Fluid magnetohydrodynamic stabilit in a heliotron with anisotropic fast particle species
The local and global fluid magnetohydrodynamic stability properties of anisotropic pressure plasmas are investigated with the Kruskal-Oberman and rigid hot particle Johnson et al energy principles. A Heliotron configuration that models the Large Helical Device with finite pressure anisotropy driven by neutral beams at beta = 4% shows that the Kruskal-Oberman model predicts stability when beta(h)/beta similar to 1/3 provided that the hot particle pressure profile is sufficiently peaked. The rigid hot particle model, on the other hand, is stable to local and global modes for broad and peaked profiles. For central deposition, the marginal pressure profiles are somewhat broader for p(parallel to) > p(perpendicular to) than for p(perpendicular to)> p(parallel to). Global n = 3 modes produce stricter stability criteria than n = 1,2 and 4 modes. Off-axis hot particle deposition yields more unstable conditions with respect to global and local modes than on-axis deposition. The mode structures localize near the plasma periphery according to the Kruskal-Oberman model and near the plasma core according to the Johnson et al model. This observation could help resolve the appropriate model to apply to the experimental conditions in Heliotron devices.