Continuum gyrokinetic modeling of a high-field axisymmetric mirror*

Magnetic mirrors have achieved MHD stability in the last two decades due to expanded flux regions at the ends, line-tying, biasing, sloshing ions, and other strategies [1]. Increased stability and enhanced heating have allowed modern mirrors to approach the keV electron temperature milestone [1]. Leveraging this knowledge and advancements in high-temperature superconducting (HTS) technology, the Wisconsin HTS Axisymmetric Mirror (WHAM) aims to produce a compact device with fusion-relevant energy densities and evaluate the feasibility of mirror-based fusion plants. To study parallel and perpendicular dynamics comprehensively, this study uses the Gkeyll code for 5D gyrokinetic studies of magnetic mirrors [2]. One-dimensional studies verified parallel dynamics and additional algorithmic work has maintained these dynamics with reduced computational resources [3]. Significant gains include the incorporation of general geometry, non-uniform spatial and velocity grids, an ad-hoc positivity fix, coupling to CQL3D for initial conditions, and moving Gkeyll to a multi-GPU implementation. We present results from full 5D gyrokinetics of a high-field magnetic mirror, supported by simulations using single field lines and axisymmetric cross-sections to verify algorithmic implementations, and to study possible residual turbulence and how it is affected by sheared flow.

[1] D. D. Ryutov, Phys. Plasmas (2011). [2] https://gkeyll.readthedocs.io. [3] M. Francisquez et al., Phys. Plasmas (2023).