Electron Influence on the Parallel Proton Firehose Instability in 10-Moment, Multi-Fluid Simulations

TL;DR

This study uses advanced multi-fluid simulations to show that electron pressure anisotropy significantly influences the saturation of the parallel proton firehose instability in high-beta plasmas, highlighting the importance of electron dynamics.

Contribution

First multi-fluid simulation of the parallel proton firehose instability that includes electron pressure anisotropy effects without artificial viscosity.

Findings

Electrons significantly impact the saturation process.

Electron energization is pronounced even at lower beta values.

Resolving electron pressure anisotropy is crucial for accurate plasma modeling.

Abstract

Instabilities driven by pressure anisotropy play a critical role in modulating the energy transfer in space and astrophysical plasmas. For the first time, we simulate the evolution and saturation of the parallel proton firehose instability using a multi-fluid model without adding artificial viscosity. These simulations are performed using a 10-moment, multi-fluid model with local and gradient relaxation heat-flux closures in high-$\beta$ proton-electron plasmas. When these higher-order moments are included and pressure anisotropy is permitted to develop in all species, we find that the electrons have a significant impact on the saturation of the parallel proton firehose instability, modulating the proton pressure anisotropy as the instability saturates. Even for lower $\beta$s more relevant to heliospheric plasmas, we observe a pronounced electron energization in simulations using the gradient relaxation closure. Our results indicate that resolving the electron pressure anisotropy is important to correctly describe the behavior of multi-species plasma systems.