Speaker
Qingquan Yu
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1039.pdf
Effect of externally applied resonant magnetic perturbations on the
stability of magnetic island
Q. Yu, S. Günter and K. Lackner
Max-Planck-Institut für Plasmaphysik, 85748 Garching, Germany
The effect of externally applied resonant magnetic perturbations (RMPs) on the
stability of magnetic island is investigated based on two-fluid equations. The growth of the
m/n=2/1 magnetic island (m and n are the poloidal and toroidal mode numbers), driven by
an unfavorable plasma current density profile and bootstrap current perturbation, is found to
be suppressed by static RMPs of the same helicity and of moderate amplitude (~ 10-4 of the
toroidal field), if the local bi-normal electron fluid velocity at the resonant surface is
sufficiently large. While without applying RMPs, the 2/1 island saturates at a width of 0.2a
(a is the plasma minor radius) in the nonlinear phase even when neglecting the bootstrap
current perturbation. A significant change in the local equilibrium plasma current density
gradient by small amplitude RMPs is also found for realistic ASDEX Upgrade plasma
parameters, which together with the diamagnetic drift and the associated ion polarization
current affect the island stability. The two-fluid effects, including the electron inertia, on
the island stability are found to be larger for a lower plasma resistivity and expected to be
more important for a fusion reactor like ITER. Our results indicate that error field can be
stabilizing for the island growth, if the error field amplitude is not too large and the local
bi-normal electron fluid velocity is not too low, and that applied rotating RMPs with an
appropriate frequency can be utilized to change the local plasma current density gradient
around the resonant surface and to suppress the 2/1 island growth in high temperature
plasmas even for a low bi-normal electron fluid velocity. It is known that the 2/1 mode can
lead to significant decreases in plasma confinement or even disruptions in tokamak
discharges and should be stabilized.
