Effect of velocity space anisotropicity on the nonlinear dynamics of energetic particle modes in JT-60U

Bierwage, A.

The role of velocity space anisotropicity on the linear growth and nonlinear evolution of energetic particle modes and associated transport is studied using the MHD-kinetic hybrid code MEGA. For simplicity, a shifted-circle model equilibrium and slowing-down model distribution for fast ions are used. Parameters are based on a JT-60U discharge where so-called Abrupt Large Events were observed. The goal of this study is to confirm speculations made on the basis of previous simulation results. It is shown that a secondary mode near the magnetic axis is driven by counter-injected beam ions. For fixed fast ion beta, beam-like anisotropic distribution functions cause faster instability growth than isotropic distributions. Fast ion transport is also enhanced.