A novel splitting method for Vlasov-Ampere

TL;DR

This paper introduces a new splitting method for the Vlasov-Ampere equations that improves the accuracy of fluid moment calculations by combining local fluid approximations with a novel operator splitting technique.

Contribution

The paper presents a novel splitting approach that separates inter-velocity band coupling from intra-band dynamics, enabling high-order accuracy for fluid moments.

Findings

Achieves high-order accuracy for mass, momentum, and energy.

Verified effectiveness on standard Vlasov-Poisson test cases.

Reduces accuracy restrictions of traditional operator splitting methods.

Abstract

Vlasov equations model the dynamics of plasma in the collisionless regime. A standard approach for numerically solving the Vlasov equation is to operator split the spatial and velocity derivative terms, allowing simpler time-stepping schemes to be applied to each piece separately (known as the Cheng-Knorr method). One disadvantage of such an operator split method is that the order of accuracy of fluid moments (e.g., mass, momentum, and energy) is restricted by the order of the operator splitting (second-order accuracy in the Cheng-Knorr case). In this work, we develop a novel approach that first represents the particle density function on a velocity mesh with a local fluid approximation in each discrete velocity band and then introduces an operator splitting that splits the inter-velocity band coupling terms from the dynamics within the discrete velocity band. The advantage is that the inter-velocity band coupling terms are only needed to achieve consistency of the full distribution functions, but the local fluid models within each band are sufficient to achieve high-order accuracy on global moments such as mass, momentum, and energy. The resulting scheme is verified on several standard Vlasov-Poisson test cases.