Mach Number Dependence of Electron Heating in High Mach Number Quasiperpendicular Shocks

TL;DR

This study investigates how electron heating in high Mach number quasi-perpendicular shocks depends on Mach number, revealing different behaviors for microinstability-driven heating mechanisms through simulations and models.

Contribution

It introduces a combined PIC simulation and extended quasilinear analysis to distinguish Mach number effects on electron heating via MTSI and BI instabilities.

Findings

Electron temperature via MTSI is Mach number independent.

Electron temperature via BI increases with Mach number.

A critical Mach number of a few tens triggers steep electron heating rise.

Abstract

Efficiency of electron heating through microinstabilities generated in the transition region of a quasi-perpendicular shock for wide ange of Mach numbers is investigated by utilizing PIC (Particle-In-Cell) simulation and model analyses. In the model analyses saturation levels of effective electron temperature as a result of microinstabilities are estimated from an extended quasilinear (trapping) analysis for relatively low (high) Mach number shocks. Here, MTSI (modified two-stream instability) is assumed to become dominant in low Mach number regime, while BI (Buneman instability) to become dominant in high Mach number regime, respectively. It is revealed that Mach number dependence of the effective electron temperature in the MTSI dominant case is essentially different from that in the BI dominant case. The effective electron temperature through the MTSI does not depend much on the Mach number, although that through the BI increases with the Mach number as in the past studies. The results are confirmed to be consistent with the PIC simulations both in qualitative and quantitative levels. The model analyses predict that a critical Mach number above which steep rise of electron heating rate occurs may arise at the Mach number of a few tens.