One dimensional gyrokinetics of a high-field magnetic mirror

Magnetic mirrors have achieved MHD stability in the last two decades thanks to a combination of expanded flux regions at the ends, clever use of line-tying, biasing, sloshing ions and other strategies [1]. The increased stability and enhanced heating has allowed modern mirrors to approach the keV electron temperature milestone [2]. Leveraging this knowledge, and the latest 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 inform the feasibility of mirror-based fusion plants. This experiment relies on the formation of a strong positive potential produced by the initial rapid loss of electrons due to their larger scattering frequency [3] to enhance electron confinement. In this work, we present two types of one-dimensional (along a field line) simulations with Gkeyll's gyrokinetic solver [4], one with kinetic electrons and the other with adiabatic electrons, through which we examine end-losses and the self-consistent formation of the (Pastukhov) potential. These gyrokinetic simulations are compared against a kinetic simulation which resolves $v_\|$ and uses a fluid equation for the evolution of $T_\perp$. Results are compared to previous analytical approximations based on Fokker-Planck calculations in the central region of the plasma [5]. Lastly, we discuss the challenges associated with the continuum gyrokinetic modeling of high-field mirror plasmas and the three-dimensional study of microturbulence and interchange turbulence in these devices.