# Influence of 3D plasmoid dynamics on the transition from collisional to kinetic reconnection

## TL;DR

This paper uses first-principles kinetic simulations to study how 3D plasmoid dynamics influence the transition from collisional to kinetic magnetic reconnection, revealing rapid current layer thinning and turbulence.

## Contribution

First kinetic 3D simulation demonstrating the impact of plasmoid instability on the transition to kinetic reconnection, including current layer thinning and turbulence development.

## Key findings

- Current layer thins rapidly due to Joule heating before plasmoid instability onset.
- Linear growth rates match semi-collisional theory for standard tearing modes.
- Transition to kinetic reconnection occurs in thin layers formed between flux-ropes.

## Abstract

Within the resistive magnetohydrodynamic model, high-Lundquist number reconnection layers are unstable to the plasmoid instability, leading to a turbulent evolution where the reconnection rate can be independent of the underlying resistivity. However, the physical relevance of these results remains questionable for many applications. First, the reconnection electric field is often well above the runaway limit, implying that collisional resistivity is invalid. Furthermore, both theory and simulations suggest that plasmoid formation may rapidly induce a transition to kinetic scales, due to the formation of thin current sheets. Here, this problem is studied for the first time using a first-principles kinetic simulation with a Fokker-Planck collision operator in 3D. The low-$\beta$ reconnecting current layer thins rapidly due to Joule heating before onset of the oblique plasmoid instability. Linear growth rates for standard ($k_y = 0$) tearing modes agree with semi-collisional boundary layer theory, but the angular spectrum of oblique ($|k_y|>0$) modes is significantly narrower than predicted. In the non-linear regime, flux-ropes formed by the instability undergo complex interactions as they are advected and rotated by the reconnection outflow jets, leading to a turbulent state with stochastic magnetic field. In a manner similar to previous 2D results, super-Dreicer fields induce a transition to kinetic reconnection in thin current layers that form between flux-ropes. These results may be testable within new laboratory experiments.