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Effects of Energetic Beam Ions on Stability Properties of Prolate FRCs

Author: Elena V Belova
Requested Type: Consider for Invited
Submitted: 2012-12-07 16:52:30

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Contact Info:
PPPL
PPPL
Princeton, NJ   08543
USA

Abstract Text:
Stability properties of prolate Field-Reversed Configurations (FRCs) have been studied numerically using the nonlinear hybrid and MHD simulation code HYM, including the effects of energetic neutral beam ions. It is shown that the beam ions can have a stabilizing or destabilizing effect on the global modes in FRCs, depending on the beam parameters, the toroidal mode number, and mode polarization. The energetic beam ions tend to coalesce between the magnetic null and the separatrix near the FRC midplane. For strong beams, the beam profiles are highly localized. Beam ions can have two possible effects on FRC stability: direct, via wave-particle resonances and indirect due to changes in the equilibrium profiles. Both can be stabilizing or destabilizing. It is shown that large beam ion toroidal velocity V>5VA is needed for stabilization of the n=1 tilt mode, and that relatively large beam ion temperature is also beneficial for stability. For smaller injection velocities, beam-driven instabilities of higher-n modes have been observed, but these instabilities saturate nonlinearly at large amplitudes by changing the beam ion profiles and confinement. Simulation results are compared with a qualitative analysis based on a generalized energy principle.

Characterization: 1.2,2.0

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