On Magnetic Compression in Gyrokinetic Field Theory

TL;DR

This paper develops a gyrokinetic field theory model that accurately incorporates magnetic compressibility effects in low-beta plasmas, ensuring energetic consistency and analyzing gyrocenter drifts in anisotropic pressure conditions.

Contribution

It introduces a gauge transformation-based Lagrangian for gyrokinetics that includes magnetic compressibility and guarantees energetic consistency, extending previous linear theory results.

Findings

Magnetic compressibility effects are incorporated into gyrokinetic models.

The model ensures exact energetic consistency in plasma dynamics.

Contributions to current divergence cancel up to order beta, confirming previous linear theory results.

Abstract

The issue of finite magnetic compressibility in low-beta magnetised plasmas is considered within the gyrokinetic description. The gauge transformation method of Littlejohn is used to obtain a Lagrangian which contains this effect additionally. The field theory version obtains a system model which guarantees exact energetic consistency. Gyrocenter drifts under this model are considered within a Chew-Goldberger-Low MHD equilibrium allowing for pressure anisotropy. The contributions to the current divergence balance, hence the dynamics, due to the difference between the curvature and grad-B drifts and to the compressibility are shown to cancel up to corrections of order beta. This recovers an earlier result with the same conclusion within linear theory of kinetic ballooning modes.