kelly Epp2, Akira Hirose1, Chijin Xiao1, General Fusion Team2 1 University of Saskatchewan, Saskatoon, Canada 2 General Fusion, Vancouver, Canada *e-mail: cpd716@mail.usask.ca The magnetic compression experiment at General Fusion was a repetitive non-destructive test to study plasma physics applicable to Magnetic Target Fusion compression. A spheromak compact torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped inner flux conserver, and an insulating outer wall. External coil currents keep the CT off the outer wall (levitation) and then rapidly compress it inwards. The optimal external coil configuration greatly improved both the levitated CT lifetime and the rate of shots with good compressional flux conservation. As confirmed by spectrometer data, the improved levitation field profile reduced plasma impurity levels by suppressing the interaction between plasma and the insulating outer wall during the formation process. Significant field and density compression factors were routinely observed. Matching the decay rate of the levitation currents to that of the CT currents resulted in a reduced level of MHD activity and a higher frequency of long-lived CTs. We developed an energy and toroidal flux conserving finite element axisymmetric MHD code to study CT formation and compression. The Braginskii MHD equations with anisotropic heat conduction were implemented. The code also has the capability to start magnetic compression from a Grad-Shafranov equilibrium. There are simulated diagnostics for B probes, q-profile, interferometers, and Ion-Doppler measurements. To simulate plasma / insulating wall interaction, we couple the vacuum field solution in the insulating region to the full MHD solution in the remainder of the domain. A plasma-neutral model including ionization, recombination, charge-exchange reactions, and a neutral particle source, was implemented, primarily in order to reduce viscous heating of the ions during formation. We see good agreement between simulated and experimental results. ____________ (EPS 2018)_____________

Speaker: Carl Dunlea

14:00 P5.1105 Effects of tungsten divertor baffling on plasma detachment during the high power operation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1105.pdf Effects of tungsten divertor baffling on plasma detachment during the high power operation C. F. Sang1, G. S. Xu2, L. Wang2, Q. Wang1, D. Z. Wang1 1 Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian, China 2 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China The steady-state operation of next-step fusion devices requires both the deposited heat flux density on the divertor target below 10 MW/m2 and plasma temperature at the target below 5 eV to ensure adequate lifetime. Therefore, it will be essential to achieve highly dissipative or detached divertor conditions for the control of heat flux and erosion in a fusion reactor. One of the most effective methods to promote the achievement of detachment is to improve neutral trapping and impurity screening in the divertor by changing the divertor structure [1]. Previous experiment and modeling works on JET, DIII-D, C-mod and JT-60U studies highlight the importance of the divertor target shape and baffling on the plasma detachment [1-6]. However, some critical questions still remain: (1) most of the previous works were based on carbon-target, it is still unknown that whether it is still feasible for tungsten target? (2) what is the range of input power that the current size tokamaks can operate leveraging the benefits from a closed divertor? These question should be answered during the physical design of the lower tungsten divertor of the Experimental Advanced Superconducting Tokamak (EAST). In this work, the physical design of EAST lower divertor will be presented, and a systematic analysis of the target shape and closure effects on the plasma detachment is carried out by using SOLPS to address these questions. References [1] A. Loarte, Plasma Phys. Control. Fusion 43 (2001) R183. [2] C. F. Sang, P.C. Stangeby et al., PPCF 59 (2017) 025009 [3] C. F. Sang, H. Y. Guo et al., Nucl. Fusion 57 (2017) 056043. [4] H. Y. Guo, C. F. Sang et al., Nucl. Fusion 57 (2017) 044001 [5] B. Lipschultz et al., Fusion Sci. Technol. 51 (2007) 369. [6] S. Tsuji et al., J. Nucl. Mater. 220-222 (1995) 400. *This work was supported by National Key R&D Program of China No. 2017YFA0402500 and 2017YFE0300400, National Natural Science Foundation of China under Grant Nos. 11775044 and AHNFS under contract No. 1808085J07.

Speaker: C. F. Sang

14:00 P5.2001 Magnetised thermal filamentation and focussing in laser-plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2001.pdf Magnetised Thermal Filamentation and Self-Focussing Laser-Plasmas H. C. Watkins1, R. J. Kingham1 1 Imperial College London, London, United Kingdom The use of magnetic fields in Inertial Confinement Fusion (ICF) experiment 1,2 requires the introduction of the Braginskii magnetised anisotropic transport coefficients3. We study the effect of the magnetised thermal conductivity on the propagation of a long-pulse laser in the underdense plasma regime relevant to ICF parameters. An analytic model is derived for the laser self-focussing and shows the shortening of the self-focal length of a laser beam in a plasma because of the magnetised reduction of the plasma thermal conductivity. Furthermore the thermal mechanism filamentation4,5 of a laser under a magnetised plasma has an increased spatial growth rate. These analytic results are compared with the PARAMAGNET laser-plasma code and found to be in good agreement. We discuss the effect of these results on recent magnetised inertial fusion experiments where filamentation can be detrimental to laser propagation and uniform laser heating. The application of external magnetic fields to laser-plasma experiments requires the inclusion of the extended electron transport terms in simulation6. References: 1 D.S. Montgomery, B.J. Albright, D.H. Barnak, P.Y. Chang, J.R. Davies, G. Fiksel, D.H. Froula, J.L. Kline, M.J. Macdonald, A.B. Sefkow, L. Yin, and R. Betti, Phys. Plasmas 10703, (2015). 2 L.J. Perkins, D.D.M. Ho, B.G. Logan, G.B. Zimmerman, M.A. Rhodes, D.J. Strozzi, D.T. Blackfield, and S.A. Hawkins, Phys. Plasmas (2017). 3 S. I. Braginskii, Rev. Plasma Phys. (1965). 4 E.M. Epperlein, Phys. Rev. Lett. 65, 2145 (1990). 5 P. Kaw, G. Schmidt, and T. Wilcox, Phys. Fluids 1522, (1988). 6 M. Read, R. Kingham, and J. Bissell, in J. Phys. Conf. Ser. (2016), p. 12111.

Speaker: Henry Watkins

14:00 P5.2002 Recent advances in the modeling of stimulated Raman scattering

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2002.pdf Recent advances in the modeling of stimulated Raman scattering D. Bénisti CEA, DAM, DIF 91297 Arpajon Cedex, France In this talk, we first present a quick overview of the recent theoretical results obtained, both, in nonlinear wave-particle interaction and in the use nonlocal variational principles to describe wave propagation. As an application, we show how to solve theoretically for the nonlinear growth and saturation of the cold-beam plasma instability, and we introduce a set of coupled envelope equations that the model stimulated Raman scattering. These equations account for nonlinear kinetic effects, plasma inhomogenity and non stationarity in a three-dimensional ge- ometry, and interspeckle coupling. They proved to provide accurate results as regards Raman reflectivity in the nonlinear kinetic regime, within computation times reduced by about five orders of magnitude compared to a Particle-In-Cell code. In spite of their accuracy and effectiveness, the envelope equations cannot be solved directly in the hydrodynamical codes used for inertial confinement fusion. Consequently, one needs to introduce simplified models, and such a model, that accounts for nonlinear kinetics effects, is introduced. Comparaisons between the results obtained with this model and the complete set of equations are given, and the interplay between both approaches is discussed.

Speaker: Didier Bénisti

14:00 P5.2003 Cross-beam energy transfer (CBET) in ICF: the effect of laser speckles in presence of ponderomotive self-focusing

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2003.pdf Cross-beam energy transfer (CBET) in ICF : the effect of laser speckles in presence of ponderomotive self-focusing Stefan Hüller1, Gaurav Raj1, Wojciech Romus2, and Denis Pesme1 1 Centre de Physique Théorique, CNRS, Ecole Polytechnique, Palaiseau, France 2 Faculty of Science, University of Alberta Edmonton, Canada T6G 2E9 Both in the direct- and the indirect drive scheme for Intertial Confinement Fusions (ICF) Crossed beam Energy Transfer (CBET) between laser beams is still a major issue. Part of this problem is the complexity of the process involving both the plasma hydrodynamics and its interaction with the numerous incident laser beams. We model CBET by taking into account the speckle (hot spot) substructure of “smoothed” laser beams that has been disregarded in most of the previous studies. By means of numerical simulations with a wave coupling model [1], it can be shown that transfer from laser hot spots of one beam to the another beam, via self-focusing in presence of plasma flow [2,3] and “beam bending”[4,5], proves to affect considerably the angular spread of the light behind the region of beam overlap for laser intensities I λ2 > 1014 W cm-2 μm2 . For this reason the angular distribution of transmitted light from smoothed laser beams (with speckles) is very different from the angular distribution of beam when the beam speckle structure is disregarded. We also show the importance of non-linear, shock-like structures of ion waves and of the so- called plasma-induced smoothing to CBET. [1] G. Raj and S. Hüller, Phys. Rev. Lett. 118, 055002 (2017). [2] R. W. Short, R. Bingham, and E. A. Williams, Phys. Fluids 25, 2302 (1982). [3] A. J. Schmitt, Physics of Fluids 1, 1287 (1989). [4] B. Bezzerides, Physics of Plasmas 5, 2712 (1998). [5] D. E. Hinkel, E. A. Williams, and C. H. Still, Phys. Rev. Lett.77, 1298 (1996).

Speaker: Stefan Hüller

14:00 P5.2004 Experimental investigation on spherical hohlraum energetics at the SG laser facilities

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2004.pdf Experimental investigation on spherical hohlraum energetics at the SG laser facilities W. Y. Huo1, Z. C. Li2, Y. H. Chen1, X. F. Xie2, G. L. Ren1, K. Lan1 1 Institute of Applied Physics and Computational Mathematics, Beijing, China 2 Research Centre of Laser Fusion, China Academy of Engineering Physics, Mianyang, China The integrated experiments at the National Ignition Facility indicate that the radiation asymmetry control in the cylindrical hohlraums is an extremely challenging problem in achieving ignition by using indirect drive. Recently, Lan et al. have proposed the octahedral spherical hohlraum which has the natural superiority in providing high radiation symmetry. As new and promising hohlraums, the octahedral spherical hohlraum attracts much research interests. In indirect drive inertial confinement studies, hohlraum energetics is one of the fundamental problems. In this presentation, we report on the spherical hohlraum experiments performed at the SG series laser facilities. At the SGIII-prototype laser facility, we performed the first spherical hohlraum energetics experiment. In this experiment, we used the vacuum spherical hohlraum with 2 laser entrance holes. The radiation temperature is measured by using an array of flat-response x-ray detectors (FXRDs) through a laser entrance hole at different angles. The radiation temperature and M-band fraction inside the hohlraum are determined by the shock wave technique. The experimental results show that there is no intrinsic difference in energetics between spherical hohlraums and cylindrical hohlraums. At the SGIII laser facility, we performed the first octahedral spherical hohlraum energetics experiment. The 32 of 48 laser beams enter the hohlraum through six laser entrance holes. We used 5 FXRDs to measure the radiation flux emitted from different regions inside the octahedral spherical hohlraum. The radiation temperature inside the hohlraum is determined by the shock wave technique. In this experiment, some interesting phenomena are observed in the backscatter light induced by SRS.

Speaker: Wenyi Huo

14:00 P5.2006 Efficient ps. Laser Ion Acceleration toward High Neutron Yield

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2006.pdf Efficient ps. Laser Ion Acceleration toward High Neutron Yield K.Mima1)*. A.Yogo2), R.Hanayama1), A.Sunahara3), T.Asahina2), H.Nagatomo2), H.Nishimura2), Y.Arikawa2), Y.Abe2), M.Nakai2), H. Kondo3), H.Tanaka4), S.Nakai1) and Y.Kato1) 1) The Graduate School for C. of N. Photonics Industries (GPI), Hamamatsu,, Japan 2) Institute of Laser Engineering (ILE), Osaka University, 565-0871, Suita, Osaka Japan 3) Purdue University, Indiana, USA 4) Hamamatsu Photonics K.K. (HPK), Hamamatsu, Japan, 5) Reactor Research Institute, Kyoto University, Kumatori, Osaka, Japan *K.Mima: k.mima@gpi.ac.jp) Laser driven neutron sources and their applications have been explored in the projects of the A-STEP program of the JST, since 2016 at ILE, Osaka University and GPI, Hamamatsu. In this paper, new findings for the efficient laser ion acceleration and neutron generation are reported. The higher ion and neutron yield are realized by producing a pre-plasma before the main pulse in the TNSA. According to the simulations, the short pulse laser absorption and hot electron slope temperature are higher when a pre-plasma is formed on a solid target surface. So, the accelerated ion number and energy are expected to be higher. But, because of the pre-heating, the rear surface of a thin foil expands and then the TNSA field is reduced. The new finding is to steepen the rear surface density profile by controlling the shock breakout time, It is explored by the radiation hydro-simulation. We found that the steepened rear surface density profile is realized by adjusting the pre-pulse intensity and duration and the target thickness. The PIC simulations were carried out to see the pre-pulse effects. According to the results, the total ion energy and the cut-off energy increases by one order with a proper pre-pulse and the target thickness. As preliminary experiments, the pitcher-catcher schemes were studied with the LFEX laser at ILE and the repetition rate short pulse laser at HPK and GPI. In the LFEX experiments, the 0.5-1 kJ, multi picosecond pulse irradiated a CD foil with proton contamination for accelerating deuteron and proton. The accelerated proton and deuteron number for the energy higher than 10 MeV reaches 1014 /shot, which is 10 times higher than that without pre-pulse. The more discussions on the simulations and experiments will be presented.

Speaker: K.Mima

14:00 P5.2007 Numerical studies of beam smoothing methods and its influence on filamentation instability

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2007.pdf Numerical studies of beam smoothing methods and its influence on filamentation instability Bin Li, Zhanjun Liu, Liang Hao, Chunyang Zheng, Jiang Xiang Institute of Applied Physics and Computational Mathematics (IAPCM), Beijing, China Large scale filamentation instability in Hohlraum is investigated by a three dimensional parallel laser plasma simulation code LAP3D [1] developed at IAPCM. The focus lies on how to controlling the instability by spatial and temporal smoothing methods [2], respectively. Spatial smoothing method is illustrated by propagation of a beam smoothed by the continuous phase plate (CPP) , the research of which includes as follows: 1) features of filamentation instability when it develops [3] ; 2) the threshold of the instability for a CPP beam; 3) influence of distribution of strong speckles on the instability; 4) conditions for the onset of the beam deflection [4]. Spatial smoothing method is illustrated by propagation of a beam smoothed by the spectral dispersion smoothing (SSD), the research of which includes as follows: 1) influence of modulated frequency on the beam propagation [5]; 2) the threshold of filamentation instability for such a beam. REFERENCES [1] Xiaoyan Hu, Liang Hao, Zhanjun Liu, Chunyang Zheng, Bin Li, Hong Guo, AIP ADVANCES, 5,8(2015). [2] John Lindl, Phys Plasmas, 2, 11(1995). [3] Bin Li, Xiaoyan Hu, Chunyang Zheng, Zhanjun Liu, High Power Laser and Particle Beams,28,11(2016). [4] Bin Li, Zhanjun Liu, Chunyang Zheng, Xiaoyan Hu, High Power Laser and Particle Beams,26,12(2014). [5] Bin Li, Zhanjun Liu, Liang Hao, Xiaoyan Hu, Chunyang Zheng, Jiang Xiang, Chinese Journal of Lasers, 2017,44(12):1201004.

