Author: Richard Fitzpatrick
Requested Type: Poster
Submitted: 2016-02-15 12:56:13
Institute for Fusion Studies, UT Austin
Dean Keaton & Speedway
Austin, Texas 78723
The effect of the perturbed ion polarization current on the stability of
neoclassical tearing modes is calculated using an improved, neoclassical, four-field, drift-MHD model. The calculation involves the self-consistent
determination of the pressure and scalar electric potential profiles in the vicinity of the associated magnetic island chain, which allows the chain's propagation velocity to
be fixed. Two regimes are considered. First, a regime
in which neoclassical ion poloidal flow damping is not strong enough to enhance the magnitude of the polarization
current (relative to that found in slab geometry). Second, a regime in which neoclassical
ion poloidal flow damping is strong enough to significantly enhance the magnitude of the polarization current.
In both regimes, two types of solution are considered. First, a freely rotating solution (i.e., an island chain that
is not interacting with a static, resonant, magnetic perturbation).
Second, a locked solution (i.e., an island chain that has been brought to rest in the laboratory frame via interaction
with a static, resonant, magnetic perturbation). In all cases, the polarization current is found to be either always stabilizing, or stabilizing provided that
eta_i does not exceed some threshold value. In certain ranges of eta_i, the polarization current is found to have have a stabilizing effect
on a freely rotating island, but a destabilizing effect on a corresponding locked island.