5th Runaway Electron Meeting (REM-2017)

Jun 5, 2017, 2:00 PM → Jun 8, 2017, 6:00 PM Europe/Prague

Chateau Liblice

Jakub Urban, Jan Mlynář, Yves Peysson

A meeting of scientists working on topics related to runaway electrons: theory, modelling, experiments, data analyses, diagnostic developement, mitigation systems, coordination of scientific projects, etc. REM-2017 builds on the previous REM meetings organised in Sweden (2013, 2014) and France (2015, 2016). You are cordially invited to meet other people dedicated to your field of expertise in a beautiful castle in the central Bohemia.

Slides REM 2017 presentations. (Protected)

Mon, June 5

2:00 PM Arrival and discussions

3:30 PM Coffee & tea

COMPASS tour: Monday afternoon 2

Bus departure to Liblice

Bus departure from IPP Prague

7:00 PM Dinner

Tue, June 6

Opening

10:20 AM Coffeebreak

12:00 PM Lunch

3:20 PM Coffeebreak

7:00 PM Dinner

Wed, June 7

Wednesday: 1

1 Overview of latest COMPASS Disruption-RE results

The contribution will summarise the three main topics recetly investigated within the COMPASS RE campaigns: MHD related losses of RE, MGI injection with RE beam generation in the ramp-up phase and slow gas puff injection into low density plasma. Details on the recent progress in diagnostics will be also presented.

Speaker: Ondřej Ficker

Slides REM2017_DisruptionRE_COMPASS_Ficker.pptx

2 Runaway electron studies during the flattop phase in COMPASS

This contribution will focus on the description of runaway electrons during the flattop phase in COMPASS discharges.

Speaker: Eva Macúšová

Slides REM_macusova.pdf

10:20 AM Coffee & tea

Wednesday: 2

3 A synthetic synchrotron diagnostic for runaways

Runaway electrons in tokamaks will emit synchrotron radiation due to their gyration around magnetic field lines. Because of the strong forward beaming of the radiation, the observed synchrotron images and spectra depends on both the energy, pitch angle and radial distribution of electrons, making synchrotron radiation a strong candidate for indirectly measuring the runaway electron distribution function. Inferring the runaway electron distribution function from synchrotron radiation measurements is however made difficult by various geometric effects. In this contribution, we present the numerical tool SOFT (for Synchrotron-detecting Orbit Following Toolkit), which simulates synchrotron images and spectra, and is able to take geometric effects into account. By applying the tool to an Alcator C-Mod discharge, we analyse the effect of runaway energy, pitch angle and radial distribution on the observed synchrotron spot, and by coupling SOFT to the numerical Fokker-Planck solver CODE, we obtain a synthetic synchrotron image that is in good agreement with experiment.

Speaker: Mr Mathias Hoppe (Chalmers University of Technology)

Slides REM2017_Hoppe.pdf

4 Synchrotron emission in Alcator C-Mod: spectra at three B-fields and visible camera images

Alcator C-Mod's high magnetic field allows runaway electron synchrotron emission to be observed in the visible wavelength range. Visible spectrometers were used to measure synchrotron spectra at three magnetic fields: 2.7, 5.4, and 7.8 T. Assuming fixed energy and pitch, the spectral shape is expected to shift toward shorter wavelengths with increasing magnetic field. However, the similarities among measured spectra indicate that runaway electron energies decrease with increased field and are thus limited by synchrotron radiation. Additionally, distortion-corrected visible camera images show the spatial distribution and evolution of runaways in C-Mod. Initial results show good agreement between experiment and the new synthetic diagnostic SOFT (Synchrotron-detecting Orbit-Following Toolkit) [1]. [1] M. Hoppe, et al. Synthetic synchrotron diagnostic for runaway electrons in tokamaks. In progress.

Speaker: Mr Alex Tinguely (MIT)

Slides tinguely_REM2017_presentation.pdf tinguely_REM2017_presentation.pptx

12:00 PM Lunch

Wednesday: 3

5 Run-away studies in JET

Generation of run-aways electron (RE) beams is one of the major risks for the successful exploitation of ITER. In the past 15 years JET has been exploring the physics of run-away creation and the dynamics of the beam with different wall materials, namely carbon and Berylium/Tungsten mix (ITER-like wall). Recently, it has been observed experimentally that a full-blown run-away beam cannot be mitigated in JET using disruption mitigation valves (DMV) in contrast to smaller devices (DIII-D or ASDEX Upgrade). The working hypothesis to explain this observation is that the run-away beam is screened by the high density cold plasma background surrounding the beam. These observations have prompted the launch of an international project (ITER Organisation, the US Department of Energy and EURATOM) for the installation of a shattered pellet injector (SPI) on the JET device with the purpose to demonstrate that it has the necessary capability for reliable and robust mitigation of the effects of disruptions and vertical displacement events (VDEs) while preventing runaway formation. The main focus in the next JET 2018 experimental campaigns is to assess the efficacy of SPI on runaway avoidance and runaway energy dissipation which are the presently foreseen two lines of defence in ITER. This presentation will review the key results achieved by run-away experiments in JET, provide a summarized description of the future shattered pellet injector and also the key objectives of the run-away experiments in 2018.

