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Author: Andrea L Becerra
Requested Type: Poster
Submitted: 2016-02-15 15:38:25

Co-authors: C.C. Hegna, C.R. Sovinec, S.E. Kruger, J.R. King, S.A. Sabbagh

Contact Info:
University of Wisconsin, Madison
1500 Engineering Dr, 510 ERB
Madison, WI   53706
United States

Abstract Text:
RWM stability properties of NSTX equilibria are pursued using the general geometry thin resistive wall boundary condition in NIMROD. The boundary condition operates by matching the magnetic field inside the computational domain with external fields found using the Green’s function method in the GRIN vacuum-field solver at the wall. This work uses a time series of reconstructed equilibria from an NSTX shot during which normalized beta is scanned, passing through the n=1 no-wall stability limit. The RWM is stabilized by kinetic effects during this shot, making EFIT equilibrium reconstructions above the ideal plasma stability limit possible [1]. Previous simulations with NIMROD determined a range for the critical normalized beta for RWM stability, which was consistent with the no-wall stability limits calculated by the ideal MHD code DCON. Now, equilibrium reconstructions closer to marginal stability in normalized beta are studied to produce a more accurate estimate for the critical beta for RWM onset, and these values are compared to DCON results. Unstable n=2 and n=3 RWMs are also seen in linear runs, and nonlinear runs are performed to understand how these modes couple.

[1] J. W. Berkery, S. A. Sabbagh, H. Reimerdes, et al, Phys. Plasmas 17, 082504 (2010)

*Research supported by U. S. DoE under grant no. DE-FG02-86ER53218.