Nonlinear finite-Larmor-radius effects in reduced fluid models*

The polarization and magnetization effects associated with the process of dynamical reduction leading to nonlinear gyrokinetic theory [1] are shown to introduce nonlinear finite-Larmor-radius (NFLR) effects into nonlinear reduced-fluid equations [2]. 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 standard FLR corrections, which are associated with the transformation from particle phase-space dynamics to guiding-center phase-space dynamics. The reduced fluid equations with NFLR corrections are derived from a variational principle and, thus, automatically possess an exact energy conservation law. Simulation results show agreement with linear theory, nonlinear energy conservation, and mode coupling of Alfven and sound waves. \newline [1] A.J. Brizard and T.S. Hahm, Rev. Mod. Phys. {\bf 79}, 421 (2007). \newline [2] A.J. Brizard, Phys. Plasmas {\bf 12}, 092302 (2005).