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(TH/P2-12) Nonlinear MHD and Energetic Particle Modes in Stellarators

H.R. Strauss¹⁾, G.Y. Fu²⁾, L.E. Sugiyama³⁾, W. Park²⁾, J. Breslau^2)
 
1) New York University, New York, NY, USA
²⁾Princeton Plasma Physics Laboratory, Princeton, NJ, U.S.A
³⁾Massachusetts Institute of Technology, Cambridge, MA, U.S.A

Abstract.  The M3D code has been applied to ideal, resistive, two fluid, and hybrid simulations of compact quasi axisymmetric stellarators. When beta exceeds a threshold, low poloidal mode number (m = 6 $\sim$ 18) modes grow exponentially, clearly distinguishable from the equilibrium evolution. Simulations of NCSX have beta limits are significantly higher than the infinite mode number ballooning limits. In the presence of resistivity, these modes occur well below the ideal limit. Their growth rate scaling with resistivity is similar to tearing modes. With sufficient viscosity, the growth rate becomes slow enough to allow calculations of magnetic island evolution. Hybrid gyrokinetic simulations with energetic particles indicate that global shear Alfvén TAE - like modes can be destabilized in stellarators. Computations in a two - period compact stellarator obtained a predominantly n = 1 toroidal mode with about the expected TAE frequency. Work is in progress to study fast ion-driven Alfvén modes in NCSX.

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