Compressional Alfv´eneigenmodes excited by runaway electrons Chang Liu Princeton Plasma Physics Laboratory, Princeton, NJ, United States of America E-mail:
[email protected] Dylan P. Brennan Princeton University, Princeton, NJ, United States of America Andrey Lvovskiy Oak Ridge Associated Universities, Oak Ridge, TN, United States of America Carlos Paz-Soldan General Atomics, San Diego, CA, United States of America Eric D. Fredrickson Princeton Plasma Physics Laboratory, Princeton, NJ, United States of America Amitava Bhattacharjee Princeton Plasma Physics Laboratory, Princeton, NJ, United States of America Princeton University, Princeton, NJ, United States of America Abstract. Compressional Alfv´en eigenmodes (CAE) driven by energetic ions have been observed in magnetic fusion experiments. In this paper, we show that the modes can also be driven by runaway electrons formed in post-disruption plasma, which may explain kinetic instabilities observed in DIII-D disruption experiments with massive gas injection. The mode-structure is calculated, as are the frequencies which are arXiv:2009.11801v3 [physics.plasm-ph] 2 Oct 2020 in agreement with experimental observations. Using a runaway electron distribution function obtained from a kinetic simulation, the mode growth rates are calculated and found to exceed the collisional damping rate when the runaway electron density exceeds a threshold value. The excitation of CAE poses a new possible approach to mitigate seed runaway electrons during the current quench and surpassing the avalanche. Compressional Alfv´eneigenmodes excited by runaway electrons 2 1. Introduction The generation of high-energy runaway electrons poses one of the major threats to the safety and reliable performance of tokamak fusion reactors [1].