Proton temperature-anisotropy-driven instabilities in weakly collisional plasmas: Hybrid simulations

TL;DR

This study uses hybrid simulations to explore how proton temperature anisotropy-driven instabilities develop in weakly collisional, high beta plasmas, revealing the roles of fire hose and mirror instabilities in regulating anisotropy.

Contribution

It demonstrates the impact of Coulomb collisions on instability development and shows how these instabilities generate wave energy influencing plasma transport properties.

Findings

Oblique fire hose instability reduces parallel anisotropy.

Mirror instability creates structures that scatter protons.

Instabilities produce wave energy comparable to collisionless plasmas.

Abstract

Kinetic instabilities in weakly collisional, high beta plasmas are investigated using two-dimensional hybrid expanding box simulations with Coulomb collisions modeled through the Langevin equation (corresponding to the Fokker-Planck one). The expansion drives a parallel or perpendicular temperature anisotropy (depending on the orientation of the ambient magnetic field). For the chosen parameters the Coulomb collisions are important with respect to the driver but are not strong enough to keep the system stable with respect to instabilities driven by the proton temperature anisotropy. In the case of the parallel temperature anisotropy the dominant oblique fire hose instability efficiently reduces the anisotropy in a quasilinear manner. In the case of the perpendicular temperature anisotropy the dominant mirror instability generates coherent compressive structures which scatter protons and reduce the temperature anisotropy. For both the cases the instabilities generate temporarily enough wave energy so that the corresponding (anomalous) transport coefficients dominate over the collisional ones and their properties are similar to those in collisionless plasmas.