Speaker: Bin Li

14:00 P5.2008 Temporal characteristics of hot electron generation inside kJ-laser irradiated Cu foils

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2008.pdf Temporal characteristics of hot electron generation inside kJ-laser irradiated Cu foils O. Renner1,2, M. Šmíd1, T. Schlegel3, A. Colaitis4, V.T. Tikhonchuk5, F.B. Rosmej6,7 1 Institute of Physics & ELI-Beamlines, Czech Academy of Sciences, Prague, Czech Republic 2 Institute of Plasma Physics & PALS Facility, Prague, Czech Republic 3 GSI Helmholtzzentrum f. Schwerionenforschung GmbH, Darmstadt, Germany 4 University of Rochester, Laboratory for Laser Energetics, Rochester, USA 5 Centre Lasers Intense et Applications, University of Bordeaux-CNRS-CEA, France 6 Sorbonne Université, Faculté des Sciences et Ingénierie, Paris, France 7 LULI, École Polytechnique, CEA, CNRS, Palaiseau, France Hot electron (HE) production driven by instabilities accompanying the laser plasma interaction [1] is of paramount interest for the inertial confinement fusion science and high energy density physics. Their accurate characterization is crucial for interpretation of high-intensity laser matter experiments. Here we report studies of non-thermal atomic states in kJ-laser produced plasmas allowing to characterize HE generation with respect to their fraction and temporal evolution. The action of HE was visualized via high-resolution x-ray spectra emitted from the laser-deflected part of the 1.5-µm-thick Cu foil. Hot electrons are penetrating the accelerated foil and produce the K-shell emission in rather cold dense matter that otherwise would not emit x-rays. A quantitative analysis of the measured spectra based on 2D hydrosimulations [2] and non-Maxwellian kinetics [3] indicates that hot electrons are produced significantly after the laser maximum. Good agreement between experimental observations and simulations indicates that a combination of advanced high-resolution x-ray spectroscopy and non-thermal atomic physics spectral modelling offers a novel method to characterize hot electrons inside the laser accelerated solid density matter. In the same time, fine spectral features identified in x-ray emission originating from several Cu charge states represent a set of precise spectroscopic data capable to benchmark the state-of-the-art multiscale nonlinear hydrodynamic modelling of the laser-plasma interaction. The authors acknowledge the support of Eurofusion Project No. AWP17-ENR-IFE-CEA-01. [1] G. Cristoforetti et al, Phys. Plasmas 25 (2018) 012702. [2] A. Colaitis et al, Phys. Rev. E 92 (2015) 041101. [3] F.B. Rosmej, X-ray emission spectroscopy and diagnostics of non-equilibrium fusion and laser produced plasmas. Taylor & Francis (2012).

Speaker: Oldrich Renner

14:00 P5.2009 Transverse beam structure formation in Crossed Beam Energy Transfer

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2009.pdf Transverse Beam Structure Formation in Crossed Beam Energy Transfer H. Schmitz1 , R. Trines1 , B. Bingham1 1 STFC Rutherford Appleton Laboratory, Didcot, United Kingdom Crossed Beam Energy Transfer (CBET) plays a large role in both direct drive as well as indirect drive inertial confinement fusion. CBET is responsible for redirecting energy from one beam into another and reshaping the profiles of the laser beams. For this reason CBET has been at the focus of research activities for a number of years. Despite this, the details of the energy transfer and beam reshaping are not yet fully understood. Usually it is assumed that transverse beam reshaping is due to the effect that the matching conditions for Brillouin or Raman scattering are only met at certain locations in the non-uniform flowing plasma around the target. In order to interact the beams and the plasma wave must meet matching conditions for the frequency and wave vector, corresponding to energy and momen- tum conservation. However, for the case of Brillouin scattering the bandwidth of the laser beams can be larger than the frequency of the ion acoustic oscillation. For finite bandwidths the match- ing conditions are relaxed and don’t have to be fulfilled exactly at the beams’ central frequency and wave vector. As an example of this case, two beams with identical frequency can exchange energy through an ion acoustic wave in a uniform plasma at rest. We present 2D, direct numerical simulation of Brillouin Scattering using a hydrodynamic code coupled to a full Maxwell solver. In this way we avoid the expense of full PIC simulations while, on the other hand, not restricting the model to a single frequency envelope approximation. The simulations show transverse structuring of the outgoing beams caused by the depletion of the incoming beam energy. For these conditions beam reshaping can not be explained by local fulfilment of the matching conditions and an alternative explanation must be found. In order to investigate the cause of the structure formation a theoretical model is developed. The model shows that the beam reshaping is caused by the same effects as pulse compression in Brillouin backscattering.

Speaker: Holger Schmitz

14:00 P5.2010 Ultra-intense laser interaction with nanostructured near-critical plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2010.pdf Ultra-intense laser interaction with nanostructured near-critical plasmas A.Formenti1 , L.Fedeli 1 , L.Cialfi1 , A.Pazzaglia1 , M.Passoni1 1 Politecnico di Milano, Milano, Italy Ultra-intense laser interaction with near-critical plasmas is characterized by a rich physics and is ac- tively investigated for a wide range of applications, from laser-driven secondary sources[1, 2] to the ex- ploration of astrophysically relevant scenarios[3]. An appealing solution to produce near-critical plas- mas with finely controlled properties is to irradiate nanostructured low-density materials[4]. Due the combined extremely fast dynamics and high tempo- ral contrast of modern-day ultra-intense lasers, the nanostructure can survive long enough to affect the Figure 1: Nanostructured foam irradiated at interaction. a0 = 5. Electron density is shown in greyscale, In this contribution we present a thorough investi- while EM field intensity is shown in col- gation of laser-interaction with near-critical nanos- orscale. tructured plasmas, via 2D[5] and 3D[6] Particle-In- Cell (PIC) simulations[7]. For the plasma we consider both simplified models (i.e. a collection of nanospheres) and realistic 3D nanostructured morphologies (i.e. fractal-like foam aggregates, ordered and random arrays of nanowires). We compare their behavior with that of a homoge- neous near-critical plasma. We find that several important observables are influenced by the nanostructure and so a realistic description of its morphology is essential to properly under- stand the physical processes at play in this scenario. These results suggest possible paths to guide the design of future experiments involving near-critical plasmas. References [1] M. Passoni et al., Physical Review Accelerators and Beams 19, 061301 (2016) [2] D.J. Stark et al., Physical Review Letters 115, 025002 (2015) [3] A.Grassi, M.Grech, F.Amiranoff, A.Macchi, C.Riconda, Physical Review E 96:033204 (2017) [4] A.Zani, D.Dellasega, V.Russo, M.Passoni. Carbon 56, 358-365 (2012) [5] L.Fedeli, A.Formenti, C.E.Bottani, M.Passoni, The European Physical Journal D 71.8, 202 (2017) [6] L.Fedeli, A.Formenti, L.Cialfi, A.Pazzaglia, M.Passoni, Scientific Reports, In press (2018) [7] A. Sgattoni et al. PRACE white paper. arXiv:1503.02464 (2015)

Speaker: Arianna Formenti

14:00 P5.2011 Numerical investigations on fusion ignition process in plasma formed by the interaction of energetic and high current ion beams

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2011.pdf Numerical investigations on fusion ignition process in plasma formed by the interaction of energetic and high current ion beams Stavros D. Moustaizis1, P. Lalousis2, I. Pologiorgi1 and S. Vlastos1 1 Technical University of Crete, Lab of Matter Structure and Laser Physics, Chania, Crete, Greece 2 Institute of Electronic Structure and Laser FORTH, Heraklion, Greece Abstract Numerical investigations on the interaction of two energetic and high current density ion beams trapped in a volume with external applied magnetic field enable to study nuclear fusion process for different ion species. The final plasma is formed by the interaction of the two beams and is composed by the two different ion species of the beams and by low density electrons. The configuration of the beams could be constituted in a first case by one proton beam and one 11B beam and in a second case by two deuterium beams. The proposed scheme for the high power ion beams production is based on both the Magnetically Insulated Diode (MID) and Pulsed Power (PP) techniques. These techniques allow generating high energy ion beams up to hundreds of keV with current density up to few tens of A/cm2, with relatively low electron density. The application of this scheme for fusion overcomes the difficulty 11 concerning the Hydrogen - B fuel for which the cross section for reactions is efficient for energies higher than 250 keV. The low electron density in the formed plasma minimizes the bremsstrahlung radiation losses, especially for the case of the Hydrogen-11B fusion plasma. The temporal evolution of the plasma parameters and especially the reaction rate was investigated using a multi-fluid, zero dimension, and global energy code. The code allow to estimate the alpha heating effect on the temporal evolution of the formed plasma temperature and the maximum value of the reaction rate, especially for the Hydrogen-11B fusion case, where each reaction produce three alphas with total energy of 8.7 MeV. The numerical study allows estimating the time interval to obtain the maximum of the reaction rate as a function of the initial conditions concerning the energy and the current density of the ion beams. The present work based on existing technologies (MID and PP) and will contribute on the design and potential development of Compact Magnetic Fusion Devices (CMFD) with output energy of the order of 100 MW.

Speaker: Stavros Moustaizis

14:00 P5.2012 Development of gas cluster ion beam source for sims analysis

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2012.pdf DEVELOPMENT OF GAS CLUSTER ION BEAM SOURCE FOR SIMS ANALYSIS Sang Ju Lee, Myoung Choul Choi*, Chang Min Choi, Boo Ki Min, Jung Jin Kim Mass Spectrometry & Advanced Instrument Group, Korea Basic Science Institute, Ochang Center, Chungbuk 28119, Korea Gas cluster ion beam (GCIB) has been making a new possiblities in analytical instruments. Especially, for secondary ion mass spectrometry (SIMS), the GCIB is a powerful technique [1] for the in-depth chemical structure analysis of organic materials [2,3]. Currently, cluster ion beam is widely used as a primary analyser gun for analysing organic and biological samples in secondary ion mass spectrometer. We developed our own Ar gas cluster ion beam source and column. Gas cluster is generated by precision nozzle. But it needs an extra parts (ionizer) to ionize neutral gas clusters. The ionizer structure have been simulated to know efficient control electrode and deliver high current extraction. Simulation show that the extraction electrode having a dependence of electrode and deliver high current extraction. Simulation has been performed by SIMION 8.1 code. The results from simulation show that the extraction electrode having a dependence of electron trajectory in ionization area. The voltage of extraction electrode directly control the path of electron. So, we assume that the resident time of electron is proportional to ionization probability of neutral gas. In this point of view, the extraction electrode can be an efficient ion beam control electrode. The extraction electrode were tested by varying their voltage. The voltage range was controlled within “0 ~ 1,000V”. Experimental results well accord with simulation results. Generated ion beam current from the ionizer is higher than 200 nA. The precision nozzle, their chamber, and skimmer are constructed and integrated with the ionizer chamber. KBSI gas cluster ion beam source has been developed with SIMION 8.1 code. This gas cluster ion beam well be focused on analysing organic material and bio samples. To do this, various ion beam source and cluster has been designed and developed. [1] N. Winograd, Anal. Chem. 77(7), 2005, 125A. [2] I. Yamada, J. Matsuo, Z. Insepov, D. Takeuchi, M. Akizuki, and N. Toyod, J. Vac. Sci. Technol. A, 14(3), 1996, 781 [3] Peter J. Cumpson, J.F. Portoles, A. J. Barlow, N. Sano, M. Birch, Surf. Interface Anal., 45(13), 2013, 1859

Speaker: Sang Ju Lee

14:00 P5.2013 Efficient Raman laser amplification with short pulses

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2013.pdf Efficient Raman laser amplification with short pulses J. Hornicek1 , O. Klimo1,2 , J. Limpouch1 , S. Weber2 1 FNSPE, Czech Technical University in Prague, 11519 Prague, Czech Republic 2 Institute of Physics of the ASCR, ELI-Beamlines, 18221 Prague, Czech Republic Amplification of the ultrashort pulses is limited by the damage threshold of optical compo- nents used in the laser system. For multi-PW laser system, the components like for example gratings in the compressor have to be very large, they are difficult to produce and expensive. An alternative is to use the plasma medium, where the energy from a longer higher-frequency pump pulse can be transferred to a short lower-frequency seed pulse via stimulated Raman or Brillouin scattering. The plasma medium can support much stronger fields and the maximum intensity threshold is increased by several orders of magnitude. On the other hand, the efficiency and stability of these processes are limited by the growth of unwanted instabilities. We concentrate on the stimulated Raman scattering and propose an efficient and stable way how to transfer energy between two laser pulses. Two most common high power laser systems are considered here. These are a higher energy Nd:Glass system delivering a longer pulse which serves as a pump pulse and a lower energy Ti:Sapphire laser system which delivers a short seed pulse. To make such configuration feasible, either the seed pulse frequency must be decreased below the one of the pump pulse or the pump pulse must be converted to higher frequency. In this contribution, we consider the later one and we assume that the pump pulse is frequency doubled using a thin KDP crystal like in [1]. In such a case, the frequency mismatch between the pump and the seed pulse implies a relatively dense plasma where the interaction becomes unstable on a short time scale. To suppress the growth of instability, the interaction time between the laser pulses and the plasma medium is shortened to few hundred femtoseconds and the intensity of the both pulses is relatively high so that the energy transfer is relatively efficient on the very short time scale. Using this approach, we can achieve about 60% conversion efficiency from the pump pulse to the seed pulse in our 1D Particle-in-cell simulations using the code EPOCH. The results are also confirmed in 2D simulations as it turns out that multi-dimensional effects like filamentation and self-focusing are not important on the short time scale of the interaction. Our work is supported by Czech Science Foundation project 18-09560S. References [1] M. Hornung et al., Appl. Sci. 5, 1970–1979 (2015)

Speaker: Ondrej Klimo

14:00 P5.2014 High-intensity laser-plasma interaction

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2014.pdf High-intensity laser-plasma interaction S. Marini1 , M. Grech1 , M. Raynaud2 , C. Riconda1 1 LULI, Sorbonne Université, CNRS, École Polytechnique, CEA, Université Paris-Saclay, F-75252 Paris cedex 05, France 2 Laboratoire des Solides Irradiés, CEA/DRF/IRAMIS, École Polytechnique, CNRS, Université Paris-Saclay, F-91128 Palaiseau, France Ultrashort high-intensity laser interaction with a sharp-edged over-dense plasma has become an attractive mechanism for the generation of fast particles [1]. Through suitable physical condi- tions between the laser and periodic gratings on the vacuum plasma interface, it is possible to excite Surface Plasma Waves (SPW), increasing the absorption of the laser energy up to 75% [2] as well as accelerating particles to the relativistic limit [2, 3]. The physical conditions for the SPW excitation vary depending on both the plasma density and the laser intensity [3], in particular, relativistic corrections to the electron density need to be considered. In this work, we suggest how to take into account these characteristics theoretically in the dispersion relation and we verify the outcoming resonant matching conditions using a two-dimensional Particle In Cell (PIC) code [4]. These results can be used to optimize and control all possible applications of high-intensity laser-plasma interaction [1, 2, 3]. References [1] A. Bigongiari, M. Raynaud, C. Riconda, and A. Héron, Phys. Plasmas 20, 052701 (2013) [2] A. Bigongiari, M. Raynaud, C. Riconda, A. Héron, and A. Macchi, Phys. Plasmas 18, 102701 (2011) [3] M. Raynaud, A Héron, and J-C Adam, Plasma Phys. Controlled Fusion 60, 014021 (2018) [4] J. Derouillat, A. Beck, F. Pérez, T. Vinci, M. Chiaramello, A. Grassi, M. Flé, G. Bouchard, I. Plotnikov, N. Aunai, J. Dargent, C. Riconda, M. Grech, Computer Physics Communications 222, 351 (2018)

Speaker: Samuel Marini

14:00 P5.2015 Relativistic effects in plasma produced with sub-nanosecond 3-TW laser

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2015.pdf Relativistic effects in plasma produced with sub-nanosecond 3-TW laser J. Krása1, D. Klír2,3, K. Řezáč2,3, J. Cikhardt2,3, M. Krůs1,3, A. Velyhan1, M. Pfeifer1,3, J. Dostál3,1, R. Dudžák1,3, M. Krupka3, J. Kaufman1, T. Pisarczyk4, Z. Kalinowska4, T. Chodukowski4 1 Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic 2 Faculty of Electrical Engineering, Czech Technical University in Prague, Czech Republic 3 Institute of Plasma Physics of the Czech Academy of Sciences, Prague, Czech Republic 4 Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland This contribution deals with observations of relativistic electrons produced in a laser plasma interaction experiment at the PALS laser system operated at the Institute of Plasma Physics in Prague, Czechia. The PALS laser is a near-infrared 3-TW iodine laser designed to deliver irradiance on target of 1016 Wcm-2 in 300 ps pulses at the wavelength of 1.315 m. Plastic and metallic foils of 50 – 500 m in thickness were irradiated with I2  51016 W cm2 m2. Under these conditions we have observed relativistic electrons expanding into the vacuum with maximum energy going beyond 4 MeV in the backward direction, i.e. against of the focused laser beam. The relativistically accelerated forward electrons passing through foil targets were directly observed around the normal of the rear target surface. The applied laser intensity was increased by the self-focusing above the relativistic threshold. Our experiments have shown that the experimental conditions may be appropriate for thermal and relativistic self-focusing. The application of a unique femtosecond interferometry technic [1] allowed us to observe bunches of trapped electrons occurring in the plasma expanding against the focused laser beam. [1] T. Pisarczyk, et al., Phys. Plasmas 21, 012708 (2014).

