Particle simulation analysis of energetic-particle and Alfvn-mode dynamics in JT-60U discharges

Vlad, G.*; Briguglio, S.*; Fogaccia, G.*; Shinohara, Koji; Ishikawa, Masao; Takechi, Manabu; Zonca, F.*

The results of particle simulations of a typical NNB-heated JT-60U discharge, performed by the HMGC particle-in-cell code, are presented. We observe that the linear-growth phase is dominated by a fast-growing mode, localized at half radius, near the maximum of the energetic-ion pressure gradient and with a significant coupling with the Alfvn continuum, showing the energetic-particle-driven nature of the mode. As the nonlinear effects become important, a macroscopic outward displacement of the energetic ions is observed, producing a significant reduction of their density in the central region. These results seem to match quite well the dynamics of the abrupt large-amplitude event (ALE) experimentally observed in the JT-60U discharge. The time scale and frequency spread of the ALE are well reproduced too.