Speaker: Dr Emmanuel Joffrin (CEA Cadarache)

Slides REM-presentation-JoffrinV2.pdf REM-presentation-JoffrinV2.pptx

2:40 PM Coffee & tea

Outdoor activity

GOLEM experiments

We will have an opportunity to operate GOLEM on-line

7:00 PM Dinner

Thu, June 8

Thursday: 1

6 INVESTIGATING PRIMARY RUNAWAY ELECTRON GENERATION MECHANISMS WITH TEST PARTICLES IN NON-LINEAR MHD DISRUPTION SIMULATIONS

During a tokamak disruption, a large electric field is formed which can lead to the generation of a runaway electron (RE) beam. In large machines, runaway beams are sufficiently intense and energetic to represent a serious threat for operations. Therefore, the comprehension of the physics of RE and of their mitigation is of fundamental importance for future operations. Up to now, most RE modelling works have assumed axisymmetric MHD fields. This hypothesis is however clearly not valid during disruptions, which motivates our effort to investigate RE physics in 3D fields representative of disruptions. For this purpose, a fast particle tracking module was developed within the non-linear MHD code JOREK [1]. The tracker computes relativistic particle trajectories using either a Full Orbit (FO) or a Guiding Center (GC) model in 3D time-varying MHD fields from JOREK. The module was successfully verified checking the conservation of the invariants of motion and the GC-FO agreement in a number of configurations. In this work we investigate the possible primary RE generation mechanisms by simulating the behaviour of a test-particle population in JOREK - JET MGI-triggered disruption simulations [2][3] using the GC tracker. In order to become runaway, an electron has to remain confined throughout the Thermal Quench (TQ) and the electric field acceleration has to overcome the collisional drag. We quantify first the fraction of TQ survivors for a given electron energy, cutting acceleration terms in the equation of motion, making a link with local transport properties in the stochastic magnetic field. Secondly, we investigate the possibility of running away, restoring acceleration terms, in particular the parallel electric field and a drag force representative of collisional effects. Pointwise comparisons between the FO and the GC description are used to verify the GC model validity. [1] C. Sommariva, to be submitted to NF, 2017 [2] A. Fil et al., Physics of Plasmas, vol. 22, pp. 062509, 2015 [3] E. Nardon et al., Plasma Phys. Control. Fusion, vol. 59, pp. 014006, 2016

Speaker: Mr Cristian Sommariva (CEA-Cadaracher/IRFM)

Slides csommariva_REM_2017.pdf

7 Runaway electrons and JT-60SA

Speaker: Mr Konsta Sarkimaki (Aalto University)

Slides JT-60SA_REM_2017.pdf

10:20 AM Tea & coffee

10:40 AM Check-out time

Thursday: 2

8 Improved fluid models of runaway generation and decay

Full kinetic modeling of runaway dynamics is remarkably expensive computationally due to the range in scales involved, requiring simultaneous resolution of both the near-isotropic thermal electron population in the eV energy scale, as well as the strongly anisotropic runaways in the tens-of-MeV range. Because of this, a fluid description of runaway dynamics is highly desirable, where runaway generation and decay rates are expressed only in terms of background plasma parameters. In this contribution, using the most accurate models available for radiation losses and knock-on collisions, we present a first look at revised runaway growth rates. We discuss the applicability of such a fluid description, derive more accurate growth rates as well as extend present theories to also describe the decay of a runaway beam within the same framework.

Speaker: Mr Ola Embréus (Chalmers University of Technology)

Slides Embreus_REM2017.pdf

9 Overview of 2016 TCV experiments

Speaker: Joan Decker

Slides REM-decker-2017.pdf

12:00 PM Lunch

Thursday: 3

10 Overview of ITER Hard X-Ray Monitor

There are very few methods that have the capability to provide energy-resolved measurements of Runaway Electrons. Hard X-Ray Monitor (HXRM) allows an estimation of the maximum runaway electron energy and the energy distribution function inferred from energy-resolved measurements. Implementation of HXRM system has been relatively easy on other worldwide Tokamaks. However, at ITER this will be challenging due to the intended position of the detectors which will be mounted inside the port-plug behind the diagnostic first wall module. The detectors will be subject to a range of extreme environmental conditions. These will comprise electromagnetic loads, seismic loads, thermal loads and neutronic loads which require careful selections of detectors and to ensure that the performance of detectors should meet detection requirements. This presentation provides an overview of modelling of HXR emission by runaway electrons for assessment of signal-strength, study of potential detectors, performance analysis of the diagnostic system and applicable design considerations. It has been established that the proposed design meets the measurement requirements within reasonable margins and has a broad dynamic range. Disclaimer: “The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.”

Speaker: Mr Santosh Pandya (Institute for Plasma Research)

Slides REM_2017_ITER_HXR_Design_V2.pptx

Thursday: Closing

11 Summary of 5th REM 2017

In this concluding summary presentation the main results from the meeting will be collected. This should allow the participants to remind and put into context some of the highlights of the REM 2017. Contributors to the REM are welcome to propose one slide and a few concluding remarks into this presentation and, in particular, to think over suitable conclusions, comments and questions for the subsequent discussion.

Speaker: Jan Mlynář

3:00 PM Coffee & tea

Bus departure to Prague