Tearing Driven Reconnection: Energy Conversion Involving Firehose Kinetic Instabilities (2D Hybrid M\"obius Simulations)

TL;DR

This paper investigates energy conversion during tearing-driven magnetic reconnection in weakly collisional plasmas using innovative 2D hybrid M"obius simulations, revealing key roles of ion heating, anisotropy, and firehose instabilities.

Contribution

It introduces a novel M"obius topology simulation method that enhances efficiency and provides new insights into energy transfer and plasma heating during magnetic reconnection.

Findings

Most energy conversion occurs during the nonlinear phase of instability.

Heating is concentrated within magnetic islands and near X-points.

Firehose instabilities regulate ion temperature anisotropy by energy redistribution.

Abstract

This study focuses on energy conversion related to tearing-driven magnetic reconnection in the context of weakly collisional astrophysical plasmas. We present results from a two-dimensional hybrid particle-in-cell simulation employing novel periodic conditions with a topology akin to the M\"obius strip, which double the computation efficiency as compared to regular periodic conditions. Evaluation of the ion electric work rate ($\mathbf{j}_i \cdot \mathbf{E}$) and pressure strain interaction ($\mathbf{P}_i : \mathbf{\nabla u}_i)$ shows that most of the energy conversion occurs during the nonlinear phase of the instability, where magnetic energy is transferred towards ion kinetic energy (bulk outflows) and internal energy (heating). These energy conversion rates are of the same order but inhomogeneous. Heating predominantly occurs within the magnetic islands, while near the X-points, nearly the same amount of magnetic energy is transferred to bulk plasma flow and heating. The reconnected plasma moreover exhibits an ion temperature higher parallel than perpendicular to the local magnetic field $\mathbf{B}$. This temperature anisotropy is sustained by the islands contraction, but eventually gets regulated by the firehose instabilities, which main effect is to redistribute the internal energy from the parallel to the perpendicular direction.