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(TH/P2-05) Nonlinear MHD Dynamics of Tokamak Plasmas on Multiple Time Scales

S.E. Kruger1), D.D. Schnack1), D.P. Brennan2), T.A. Gianakon3), C.R. Sovinec4)
1) SAIC, San Diego, CA, USA
2) General Atomics, San Diego, California, USA
3) Los Alamos National Laboratory, Los Alamos, New Mexico, USA
4) University of Wisconsin-Madison, Madison, Wisconsin, USA

Abstract.  Two types of nonlinear simulations using the NIMROD code are presented. In the first simulation, we model the disruption occurring in DIII-D discharge 87009 as an ideal MHD instability driven unstable by neutral-beam heating. The mode grows faster than exponential, but on a time scale that is a hybrid of the heating rate and the ideal MHD growth rate as predicted by analytic theory. The scaling continues well into the nonlinear regime including times where the field lines become rapidly stochastic. The second type of simulations, which occur on a much longer time scale, focus on the neoclassical tearing mode. A new closure has been implemented into NIMROD which incorporates the most salient features of neoclassical physics relevant for these modes: poloidal flow damping, enhancement of the polarization current, and perturbed bootstrap current. The new closure successfully reproduces the required analytic stability limits and is computationally tractable unlike more for Chew-Goldberger-Low-type formulations. The results of both simulations are reviewed and their implications for experiments are discussed.

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IAEA 2003