Simulation of Energetic Particle Driven Instabilities

Abstract

Research on the simulation of energetic particle driven instabilities in the Large Helical Device (LHD) has been actively conducted in recent decades. The progress achieved has been substantial since the last comprehensive review by Todo et al. [29]. Since then, many new simulations have been conducted to investigate the energetic particle driven instabilities in LHD. The simulation studies are mainly focused on the energetic particle driven geodesic acoustic modes (EGAMs), covering both linear properties and nonlinear frequency chirping, as well as the energy channel and anomalous bulk ion heating. In addition, there are also notable studies on the Alfvén eigenmodes (AEs). The energetic particle transport caused by AEs is investigated in different ways. The interchange modes are also simulated under different conditions. In addition to the published works mentioned above, there are also new findings. Both the low-frequency and high-frequency branches of the EGAM are investigated, and various types of energetic particle velocity distribution functions are modeled with different charge-exchange loss rates. The transition between the low-frequency and high-frequency branches of EGAM is determined by the slope of the energetic particle velocity distribution. The low-frequency branch is excited under the condition of a slowing-down distribution, while the high-frequency branch is excited with a bump-on-tail distribution. Furthermore, the bulk pressure perturbation and the energetic particle pressure perturbation are in anti-phase for the low-frequency branch, while they are in-phase for the high-frequency branch.