Speaker: Josef Krasa

14:00 P5.2016 Transition to self-focusing regime in a spatially modulated electrostatic field particle accelerator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2016.pdf Transition to self-focusing regime in a spatially modulated electrostatic field particle accelerator F. Russman1, S. Marini2, E. Peter1, G. I. de Oliveira3 , F. B. Rizzato1 1 Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil 2 LULI, Sorbonne Université, CNRS, École Polytechnique, CEA Université Paris-Saclay, Paris, France 3 Instituto de Física, Universidade Federal do Mato Grosso do Sul, Campo Grande, Brazil A charged particle can be self-focused and accelerated simultaneously by an electrostatic modulated wave. It occurs under proper conditions, which depend on the initial longitudinal and transversal velocities of the particle, the amplitude, phase-velocity and the shape (longitudinal and transverse length scales) of the wave. However, there are also three different regimes: the particle could pass through the wave suffering no substantial acceleration (passing regime); the particle could be reflected by the wave (reflecting regime); and, the particle could be accelerated with no self-focusing. In this work, we provide the full set of equations of the proposed model and a modulational approximation that describes the dynamics of the particle in the case of no acceleration. We explore here how occur the transitions between these regimes by analysing the dynamics of the particle through numerical simulations.

Speaker: Eduardo Alcides Peter

14:00 P5.2017 Characterisation of laser-driven positron beams for injection in secondary stages

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2017.pdf Characterisation of laser-driven positron beams for injection in secondary stages A. Alejo1, G. Sarri1 1 Centre for Plasma Physics, Queen’s University Belfast, United Kingdom The generation of high-quality relativistic positron beams has gained significant attention in experimental physics, due to their potential relevance in a wide range of scientific and engineering areas, ranging from fundamental science to practical applications. Optimising the spectral and spatial quality of these beams is crucial not only for these applications, but also for the possibility of using these laser-driven sources as injectors for further stages of acceleration, being them plasma-based or radio-frequency. Here we report on experimental and numerical results on determining and optimising the emittance of these beams, whilst preserving high peak current. This work is justified by the necessity of generating small-scale and rather inexpensive positron beam accelerators with superior spatial and spectral qualities. For instance, these results indicate that ultra-relativistic and high-current positron beams with geometrical emittance below 0.1mm·mrad can be generated using already existing technology. This value is already comparable to the emittance in more conventional radio-frequency positron accelerators, such as the LEP injector (0.2 mm·mrad), indicating the possibility of direct injection without the necessity of beam manipulation and storage. These results are of central importance for the development of laser-driven particle sources and, in perspective, for the construction of an all-optical electron-positron collider, main interest of several national and international projects world-wide, such as the European-funded EuPRAXIA. References: [1] G. Sarri et al., Phys. Rev. Lett. 110, 255002 (2013). [2] G. Sarri et al., Plasma Physics Controlled Fusion 59, 014015 (2016). [3] G. Sarri et al., Plasma Physics Controlled Fusion 55, 124017 (2013). [4] A. Alejo and G. Sarri, Plasma Physics Controlled Fusion, to be submitted (2018). [5] EuPRAXIA: http://www.eupraxia-project.eu/

Speaker: Aaron Alejo

14:00 P5.2018 Launching electromagnetic cascades in high-intensity laser fields

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2018.pdf Launching electromagnetic cascades in high-intensity laser fields T. G. Blackburn1 , A. Ilderton2 , S. P. D. Mangles3 , C. D. Murphy4 , C. P. Ridgers4 , M. Marklund1 1 Department of Physics, Chalmers University of Technology, Gothenburg, Sweden 2 Centre for Mathematical Sciences, Plymouth University, Plymouth, UK 3 The John Adams Institute for Accelerator Science, Imperial College London, London, UK 4 York Plasma Institute, Department of Physics, University of York, York, UK A cascade of photon emission and electron-positron pair creation is launched when a high- energy electron or photon traverses a region of sufficiently strong electromagnetic field, such as at the focus of a high-power laser. Cascades in the highly nonlinear regime, where the laser strength parameter a0 1 and the quantum parameter χ ∼ 1, are relevant to the study of astrophysical plasmas, such as in pulsar magnetospheres, and will be a ubiquitous feature of high-intensity experiments at the next generation of laser facilities. When combined with the ultrarelativistic, ultrashort electron beams available from laser-wakefield acceleration, today’s high-intensity lasers have the capability to probe this regime, where the recoil from emission of multiple photons (radiation reaction) dominates the electron dynamics [1, 2]. If the fields are strong enough that χ ∼ 1, the photons will produce electron-positron pairs, and the daughter electrons and positrons will lose energy to secondary radiation. We discuss the prospects for observation of such a cascade in two experimental geometries: one in which a multi-GeV, laser-wakefield accelerated electron beam collides directly with a laser pulse, pro- ducing photons via nonlinear Compton scattering [3]; and one in which the electron beam first collides with a high-Z foil, producing GeV photons via bremsstrahlung that go on to collide with a high-intensity laser pulse [4]. References [1] J. M. Cole et al., Experimental Evidence of Radiation Reaction in the Collision of a High-Intensity Laser Pulse with a Laser-Wakefield Accelerated Electron Beam, Phys. Rev. X 8, 011020 (2018) [2] K. Poder et al., Evidence of strong radiation reaction in the field of an ultra-intense laser, arXiv:1709:01861 (2017) [3] T. G. Blackburn, A. Ilderton, C. D. Murphy and M. Marklund, Scaling laws for positron production in laser– electron-beam collisions, Phys. Rev. A 96, 022128 (2017) [4] T. G. Blackburn and M. Marklund, Nonlinear Breit-Wheeler pair creation with bremsstrahlung γ rays, arXiv:1802.06612 (2018)

Speaker: Thomas George Blackburn

14:00 P5.2019 Optimization of gamma photons collision setups for two photon Breit-Wheeler pair production in the laboratory

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2019.pdf Optimization of gamma photons collision setups for two photon Breit- Wheeler pair production in the laboratory E. d’Humières1,2, X. Ribeyre1, O. Jansen3, A. Arefiev3, T. Toncian4, L. Esnault1, S. Jequier1, J.-L. Dubois1, S. Hulin1, Y. Sentoku2, and V. Tikhonchuk1 1 Univ. Bordeaux-CNRS-CEA, France 2 Univ. of Nevada, Reno, USA 3 Univ. of California, San Diego, USA 4 Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany Linear Breit-Wheeler pair creation is the lowest threshold process in photon-photon interaction, controlling the energy release in Gamma Ray Bursts and Active Galactic Nuclei, but it has never been directly observed in the laboratory. We have recently proposed a new experimental setup based on the collision of MeV photon sources produced by high intensity lasers [1]. Using numerical simulations, we have therefore optimized the generation of collimated gamma beams with high energy conversion efficiency using high intensity lasers and innovative targets. The results of this optimization campaign will be detailed. When two of these gamma beams collide at particular angles, our analytical calculations demonstrate a pair beaming effect easing their detection in the laboratory [2]. This effect has been confirmed in photon collision simulations using a recently developed innovative algorithm [3] that allows us to propose robust experimental designs on facilities like APOLLON, PETAL and ELI-NP. Moreover, we have studied the effect of the differential Breit-Wheeler cross section on this pair beaming. This effect changes the angular and energy distribution of the produced pairs in the laboratory frame. An alternative scheme using Bremsstrahlung radiation produced by next generation high repetition rate laser systems at lower intensities is also being explored and we will present the results of first optimization campaigns in this regime. This research was supported by the French National Research Agency under Grant ANR-17-CE30-0033-01, and the US Air Force project AFOSR No. FA9550-17-1-0382 References: [1] X. Ribeyre, et al., Phys. Rev. E, 93, 013201 (2016). [2] X. Ribeyre et al., Plasma Phys. Cont. Fusion 59, 014024 (2017) . [3] O. Jansen et al., Jour. Comp. Phys., 355, 582 (2018).

Speaker: Emmanuel d'Humières

14:00 P5.2020 Attosecond pulse from laser-irradiated near-critical-density plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2020.pdf Attosecond pulse from laser-irradiated near-critical-density plasmas Y. X. Zhang1,2 , B. Qiao1,3 , X. R. Xu1 , H. X. Chang1 , H. Zhang3 , C. T. Zhou1,3 , M. Zepf 2,4 ,X. T. He1,3 1 School of Physics, Peking University, Beijing, China 2 Helmholtz Institute Jena, Jena, Germany 3 Collaborative Innovation Center of IFSA (CICIFSA), Shanghai, China 4 Department of Physics and Astronomy, Queen’s University, Belfast, United Kingdom The birth of high-intensity attoseocnd source has extended human measurement and control techniques into atomic-scale electronic dynamics. High harmonic generation from laser-plasma interaction has been regarded as one of the most promising routes to obtain such attosecond light. Here, we propose a new practical approach of obtaining intense attosecond pulses by a laser pulse interacting with near-critical-density (NCD) plasmas. The unique interaction dynam- ics in NCD plasmas have been identified theoretically and by particle-in-cell simulations (Fig. 1), which show that three distinct dense electron nanobunches are formed each half a laser cycle and two of them can induce intense attosecond pulses in respectively the reflected and transmit- ted directions by the so-called “coherent synchrotron emission” (CSE) mechanism. Comparing with CSE in solids, not only the required stringent conditions on laser and target are relaxed, but also the radiation intensities are enhanced by two orders of magnitude. (a) (b) (c) (d) Figure 1: Schematic figures to show different nonlinear dynamics at different moments in NCD targets References [1] B. Dromey, S. Rykovanov, M. Yeung, R. Horlein, D. Jung, D. C. Gautier, T. Dzelzainis, D. Kiefer, S. Palaniyppan, R. Shah, J. Schreiber, H. Ruhl, J. C. Fernandez, C. L. S. Lewis, M. Zepf, and B. M. Hegelich, Nat. Phys. 8, 804 (2012). [2] Y. X. Zhang, B. Qiao, X. Xu, H. X. Chang, H. Lu, C. T. Zhou, H. Zhang, S. P. Zhu, M. Zepf, and X. T. He, Opt. Express, 25(23), 29058-29067 (2017). [3] Y. X. Zhang, B. Qiao, X. R. Xu, H. X. Chang, H. Zhang, H. Y. Lu, M. Y. Yu, C. T. Zhou, S. P. Zhu, and X. T. He, Phys. Plasmas 24(12), 123119 (2017).

Speaker: Xue Yu Zhang

14:00 P5.2021 Using laser-driven magnetized hohlraum to make a high temperature symmetrical clean X-ray radiation source

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2021.pdf Using laser-driven magnetized hohlraum to make a high temperature symmetrical clean X-ray radiation source Hang LI 1,2, Longyu KUANG 1,2, Longfei JING 1, Zhiwei LIN 1, Feng WANG 1, Shaoen JIANG 1, Jian ZHENG 2, Ke LAN 3, Jie LIU 3, Yongkun DING 1,2,3 and B. Grant LOGAN 4 1 Research Center of Laser Fusion, China Academy of Engineering Physics, China 2 CAS Key Laboratory of Basic Plasma Physics and Department of Modern Physics, University of Science and Technology of China, China 3 Institute of Applied Physics and Computational Mathematics, China 4 Lawrence Berkeley National Laboratory, USA Strong magnetic fields in high power laser laboratories play a prominent role in high energy density physics, while interaction of high power laser with high Z hohlraum is one effective way of converting laser energy to high temperature X-ray radiation source. To obtain high temperature symmetrical clean radiation source, capacitor-hohlraum target was designed based on capacitor-coil target, so megagauss axial magnetic field can be generated in hohlraum by the interaction of high power laser with the capacitor part. Then, interaction of laser with the magnetized hohlraum can be studied. Firstly, compared with the traditional hohlraum, the strong magnetic field in magnetized hohlraum can limit the plasma electron heat conduction in the laser channels, increase the plasma temperature, and reduce scattering laser. Secondly, magnetic pressure can suppress the hohlraum wall plasma motion, provide channels for laser injection, and avoid plasma filling and large-scale laser-plasma interactions. Lastly, strong magnetic field can guide hot electron out of hohlraum along the magnetic field lines, which provide clean hohlraum radiation. These are of great significance in hohlraum energetics and laser interaction with magnetized plasma. 500-700 T magnetic field was generated in a cylindrical hohlraum by the interaction of 1.8 kJ-1.0 ns-1064 nm laser with capacitor-coil target on SG-II laser facility, which was proven by B-dot probe. Magnetic field suppressed plasma filling, forming a hollow region of the plasma corona in the vacuum hohlraum, which was observed by an x-ray framing camera. Therefore, strong magnetic field is proven to effectively suppress the plasma filling in vacuum hohlraum instead of gas, providing an important potential way for hohlraum design in the laser indirect-drive inertial confinement fusion. References [1] H. Daido et al. Phys. Rev. Lett., 56, 846 (1986). [2] S. Fujioka, Z. Zhang, K. Ishihara et al. Scientific Reports, 3, 1170 (2013). [3] J.J. Santos, M. Bailly-Grandvaux, L. Giuffrida et al. NewJ.Phys. 17, 083051 (2015). [4] D. H. Froula et al. Phys. Rev. Lett. 98, 135001 (2007). [5] D.S. Montgomery et al. Phys. Plasmas 22, 010703 (2015). [6] H.B. Cai, S. P. Zhu, and X. T. He, Phys. Plasmas, 17, 072701 (2013). [7] P. Y. Chang, G. Fiksel, M. Hohenberger et al. Phys. Rev. Lett., 107, 035006 (2011). [8] L.J. Perkins et al. Phys. Plasmas 20, 072708 (2013).

Speaker: Hang Li

14:00 P5.2023 Gamma ray emission from wakefield accelerated electrons wiggling in laser filed

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2023.pdf Gamma ray emission from wakefield accelerated electrons wiggling in laser filed L. M. Chen1,2, J. Feng1, Y. Ma1, K. Huang1, W. C. Yan1,2, J. Zhang1,2 1 Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 2 Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China Hard x-ray emission from fs laser produced plasmas have a number of interesting applications in the dynamic probing of matter and in medical/biological imaging. Betatron radiation is a highly collimated laser-driven hard x-ray source with fs duration which generated by electron transversely oscillation during acceleration in underdense plasmas. However, yield and photon energy of this source is always limited by controdictory between parameters during electron acceleration. Several methods were proposed by our team for the sake of improving quality of betatron X-ray sources [1-3]. However, till now all popular methods are based on a single laser pulse, which is in charge of electron acceleration and wiggling simultaneously. The efficiency of betatron oscillation is limited in a comparably low level. In order to overcome the radiation spectra peak limited to tens of keV, we present a new method for high energy radiation emission via the accelerated electrons wiggling in an additional laser field whose intensity is one order magnitude higher than the self generation transverse field of the bubble, resulting the equivalent wiggler strength parameter K to increase about twenty times. Fitting with synchrotron radiation, we acquired the brightness for the case of laser wiggler field, which was 1.2×1023 ph/s/mrad2/mm2/0.1%BW at 1 MeV. Such a high brilliant and ultra-fast gamma ray source could be applied to time-resolved probing of the dense plasma and material, and the production of medical radioisotopes [4]. [1] W. C. Yan, L. M. Chen et al, PNAS 111, 5825(2014); [2] Y. Ma, L. M. Chen et al, Sci. Rep. 6, 30491(2016) [3] K. Huang, L. M. Chen et al, Sci. Rep. 6, 27633(2016) [4] J. Feng, L. M. Chen et al, (submitted)

Speaker: Liming Chen

14:00 P5.2024 Generation of high-charge electron bunch and ultrafast gamma-ray beam in laser-plasma accelerator

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2024.pdf Generation of high-charge electron bunch and ultrafast gamma-ray beam in laser-plasma accelerator Jiancai Xu1, Baifei Shen1, 2, 3, Tongjun Xu1, Shun Li1, Yong Yu1, Jinfeng Li1, Xinliang Wang1, Xiaoming Lu1, Cheng Wang1, Xiaoyan Liang1, Yuxin Leng1, Ruxin Li1 and Zhizhan Xu1 1 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, P. O. Box 800-211, Shanghai 201800, China 2 Department of Physics, Shanghai Normal University, Shanghai 200234, China 3 Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China High-charge electron bunch with broad energy spectrum has been experimentally produced during interaction between high-intensity femtosecond laser pulse and clustering gas jet with near critical density. The energetic electron bunch reaches the charge of 10nC with cut-off energy of 50 MeV and full divergence angle of 15°. When this high-charge energetic electron bunch shots into high-Z target with different thickness of several millimetres, ultrafast MeV position beam and gamma-ray beam are produced. The gamma-ray beam with broad energy spectrum reaches high-flux of 1010 photons per shot. This ultrafast high-flux MeV gamma-ray beams are promising sources for photonuclear reaction, non-destructive inspection and other potential applications.

