Effects of fusion-product alpha particles on plasma stability in the fusion ignition experiment IGNITEX

摘要

Summary form only given. The effects of alpha particles on the stability of MHD modes in IGNITEX plasmas are investigated analytically and numerically. The sawtooth and fishbone oscillations, which may occur in the central part of the plasma column, are associated with the n=1, m=1 internal kink modes and are considered to be a potential threat to the attainment of ignitions. The energetic trapped ions can open a stability window where both sawtooth and fishbone oscillations are suppressed. It is found that the stability window can be attained on the IGNITEX experiment because the major radius is relatively small and the magnetic field is quite high. Energetic trapped alpha particles interact through their processional drift with high-mode-number ballooning modes. Instabilities can be excited if the alpha beta exceeds a critical value. High-n ballooning modes should be stable in the IGNITEX experiment owing to its high magnetic field and the rather low bulk plasma and alpha beta values. Shear-Alfven waves may be destabilized via alpha particle transit and magnetic-drift frequency resonances. Several excitation mechanisms that correspond to different free energy sources are investigated. Instabilities may be excited by alpha particles with nonmonotonic isotropic distribution, nonuniform space distribution, and anisotropy distribution. It is shown that stable fusion ignited plasmas can be produced in IGNITEX by preventing potentially dangerous alpha instabilities. The low-beta, ohmic-heating, L-mode regime of operation is shown to be the most appropriate for a fusion ignition experiment in a laboratory.