Experimental study of toroidicity induced Alfven eigenmode (TAE) stability at high q(0)

Experiments to destabilize the toroidicity induced Alfven eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal mode number TAE gaps moves towards the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of the central alpha particle beta(alpha) required for instability. No TAE activity was observed when beta(alpha)(0) reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations predict that the alpha driven TAE was weakly unstable.