Speaker: Jiancai Xu

14:00 P5.2025 High current colliding beams as a potential source of energetic radiation and relativistic pairs

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2025.pdf High current colliding beams as a potential source of energetic radiation and relativistic pairs F. Del Gaudio1 ,T. Grismayer1 , R. Fonseca1,2 , W. B. Mori3 , L. O. Silva1 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal 2 DCTI/ISCTE Instituto Universitário de Lisboa, 1649-026 Lisboa, Portugal 3 Departments of Physics & Astronomy and of Electrical Engineering, University of California at Los Angeles, 90095 At the interaction point of TeV particle colliders, three detrimental beam driven effects are important: disruption [1], beamstrahlung radiation [2], and pair production [2]. Disruption is due to the transverse motion of the beam particles which can focus (e− e+ ) or defocus (e− e− ) on the self-fields of the counter-propagating beam. In this process, photons are emitted and can decay into new pairs by interacting with the collective field of the beams. These two effects are more pronounced in the quantum regime which is usually avoided by using flat and long shaped beams. Conversely, the upgrade of the linear collider at SLAC (FACET II) [3] and the next generation of laser wakefield accelerators (LWFA) will deliver high current ultrashort round bunches capable of reaching the quantum regime at 10s of GeV. We investigate the collision of these beams envisaging a secondary source of collimated γ ray photons and ultrarelativistic pairs [4]. We estimate the photon spectrum and the secondary pairs yield both analytically and with PIC simulations, performed with QED-OSIRIS [5]. Our analytical model and the simulations show good agreement. The collective fields topology favors the quantum effects to take place in a distinguishing region of each beam resulting in a yield of secondary pairs considerably higher than what previously predicted [2]. Our results encourage the exploitation of this setup as a secondary source of radiation and of relativistic pairs. This secondary source of photons, electron, and positrons may be of interest in reproducing astrophysical lepton jets in the laboratory, or in delivering positron beams already at ultrarelativistic energies. References [1] R. Hollebeek, Nucl. Instrum. Meth. 184, 333 (1981) [2] P. Chen, and V. Telnov, Phys. Rev. Lett. 63, 1796 (1989) [3] C. Patrignani et al. (Particle Data Group), Chin. Phys. C, 40, 100001 (2016). [4] F. Del Gaudio et al., to be submitted [5] R. Fonseca et al., Lecture Notes in Comput. Sci. 2331, 342 (2002)

Speaker: Fabrizio Del Gaudio

14:00 P5.2026 Laser muon sources: concepts and challenges

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2026.pdf Laser muon sources : concepts and challenges L. Drska Czech Technical University, Prague, Czech Republic Muons, standard constituents of elementary particle model with the mass of 207 times electron mass, are available nowdays in cosmic radiation or can be produced by accelerators [1]. The progress in laser technolology - availability of high-intensity and highrep systems [2] , inspires the study of their potential production as tertiary particles in laser-matter interaction. There exists several posibilities how to achieve this goal : Direct muon Electron / photon driven systems High-energy complex production processe 1.1 Electron-electron 1.2 Electron-nucleus particle sources (electromagnetic collisions collision processes) Photon-driven systems Weak pure lepton 2.1 Photon-photon 2.2 Photon-electron sources collisions collision Muon production via Proton / ion driven systems Medium energy pion decay (nuclear 3.1 Flying pion 3.2 Stopped pion sources processes) decay decay (surface muons) In this contribution, results of a suitability study in this area considering concrete ELI Beamlines systems (HELL, ELIMAIA, P3 ) will be presented. Main attention will be given to the processes 2.1, 2.2 and 3.2. The first calculation of the proces 1.2 [3] evidently overestimates the muon yield in a real experiment. Detection and parameter measurement of muons in this process should be the first task for the experiment, results from the study [4] are not convicing. The most effective process, alowing the development of applicable muon source could be the mechanism 3.2. Nevertheless, its possibility supposes the availabilty of a laser-driven proton / ion beam with energy of several hundred MeV. The energy of this order is necessery also for oncological applications, the progress in this intensively studied area will pave also the route for laser muonics. Proposal of an applicable source based on the process 3.2 wil be presented. Some potential applications of laser-based muon beams will be mentioned. References [1] Nagamine K.: Proc. Jpn. Acad., Ser. B 92 (2016), 265 * [2] ELI Beamlines, https://www.eli-beams.eu * [3] Titov A. I. et al.: Phys. Rev. STAB 12 (2009), 111301 * [4] Dreesen W. et al.: DOE/NV/25946 - 2262 (2014).

Speaker: Ladislav Drska

14:00 P5.2027 Laser-plasma based hadron sources for materials science applications

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2027.pdf Laser-plasma based hadron sources for materials science applications L.Fedeli1 , F.Mirani1 , A.Maffini1 , A.Formenti1 , A.Pazzaglia1 , A.Tentori1 , D.Dellasega1 , V.Russo1 , M.Passoni1 1 Politecnico di Milano, Milano, Italy In this contribution we discuss the potential of mod- erate energy laser-plasma based hadron sources for a number of applications in the fields of materi- als and nuclear sciences. Few MeVs protons can be used to probe the composition of a sample with a variety of non-destructive Ion Beam Analysis techniques[1]. Among these, Proton Induced X-ray Emission (PIXE) is of particular interest to retrieve Figure 1: Sketch showing a possible scheme to perform PIXE with a laser-driven source the concentration profiles of complex samples (e.g. cultural heritage artifacts[2]). Few MeVs protons can be used also to generate neutrons with a suitable converter for applications such as ra- diography and spectroscopy[3]. High intensity(I > 1018 W/cm2 ) lasers can drive ion sources[4] with properties in principle already suitable for some of these applications[5]. However, there are still considerable challenges from the experimental point of view, especially if the use of a compact laser system is desired. Here we present a thorough feasibility study of laser-driven PIXE[6] with a table-top 10s TW- class laser and we propose a complete, compact experimental setup. We also discuss enhanced laser-driven ion acceleration with advanced targets[7, 8], which could be beneficial both for PIXE and neutron sources. These results could pave the way for compact laser-driven hadron sources for materials science applications. References [1] H.R.Verma, Springer-Verlag ISBN 978-3-540-30279-7 (2007) [2] N.Grassi et al., X-Ray Spectrometry, 34, 306-309 (2005) [3] C.M. Brenner et al., Plasma Physics and Controlled Fusion, 58, 1 (2016) [4] A.Macchi et al., Reviews of Modern Physics 85, 751 (2013) [5] M.Barberio et al., Scientific Reports 7, 40415 (2017) [6] M.Passoni et al., In preparation (2018) [7] M.Passoni et al., Physical Review Accelerators and Beams 19, 061301 (2016) [8] I.Prencipe et al. et al., Plasma Physics and Controlled Fusion, 58, 034019 (2016)

Speaker: Luca Fedeli

14:00 P5.2028 Multi-keV X-ray source generation at the Shenguang-III prototype

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2028.pdf Multi-keV X-ray source generation at the Shenguang-III prototype Gang Xiong, Yunsong Dong, Yang Zhao, Bo Qing, Zhimin Hu, Minxi Wei, Tianming Song, Min Lv, Zhiyu Zhang, Guohong Yang, Jiyan Zhang, Jiamin Yang, Shaoen Jiang Research Center of Laser Fusion, China Academy of Engineering Physics, P. O. Box 919-986, Mianyang 621900, China Efficient multi-keV sources are essential in inertial confinement fusion and high energy density physics for radiography, opacity measurements, material testing, and so on[1-5]. In this talk, we present the recent progress in multi-keV sources developments at the Shenguang-III prototype laser facility. An underdense plasma mechanism was used to improve the laser-to-X-ray conversion efficiency. Main targets are small cylindrical cavities with 700-800 μm diameter, and 500-800 μm height. The main wall materials are Ti, V and Ni enclosed by CH tubes of 30 μm thick. Eight 3ω laser beams with total energy of about 6.4 kJ in a 1 ns square pulse were focused on the inner wall of the cavity. The absolute X-ray fluxes were measured by absolutely calibrated HXRDs and FXRDs for X-ray energy higher and lower than 4keV, respectively. HXRDs and FXRDs were installed at different angles for X-ray angular distribution measurements. K-shell X-ray spectra were recorded by crystal spectrometers. The electron temperatures were deduced from both the laser Thomson scatters and X-ray spectra. The time behaviors of the X-ray images in two energy ranges were recorded through an X-ray framing camera. The X-ray conversion efficiency was about 2-3 times higher than the traditional thick solid. Reference: [1] S. Tu et al., Phys. Plasmas 23, 013102 (2016). [2] Y. Dong et al., J. Appl. Phys. 115, 43305 (2014). [3] W. Shang et al., Appl. Phys. Lett. 102, 94105 (2013). [4] K. B. Fournier et al., Phys. Rev. Lett. 92, 165005 (2004). [5] C. A. Back et al., Phys. Rev. Lett. 87, 275003 (2001).

Speaker: Gang Xiong

14:00 P5.2029 MV/cm longitudinal terahertz fields from relativistic laser-overdense plasma interactions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2029.pdf MV/cm longitudinal terahertz fields from relativistic laser-overdense plasma interactions A. Woldegeorgis1, 2, T. Kurihara3, M. Almassarani1, 2, R. Große2, B. Beleites2, F. Ronneberger2, G. G. Paulus1, 2, A. Gopal1, 2 1 Helmholtz-Institut Jena, Jena, Germany 2 Friedrich-Schiller-Universität Jena, IOQ, Jena, Germany 3 University of Konstanz, Konstanz, Germany High-power broadband terahertz (THz) radiation can be generated when intense laser pulses interact with matter. When the intensity of the laser pulse is higher than the ionization potential, plasma is generated. The charged particle dynamics and the resultant quasi-static fields and currents generated inside the plasma can give rise to broadband electromagnetic radiation ranging from x-rays to THz radiation. In our work we focus on the generation of THz radiation from such an interaction, in particular from the rear surface of a metal foil when its front surface is shined with a TW laser pulse. Here radially polarized THz radiation is generated by the transient dynamics of charged particles exiting the rear surface. Focusing a radially polarized beam, compared to a beam with linear polarization, creates a strong and tightly focused longitudinal field. It has been shown that longitudinal THz fields have a promising potential in particle acceleration1. To date, few groups have reported on longitudinally polarized THz wave generation with field strengths in the order of a few kV/cm 2. Here we report on the generation and detection of longitudinally polarized THz pulses with field strength in excess of 1.5 MV/cm from the rear surface of a thin foil irradiated by TW laser pulses. A transverse component with field amplitude of 3 MV/cm was also measured. Noncollinear pump-probe electrooptic technique was deployed to estimate the peak electric field strength, and study the temporal and spectral properties. We employed two crystal geometries to detect the polarization of the propagating THz pulses at the focus. Fig 1. Temporal waveform of the transverse (Eρ) and longitudinal (Ez) field components measured using gallium phosphide (GaP) 110- and 100-cut crystal respectively; inset shows the corresponding normalized spectral amplitudes. References [1] E. Nanni et al., Nat. Commun. 6, 8486, 2015. [2] Y. Minami et al., APL 102, 151106, 2013; M. J. Cliffe et al., APL 105, 191112, 2014; M. J. Cliffe et al., APL 108, 221102, 2016.

Speaker: Abel Hailu Woldegeorgis

14:00 P5.2030 New routes to high-energy photon generation in laser-matter interactions

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2030.pdf New routes to high-energy photon generation in laser-matter interactions A. Gonoskov, T. Blackburn, M. Marklund Department of Physics, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden Intense laser-plasma and laser-beam interactions are promising routes for producing high- energy photons from compact setups, through, e.g. Compton scattering and bremsstrahlung [1]. The small time and space scales associated with these emission mechanisms give such sources unique properties. However, there are longstanding discussions as to the limit on the achievable photon energies. Over the last decade, rigorous efforts in the development of particle- in-cell (PIC) schemes with corrections from quantum electrodynamics (QED) have resulted in many new and exciting predictions of high-energy photon generation. It has become clear that many earlier concerns regarding the limitations of laser-plasma and laser-beam systems as sources were unwarranted. Here, we will present results based on state-of-the-art QED-PIC and analytical calculations on the generation of high-energy photons from laser-plasma [2]ăand laser-beam systems [3]. Closely connected to the emission of high-energy photons areăelectromagnetic cascades of electron-positron pairs. The latter have the potential to act as high-energy photon sources of unprecedented brightness. In the cascade process, radiation reaction and rapid electron-positron plasma production seemingly restrict the efficient production of photons to sub-GeV energies, in line with the long-standing discussion mentioned above. Here, we show how the interplay between the pair cascade and radiation reaction effects results in the possibility to emit GeV photons. The possibility to use tailored laser fields as well as particular particle sources promises not only the generation of high-energy photons, but also of controlled pair production at very high densities. Such matter?anti-matter/radiation systems could be of importance for laboratory astrophysics. References [1] F. Albert and A. G. R. Thomas, "Applications of laser wakefield accelerator-based light sources", Plasma Phys. Control. Fusion 58, 103001 (2016) [2] A. Gonoskov et al, "Ultrabright GeV Photon Source via Controlled Electromagnetic Cascades in Laser- Dipole Waves", Phys. Rev. X 7, 041003 (2017) [3] T. G. Blackburn, A. Ilderton, C. D. Murphy and M. Marklund, "Scaling laws for positron production in laser–electron-beam collisions", Phys. Rev. A 96, 022128 (2017)

Speaker: Mattias Marklund

14:00 P5.2031 Simulations of bremsstrahlung emission in interactions of ultra-intense laser pulse with foil target

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2031.pdf Simulations of bremsstrahlung emission in interactions of ultra-intense laser pulse with foil target Jiří Vyskočil1,2 , Ondřej Klimo1,2 and Stefan Weber2 1 Czech Technical University in Prague, Prague, Czech Republic 2 Institute of Physics AS CR, Dolní Břežany, Czech Republic Contemporary and upcoming multi-petawatt lasers will produce short pulses which, when focused to a spot on the order of a few microns, generate strong electromagnetic fields of inten- sities I ∼ 1 × 1022 W/cm2 , opening new possibilities in generating laboratory γ rays by a variety of processes involving fast electrons which are generated during the interaction of an intense laser pulse with a target. Two main sources of energetic photons generated in an interaction with a thin foil target are bremsstrahlung and radiation reaction (including non-linear Compton scattering). Bremsstrahlung emission from the interaction of a short ultra-intense laser pulse with solid foils is investigated using Particle-in-Cell (PIC) code EPOCH. A module for simulating bremsstrahlung has been implemented in the PIC loop to self-consistently account for the dynamics of the laser- plasma interaction, plasma expansion, and the emission of γ ray photons. The conversion effi- ciency of the energy of the laser pulse to the energy of the γ rays is studies as a function of the intensity of the driving pulse, the thickness of the target, the pre-plasma profile, and the target material. In thin targets, refluxing of hot electrons plays an important role. Simulations reveal that the angular distribution of the emitted photons exhibits a four-directional structure with the angle of emission decreasing with the increase of width of the target. It is shown that the dependence of the mean angle of emitted photons on target thickness is due to the hot electrons losing energy in the TNSA field during refluxing.

