Comprehensive Simulations of Bursting and Non-Bursting Alfvén Waves in ICRF Heated Tokamak Plasmas and Implications for Their Control via Phase Space Engineering

Recurrent bursting Alfvénic instabilities can drastically degrade plasma confinement. Unlike beam-driven shear Alfvén waves (SAWs), which often exhibit bursting behavior [1], SAWs during ion cyclotron resonance frequency heating (ICRH) typically maintain steady amplitudes [2,3], despite theoretical predictions suggesting the possibility of a bursting state [4]. This implies that the strong velocity space diffusion caused by the RF wave electric field plays a significant role in determining the wave nonlinear states.

We conducted the first comprehensive simulations of ICRH-driven tokamak plasmas on the slowing-down timescale using the kinetic-MHD hybrid code MEGA, where SAW-induced fast-ion transport is self-consistently included during the high-energy tail formation. Both ICRF-induced bursting and non-bursting toroidal Alfvén eigenmodes (TAEs) are observed. We will present the conditions that determine whether TAEs exhibit bursting behavior or maintain steady amplitudes, as well as their correlation with phase-space dynamics. A strategy for avoiding bursting SAWs through fast-ion phase space engineering via RF waves will be discussed.

[1] Wong, K. L., et al. Phys. Rev. Lett., 66, 1874 (1991).

[2] García-Muñoz, M., et al. Phys. Rev. Lett., 104, 185002 (2010).

[3] Kazakov, Ye O., et al. Nat. Phys, 13, 973 (2017).

[4] Breizman B.N., Berk H.L. et al., Phys. Plasmas 4, 1559 (1997).