Kinetic heating by Alfv\'en waves in magnetic shears

TL;DR

This study uses kinetic simulations to show how large-scale Alfvén waves decay into kinetic Alfvén waves in magnetic shears, leading to differential ion and electron heating and non-Maxwellian particle distributions, relevant to space and laboratory plasmas.

Contribution

It demonstrates a decay process of large-scale Alfvén waves into kinetic Alfvén waves in magnetic shears, revealing differential heating and non-Maxwellian features in particle distributions.

Findings

Large-scale Alfvén waves decay into kinetic Alfvén waves.

Ion and electron heating are unequal during decay.

Non-Maxwellian features appear in particle velocity distributions.

Abstract

With first-principles kinetic simulations, we show that a large-scale Alfv\'en wave (AW) propagating in an inhomogeneous background decays into kinetic Alfv\'en waves (KAWs), triggering ion and electron energization. We demonstrate that the two species can access unequal amounts of the initial AW energy, experiencing differential heating. During the decay process, the electric field carried by KAWs produces non-Maxwellian features in the particle VDFs, in accordance with space observations. The process we present solely requires the interaction of a large-scale AW with a magnetic shear and may be relevant for several astrophysical and laboratory plasmas.