Phase Diagram for Magnetic Reconnection in Heliophysical, Astrophysical and Laboratory Plasmas

TL;DR

This paper introduces a phase diagram for magnetic reconnection, categorizing various plasma regimes across heliophysical, astrophysical, and laboratory contexts based on key dimensionless parameters, and highlights new reconnection phases involving multiple X-lines and collisionless physics.

Contribution

It presents a comprehensive phase diagram for magnetic reconnection that includes novel multiple X-line and hybrid phases, linking macroscopic and kinetic plasma dynamics across diverse environments.

Findings

Identification of new reconnection phases involving multiple X-lines.

The hybrid phase couples collisional and collisionless dynamics.

Application of the phase diagram to various astrophysical and laboratory plasmas.

Abstract

Recent progress in understanding the physics of magnetic reconnection is conveniently summarized in terms of a phase diagram which organizes the essential dynamics for a wide variety of applications in heliophysics, laboratory and astrophysics. The two key dimensionless parameters are the Lundquist number and the macrosopic system size in units of the ion sound gyroradius. In addition to the conventional single X-line collisional and collisionless phases, multiple X-line reconnection phases arise due to the presence of the plasmoid instability either in collisional and collisionless current sheets. In particular, there exists a unique phase termed "multiple X-line hybrid phase" where a hierarchy of collisional islands or plasmoids is terminated by a collisionless current sheet, resulting in a rapid coupling between the macroscopic and kinetic scales and a mixture of collisional and collisionless dynamics. The new phases involving multiple X-lines and collisionless physics may be important for the emerging applications of magnetic reconnection to accelerate charged particles beyond their thermal speeds. A large number of heliophysical and astrophysical plasmas are surveyed and grouped in the phase diagram: Earth's magnetosphere, solar plasmas (chromosphere, corona, wind and tachocline), galactic plasmas (molecular clouds, interstellar media, accretion disks and their coronae, Crab nebula, Sgr A*, gamma ray bursts, magnetars), extragalactic plasmas (Active Galactic Nuclei disks and their coronae, galaxy clusters, radio lobes, and extragalactic jets). Significance of laboratory experiments, including a next generation reconnection experiment, is also discussed.