The Structure of Plasma Heating in Gyrokinetic Alfv\'enic Turbulence

TL;DR

This study uses high-resolution gyrokinetic simulations to analyze plasma heating in kinetic Alfvén wave turbulence, revealing that heating structures are not confined to current sheets and that electrons and ions are heated differently.

Contribution

It demonstrates that plasma heating structures are more widespread than current sheets and distinguishes electron and ion heating pathways in KAW turbulence.

Findings

Heating structures are not confined to current sheets.

Electrons are predominantly heated parallel to the magnetic field.

Ions mainly experience perpendicular heating.

Abstract

We analyze plasma heating in weakly collisional kinetic Alfv\'en wave (KAW) turbulence using high resolution gyrokinetic simulations spanning the range of scales between the ion and the electron gyroradii. Real space structures that have a higher than average heating rate are shown not to be confined to current sheets. This novel result is at odds with previous studies, which use the electromagnetic work in the local electron fluid frame, i.e. $\mathbf{J} \!\cdot\! (\mathbf{E} + \mathbf{v}_e\times\mathbf{B})$, as a proxy for turbulent dissipation to argue that heating follows the intermittent spatial structure of the electric current. Furthermore, we show that electrons are dominated by parallel heating while the ions prefer the perpendicular heating route. We comment on the implications of the results presented here.