Multi-time-scale energetic particle dynamics in JT-60U simulated with MHD activity, sources and collisions

Bierwage, A.; Shinohara, Koji; Todo, Yasushi*; Yagi, Masatoshi

The global nonlinear hybrid code MEGA was extended with a fast ion source and a collision model, so that the formation of the fast ion slowing-down distribution (long time scale, 1ms-1s) and the interaction between the fast ions and MHD waves (short time scale, 0.001-1ms) can be simulated simultaneously. This self-consistent approach, without artificial interfaces, allows to simulate meso-time-scale dynamics (0.1-10ms), such as recurring bursts of MHD activity and the resulting relaxations of the fast ion distribution. When applied to a JT-60U plasma driven by 400 keV negative-ion-based neutral beams (N-NB), the code successfully reproduced experimentally observed bursts of chirping modes. Thus validated, the new multi-time-scale simulations allows for the first time to study the physics of burstiness and frequency chirping in a realistic setting, and first results are presented and discussed. The advances made constitute an important step towards predictive simulations.