Stochastic ion and electron heating on drift instabilities at the bow shock

TL;DR

This paper investigates how drift instabilities at the Earth's bow shock cause stochastic heating of ions and electrons, using MMS spacecraft data and laboratory diagnostics to understand energy transfer mechanisms.

Contribution

It identifies the specific drift instabilities responsible for stochastic ion and electron heating and introduces a diagnostic function to analyze energy transfer processes.

Findings

Ion heating linked to Lower-Hybrid-Drift instability

Electron heating associated with Electron-Cyclotron-Drift instability

Stochastic acceleration occurs via electric field gradients on electron gyroradius scales

Abstract

The analysis of the wave content inside a perpendicular bow shock indicates that heating of ions is related to the Lower-Hybrid-Drift (LHD) instability, and heating of electrons to the Electron-Cyclotron-Drift (ECD) instability. Both processes represent stochastic acceleration caused by the electric field gradients on the electron gyroradius scales, produced by the two instabilities. Stochastic heating is a single particle mechanism where large gradients break adiabatic invariants and expose particles to direct acceleration by the DC- and wave-fields. The acceleration is controlled by function $\chi = m_iq_i^{-1} B^{-2}$div($\mathbf{E}$), which represents a general diagnostic tool for processes of energy transfer between electromagnetic fields and particles, and the measure of the local charge non-neutrality. The identification was made with multipoint measurements obtained from the Magnetospheric Multiscale spacecraft (MMS). The source for the LHD instability is the diamagnetic drift of ions, and for the ECD instability the source is ExB drift of electrons. The conclusions are supported by laboratory diagnostics of the ECD instability in Hall ion thrusters.