Discrete unified gas kinetic scheme for multiscale plasma simulations

Plasma systems exhibit inherently multiscale behavior with strong cross-scale couplings, posing significant challenges to conventional modeling approaches that typically rely on separate fluid and kinetic descriptions in collisional and collisionless regimes. In this work, we propose a discrete unified gas kinetic scheme (DUGKS) for multiscale plasma simulations based on the BGK-Vlasov-Maxwell system. The method seamlessly bridges fluid and kinetic descriptions within a unified framework, enabling accurate simulations across a wide range of Knudsen numbers, normalized Debye lengths, and Larmor radii, without numerical constraints imposed by these small-scale parameters. A key feature of the method is a semi-implicit coupling of particle transport and collision, which eliminates stiffness arising from strong collisions in low-Knudsen regimes. The macroscopic moments of the resulting distribution function are then semi-implicitly coupled to Maxwell’s equations, allowing stable electromagnetic field evolution even in quasi-neutral regimes with vanishing Debye length. To address strong electromagnetic forces, a forward non-splitting semi-Lagrangian scheme is employed in velocity space, effectively removing CFL constraints and mitigating stiffness in small Larmor radius regimes. The synergy of these components makes the proposed DUGKS an asymptotic-preserving scheme that automatically recovers consistent discretizations of the appropriate limiting models, including the two-fluid model in collisional regimes and the Vlasov model in collisionless regimes. Comprehensive numerical experiments confirm the accuracy, stability, and efficiency of the proposed DUGKS, highlighting its potential for capturing transitions across fluid and kinetic regimes in multiscale plasma systems.