Speaker
Christoph Slaby
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1098.pdf
Numerical investigation of fast-ion driven modes in Wendelstein 7-X
C. Slaby1 , A. Könies1 , R. Kleiber1 , S. Äkäslompolo1
1 Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstaße 1, 17491
Greifswald, Germany
Fast ions in fusion plasmas are typically generated by heating methods such as neutral beam
injection or ion cyclotron resonance heating. In future fusion reactors, there will additionally
be fast alpha particles created from the deuterium-tritium fusion reaction. The fast ions need to
remain in the plasma for a time period that is comparable to the slowing-down time in order to
thermalize. If they leave the plasma prematurely, energy losses and possibly damage to plasma-
facing components are the consequences [1].
Especially in a stellarator, due to the lack of a continuous symmetry, the confinement of fast
particles is not guaranteed in general. Hence, one of the optimization goals of Wendelstein 7-X
is the good confinement of fast ions [2].
However, in the process of slowing down, even the well-confined the fast particles can excite
Alfvénic perturbations in the plasma, which have been shown to enhance fast-ion transport [1].
This paper investigates the resonant interaction of fast particles with Alfvénic perturbations
in the Wendelstein 7-X stellarator using the non-linear CKA-EUTERPE code package [3]. The
approach is perturbative in the sense that an MHD mode structure is calculated by CKA, which
is used by the gyro-kinetic code EUTERPE to compute the power transfer from the fast particles
to the mode. The mode structure remains fixed for the entire simulation run.
Our simulations include a triple-slowing-down distribution of the fast ions coupled with re-
alistic fast-ion density profiles computed by the ASCOT code [4, 5]. A fast-ion collision oper-
ator is included in the EUTERPE modeling to assess the effects of pitch-angle collisions and
slowing-down drag on the non-linear dynamics of the mode and its transport properties.
References
[1] H. H. Duong et al., Nucl. Fusion 33, 749 (1993)
[2] G. Grieger et al., Phys. Fluids B (7), 2081 (1992)
[3] T. B. Fehér, Ph.D. thesis, University Greifswald, 2013
[4] J. A. Heikkinen, S. K. Sipilä, Phys. Plasmas 2, 3724 (1995)
[5] E. Hirvijoki et al., Comp. Phys. Comp. 185, 1310 (2014)
