Simulation Study of Interaction between Energetic Ions and Alfv n Eigenmodes in LHD

"Interaction between energetic ions and Alfv n eigenmodes (AE modes) in LHD was investigated with numerical approaches. The spatial profile and frequency of the AE modes in an LHD plasma #47645, where the creation of holes and clumps in the energetic ion energy spectrum associated with AE modes was observed with the neutral particle analyzer (NPA) [M. Osakabe et al., Nucl. Fusion 46, S911 (2006)], were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with the Poincar plots where an oscillating AE mode for each plot is employed. The radial width of the phase space regions trapped by the AE modes corresponds to the transport distance of energetic ions. As island width depends on AE mode amplitude, it was found that AE mode amplitude of deltaB_r / B~10^-3 is consistent with the energetic-ion transport over 10% of the minor radius that is suggested by the difference in slowing-down time between the holes and clumps observed with the NPA in the LHD experiment. Furthermore, a numerical code which simulates the time evolution of energetic particles and AE mode amplitude and phase in a self-consistent way has been newly developed for three-dimensional equilibria such as LHD. Alfv n eigenmode bursts in LHD plasma were simulated with neutral-beam injection and collisions taken into account.