Self-consistent simulation of compressional Alfv\'en eigenmodes excited by runaway electrons

Alfv\'enic modes in the current quench (CQ) stage of the tokamak disruption have been observed in experiments. In DIII-D the excitation of these modes is associated with the presence of high-energy runaway electrons, and a strong mode excitation is often associated with the failure of RE plateau formation. In this work we present results of self-consistent kinetic-MHD simulations of RE-driven compressional Alfv\'en eigenmodes (CAEs) in DIII-D disruption scenarios, providing an explanation of the CQ modes. Simulation results reveal that high energy trapped REs can have resonance with the Alfv\'en mode through their precession motion, and the resonance frequency is proportional to the energy of REs. The mode frequencies and their relationship with the RE energy are consistent with experimental observation. The perturbed magnetic fields from the modes can lead to spatial diffusion of runaway electrons including the nonresonant passing ones, thus providing the theoretical basis for a potential approach for runaway electron mitigation.