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

The excitation and stabilization of Alfvén 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 Alfvén eigenmodes (TAEs) were observed in weak shear plasmas with ⟨β h ⟩ ⩾ 0.1% and 0.4 ⩽ v b|| /v A ⩽ 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 ⟨β h ⟩ ⩾ 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.