Speaker: Jiri Vyskocil

14:00 P5.2034 X-ray and ion emission studies from low density gold targets

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2034.pdf X-ray and ion emission studies from low density gold targets Channprit Kaur1, 2, S. Chaurasia1, A. Rossall3 , Nataliya G Borisenko4, A. I. Gromov4, , A. A. Akunet4, M. N. Deo1 1 High Pressure & Synchrotron Radiation Physics Division, BARC, Mumbai 400085, India 2 Homi Bhabha National Institute, Mumbai-400094, India 3 International Institute for Accelerator Applications - Medium Energy Ion Scattering Facility Huddersfield, United Kingdom 4 P. N. Lebedev Physics Institute, Leninsky Pr 53, Moscow, Russia The utilization of laser plasma produced X-rays for investigating the plasma’s emission and absorption properties and in measurement of opacity, radiography, ICF is well known. This triggers the demand of high conversion efficiency (CE) for achieving a bright X-ray source. In this work, enhancement in X-ray emission and reduction of kinetic energy of ions from low density gold foam plasma is demonstrated by performing experiment and its validation with hydrodynamic simulation. The plasma is produced by irradiation of solid gold and gold foam targets (densities 0.193 g/cc, 0.128 g/cc and 0.0965 g/cc) with 500 ps laser at intensities in the range of 4 x 1013-1014 W/cm2. Time resolved X-ray emission is observed by X-ray streak camera with 10 ps resolution. The X-ray measured by streak camera from low density gold foam shows 8.5 % enhancement in comparison to solid gold. On the other hand, there is decrease in velocity of ions in case of low density gold foam. The angular distribution of peak ion velocity is measured by employing Time-of-Flight technique with four ion collectors placed at different angles (22.5º, 45º, 52º and 63º) from target normal. The maximum peak velocity of ions is 6.8 times high in case of solid gold (31x104 m/s) in comparison to 0.0965 g/cc (4.5 x104 m/s) gold foam towards target normal. Lower charge states of gold ions are found in case of solid gold which are absent in gold foam as detected by Thomson Parabola ion Spectrometer. However the difference in integrated ion flux for both cases is less indicating the process of volumetric absorption. A hydrodynamic simulation is performed by using POLLUX code. The results supports the volumetric absorption of laser light in case of low density gold foam and shows a good match with our experimental results. The detailed analysis will be presented in the conference.

Speaker: Channprit Kaur

14:00 P5.2037 Modeling Ultra-high Frequency Radiation Emission in PIC Codes

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2037.pdf Modeling Ultra-high Frequency Radiation Emission in PIC Codes M. Pardal1 , A. Sainte-Marie1 , A. Reboul-Salze1 , J. Vieira1 , R.A.Fonseca1,2 1 GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal, 2 DCTI/ISCTE, Instituto Universtitário de Lisboa, Lisbon, Portugal From the mysterious γ ray bursts, which can be studied through the spatiotemporal structure of the radiation we receive, to the creation of sources of x-rays capable of probing nanoscale structures, radiation emission by relativistic charges is a key research field in plasma physics. The processes behind radiation emission in plasmas result from many body interactions, are strongly non-linear, and involve relativistic effects, so they are best modeled through Particle-In- Cell (PIC) simulations. However, describing this radiation directly in PIC simulations is very challenging given the large disparity between the temporal and spatial scales associated with such phenomena. Additionally, the spatiotemporal features of the emitted radiation cannot be fully captured by current algorithms that describe radiation emission in the Fourier space (see e.g. [1]). Understanding and describing the spatiotemporal properties of the radiation, however, is crucial to many fields, such as super-resolution microscopy [2] and astrophysics [3]. Here we develop a diagnostic that is able to cap- ture the unexplored spatiotemporal structure of the emitted radiation from simulated trajectories of par- ticles, using the Liénard-Wiechert potentials. The diagnostic can work as post-processing tool, using the trajectories from PIC codes. On Figure 1 we dis- play the results of a run with 256 particles which undergo a helical-like motion. We have also incor- porated the diagnostic directly into the PIC loop, Figure 1: Transverse electric field in a spher- which allows us to capture the radiation from a sig- ical surface placed far from the particles. nificant fraction of the particles in the plasma. We describe the code integration into OSIRIS [4], a massively parallel, fully relativistic PIC code. This approach gives direct access to the spa- tiotemporal radiation emission properties as the PIC simulation progresses. References [1] J. L. Martins et al., Proc. to SPIE 7359, (2009) [2] S. Hell et al., Optics Letters 11, 780-782, (1994) [3] F. Tamburini, et al., Nature Physics 7, 195-197 (2011) [4] R. Fonseca et al., LNCS 2331, (2002)

Speaker: Miguel Pardal

14:00 P5.2038 Single attosecond pulse generation by two chirped laser pulses interaction with plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2038.pdf Single attosecond pulse generation by two chirped laser pulses interaction with plasmas M. Y. Shi1 , Y. X. Zhang1,2 , S. Rykovanov1 , M. Zepf 1,3 1 Helmholtz Institute Jena, Jena, Germany 2 School of Physics, Peking University, Beijing, China 3 Department of Physics and Astronomy, Queen’s University, Belfast, United Kingdom Extreme ultra-violent (XUV) and X-rays with duration of a few tens of attoseconds can be used as ideal tools to explore nonlinear ultrafast dynamical processes in atoms and molecules, such as the doubly-ionization, atomic core excitation and atto-ionization of Fano resonances processes. Such attosecond light can be produced with phase-locked high harmonics generation (HHG) by laser-matter (gas or plasma targets) interaction. For many applications, usually the generation of high-energy isolated attosecond light pulses is much more advantageous, becasue intense isloated attosecond pulses will open the door to nonlinear processes in XUV or X-ray spectra region with attosecond resolution in the perturbative domin, especially for pump-probe technologies. Several technologies such as polarization gating, spatiotemporal gating and temporal gating, have been proposed to isolate pulses. Besides, a single attosecond pulse can be also obtained by controlling the carrier envelope phase (CEP) of a short laser pulse with a duration shorter than 5fs. However, applications of gating technologies can cause decays of attosecond light intensities and conditions of controlling CEP are too strict to be realized in experiments. Here, we propose to generate an intense attoseocnd pulse by using two laser pulses, a normal one and a chirped one, interacting with overdense plasmas. By tuning the initial phase and the linear chirp parameters, the numbers of attoseocond pulses and intensities can be controlled . References [1] M. Yeung, S. Rykovanov, J. Bierbach, L. Li, E. Eckner, S. Kuschel, A. Woldegeorgis, C. Rödel, A. Sävert, G. G. Paulus, M. Coughlan, B. Dromey, and M. Zepf, Nat. Photonics 11, 32-35 (2017). [2] S. G. Rykovannov , M. Geissler , J. Meyer-ter-Vehn , and G. D. Tsakiris , New J. Phys. 10, 025025 (2008). [3] Y. X. Zhang, B. Qiao, X. R. Xu, H. X. Chang, M. Y. Yu, C. L. Zhong, C. T. Zhou, S. P. Zhu, and X. T. He, Phys. Plasmas 25, 023302 (2018).

Speaker: Mingyuan Shi

14:00 P5.2039 Timepix chip interface detectors for x-rays, gammas and electrons monitor on laser produced plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.2039.pdf Timepix chip interface detectors for X-rays, gammas and electrons monitor on Laser Produced Plasmas G. Claps1,2, D. Pacella1, F. Cordella1, F. Murtas2, D. Batani3, L. Volpe4, G. Gatti4 1 ENEA Fusion and Nuclear Safety Department, Via E. Fermi 45, 00044, Frascati, Italy 2 INFN – Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044 Frascati, Italy 3 CELIA, Université Bordeaux 1, 351, Cours de la Liberation, 33405 Talence, France 4 CLPU, P. Científico, Calle del Adaja, 8, 37185 Villamayor de la Armunia, Salamanca, Spain The physics of Laser Produced Plamas (LPPs) needs some particular diagnostic requirements. In particular the X monitor of the plasma is difficult because typically X-ray emission is concentrated in burst from few tens of ps to few ns, according to the power and pulse time width of the laser. Then a measurement of photon flux is unfeasible. For the X-ray monitor we realized the GEMpix [1], a proportional gas detector based on 3 consecutive Gas Electron Multiplier (GEM) with a front-end electronic based on four Timepix [2] chips, with 512 x 512 squared pixels, 55 micron wide. It can work in a range of X-ray fluence of 6 orders of magnitude. For LPPs, we exploit its ability to work Time over Threshold (ToT) mode: each pixel registers digital counts proportional to the total charge released in the gas. Charge can be amplified from the GEMs with a gain which can change on 4 order of magnitude, and then with a big dynamic range. However, Spatial resolution depends on the intrinsic gain, ranging from one to tens of pixels. In this work, we will present some results obtained on the Eclipse laser facility (CELIA, Bordeaux, France) [3]. Together with X-rays, other particles can be produced from LLPs, especially high energy gamma photons and electrons. In this case we characterized the new Timepix3 [4] chip, based on silicon. It is a single chip of 256 x 256 pixels with a bump-bonded 300 um thick silicon layer. Interaction of gammas with detector releases some characteristic tracks due mainly to the Compton scattered electron. Similar tracks are released by electrons. For each track we defined some parameters: cluster size, total charge (ToT mode), roundness, linearity and so on. Based on these parameters we characterized the response of the detector using some gamma and electron sources, in order to discriminate different energies. In this manner, we defined some energy bands for gamma and electron particles. Then this detector has been applied on VEGA laser facility (Salamanca, Spain) to characterize in energy of the gammas coming from laser plasma interaction. The use of a 2D detector allowed to separate the tracks, then, based on the source detector calibration and defining the track parameters, we distinguished in energy the gamma photons. [1] F. Murtas, 3rd International conference on micropattern gaseous detectors, 1–6july, 2013, Zaragoza, Spain [2] X. Llopart et al., Nucl. Instr. and Meth. A 581 (2007) 485. [3] G. Claps et al., The GEMpix detector as new soft X-rays diagnostic tool for laser produced plasmas (2016) Review of Scientific Instruments, 87 (10), art. no. 103505 [4] T. Poikela et al., Timepix3: a 65K channel hybrid pixel readout chip with simultaneous ToA/ToT and sparse readout, 15th international workshop on radiation imaging detectors 23–27 June 2013, Paris, France

Speaker: Gerardo Claps

14:00 P5.3001 Simple description of collective modes in strongly coupled plasma fluids

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3001.pdf Simple description of collective modes in strongly coupled plasma fluids Sergey Khrapak Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 82234 Weßling, Germany; Aix-Marseille University, CNRS, PIIM, 13397 Marseille, France; Joint Institute for High Temperatures, Russian Academy of Sciences, 125412 Moscow, Russia Collective dynamics in strongly coupled plasmas is an important research topic with interdis- ciplinary relations (e.g. to collective motion in other condensed matter systems). The purpose of this presentation is to introduce a simple analytical approach to the description of collective modes in strongly coupled plasma-related fluids. The approach is based on the quasi-crystalline or quasi-localized charge approximation, which relates wave dispersion relations to the pair- wise interaction potential and the equilibrium radial distribution function (RDF), characterizing the fluid structural properties. It turns out that for soft long-ranged interactions occurring in the plasma-related context a simplest model RDF, which takes into account the excluded volume (correlational hole) effect, can be very useful. It allows to obtain simple and elegant analytical expressions for the dispersion relations, which demonstrate good accuracy at long wavelengths. Several examples will be presented, including one-component plasmas in two and three di- mensions and weakly screened Yukawa systems (dusty plasmas) in three dimensions. Detailed comparison with the results from numerical simulations will be given. Applications to other systems with soft pairwise interactions will be briefly discussed. This work was supported by the A*MIDEX project (Nr. ANR-11-IDEX-0001-02) funded by the French Government “Investissements d’Avenir” program managed by the French National Research Agency (ANR).

Speaker: Sergey A. Khrapak

14:00 P5.3002 Dense plasma jets used in dusty plasma experiments

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3002.pdf Dense plasma jets used in dusty plasma experiments A. Scurtu1, D. Ticos1, N. Udrea1, M.L. Mitu1, C.M. Ticos1 1 National Institute for Laser, Plasma and Radiation Physics, Bucharest-Magurele,Romania A coaxial plasma gun has been successfully used to accelerate dust particles at hypervelocity [1], to operate as a useful tool for cleaning various surfaces covered with dust [2-3], or to produce dense plasma jets for testing fusion materials [4]. In our recent experiments we studied the interaction between a pulsed plasma jet ejected from a coaxial gun and a dust crystal produced in a radio-frequency plasma. The essential feature of our new experiments is the passing of the plasma jet through a thin slit or through small holes to get a thin layer of plasma or a “multi-jet” to interact with just one layer of the crystal. The coaxial plasma gun was powered by a capacitor charged up at 2 kV. The ejected plasma had a speed of a few km s-1, a peak electron temperature of ~10 eV, and peak electron density of ~1021 m-3. Interesting phenomena such as dust particle acceleration, particle oscillations and dusty plasma instabilities were observed. References: [1] C.M. Ticos, Z. Wang, L. A. Dorf, G. A. Wurden, A plasmadynamic hypervelocity dust injector for the National Spherical Torus Experiment, Rev. Sci. Instr. 77, 10E304 (2006). [2] C.M. Ticos, A. Scurtu, D. Toader, N Banu, Experimental demonstration of Martian soil simulant removal from surfaces using a pulsed plasma jet, Rev. Sci. Instr. 86, 033509 (2015). [3] C.M. Ticos, A. Scurtu, D. Ticos, A pulsed 'plasma broom' for dusting off surfaces on Mars, New J. Phys. 19, 063006 (2017). [4] C.M. Ticos et al., Cracks and nanodroplets produced on tungsten surface samples by dense plasma jets, Appl. Surf. Sci. 434 , 1122-1128 (2018).

Speaker: Adrian Scurtu

14:00 P5.3003 The equation of state and transport properties of metal vapors in supercritical fluid regime

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3003.pdf The equation of state and transport properties of metal vapors in supercritical fluid regime A.L. Khomkin, A.S. Shumikhin Joint Institute for High Temperatures of RAS, Moscow, Russia In this work, using the chemical model of the atomic plasma “3+” proposed in [1], we present a joint calculation of the equation of state and transport properties of supercritical fluid of metal vapors within the unified approach. It consists of free non-ideal electrons and ions and atoms immersed in jellium. Given the presence of jellium, we named this model the “3+” model. Jellium is constituted by tails of wave functions of bound electrons. Jellium provides the appearance of collective quantum energy—cohesion. Jellium does not change the balance and the electroneutrality equations. The main feature of jellium is its collectivity and the ability to conduct the current. The interaction between free charges is described in nearest neighbor approximation (NNA). We show that the corrections for the charge-charge interaction and interatomic interaction compensate each other by calculating the composition and the equation of state. The equation of state and electrical conductivity were calculated in supercritical regime and for binodal for various group of metals: alkali (Cs, Rb, Na), alkali earth (Be), transition (Cu, Fe, W etc.) and posttransition (Al, Pb etc.). The obtained results are compared with data of physical and numerical experiments [2-5]. Calculations in the framework of the “3+” model show a good agreement with both physical and numerical experiments. We calculated also the critical point parameters (density, temperature, pressure and electrical conductivity) for various groups of metals. References 1. A.L. Khomkin, A.S. Shumikhin, J. Exp. Theor. Phys. 124, 1001 (2017). 2. A.W. DeSilva, A.D. Rakhel, Contrib. Plasma Physics 45, 236 (2005). 3. J. Clerouin, P. Noiret, V.N. Korobenko, A.D. Rakhel, Phys. Rev. B 78, 224203 (2008). 4. F. Hensel, J. Phys.: Condens. Matter 2, SA33 (1990). 5. D. Li et al, Sci. Rep. 4, 5898 (2015).

Speaker: Aleksey Shumikhin

14:00 P5.3004 Mode coupling in cold 2D Yukawa liquid

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3004.pdf Mode coupling in cold 2D Yukawa liquid Wen Wang, Hao-Wei Hu, Hsiang-Ying Chen and Lin I Department of Physics, National Central University, Jhongli, Taiwan 320 Microscopically, around melting, a cold liquid can be viewed as a strongly coupled many-body system under weak stochastic thermal agitation, which excite collective motion over a broad range of scales. Nevertheless, whether multi-scale modes can be decomposed from particle micro-motion information and how modes are coupled remain open issues. In this work, these issues for the cold 2D Yukawa liquids are numerically addressed for the first time through empirical mode decomposition method. Spatiotemporal mode-mode cascading is observed. Their correlation to the large scale structural rearrangement is presented and discussed.

