Conductivity tensor for anisotropic plasma in gyrokinetic theory

Abstract

It has been argued that oblique firehose and mirror instabilities are important candidates for the regulation of temperature anisotropy in solar wind. To quantify the role of anisotropy driven instabilities, global kinetic simulations of the solar wind would be extremely useful. However, due to long time scales involved, such simulations are prohibitively expensive. Gyrokinetic theory and simulations have proven to be valuable tools for the study of low frequency phenomena in nonuniform plasmas; however, there are discrepancies between the anisotropy driven instabilities appearing in the gyrokinetic theory and those of a fully kinetic one. We present a derivation of the conductivity tensor based on the arbitrary frequency gyrokinetics and show that relaxing the condition ω/Ω≪1, where ω is the wave frequency, and the Ω is the cyclotron frequency, eliminates these discrepancies, while preserving the advantages of the gyorkinetic theory for global kinetic simulations.