Precession drift reversal and rapid transport of trapped energetic particles due to an energetic particle driven instability in the Large Helical Device

Energetic particle transport by a magnetohydrodynamic (MHD) instability driven by helically trapped energetic particles is studied for a high-performance Large Helical Device plasma with kinetic-MHD hybrid simulations. It is observed in the simulation that an MHD mode with poloidal/toroidal mode numbers ????/????=2/1driven by helically trapped energetic particles causes a significant redistribution of perpendicular energetic particle pressure profile. The frequency of the MHD mode decreases rapidly at the saturation of the instability and changes sign, which indicates a reversal of the mode propagation direction. It is found that the helically trapped energetic particles interacting strongly with the MHD mode change the precession drift direction at the same time as the reversal of the MHD mode propagation direction. The helically trapped energetic particles with the precession drift reversal are transported rapidly in the radially outward direction before the original precession drift direction is recovered. The precession drift reversal and the outward transport are caused by interaction with the electric field of the MHD mode. The vast majority of trapped energetic particles which interact strongly with the MHD mode experience precession drift reversal, leading to a significant redistribution of the perpendicular energetic particle pressure profile.Numerical computations were performed on the Plasma Simulator (NEC SX-Aurora TSUBASA) of NIFS with the support and under the auspices of the NIFS Collaboration Research program (No. NIFS20KNST169), the JFRS-1 of the International Fusion Energy Research Centre, and the Supercomputer Fugaku of the RIKEN Center for Computational Science (Project ID: hp210178). This work was supported by MEXT as Program for Promoting Research studies on the Supercomputer Fugaku (Exploration of burning plasma confinement physics).