Marginally Stable Current Sheets in Collisionless Magnetic Reconnection

TL;DR

This paper investigates the conditions under which collisionless, guide-field current sheets become unstable to plasmoid formation, revealing that plasmoids can form in shorter, more elongated sheets than previously thought.

Contribution

It provides new insights into the marginal stability criteria for plasmoid formation in collisionless magnetic reconnection with a guide field.

Findings

Plasmoids can form in current sheets with smaller aspect ratios than in collisional regimes.

The plasma flow channel in marginally stable sheets maintains an inverse aspect ratio of about 0.1.

Identifies regimes where collisionless current sheets become plasmoid unstable.

Abstract

Non-collisional current sheets that form during the nonlinear development of magnetic reconnection are characterized by a small thickness, of the order of the electron skin depth. They can become unstable to the formation of plasmoids, which allows the magnetic reconnection process to reach high reconnection rates. In this work, we investigate the marginal stability conditions for the development of plasmoids when the forming current sheet is purely collisionless and in the presence of a strong guide field. We analyze the geometry that characterizes the reconnecting current sheet, and what promotes its elongation. Once the reconnecting current sheet is formed, we identify the regimes for which it is plasmoid unstable. Our study shows that plasmoids can be obtained, in this context, from current sheets with an aspect ratio much smaller than in the collisional regime, and that the plasma flow channel of the marginally stable current layers maintains an inverse aspect ratio of $0.1$.