Characteristics of Alfven eigenmodes, burst modes and chirping modes in the Alfven frequency range driven by negative ion based neutral beam injection in JT-60U

The excitation and stabilization of Alfven eigenmodes and their impact on energetic ion confinement were investigated with negative ion based neutral beam injection at 330-360 keV into weak or reversed magnetic shear plasmas on JT-60U. Toroidicity induced Alfven eigenmodes (TAEs) were observed in weak shear plasmas with (βh) ≥ 0.1% and 0.4 ≤ υbparallel/υA ≤ 1. The stability of TAEs is consistent with predictions by the NOVA-K code. New burst modes and chirping modes were observed in the higher β regime of (βh) ≥ 0.2%. The effect of TAEs, burst modes and chirping modes on fast ion confinement has been found to be small so far. It was found that a strongly reversed shear plasma with internal transport barrier suppresses AEs. (author)