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. These mirrors rely 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. 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 in these devices.

[1] D. D. Ryutov, et al. Phys. Plasmas 18, 092301 (2011).

[2] P.A. Bagryansky, et al. Phys. Rev. Lett. 114, 205001 (2005).

[3] V. P. Pastukhov. Nucl. Fusion 14, 3 (1974).

[4] The Gkeyll code: https://gkeyll.readthedocs.io/en/latest/

[5] D. P. Chernin, M. N. Rosenbluth. Nucl. Fusion 18, 47 (1978); R. H. Cohen et al. Nucl. Fusion 18, 1229 (1978).