Variational mean-fluctuation splitting and drift-fluid models

TL;DR

This paper applies a variational approach to derive and analyze drift-fluid models from guiding-center kinetic theory, addressing anisotropic pressures, magnetization effects, and coupling challenges with electromagnetic fields.

Contribution

It introduces a variational splitting method for drift-kinetic equations, enhances drift-fluid models with magnetization terms, and proposes a simplified guiding-center theory for hybrid kinetic-fluid applications.

Findings

Magnetization currents impact momentum conservation in drift-fluid models.

Coupling drift-fluid models with Maxwell's equations presents significant challenges.

A simplified guiding-center theory offers potential solutions for hybrid models.

Abstract

After reviewing the variational approach to splitting mean flow and fluctuation kinetics in the standard Vlasov theory, the same method is applied to the drift-kinetic equation from Littlejohn's theory of guiding-center motion. This process sheds a new light on drift-ordered fluid (drift-fluid) models, whose anisotropic pressure tensor is then considered in detail. In addition, current drift-fluid models are completed by the insertion of magnetization terms ensuring momentum conservation. Magnetization currents are also shown to lead to challenging aspects when drift-fluid models are coupled to Maxwell's equations for the evolution of the electromagnetic field. In order to overcome these difficulties, a simplified guiding-center theory is proposed along with its possible applications to hybrid kinetic-fluid models.