Energetic particle driven instability in wall-stabilized high- plasmas

Matsunaga, Go; Shinohara, Koji; Aiba, Nobuyuki; Sakamoto, Yoshiteru; Isayama, Akihiko; Asakura, Nobuyuki; Suzuki, Takahiro; Takechi, Manabu; Oyama, Naoyuki; Urano, Hajime; JT-60 Team

We have observed a fishbone like bursting mode in high- plasmas above the ideal -limit without a conducting wall. The mode frequency is chirping down, and its initial value is close to precession frequency of trapped fast ions produced by perpendicularly injected neutral beams. This mode can often induce the resistive wall mode (RWM) onset. The mode is mainly observed in the high- plasma where ideal kink-ballooning mode (IKBM) and RWM are marginally stable. Since this mode and RWM were simultaneously observed, the mode is attributed to the interaction between the trapped fast ions and a marginally stable IKBM stabilized by conducting wall. From these results, the observed mode was named as "Energetic particle driven Wall Mode (EWM)." Interestingly, the EWM can change edge localized mode (ELM) behavior. Namely, it was observed that ELM was synchronized with the EWM.