INFLUENCE OF TRAPPED THERMAL PARTICLES ON INTERNAL KINK MODES IN HIGH-TEMPERATURE TOKAMAKS

The effects of thermal trapped particles on the n = 1 internal kink mo de are studied using drift kinetic theory. Strong modifications of the magnetohydrodynamic (MHD) results are found, and marginal stability g enerally occurs at nonzero rotation frequency. For equal electron and ion temperatures, the trapped particles increase the marginal poloidal beta at q = 1 substantially above the MHD value. For unequal electron and ion temperatures, the drift resonance with the hotter species bec omes increasingly destabilizing and for sufficiently unequal temperatu res, this leads to instability below the ideal-MHD threshold. Treatmen t of trapped thermal particles requires consideration of the effects o f an electrostatic potential. The potential is weakly stabilizing for the internal kink mode. Furthermore, finite beta couples unstable, nea rly electrostatic, trapped particle modes to the internal kink mode. A t high beta, thermal fluctuations of the trapped particle modes can le ad to significant internal kink displacements.