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-magnetohydrodynamic 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 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.

Keywords

• beta-induced Alfvén eigenmode
• tearing mode
• wave-particle interaction
• mode coupling
• energetic particles