|belova_icc06.pdf||2006-02-21 16:04:27||Elena Belova|
Effects of Energetic Beam Ions on Stability Properties of Field Reversed Configurations
Author: Elena V. Belova
Submitted: 2005-12-21 19:03:59
Co-authors: R.C. Davidson, H. Ji, M. Yamada, S.P. Gerhardt, M. Inomoto
P.O. Box 451
Princeton, NJ 08543
The HYM code has been used to study FRC formation by counter-helicity spheromak merging, and stability properties of FRCs formed by this method have been investigated, including the effects of close-fitting conducting shell and neutral beam injection (NBI). Calculations have been performed for FRCs with elongation E~1. Linear stability and nonlinear evolution of co-interchange (kink) modes with toroidal mode numbers n=1-4 have been studied. It is shown that the beam ions can have a stabilizing or destabilizing effect on the global modes in FRCs, depending on the toroidal mode number n, the mode polarization, and the beam parameters. It is found that linear simulation results agree well with a qualitative analysis based on a generalized energy principle. Nonlinear simulations show that the beam-driven instabilities saturate nonlinearly at low amplitudes due to changes in the distribution function of the beam ions. A new stability regime has been found for FRCs with E~1 and S*=20, which requires a close-fitting conducting shell and energetic beam ion stabilization. It is shown that the n=1 and n=2 MHD modes can be effectively stabilized by combination of conducting shell and beam ion effects, and residual weakly unstable n>2 modes saturate nonlinearly at low amplitudes. The resulting configuration remains stable with respect to all global MHD modes, as long as the FRC current is sustained.