Speaker
Novimir Antoniuk Pablant
Description
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.
