Electromagnetic gyrokinetic mode simulations in XGC with an improved finite-grid stable implicit particle-in-cell algorithm

An implicit particle-in-cell method for electromagnetic gyrokinetics using parallel velocity as a coordinate has been developed in the XGC code as a means of avoiding the Ampère cancellation problem for long-wavelength MHD-type modes [1]. Here, we present an improved formulation for the implicit method, based on the work in [2], which demonstrates robust stability properties with respect to both finite-grid and temporal instabilities. We demonstrate the ability of the scheme to simulate various electromagnetic modes such as the shear Alfvén wave, kinetic ballooning modes [3], and low-n cylindrical tearing modes [4]. Finally, we study the performance of the scheme by evaluating the cost of solving the system of equations arising from the implicit discretization.

[1] B. Sturdevant, S. Ku, L. Chacón, et al., Phys. Plasmas, 28, 072505 (2021).

[2] B. Sturdevant and L. Chacón, J. Comput. Phys., 464, 111330 (2022).

[3] T Görler, et al., Phys. Plasmas, 23, 072503 (2016)

[4] Y. Chen, et al., Phys. Plasmas, 22, 042111 (2015)