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

Fishbone-like burst modes (FBs) and toroidal Alfvén eigenmodes (TAEs) excited by energetic ions were observed for the first time in CHS heliotron/torsatron plasmas heated by co-injected neutral beams, where the rotational transform 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 increase in the energetic ion loss flux. FBs of m = 2/n = 1 induce sawtooth oscillations in the latter half of a discharge where the plasma b becomes high. Only when the beam velocity exceeds about half of the central Alfvén velocity and the net plasma current is induced to the required level are TAEs with n = 1 and n = 2 excited; these are localized in the plasma core region, where the magnetic shear is appreciably reduced by the net plasma current. So far, TAE induced energetic ion loss has not been observed.