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Session KP01 - Poster Session III.
POSTER session, Tuesday afternoon, March 23
Exhibit Hall, GWCC

[KP01.84] Nonlinear MHD modeling of Marginally Stable Modes in DIII-D Plasmas with the NIMROD Code

Dalton D. Schnack, Alfonso Tarditi (Science Application International Corporation, San Diego, CA, USA), Ming S. Chu (General Atomics, San Diego, CA, USA)

The evolution of marginally stable global MHD modes in DIII-D type plasmas is studied with the nonlinear MHD/multifluid code NIMROD. The initial plasma equilibrium is a model DIII-D discharge with beta value just below the marginal stability limit. By increasing "self-similarly" the pressure profile (heating), slowly compared to the time scale of the unstable mode, it is possible to drive "smoothly" a marginally stable mode through its instability threshold, beyond the beta critical. The relatively slow initial growth of the unstable modes immediately past the threshold allows to diagnose the change in growth rate vs. time caused by the heating process. A theoretical analysis of this process based on ideal MHD [1] predicts the onset of an unstable mode with a hybrid time scale between the MHD and transport time scales. A comparison of the NIMROD simulation results with theory-based calculation is presented.

[1]J.D. Callen et al., Bull. APS Vol.43 (1998), p. 1762

Part K of program listing