Nonlinear finite-Larmor-radius effects in reduced fluid models

TL;DR

This paper introduces nonlinear finite-Larmor-radius effects into reduced fluid models derived from gyrokinetic theory, providing new insights into plasma wave dynamics and energy conservation.

Contribution

It extends previous reduced-fluid models by incorporating intrinsically nonlinear FLR effects from gyrocenter transformations, supported by linear and nonlinear simulation results.

Findings

The equations capture coupled Alfvén and sound wave dynamics.

Simulations show energy conservation in both geometries.

The model differs from standard FLR corrections by including nonlinear effects.

Abstract

The polarization and magnetization effects associated with the dynamical reduction leading to the nonlinear gyrokinetic Vlasov-Maxwell equations are shown to introduce nonlinear finite-Larmor-radius effects into a set of nonlinear reduced-fluid equations previously derived by Lagrangian variational method [A.J. Brizard, Phys. Plasmas 12, 092302 (2005)]. These intrinsically nonlinear FLR effects, which are associated with the transformation from guiding-center phase-space dynamics to gyrocenter phase-space dynamics, are different from the standard FLR corrections associated with the transformation from particle to guiding-center phase-space dynamics. We also present the linear dispersion relation and results from a nonlinear simulation code using these reduced-fluid equations. The simulation results (in both straight and dipole geometries) demonstrate that the equations describe the coupled dynamics of Alfven and sound waves and that the total simulation energy is conserved.