Speaker
Jorge Alberto Alcusón
Description
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
