Simulations of nonlinear interaction between beta-induced Alfvén eigenmode and tearing mode

Abstract

The nonlinear interaction between the m/n=2/1 beta-induced Alfvén eigenmode (BAE) and the m/n=2/1 tearing mode (TM) observed in the HL-2A experiment is systematically studied with the hybrid kinetic-MHD code M3D-K. It is found that the nonlinear growth of TM can lead to a gradient buildup on the magnetic island (MI) edge, and then triggers the destabilization of the linearly-stable BAE. Then, the triggered BAE together with TM can produce a significant redistribution of energetic particles. For BAE linearly-dominant-unstable case, the TM activity results in the inward motion of BAE mode structure, and the BAE can have a delay effect on the MI saturation. Furthermore, a high-frequency axisymmetric m/n=0/0 “breathing” mode (BM) is generated by the mode coupling of BAE and TM, agreeing well with the experimental observation, and causes the synchronized periodic oscillation of MI width.

Simulations of beta-induced Alfvén eigenmode mitigation by off-axis energetic particle distribution

“…The M3D-K code has been extensively applied to investigate the interaction between EP and MHD instabilities, e.g. tearing mode [31][32][33], fishbone [34,35], BAE [36,37], TAE [38,39], reversed shear Alfvén eigenmode [40,41].…”