Drift-cyclotron loss-cone instability in 3D simulations of a sloshing-ion simple mirror
Abstract
The kinetic stability of collisionless, sloshing beam-ion (45{\deg} pitch angle) plasma is studied in a 3D simple magnetic mirror, mimicking the Wisconsin High-temperature superconductor Axisymmetric Mirror (WHAM) experiment. The collisional Fokker-Planck code CQL3D-m provides a slowing-down beam-ion distribution to initialize the kinetic-ion/fluid-electron code Hybrid-VPIC, which then simulates free plasma decay without external heating or fueling. Over 1-10 s, drift-cyclotron loss-cone (DCLC) modes grow and saturate in amplitude. DCLC scatters ions to a marginally-stable distribution with gas-dynamic rather than classical-mirror confinement. Sloshing ions can trap cool (low-energy) ions in an electrostatic potential well to stabilize DCLC, but DCLC itself does not scatter sloshing beam-ions into said well. Instead, cool ions must come from external sources such as charge-exchange collisions with a low-density neutral population. Manually adding cool ~1 keV ions improves beam-ion confinement several-fold in Hybrid-VPIC simulations, which qualitatively corroborates prior measurements from real mirror devices with sloshing ions.
Keywords
Cite
@article{arxiv.2412.04656,
title = {Drift-cyclotron loss-cone instability in 3D simulations of a sloshing-ion simple mirror},
author = {Aaron Tran and Samuel J. Frank and Ari Y. Le and Adam J. Stanier and Blake A. Wetherton and Jan Egedal and Douglass A. Endrizzi and Robert W. Harvey and Yuri V. Petrov and Tony M. Qian and Kunal Sanwalka and Jesse Viola and Cary B. Forest and Ellen G. Zweibel},
journal= {arXiv preprint arXiv:2412.04656},
year = {2025}
}
Comments
Accepted at Journal of Plasma Physics; 36 pages, 14 figures