Speaker
Ridhima Sharma
Description
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
