Electron heating in kinetic-Alfven-wave turbulence

We report analytical and numerical investigations of subion-scale turbulence in low-beta plasmas using a rigorous reduced kinetic model. We show that efficient electron heating occurs and is primarily due to Landau damping of kinetic Alfven waves, as opposed to Ohmic dissipation. This collisionless damping is facilitated by the local weakening of advective nonlinearities and the ensuing unimpeded phase mixing near intermittent current sheets, where free energy concentrates. The linearly damped energy of electromagnetic fluctuations at each scale explains the steepening of their energy spectrum with respect to a fluid model where such damping is excluded (i.e., a model that imposes an isothermal electron closure). The use of a Hermite polynomial representation to express the velocity-space dependence of the electron distribution function enables us to obtain an analytical, lowest-order solution for the Hermite moments of the distribution, which is borne out by numerical simulations.

Automated summary

We conducted analytical and numerical investigations on subion-scale turbulence in low-beta plasmas using a rigorous reduced kinetic model. The results show that electron heating is primarily caused by Landau damping of kinetic Alfven waves rather than Ohmic dissipation. This collisionless damping is facilitated by the weakening of advective nonlinearities near intermittent current sheets, where free energy concentrates. The linearly damped energy of electromagnetic fluctuations explains the steepening of their energy spectrum compared to a fluid model.