Global MHD modes excited by energetic ions in heliotron/torsatron plasmas

Fishbone-like burst modes (FBs) and toroidal Alfven eigenmodes (TAEs) excit ed by energetic ions were observed for the first time in CHS heliotron/tors atron plasmas heated by co-injected neutral beams, where the rotational tra nsform is increased by the induced beam driven current. FBs of m = 3/n = 2 (where m, n are the poloidal and toroidal mode numbers) induce a pulsed inc rease in the energetic ion loss flux. FBs of m = 2/n = 1 induce sawtooth os cillations in the latter half of a discharge where the plasma beta becomes high. Only when the beam velocity exceeds about half of the central Alfven velocity and the net plasma current is induced to the required level are TA Es with n = 1 and n = 2 excited; these are localized in the plasma core reg ion, where the magnetic shear is appreciably reduced by the net plasma curr ent. So far, TAE induced energetic ion loss has not been observed.