Suppression of electron thermal conduction by whistler turbulence in a sustained thermal gradient

TL;DR

This study uses particle-in-cell simulations to show that whistler turbulence can significantly suppress electron thermal conduction in collisionless plasmas with thermal gradients, with implications for astrophysical plasma environments.

Contribution

It demonstrates that large-amplitude whistler waves can resonantly scatter electrons, reducing heat flux independently of the thermal gradient, and highlights the role of whistler propagation speed in thermal transport.

Findings

Whistler waves grow to large amplitude and scatter electrons.

Steady state heat flux is largely independent of thermal gradient.

Whistler propagation speed controls thermal conduction rate.

Abstract

The dynamics of weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field is explored with particle-in-cell simulations and modeling. Two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude, $\delta B / B_{0} \simeq 1$, and resonantly scatter the electrons, significantly reducing the heat flux. A surprise is that the resulting steady state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high $\beta$ astrophysical plasmas such as hot accretion flows and the intracluster medium of galaxy clusters.