Properties of energetic particle modes in N-NB driven JT-60U plasmas

JT-60Uプラズマにおける負イオン中性粒子ビーム駆動高エネルギー粒子モードの性質

Bierwage, A.; 藤堂 泰*; 相羽 信行; 松永 剛; 篠原 孝司; 矢木 雅敏

Bierwage, A.; Todo, Yasushi*; Aiba, Nobuyuki; Matsunaga, Go; Shinohara, Koji; Yagi, Masatoshi

Energetic particle mode (EPM) dynamics are simulated using the hybrid code MEGA. The scenario considered is based on JT-60U shot E039672, just before the onset of a so-called Abrupt Large Event (ALE). The properties of modes with toroidal mode numbers n=1-4 are analyzed. The n=1 harmonic dominates when drive is relatively weak; e.g., after a relaxation event has taken place. The n=3 harmonic dominantes when drive is strong, but only for a relatively short time until the fast ions have been redistributed. In single-n simulations, the peak amplitude of the n=3 mode exhibits a sharp increase when the drive exceeds a certain threshold. This is shown to be due to a convective amplification process. The sharp transition is moderated when the n=1 mode is taken into account. It is concluded that both n=1 and n=3 modes play an important role during ALEs, but the trigger mechanism for the onset of an ALE is still obscure.