Self-inhibiting thermal conduction in high-beta, whistler-unstable plasma

摘要

A heat flux in a high-$\beta$ plasma with low collisionality triggers thewhistler instability. Quasilinear theory predicts saturation of the instabilityin a marginal state characterized by a heat flux that is fully controlled byelectron scattering off magnetic perturbations. This marginal heat flux doesnot depend on the temperature gradient and scales as $1/\beta$. We confirm thistheoretical prediction by performing numerical particle-in-cell simulations ofthe instability. We further calculate the saturation level of magneticperturbations and the electron scattering rate as functions of $\beta$ and thetemperature gradient to identify the saturation mechanism as quasilinear.Suppression of the heat flux is caused by oblique whistlers withmagnetic-energy density distributed over a wide range of propagation angles.This result can be applied to high-$\beta$ astrophysical plasmas, such as theinstracluster medium, where thermal conduction at sharp temperature gradientsalong magnetic-field lines can be significantly suppressed.