Speaker: Wen Wang

14:00 P5.3005 Correlational approach to study interparticle interactions in complex plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3005.pdf Correlational approach to study interparticle interactions in complex plasmas E.A. Lisin, O.S. Vaulina, O.F. Petrov Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia Moscow Institute of Physics and Technology, Dolgoprudny, Russia A general approach to the correlational analysis of Brownian motion of strongly coupled particles in open dissipative systems is described [1]. This approach can be applied to the theoretical description of various non-ideal statistically equilibrium systems (including non-Hamiltonian systems), as well as for the analysis of experimental data. In this report, we consider an application of the correlational approach to the problem of experimental exploring the wake-mediated nonreciprocal interactions in complex plasmas. For this, we derive simple analytic equations, which allows one to calculate the derivatives of the nonreciprocal interaction forces in a strongly coupled many-particle system as well as the gradients of external field. These calculations use data on time-averaged correlations of particles displacements and velocities, which are easily measured in an experiment. In the examples of numerical simulations, we demonstrate that the proposed approach could be an effective instrument in exploring the wake of a dust particle in a plasma. Unlike the previous attempts to study the wake-mediated interactions in complex plasmas, our method does not require a special design of the experimental setup and any external influences on a system, pre-measurements and any assumptions about the form of interaction. It is based on Brownian motion analysis only and can be used to study many-particle chain-like structures in complex plasmas [1]. We also show the importance of taking dissipative and random processes into account, without which consideration of a system with a nonreciprocal interparticle interaction as linearly coupled oscillators leads to significant errors in determining the characteristic frequencies in a system. We show that dissipative and random processes determine the minimum value of the force derivative to which the particle “reacts”. References [1] E.A. Lisin, O.S. Vaulina, and O.F. Petrov, Physics of Plasmas 25(1), 013702 (2018)

Speaker: Evgeny A. Lisin

14:00 P5.3006 Essential changes of structural and dynamical properties in a Yukawa system caused by amplitude instability

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3006.pdf Essential changes of structural and dynamical properties in a Yukawa system caused by amplitude instability I. I. Lisina1, O. S. Vaulina1, 2, and E. A. Lisin1, 2 1 Joint Institute for High Temperatures RAS, Moscow, Russia 2 Moscow Institute of Physics and Technology, Dolgoprudny, Russia The majority of theoretical studies on stability of a non-ideal media are based on the analysis of linearized equations of motion and consideration of the dissipative or/and the dispersive instabilities due to small deviations of particles from their equilibrium positions. However, with the increase in particle kinetic temperature the amplitude instability can also develop. Here we present the analysis of physical properties of a non-ideal particle system with a temperature growth. We propose to investigate the amplitude stability, i.e. the stability to any-size deviations (not just small ones) of particles from their equilibrium positions. The presented approach to the amplitude instability prediction is based on the determination of an inflection point for the potential energy of a system with an increase of its kinetic temperature. We consider the process of formation of amplitude instability in a two-particle Yukawa system for wide values range of screening parameter, friction coefficient, and gradients of external electric field. Numerical simulations have shown that an increase in grain temperature leads to essential changes in the structural and dynamic properties of the system in the vicinity of the critical magnitude of the coupling parameter. The special features observed close to the critical point are caused by the formation of amplitude instability in the analyzed two-partical system (and are similar to those that causes the melting for extended systems). The new analytical approach proposed here can also be an effective tool for studying amplitude instability in systems of interacting particles suspended in plasma with directed ion flow which adds to the interaction forces a wake-mediated attractive force. The work was partially supported by the Russian Foundation for Basic Research (Grant No. 16-08-00594), the Russian Ministry of Education and Science (Project No. MK-2930.2017.8).

Speaker: Irina Lisina

14:00 P5.3007 Comparison of dust particle trajectories in Magnum-PSI with simulations in DTOKS

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3007.pdf Comparison of Dust Particle Trajectories in Magnum-PSI with Simulations in DTOKS L. Simons1 , M. Coppins1 , 1 Imperial College, Blackett Laboratory, London SW7 2AZ United Kingdom Conventially, plasma particles incident on a surface are recycled as they are neutralised, ionised and redeposited. Future magnetic confinement devices such as ITER, and in particular commercial facilities like DEMO, will require near loss-less redeposition on all plasma facing surfaces to avoid prohibitively expensive maintenance. The release of micro-scale solid and liq- uid particles known as dust from surfaces limits the effectiveness of recycling[1, 2] and causes severe energy losses[3]. With safety limits on dust production in place for ITER, dust survivabil- ity and transport are issues of critical importance for tokamak operation[4]. Comparison of dust particle motion in experiments with theoretical models is vital to developing physical models. Simulations performed by the dust tracking code DTOKS[5, 6] using plasma data generated by BOUT++[7] are compared to dust injection experi- ments performed at the Magnum-PSI facility in the Netherlands, see Figure 1. Arificial spherical tung- sten spheres with diameters of 5µm and 9µm were released into the hydrogen plasma and recorded by a fast imaging Phantom and IR camera system from two different planes, allowing their paths to be re- Figure 1: Magnum PSI Design constructed. The behaviour of dust grains in a non- turbulent linear magnetic field is reviewed and the accuracy and applicability of the physical models tested. References [1] J. Winter, Plasma Phys. Control. Fusion 46, B583 (2004). [2] S.I. Krasheninnikov, R.D. Smirnov, and D.L. Rudakov, Plasma Phys. Control. Fusion 53, 83001 (2011). [3] R.C. Isler, R. V. Neidigh, and R.D. Cowan, Phys. Lett. A 63, 295 (1977). [4] J. Roth, et al., J. Nucl. Mater. 390-391, 1 (2009). [5] J.D. Martin, M. Coppins, and G.F. Counsell, J. Nucl. Mater. 337-339, 114 (2005). [6] M. Bacharis, M. Coppins, W. Fundamenski, and J.E. Allen, Plasma Phys. Control. Fusion 54, 85010 (2012). [7] B.D. Dudson, et al., Comput. Phys. Commun. 180, 1467 (2009).

Speaker: Luke Simons

14:00 P5.3008 Charging processes of dust particles in magnetized gas discharge plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3008.pdf Charging processes of dust particles in magnetized gas discharge plasma A.A. Agatayeva1), N.Kh. Bastykova1), S.K. Kodanova1), T.S. Ramazanov1), S.A. Maiorov2) 1 Institute of Experimental and Theoretical Physics, Al-Farabi Kazakh National University, Al-Farabi 71, Almaty, 050040, Kazakhstan 2 Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilov st. 38, Moscow, 119991, Russia Investigation of the dust particle charging processes is one of the key problems in dusty plasma physics, that provides the information about charge and interaction potential of dust particles. This information is necessary for constructing dusty plasma theory, that can describe the formation, existence, evolution and destruction of ordered plasma-dust structures[1]. This theory also needed for describing the dynamic phenomena in plasma. Recent experiments have been conducted to study the charging processes of dust particles in a magnetized plasma [2]. In the presence of strong magnetic field it is obtained that the absolute value of dust particle charges is much lower than the estimations of the OML theoretical model. In this regard, the purpose of this work is to study the influence of magnetic field on the dust particle charge in gas-discharge plasma. The influence of magnetic field on the dust particle charge, on the charge fluctuation and on the charging time are investigated. The charge of dust particle is determined by the particle-in-cell method and the collision of ions with atoms is taken into account by the method of Monte Carlo [3,4]. Calculations are made for the following gas discharge plasma parameters: the electron and ion densities are 109 cm-3, the electron temperature is 3 eV and for ions is 0.03 eV. The charges of dust particles with the radius of 0.5, 1, 2, 4, 8, 10 μm were calculated at magnetic field values in the range B = . The dependence of the dust particle charge on time, as well as their charging time at different values of the magnetic field are obtained. [1] V.E.Fortov, S.A.Khrapak, A.G.Khrapak, V.I.Molotkov, O.F.Petrov, Dusty plasma , UFN, 174, 495-542 (2004) [2] U.Konopka, B.lynch, D.Funk and E.Thomas,Jr, Book of abstracts ICPDP, 138 (2017) [3] S. K. Kodanova, N. Kh. Bastykova, T. S. Ramazanov, and S. A. Maiorov, IEEE Trans. Plasma Sci.,525-527 (2016) [4] S. K. Kodanova , N. Kh. Bastykova , T. S. Ramazanov, G. N. Nigmetova, and S. A. Maiorov, IEEE Trans. Plasma Sci., 10.1109/TPS.2017.2763965 (2018)

Speaker: Assem Agatayeva

14:00 P5.3009 Negative drag force on finite-size dust grain in strongly collisional plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3009.pdf Negative drag force on finite-size dust grain in strongly collisional plasma A.I. Momot Faculty of Physics, Taras Shevchenko National University of Kyiv, Kyiv, Ukraine A finite-size charged conductive spherical 1.0 0.1 dust grain in strongly collisional weakly ionized Normalized force 0.8 0.5 plasma is considered. It is assumed that the grain 1 0.6 is charged due to collection of encountered elec- ak = 2 D trons and ions. The stationary plasma flow or the 0.4 movement of the grain with a constant velocity 0.2 v breaks the spherical symmetry of the electric 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 field and the plasma particle distribution around the grain, and the force on the charged grain ap- Figure 1: Absolute value of normalized nega- pears. The nonlinear problem for the drag force tive drag force Fe2 /(Te akD )2 vs ṽ in isothermal is solved numerically within the drift-diffusion plasma. Solid lines with dots are results of nu- approximation. merical calculations. Solid line corresponds to The analytical expression for the drag force in (1), dashed line is given by formula (98) from [1] strongly collisional plasma is presented in [1] by and dotted line is q2 kD2 ṽ/24. Eq. (98). It was obtained in the linear approximation for point-like grain. Considering the ratio of diffusion coefficients Di /De as a small parameter this expression can be expanded to ∞ 2q2 kD 2 Z x2 x(A + τ) Aṽ F =− dx 2 arctan − 1 , A = x2 τ + x2 + 1, (1) π ṽ A Aṽ x(A + τ) 0 where τ = Te /Ti , ṽ = vλD /Di , kD = 1/λD , q – grain charge, a – radius. Sign "−" in (1) means that the drag is negative. For small velocity ṽ 1 Eq. (1) gives F = −q2 kD 2 ṽ/24, which coincide up to the designations with Eq. (11) from [2]. The force acting on a charged grain is directed along its velocity, i.e. the negative drag is take place. This force depends nonmonotonically on grain velocity (see Fig. 1) and is approximately proportional to the square of grain radius. Formula (1) is applicable for quantitative estimates of the drag force on small particles a λD in both non- and isothermal plasmas. It gives the upper boundary of the negative drag force on finite-size grains [3]. References [1] A.V. Filippov, A.G. Zagorodny, A.I. Momot et al., J. Exp. Theor. Phys. 108, 497 (2009) [2] S.A. Khrapak, S.K. Zhdanov, A.V. Ivlev, and G.E. Morfill, J. Appl. Phys. 101, 033307 (2007) [3] A.I. Momot, Phys. Plasmas 24, 103704 (2017)

Speaker: Andriy Momot

14:00 P5.3010 Complex plasma investigations in the PK-4 facility

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3010.pdf Complex plasma investigations in the PK-4 facility M.Y. Pustylnik1 , V.Yu. Nosenko1 , S. Jaiswal1 , M. Schwabe1 , S. Zhdanov1 , T. Antonova1 , S. Khrapak1 , H. Thomas 1 , A.M. Lipaev2 , A.V. Zobnin2 , A.D. Usachev2 , V.I. Molotkov2 , O.F. Perov2 , V.E. Fortov2 , M.H. Thoma3 , C. Du4 1 Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, Weßling, Germany 2 Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia 3 I. Physikalisches Institut, Justus-Liebig Universität, Gießen, Germany 4 College of Science, Donghua University, Shanghai, China Complex plasmas are low-temperature plasmas containing a strongly coupled subsystem of charged solid microparticles. The subsystem of microparticles can be used as an atomistic model of classical condensed matter. It has been previously shown that complex plasmas allow to in- vestigate many generic condensed matter phenomena [1] often at the individual particle level.. Since complex plasmas contain solid particles, they are significantly affected by gravity. Un- stressed 3D microparticle systems can only be obtained under microgravity conditions. Plasmakristall-4 (PK-4) is microgravity complex plasma facility on-board the International Space Station. The heart of PK-4 is a glass tube plasma chamber of 3 cm diameter and about 20 cm working area length [2]. In this chamber, plasma is generated by means of a dc discharge, whose polarity can be switched with the frequency up to 5 kHz. Microparticles of 1-10 µm diameter can be injected into the plasma chamber. Manipulation devices like RF coils, manipu- lation laser, thermal manipulator are also available. Since PK-4 commissioning in June, 2015, four scientific campaigns have been conducted. The scientific outcome of the campaigns will be presented and discussed. The topics include charging and drift of the microparticles in a dc discharge, dust-acoustic waves and 3D structure of the shear flow. The authors greatly acknowledge the ESA-Roscosmos “Experiment Plasmakristall-4” on- board the International Space Station. References [1] A. Ivlev, H. Löwen and C.P. Royall, Complex Plasmas and Colloidal Dispersions: Particle-resolved Studies of Classical Liquids and Solids, World Scientific, Singapore (2012) [2] M. Y. Pustylnik, M. A. Fink, V. Nosenko, T. Antonova, T. Hagl, H. M. Thomas, A. V. Zobnin, A. M. Lipaev, A.D. Usachev, V. I. Molotkov, O. F. Petrov, V. E. Fortov, C. Rau, C. Deysenroth, S. Albrecht, M. Kretschmer, M. H. Thoma, G. E. Morfill, R. Seurig, A. Stettner, V. A. Alyamovskaya, A. Orr, E. Kufner, E. G. Lavrenko, G.I. Padalka, E. O. Serova, A. M. Samokutyayev, and S. Christoforetti, Rev. Sci. Instrum., 87, 093505 (2016)

Speaker: Mikhail Pustylnik

14:00 P5.3012 Benchmark cross sections for excitation of the X1Σg+ → b3Σu+ transition in molecular hydrogen

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.3012.pdf Benchmark cross sections for excitation of the X1Σ g+ → b3Σ u+ transition in molecular hydrogen M. Zawadzki1, R. Wright2, G. Dolmat2, M. F. Martin2, L. Hargreaves2, D. V. Fursa3, M. C. Zammit4, L. H. Scarlett3, J. K. Tapley3, J. S. Savage3, I. Bray3, M. A. Khakoo2 1 Gdańsk University of Technology, Gdańsk, Poland 2 California State University, Fullerton, USA 3 Curtin University, Perth, Australia 4 Los Alamos National Laboratory, Los Alamos, USA We present a joint experimental and theoretical investigation of a fundamental process in atomic and molecular physics: electron impact excitation of molecular hydrogen’s (H2) most dominant transition (X1Σg+ → b3Σu+). Excitation of this state is by far the main channel that causes the dissociation of H2 into H + H atoms at low energies. The Convergent Close-Coupling (CCC) calculations [1] predicted significant, more than factor of two, disagreements with previously recommended cross sections [2]. Khakoo et al. [3] have recently designed a novel electron scattering instrument (an electron time-of-flight spectrometer, TOF), and have measured differential scattering cross sections for the excitation of the X1Σg+ → b3Σu+ transition, as ratios to elastic scattering, with high precision. The recently developed TOF spectrometer does not suffer from transmission problems like conventional spectrometers. Using the present theoretical and experimental approaches, we have been able to get outstanding agreement between theory and experiment for the excitation of a molecule for a very important transition in this most basic of all molecules. This work heralds significant progress in electron-molecule scattering, as well as promoting our understanding of dissociation processes not found in atoms. 4.0 References • present exp. [3] 3.5 [1] M. Zammit et al., Phys. Rev. A 95, ▲ Nishimura and Danjo [4] 022708 (2017). 3.0 ♦ Khakoo et al. [5] ICS (a.u.) ■ Khakoo and Segura [6] [2] J.-S. Yoon et al., J. Phys. Chem. Ref. 2.5 Data 37, 913 (2008). ----- recommended ICS [2] 2.0 ── present CCC [3] M. Zawadzki et al., Phys. Rev. Lett. 1.5 2018, submitted. [4] H. Nishimura and A. Danjo, J. Phys. 1.0 Soc. Japan 55, 3031(1986) 0.5 [5] M. A. Khakoo et al., Phys. Rev. A 35, 0.0 2832 (1987). 5 10 15 20 25 30 [6] M. A. Khakoo and J. Segura, J. Phys. B: E0 (eV) Atom. Molec. Phys. 27, 2355 (1994). Fig.1 Integrated cross sections for excitation of the b3Σu+state of H2.

