Speaker
Josefine Henriette Elise Proll
Description
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
