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Author: Vladimir Mirnov
Requested Type: Poster
Submitted: 2016-02-15 18:26:24

Co-authors: J.P. Sauppe, E.C. Howell, C.C. Hegna, and C.R. Sovinec

Contact Info:
University of Wisconsin-Madison
1150 University Av.
Madison, Wisconsin   53706

Abstract Text:
We consider modifications to linear resistive MHD instability theory in a slab due to two categories of non-MHD effects: (1) electron and ion diamagnetic flows caused by equilibrium pressure gradients and (2) electron and ion decoupling on short scales associated with kinetic Alfven and whistler waves. The relationship between the expected stabilizing response due to the effects (1) and the destabilizing contribution caused by the dispersive waves (2) is investigated. Both these tendencies are confirmed for tearing modes by an approximate analytic dispersion relation that is derived using a perturbative approach of small ion-sound gyroradius. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in plasma slab with a doubly periodic box bounded by two perfectly conducting walls. The numerical results are consistent with the reduced analytical model within the limits of its applicability. In addition to current-driven drift-tearing instability, a second linearly unstable resistive drift type mode with largely electrostatic perturbations is also observed in computations. The scaling of its growth rate on the Lundquist number S shows non-monotonic behavior. For sufficiently large S, the growth rate increases with decreasing S. This trend continues down to a critical value of S that depends on plasma parameters, after which the growth rate rapidly decreases. This is in agreement with the analytical results predicting transition to the regime where resistive damping of the slow magnetoacoustic wave dominates the drive of the dissipative drift instability. Nonlinear NIMROD simulations of the resistive drift instability are in progress.

*The work is supported by the U.S. DOE and NSF