Speaker
Ksenia Aleynikova
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1087.pdf
Quantitative study of kinetic ballooning mode theory in magnetically
confined toroidal plasmas
K. Aleynikova1,2 , A. Zocco1 , P. Xanthopoulos1 , P. Helander1
1 1Max-Planck-Institut für Plasmaphysik, EURATOM Association, Greifswald, Germany
2 Moscow Institute of Physics and Technology, Dolgoprudny, Russian Federation
Kinetic ballooning modes (KBMs) are investigated by means of analytical theory and linear
electromagnetic gyrokinetic (GK) numerical simulations in a magnetically confined toroidal
plasma. A physics-based ordering for beta (the ratio of kinetic to magnetic plasma pressure)
with small asymptotic parameters is found. This allows us to derive several simplified limits
of previously known theory [1] and to identify regimes where quantitative agreement between
theory and numerical simulations can be achieved.
For the axisymmetric case, in simple s-alpha geometry, it is found that, for large pressure
gradients, the growth rate and frequencies computed by the gyrokinetic codes GS2 and GENE
show excellent agreement with those evaluated by using, in the quadratic forms, a diamagnetic
modification of ideal MHD. This is true only if geometric drifts are kept consistent with the
equilibrium pressure gradient.
In the stellarator Wendelstein 7-X (W7-X), we find a finite-beta stabilization of the ion-
temperature-gradient (ITG) and trapped particle (TEM) modes, as well as KBM destabiliza-
tion. The results are compared to a generic tokamak case. For large pressure gradients in W7-X
geometry the KBM frequencies agree with the analytical prediction of the diamagnetic modi-
fication of ideal magnetohydrodynamic (MHD) limit already verified for the tokamak [2]. The
KBM destabilization thresholds are predicted for different W7-X configurations. We discuss
the relation of these thresholds with the ideal MHD stability properties of the corresponding
equilibria.
References
[1] W.M. Tang, J.W. Connor, and R. J. Hastie, Nucl. Fusion 20, 1439 (1980)
[2] K. Aleynikova and A. Zocco, Physics of Plasmas 24, 092106 (2017)
