Particle simulation of bursting Alfvn modes in JT-60U

Briguglio, S.*; Fogaccia, G.*; Vlad, G.*; Zonca, F.*; 篠原 孝司; 石川 正男; 武智 学

Physics of Plasmas, 14(5), p.055904_1 - 055904_10, 2007/05

https://doi.org/10.1063/1.2710208

The results of particle-in-cell simulations of a negative neutral beam heated Alfvn-mode experiment in the JT-60U are presented. They seem to match quite well the dynamics of the abrupt large-amplitude event (ALE) experimentally observed in the reference JT-60U discharge. The time scale and frequency spread of the ALE are well reproduced too. The issue of the weaker Alfvn fluctuation phase following the ALEs, characterized by fast frequency sweeping modes, is also investigated and an interpretation of the full JT-60U bursting-mode phenomenology is presented. Finally, the simulation tool is exploited by ad hoc synthetic diagnostics on the fast ion distribution function to get a deeper insight into the ALE nonlinear dynamics. The underlying fast-growing energetic particle mode saturates as resonant energetic ions are scattered out of the resonance region and displaced outwards. The radially displaced ions resonate with outer Alfvn modes and enhance their local drive.