Simulation Study of Energetic Ion Transport due to Alfvén Eigenmodes in LHD Plasma

Abstract

The creation of holes and clumps in an energetic ion energy spectrum associated with Alfven eigenmodes wa se xamined using the neutral particle analyzer (NPA) on the LHD shot #47645. The difference in slowing- down times between the holes and clumps suggested that the energetic ions were transported over 10% of the plasma minor radius. The spatial profile and frequency of the Alfven eigenmodes were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with Poincare plots, where an oscillating Alfven eigenmode was employed for each plot .T he phase space regions trapped by the Alfven eigenmodes appeared as islands in the Poincarep lots .T he radial width of the islands corresponded to the transport distance of the energetic ions. Since island width depends on Alfven eigenmode amplitude, it was found that Alfven eigenmodes with amplitude δBr/B ∼ 10 −3 transported energetic ions over 10% of the minor radius.