Speaker: Dmitry Fursa

14:00 P5.4001 Dispersion relations for the symmetric and anti-symmetric Hasegawa surface waves in a plasma slab containing collisional electrons

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4001.pdf Dispersion relations for the symmetric and anti-symmetric Hasegawa surface waves in a plasma slab containing collisional electrons and flowing ions M.-J. Lee1, G. Jung1, Y.-D. Jung3 1 Department of Physics, Hanyang University, Seoul 04763, South Korea 2 Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588, South Korea Surface wave propagation on the interface between plasmas and a vacuum has drawn much attention because of interests in bounded plasmas and applications in various technical areas of plasma technologies and sciences. Since the actual plasmas in laboratory and space plasmas have boundaries and often take the structure of slab or planar geometry, waves propagating in a slab are of great importance. The slab plasma would support two modes of surface waves called symmetric and anti-symmetric modes, specified with respect to their parallel electric field components which are symmetric or antisymmetric with respect to the slab axis. In this work, the dispersion relations for the symmetric and anti-symmetric modes of electrostatic Hasegawa surface wave propagating in a cold dusty plasma slab whose constituents are collisional electrons, collisional streaming ions and dust grains are derived. We find that there are high- and low-frequency branches for both symmetric and anti-symmetric modes in the plasma slab. The real frequency of the wave is found to decrease as the ion collision frequency is increases for both modes. In the case of low-frequency branch, the phase velocity of the Hasegawa surface wave in a slab is always faster (slower) than that in a semi-bounded plasma for symmetric mode (anti-symmetric mode). We also found that the Hasegawa surface waves can be damped by the collisional dissipation. However, the characteristic of damping is quite different for the two modes: the magnitude of damping rate for symmetric (anti-symmetric) mode increases (decreases) as the slab thickness decrease.

Speaker: Myoung-Jae Lee

14:00 P5.4002 Investigating guide field reconnection in HED plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4002.pdf Investigating guide field reconnection in HED plasmas Simon Bolaños1,3, R. Smets3, R. Riquier4, A. Grisollet4, J. Fuchs1,2 1) LULI - CNRS, École Polytechnique, CEA: Université Paris-Saclay; UPMC Univ Paris 06: Sorbonne Universités - F-91128 Palaiseau cedex, France E-mail: simon.bolanos@polytechnique.edu 2) Institute of Applied Physics, 46 Ulyanov Street, 603950 Nizhny Novgorod, Russia 3) LPP, University P. & M. Curie, CNRS, Ecole Polytechnique, F-91128 Palaiseau, France 4) CEA, DIF, Bruyères-le-Chatel, France Magnetic reconnection (MR) is a process which occurs in many astrophysical plasmas, e.g. in solar flares, in coronal mass ejecta, or at the outer boundary of the Earth magnetosphere. However, as of now, the fundamental microphysics implied in this process is far from being well understood. Most of the investigations on this long standing issue come from numerical studies and space observations. Laboratory modelling of plasmas, including those that can be generated by high-power lasers, offer now new perspectives to investigate MR and the processes governing it. We will present recent experiments, performed using the LULI2000 facility, aimed at investigating the dynamic of magnetic reconnection in a non-coplanar configuration between two magnetic toroids induced by two near-by laser spots irradiating solids targets. Despite being distinct from the astrophysical plasmas where the beta parameter is low ( ̴10^-3 in solar corona and ̴ 1 in solar winds), such HEDP reconnection experiments are of interest to investigate fundamental issues in MR such as the influence of a guide field on the dynamic of the MR. A non-coplanar configuration between the two laser-irradiated targets, as was investigated in our experiments, allows to initialize a guide field. The reconnection rate in the experiments has been diagnosed with proton radiography which provides a unique way to measure and map directly the distribution of the strong magnetic fields and their evolution. We observe that the guide field slow down the MR, depending on the setup between the two laser-irradiated targets, and hence between the two magnetic toroids that are made to interact. The measurements are compared to simulations performed by a hybrid simulation code, the 3D HECKLE code. This simulations have been initialized, with respect to the initial magnetic toroid, by calculations using a hydro-radiative code (FCI2) and experimental measurements.

Speaker: Simon Bolaños

14:00 P5.4003 Interacting Multiscale Defects in Dust Acoustic Wave Turbulence

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4003.pdf Interacting Multiscale Defects in Dust Acoustic Wave Turbulence Po-Cheng Lin1, Lin I1 1 Department of Physics, National Central University, Jhongli, Taiwan In a single scale weakly disordered nonlinear wave, topological defects in the form of worm like filament has been observed [1]. Whether and how wave turbulence exhibits a continuous multi-scale power spectrum can also be characterized by multi-scale defects are challenging open issue due to difficulty of decomposing the modes through Fourier representation. In this work, through novel multi-dimensional empirical mode decomposition, we experimentally demonstrate the 3D dust acoustic wave turbulence can be view as a zoo of the interacting multiscale acoustic vortices with helical waveforms winding around worm-like defect filaments, similar to the multi-scale worm-like coherent vortices in the hydrodynamic turbulence. [1] Y.Y. Tsai and L. I, Phys. Rev. E. 90, 013106 (2014)

Speaker: Po-Cheng Lin

14:00 P5.4004 EquilTheTA: a web-access tool for LTE plasma thermodynamics and transport

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4004.pdf EquilTheTA: a web-access tool for LTE plasma thermodynamics and transport properties A. D’Angola1,2 , A. Laricchiuta1 , G. Colonna1 1 PLASMI Lab NANOTEC CNR Bari (Italy) 2 Scuola di Ingegneria, Università della Basilicata Potenza (Italy) EquilTheTA is a web-access tool to calculate thermodynamic and transport properties of complex plasmas in local thermodynamic equilibrium (LTE) in a wide pressure and tempera- ture range. Thermodynamic properties are calculated starting from the atomic and molecular internal partition functions, which are, in turn, evaluated from internal levels of the species. For atoms and atomic ions, the electronic energy levels are available in open databases and are extended by recurring to the Ritz-Rydberg approach to ensure completeness for each internal configuration. Equilibrium composi- 100 SiO SiO2 10–10 SiO+ SiC+ tions are calculated by using a hier- 10–20 SiC archical algorithm which solves one 10–30 CO reaction at a time [1, 2] avoiding 10–10 CO2 molar fractions CO2 10–20 the solution of large non-linear sys- CO + CO+ 2 10–30 C tems of equations. For these reasons, 10–10 C3 C2 the method is fast and accurate and 10–20 C2 C+ 2 10–30 always converges. Recently, an auto- 10–10 matic determination of the optimal re- 10–20 O2 O3 action scheme has been implemented 10–30 2 10 103 104 105 temperature (K) to speedup the convergence. Transport Figure 1: Molar fractions of SiC + O2 . properties are calculated by using high order Chapman-Enskog expansion. The transport cross section database is populated by an hybrid phenomenological/multi-potential approach, ensur- ing accurate description of binary interactions and widening the capability of the tool. The code is accessed through a friendly interface which includes the possibility of creating a plasma mix- ture starting from the species and to set the thermodynamic conditions (pressure or density, temperature). As an example, Figure 1 shows molar fractions of molecules and atomic negative ions obtained in the case of a plasma of technological interest such as SiC+O2 [3]. References [1] W. R. Smith, R. Missen, Can. J. Chem. Eng. 66 (4) (1988) 591–598. [2] G. Colonna, A. D’Angola, Comp. Phys. Comm. 163 (2004) 177–190. [3] G. Colonna et al., Plasma Sources Science and Technology 27(1) (2018) 015007.

Speaker: Antonio D'Angola

14:00 P5.4005 RF beam scattering by cylindrical filaments and interfacial density fluctuations

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4005.pdf RF beam scattering by cylindrical filaments and interfacial density fluctuations (*) S. I. Valvis1, A. Zisis2, A. Papadopoulos1, P. Papagiannis1, A. K. Ram3, K. Hizanidis1, I. G. Tigelis2, E. Glytsis1 1 National Technical University of Athens, Athens, Greece 2 National and Kapodistrian University of Athens, Athens, Greece 3 Plasma Science and Fusion Center, MIT, Cambridge MA, USA Radio Frequency (RF) waves are routinely used in tokamaks for heating, current drive, NTM control, as well as for diagnostics purposes. Frequently, RF waves, aiming towards the plasma core, propagate through a turbulent environment. The latter can exhibit strong coherent density fluctuations as well as filamentary structures mainly (though, not perfectly) aligned along the local magnetic field lines. The scattering process of RF waves by these structures is studied both analytically and numerically. RF waves can be either single plane waves or spatially confined beams. For that purpose, the filaments are considered to have cylindrical shape with infinite length with the cylinder axis not aligned with the local magnetic field and the results are compared to the ones from the study of the aligned case [1,2]. On the other hand, the interfacial density fluctuations are considered periodic with spatial periods larger, smaller or of the same order of the wavelength of the incident RF waves. The frequency range of the RF waves studied is mainly in the Electron Cyclotron (EC) range of frequencies for ITER-like and Medium Size Tokamak applications. Furthermore, the study covers a variety of density contrasts, filament sizes and fluctuation strengths. References [1] A. K. Ram and K. Hizanidis, “Scattering of radio frequency waves by cylindrical density filaments in tokamak plasmas”, Physics of Plasmas 23, 022504 (2016) [2] Z. C. Ioannidis, A. K Ram, K. Hizanidis, I. G. Tigelis, “Computational studies on scattering of radio frequency waves by density filaments in fusion plasmas”, Physics of Plasmas 24, 102115 (2017) (*) This work was supported in part by the Hellenic National Programme on Controlled Thermonuclear Fusion associated with the EUROfusion Consortium.

Speaker: Spyridon-Iason Valvis

14:00 P5.4006 Laboratory Laser-Plasma Collisionless Shocks

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4006.pdf Laboratory Laser-Plasma Collisionless Shocks T. Hodge1, D. Doria1, H. Ahmed1, L. Romagnani2, B. Coleman1, J. S. Green3, G. Sarri1, M. Swantusch4, S. White1, O. Willi4, M.E.Dieckmann5, M. Borghesi1 1 Centre for Plasma Physics, Queen's University Belfast, UK 2 Laboratoire LULUI, Ecole Polytechnique, France 3 Central Laser Facility, Rutherford Appleton Laboratory, UK 4 Institute for Laser and Plasma Physics, University of Düsseldorf, Germany 5 Department of Science and Technology (ITN), Linkoping University, Sweden Collisionless shock waves (CSW) arise in plasma when an abrupt change in plasma conditions is not caused by binary collisions but the collective behaviour of the plasma. CSW are thought to be highly common in astrophysical environments due to the low ambient density. It is thought that shocks caused by supernova remnants expanding into the interstellar medium accelerate particles that are responsible for cosmic rays measured high in the Earth’s atmosphere. CSW can also be found in our solar system as planetary bow shocks and interplanetary shocks [1][2][3]. Intense laser-plasma interactions provide a way to launch CSW in conditions relevant to astrophysical plasmas. The interaction of an intense laser pulse with a solid target produces dense plasma, which flows with high velocity, into an ambient background medium. CSW are generated by the sudden expansion of this dense plasma into a tenuous ionized background. The generation and reliable diagnoses of these shock waves in laser-plasma experiments is non-trivial. We will present results showing the experimental conditions under which it is possibly to generate such phenomena as confirmed via a series of experiments [4][5][6]over the past few years at several facilities including the VULCAN laser (Rutherford Appleton Laboratory, UK). [1] J. E. Cross, et. al., “Laboratory analogue of a supersonic accretion column in a binary star system,” no. May, pp. 1–7, 2016. [2] S. F. Martins, et. al., “Ion Dynamics and Acceleration in Relativistic Shocks,” Astrophys. J., vol. 695, no. 2, pp. L189–L193, 2009. [3] K. Koyama, et. al. , “Evidence for shock acceleration of high-energy electrons in the supernova remnant SN1006,” Nature, vol. 378, no. 6554, pp. 255–258, 1995. [4] H. Ahmed, et. al., “Experimental Observation of Thin-shell Instability in a Collisionless Plasma,” Astrophys. J. Lett., vol. 834, no. 2, pp. 1–5, 2017. [5] H. Ahmed, et. al., “Time-Resolved Characterization of the Formation of a Collisionless Shock,” vol. 110, 2013. [6] A. J. Mackinnon and L. Romagnani, “Observation of Collisionless Shocks in Laser-Plasma Experiments,” vol. 25004, no. July, pp. 1–4, 2008.

Speaker: Tom Hodge

14:00 P5.4007 Derivation and application of the magnetized Fokker-Planck and Balescu-Lenard-Guernsey collision terms

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4007.pdf Derivation and application of the magnetized Fokker-Planck and Balescu-Lenard-Guernsey collision terms C. Dong1, 2, D. Li1, 2, 3, W. Zhang1, 2, 3, J. Cao1, 2 1 Institute of Physics, Chinese Academy of Sciences, Beijing, China 2 University of Chinese Academy of Sciences, Beijing, China 3 University of Science and Technology of China, Hefei, China In the magnetized and laser fusion plasma, space and astrophysical plasma, the particles’ gyro-radii can be smaller than the Debye length when there is a strong magnetic field. This will have a significant influence on collision dynamics and many physical processes such as parallel velocity slowing down, temperature relaxation, particle diffusion, thermal transport, and so on. The Fokker-Planck collision including a uniform magnetic field is derived meanwhile the analytical expressions of magnetized Fokker-Planck coefficients have been derived explicitly within the binary collision model. The fully magnetized Fokker-Planck kinetic equation is also manipulated into the Landau form. The Balescu-Lenard-Guernsey collision term including a uniform magnetic field is derived by employing the Fokker-Planck approach. By using the fluctuating electrostatic field for quiescent plasmas, the magnetized Fokker-Planck coefficients are calculated explicitly based on the wave theory which includes the collective effects in a proper manner. Manipulating the magnetized Fokker-Planck collision term into the Landau form, the magnetized Balescu-Lenard-Guernsey collision term is obtained. The magnetized Fokker-Planck coefficients are simplified to study the temperature relaxation and stopping power. It is shown that the effect of strong magnetic field is significant on those physical processes.

Speaker: Ding Li

14:00 P5.4008 Impedance characteristics of a magnetized 13.56 MHz capacitive discharge

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4008.pdf Impedance characteristics of a magnetized 13.56 MHz capacitive discharge J.K. Joshi, S.K. Karkari and Sunil Kumar Institute for Plasma Research, HBNI, Bhat, Gandhinagar, India *e-mail: jay.joshi@ipr.res.in Capacitive driven discharges are well known due to its vast application in microelectronics industries. The operating RF frequency, ωrf, typically lies between electron and ion plasma frequencies, such that ωpe >> ωrf > ωion. The overall impedance of the discharge remains largely capacitive due to the sheath reactance; while the bulk plasma remains inductive. The plasma condition at which the reactance of the sheath and the bulk plasma mutually cancels out is identified as the electron series resonance (ESR). In this work the existence of ESR in the presence of transverse magnetic field, has been investigated from the impedance characteristics of the discharge, for a planar plate and cylindrical electrode configuration in a linear device. The impedance characteristics have been obtained from phase calibrated external power measurements. It is found that the net reactance in the case of parallel plates changes from inductive to capacitive (positive to negative) crossing zero (ESR) as the plasma density increases with applied RF power levels. However in the cylindrical configuration, discharge produced in argon remains largely inductive for the unmagnetized case; whereas it changes to capacitive in presence of axial magnetic field. For lighter gas helium, the discharge behavior remains entirely inductive with/without axial magnetic field. This observation can be attributed to effect of low frequency (ωrf ≈ ωion) RF sheaths, which results in minimal sheath widths leading to small sheath reactance. The ESR condition for the planar geometry has been qualitatively explained based on cross-field plasma conductivity model.

