Non-Linear Phenomena of Energetic-lon-Driven MHD Instabilities in LHD

Abstract Energetic ion driven MHD modes were observed in NBI heated plasmas of LHD. The observedmodes are classified into three kinds of modes, depending on the frequency range, degree of amplitudemodulation (continuous or bursting) and temporal evolution of the mode frequency with or without rapidfrequency chirping. It is important and of interest to study these phenomena related to non-linear wave- particle interactions. We have investigated the excitation conditions of continuous and bursting TAEs.Continuous TAEs are only observed just above the threshold. When drastic TAE bursts are excited, about15 Vo of the beam power is lost by each burst. This suggests that the bursting TAEs induce energetic ion transport before the thermalization. Two kinds of frequency chirping were observed in NBI heated plasma. One is rapid frequency chirping, of which chirping time scale is much shorter than a characteristic time of the change of the plasma equilibrium, and the other is slow frequency chirping.