Magnetic Reconnection in a Weakly Ionized Plasma

TL;DR

This study uses advanced multi-fluid simulations to explore magnetic reconnection in weakly ionized plasmas, revealing faster reconnection rates and plasma behaviors relevant to solar chromosphere phenomena.

Contribution

It introduces a realistic multi-fluid model considering ion-neutral interactions, finite ion inertia, and radiative losses, advancing understanding of chromospheric magnetic reconnection.

Findings

Reconnection accelerates when current sheet thins below the neutral-ion coupling scale.

Reconnection rates exceed traditional single-fluid predictions.

Formation of plasmoids indicates secondary tearing instability.

Abstract

Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al. 2012 \cite{Leake2012} by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.