Speaker: Jay Kirtikumar Joshi

14:00 P5.4009 New class of neutral current sheets with a sheared magnetic field in collisionless plasma

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4009.pdf New class of neutral current sheets with a sheared magnetic field in collisionless plasma A. A. Nechaev1 , V. V. Kocharovsky1,2 Vl. V. Kocharovsky1 , V. Yu. Martyanov3 1 Institute of Applied Physics of the RAS, Nizhny Novgorod, Russia 2 Dept. of Physics and Astronomy, Texas A&M Univ., College Station, USA 3 Intel Corp., Chandler, USA We found a wide class of self-consistent magnetostatic structures with sheared field lines and arbitrary energy distributions of particles in a collisionless plasma. A member of that class is a superposition of two neutral current sheets with orthogonal planar magnetic fields and cylindrically symmetric momentum distribution functions of particles. Each planar current sheet satisfies the stationary Vlasov–Maxwell equations and may have complicated self-consistent spatial profiles of the current density and magnetic field [1]. The resultant configurations can have an almost arbitrary profile of the shear angle of mag- netic field, in particular a non-monotonic one. We develop a regular technique to construct such structures and provide a number of new examples, including localized, periodic, and force-free sheared current sheets. We describe limitations on the anisotropy degree of particle distributions and the magnetic-to-particle energy ratio. Those sheets can be either thick or thin with respect to the typical particle gyroradius. Most of the previously known current sheet families with the sheared magnetic field lines, e.g. [2, 3, 4, 5], are included in the suggested class. We discuss possible applications of our technique for modelling current structures in various space and astrophysical plasmas, both relativistic and non-relativistic. References [1] V. V. Kocharovsky et al., Phys. Uspekhi, 59, 1165 (2016) [2] W. Alpers, Astrophys. Space Sci., 5, 425 (1969) [3] Paul J. Channell, Phys. Fluids, 19, 1541 (1976) [4] F. Wilson, T. Neukirch, Phys. Plasmas, 18, 082108 (2011) [5] B. Abraham-Shrauner, Phys. Plasmas, 20, 102117 (2013)

Speaker: Anton Nechaev

14:00 P5.4010 Practical criteria for the Weibel instability and its saturation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4010.pdf Practical criteria for the Weibel instability and its saturation Vl. V. Kocharovsky1 , V.V. Kocharovsky2 , V.Yu. Martyanov3 1 1Institute of Applied Physics RAS, Nizhny Novgorod, Russia 2 Texas A&M University, College Station, USA 3 Intel Corp., Chandler, USA We consider the Weibel, purely aperiodic instability in a collisionless plasma, relativistic or not, for the important in practice case when the particle distribution function exhibits mirror symmetry with respect to a certain plane and a wave vector of an ordinary wave perturbation is parallel to this plane. In this case, we obtain a novel analytical criterion for the Weibel instability using its analogy with a long-wavelength soft-mode instability which is well known in the solid state physics. It facilitates an analysis of the Weibel instability and agrees with the results which have been known for the certain particle distributions, including the bi-Maxwellian, power-law, and parallelepiped ones as well as various variants of the so-called waterbag distributions. Also, for a series of the special cylindrically-symmetric particle distributions we find the analytical dependence of the Weibel-instability growth rate on the wavenumber of perturbation and show that it agrees well with the criterion presented [1]. We compare in detail the various known estimates of a magnetic field saturating the Weibel instability and, in particular, point to the case when this field cannot achieve an equipartition value due to a weak anisotropy of the initial particle distribution. In the latter, poorly studied case, a relatively large-scale magnetic field is generated and, during the inverse growth-rate time, most particles follow the diffusive transport law and undergo displacements over many wavelengths of this field. We estimate a number of particles which are subject to bounce-oscillations under these conditions and come to a general criterion of the saturation of the Weibel instability [1]. We show that it is consistent with the analytical results obtained previously for the case of a strong anisotropy as well as with the numerical simulations carried out for the particular examples of a weak anisotropy of particle distribution. Finally, we present the practical examples of an implementation of both criteria for the typical situations in the space and laboratory collisionless plasmas with anisotropic particle distributions. References [1] V.V. Kocharovsky, Vl.V. Kocharovsky, V.Yu. Martyanov, S.V. Tarasov, Phys. Uspekhi, 59, 1165 (2016)

Speaker: Vladimir Kocharovsky

14:00 P5.4011 Dynamics of positrons during relativistic electron runaway

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4011.pdf Dynamics of positrons during relativistic electron runaway O. Embréus1 , K. Richards1 , G. Papp2 L. Hesslow1 , M. Hoppe1 , T. Fülöp1 1 Department of Physics, Chalmers University of Technology, SE-41296 Göteborg , Sweden 2 Max-Planck-Institute for Plasma Physics, D-85748 Garching, Germany Sufficiently strong electric fields in plasmas can accelerate charged particles to relativistic en- ergies via the runaway mechanism. In this contribution we describe the dynamics of positrons that are created during a runaway avalanche, and calculate the fraction of created positrons that become runaway accelerated. We find a sensitive electric-field dependence that is unlike the electron runaway growth rate due to the fact that positrons are born anisotropically in the direction opposite to their direction of acceleration. For runaway in systems larger than a pair-production mean-free path, we derive a threshold electric field above which the direct pair production in collisions will dominate the pair produc- tion due to photons produced in hard X-ray emission, which is traditionally the main positron producing mechanism. This pair-production threshold field is found to be of the order of tens of avalanche threshold fields. We present analytical and numerical solutions of the positron kinetic equation with a strong constant electric field, illustrating similarities and differences between the runaway dynamics of positrons and electrons. The numerical study provides the rate coefficients of created positrons that become runaway accelerated or thermalized. These are used to estimate the amount of annihilation radiation that will be detected during tokamak runaway scenarios as a function of background parameters, which can be compared to the amount of hard X-rays near 511 keV emitted by the runaway electron population. We find that the signal-to-noise ratio becomes worse when the plasma charge increases, whereas the total photon count increases. This tradeoff can be important in scenario development for positron detection experiments, which may be useful for assessing the validity of present models for runaway acceleration during disruptions.

Speaker: Ola Embreus

14:00 P5.4013 Study of Sagdeev solutions and their stability against mutual collisions in the ion-acoustic regime based on kinetic simulation

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4013.pdf Study of Sagdeev solutions and their stability against mutual collisions in the ion-acoustic regime based on fully kinetic simulation S. M. Hosseini Jenab, G. Brodin 1 Department of Physics, Umeå University, Sweden The Sagdeev pseudo-potential method [3] has been used in studying in a range of plasmas in order to find nonlinear solutions to the system. In this study, we have focused on the collision of these solutions in the ion-acoustic regime. The objective is to establish if the Sagdeev so- lutions can be considered as proper solitons in a fully kinetic regime[1, 2]. By following their temporal evolutions in the kinetic simulation box, we have tested their stability against mutual collisions. The study utilizes a fully kinetic simulation approach and adopts the Vlasov equa- tion to follow the temporal evolution of plasma constituents. The numerical approach to solve the Vlasov-Poisson set of equation is based on Vlasov-Hybrid simulation (VHS) method which follows phase points trajectories in the phase space and guarantees the positiveness of the dis- tribution function. In order to reproduce the potential profile of the solitons as the initial state of simulations, the Sagdeev pseudo-potential approach is employed numerically. It is shown that the ions’ dynamics (specifically the reflected population) have a strong effect on the collision process. References [1] H. Abbasi, S. M. Hosseini Jenab, and H. H. Pajouh. Preventing the recurrence effect in the vlasov simulation by randomizing phase-point velocities in phase space. Physical Review E, 84(3):036702, 2011. [2] S. M. Hosseini Jenab and F. Spanier. Fully kinetic simulation study of ion-acoustic solitons in the presence of trapped electrons. Physical Review E, 95(5):053201, 2017. [3] R. Sagdeev. Cooperative phenomena and shock waves in collisionless plasmas. Rev plasma phys, 4:23, 1966.

Speaker: Seyyed Mehdi Hosseini Jenab

14:00 P5.4014 Perpendicular relativistic shocks in magnetized pair plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4014.pdf Perpendicular relativistic shocks in magnetized pair plasmas I. Plotnikov1,2, A. Grassi3,4,5, M. Grech3 1 Institut de Recherche en Astrophysique et Planétologie, Toulouse, France 2 Department of Astrophysical Sciences, Princeton, USA 3 Laboratoire d'Utilisation des Lasers Intenses, Paris, France 4 Dipartimento di Fisica Enrico Fermi, Pisa, Italy 5 Istituto Nazionale di Ottica, Pisa, Italy Perpendicular relativistic shocks in magnetized pair plasmas [1] are investigated using two-dimensional Particle-In-Cell (PIC) simulations. In a first part of this work, a systematic survey, from unmagnetized to strongly magnetized plasmas (upstream flow magnetizations from σ = 10-6 to 10), is presented for an initial flow Lorentz factor γ0 = 10. The mechanisms behind shock formation (from Weibel-mediated to magnetic-reflection), the global structure of the shock, and comparison to MHD predictions are discussed for the whole range of upstream magnetizations. The characteristic time of shock formation is also investigated focusing on both density compression and isotropization of the downstream plasma. The second part of this work focuses on particle acceleration in the shock. It is found to be efficient at weak to intermediate magnetizations and fully suppressed for σ >10-2. The relative importance of diffusive shock acceleration and shock drift acceleration will be discussed, the spatial diffusion coefficients extracted from the simulations presented. A scaling of the accelerated particle maximum energy with the upstream flow magnetization γmax ∝ σ-1/2 for 10-3< σ <10-2 will be presented and the difference with that obtained by Sironi et al. [2] at lower magnetization will be discussed. [1] Plotnikov, Grassi and Grech, arXiv:1712.02883. [2] Sironi, Spitkovsky and Arons, ApJ 771, 54 (2013).

Speaker: Illya Plotnikov

14:00 P5.4015 Heating and stabilization of mirror confined plasma by rotating magnetic field

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.4015.pdf Heating and stabilization of mirror confined plasma by rotating magnetic field I. Be’ery1, O. Seeman1,2 1 Rafael Plasma Laboratory, Israel 2 Technion, Israel institute of technology, Israel The effect of rotating magnetic field (RMF) on hydrogen plasma confined in magnetic mirror machine is studied. The coupling and heating of right-handed RMF is much stronger than left-handed RMF, which indicates the coupling is mainly to helicon modes. At low trap magnetic field, the right-handed RMF increases the flute instability growth rate and the angular velocity of plasma rotation. With higher trap magnetic field, the right-handed RMF stabilizes the flute instability. The mechanisms of RMF coupling and stabilization are discussed.

Speaker: Ilan Be'ery

16:00 → 16:30 COFFEE

16:30 → 17:40 PLENARY SESSION

Chair: C. Riconda

Convener: C. Riconda

16:30 I5.014 Complex plasma research on the International Space Station (overview and novel directions)

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.014.pdf Complex plasma research on the International Space Station (overview and novel directions) H.M. Thomas1, M. Schwabe1, M.Y. Pustylnik1, C. Knapek1, S.A. Khrapak1, V.I. Molotkov2, A.M. Lipaev2, O.F. Petrov2 and V.E. Fortov2 1 Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 82234 Weßling, Germany 2 RAS – Joint Institute for High Temperatures, Izhorskaya 13/19, Moscow, 127412, Russia Complex plasmas are plasmas containing solid particles typically in the micrometer range. These microparticles are highly charged and become an additional, dominating component of the plasma. Complex plasmas are ideal model systems to study strong coupling phenomena in classical condensed matter. They offer the unique opportunity to go beyond the limits of continuous media down to the fundamental length scale of classical systems - the interparticle distance - and thus to investigate all relevant dynamic and structural processes using the fully resolved motion of individual particles, from the onset of cooperative phenomena to large strongly coupled systems. Unlike “regular” plasma species the charged microparticles are strongly affected by gravity. An electric field in the sheath or a temperature gradient are usually employed to compensate for gravity, which provides favourable conditions to study 2D or stressed 3D systems on ground. However, in order to perform precision measurements with large isotropic 3D systems in the bulk plasma, microgravity conditions are absolutely necessary. Since 2001 this research under microgravity conditions has continuously been performed on the International Space Station ISS within the Russian/German(European) Plasmakristall(PK)-Program. In long-term research laboratories PKE-Nefedov (2001-2005), PK-3 Plus (2006-2013) and PK-4 (2014-ongoing), fundamental processes in liquid or crystalline complex plasmas as well as generally in plasma physics were addressed. Highlights are: refinement of theory of ion drag, electrorheological plasmas, lane formation or phase separation in binary mixtures, crystallisation and melting, wave propagation, shear flow and transition to turbulent motion. In this presentation we will review important results from microgravity experiments and will discuss the perspectives for future research. Acknowledgements: The projects on the ISS were funded by DLR, BMWi, ESA, State of Bavaria, MPG, JIHT-RAS, and ROSCOSMOS.

Speaker: Hubertus M. Thomas

17:05 I5.015 The Advent of Non-linear Optical Components Made From Plasmas

See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.015.pdf The Advent of Non-linear Optical Components Made From Plasmas R. K. Kirkwood, D. Turnbull*, T. Chapman, S. Wilks, M. Rosen, R. London, L. Pickworth, A. Colaitis, W. Dunlop, P. Poole, J. Moody, D. Strozzi, P. Michel, L. Divol, O. Landen, B. MacGowan, B. Van Wonterghem, K. Fournier, and B. Blue Lawrence Livermore National Laboratory, P.O. Box 808 Livermore Ca. USA *also at Laboratory of Laser Energetics, 250 E. River Rd, Rochester, NY USA When the worldwide program in Inertial Confinement Fusion (ICF) pushed forward to build MJ scale lasers it was recognized that the stimulated scattering processes that occur when individual laser beams interact with a small scale plasma, would also allow beams to interact with each other and exchange significant energy and power with the increased scale length expected in the target plasmas produced by these lasers [1]. As a result NIF and other lasers now provide the capability to adjust the wavelengths of the individual beams to control the seeding of Stimulated Brillouin Scattering of one beam by another via the process of Cross Beam Energy Transfer (CBET) [1]. From the outset of indirect drive experiments on NIF, CBET controlled by wavelength tuning was shown to be effective in redistributing large fractions of the incident power between the cones of beams, which improved implosion symmetry and performance in important cases [1,2]. As a result many lasers now exist with wavelength tuning to control CBET as does a wide range of data to validate CBET models. These capabilities are presently being rapidly employed to produce optical devices made of plasma using CBET interactions for many applications [3,4]. The most recent demonstration is a plasma-based optic that combines the energy and fluence of many laser beams into a single bright beam, thus creating a new technique for designing future high energy density physics experiments. The technique has shown for the first time that a plasma can combine beams to produce a single beam that emerges from the target with energy and fluence beyond that of any of the input beams for delivery to another experimental target. In an initial demonstration, multiple beams of the National Ignition Facility (NIF) laser have been combined in a plasma to produce a directed pulse of light with 4 + 1 kJ of energy in its 1 ns duration which is 3.6 times the energy and 3.2 times the fluence of any of the incident beams during that period and is NIFs brightest 1ns duration beam of UV light [4]. Work performed at Lawrence Livermore National Lab., Contract DE-AC52-07NA27344. [1] R. K. Kirkwood et al Plasma Phys. Control. Fusion 55, 103001 (2013). [2] O. Hurricane et al Nature 506, 343–348 (2014). [3] D. Turnbull, et al, Phys. Rev. Lett. 116, 205001 (2016). [4] R. K. Kirkwood et al Nature Physics online: 2 Oct. 2017, and Nature Physics, 14, 80, January (2018).

Speaker: Robert Keith Kirkwood

17:40 → 17:55 PRIZE PRESENTATION

Itoh prize, Ph.D. poster prizes

17:55 → 18:15 CLOSING CEREMONY

Chair: R. Dendy