An Adaptive, Implicit, Conservative 1D-2V Multi-Species Vlasov-Fokker-Planck Multiscale Solve in Planar Geometry

TL;DR

This paper introduces an implicit, adaptive velocity-space discretization method for multi-species Vlasov-Fokker-Planck equations in planar geometry, ensuring conservation and efficiency in complex plasma simulations.

Contribution

It extends a conservative adaptive velocity-space scheme to inhomogeneous systems with implicit time stepping, addressing temperature disparity and inertial effects.

Findings

Demonstrates accurate shock-wave propagation simulations

Achieves conservation of mass, momentum, and energy within nonlinear tolerance

Shows improved efficiency and accuracy in complex plasma scenarios

Abstract

We consider a 1D-2V Vlasov-Fokker-Planck multi-species ionic description coupled to fluid electrons. We address temporal stiffness with implicit time stepping, suitably preconditioned. To address temperature disparity in time and space, we extend the conservative adaptive velocity-space discretization scheme proposed in [Taitano et al., J. Comp. Phys., 318, 391-420, (2016)] to a spatially inhomogeneous system. In this approach, we normalize the velocity-space coordinate to a temporally and spatially varying local characteristic speed per species. We explicitly consider the resulting inertial terms in the Vlasov equation, and derive a discrete formulation that conserves mass, momentum, and energy up to a prescribed nonlinear tolerance upon convergence. Our conservation strategy employs nonlinear constraints to enforce these properties discretely for both the Vlasov operator and the Fokker-Planck collision operator. Numerical examples of varying degrees of complexity, including shock-wave propagation, demonstrate the favorable efficiency and accuracy properties of the scheme.