# Fast Recursive Reconnection and the Hall effect: Hall-MHD Simulations

## TL;DR

This paper uses Hall-MHD simulations to explore how the Hall effect influences recursive magnetic reconnection, revealing transitions between different reconnection regimes and significant modifications to reconnection dynamics and structures.

## Contribution

It demonstrates how the Hall effect alters recursive reconnection processes when ion inertial scales are approached, extending understanding of reconnection regimes.

## Key findings

- Transition from plasmoid-dominant to Hall-dominant reconnection regime.
- Significant changes in X-point structure and reconnection rate due to Hall effect.
- Modified dissipation properties and power spectra in Hall-influenced reconnection.

## Abstract

Magnetohydrodynamic (MHD) theory and simulations have shown that reconnection is triggered via a fast "ideal" tearing instability in current sheets whose inverse aspect ratio decreases to $a/L\sim S^{-1/3}$, with $S$ is the Lundquist number defined by the half-length $L$ of the current sheet (of thickness $2a$). Ideal tearing, in 2D sheets, triggers a hierarchical collapse via stretching of X-points and recursive instability. At each step, the local Lundquist number decreases, until the subsequent sheet thickness either approaches kinetic scales or the Lundquist number becomes sufficiently small. Here we carry out a series of Hall-MHD simulations to show how the Hall effect modifies recursive reconnection once the ion inertial scale is approached. We show that as the ion inertial length becomes of the order of the inner, singular layer thickness at some step of the recursive collapse, reconnection transits from the plasmoid-dominant regime to an intermediate plasmoid+Hall regime and then to the Hall-dominant regime. The structure around the X-point, the reconnection rate, the dissipation property and the power spectra are also modified significantly by the Hall effect.