A Hard Energy Spectrum in 3D Guide-Field Magnetic Reconnection

TL;DR

This paper investigates 3D relativistic guide-field magnetic reconnection in pair plasmas, revealing that 3D effects help sustain a hard nonthermal energy spectrum even with strong guide fields, contrasting 2D results.

Contribution

It demonstrates through 3D PIC simulations that guide-field reconnection maintains a hard nonthermal spectrum, highlighting differences from 2D reconnection studies.

Findings

3D reconnection reduces nonthermal particle production less than 2D.

A hard nonthermal energy spectrum persists in 3D even with strong guide fields.

3D effects are crucial for understanding energy spectra in magnetic reconnection.

Abstract

Magnetic reconnection has long been known to be the most important mechanism not only for mixing the plasmas by changing the magnetic field topology but also for releasing the magnetic field energy into the plasma kinetic energy. During magnetic energy release, it is possible for some of the heated plasma to be accelerated to energies much higher than the thermal energy. Recently, the energy partitioning of the thermal and the nonthermal energy has been studied by using particle-in-cell (PIC) simulations, and it has been shown that the acceleration efficiency of nonthermal particles increases with increasing the plasma temperature, and the nonthermal energy density occupies more than 90% in the total heated plasma when the Alfven velocity is close to the speed of light c. However, the acceleration efficiency decreases as the guide magnetic field increases. So far the acceleration efficiency has been mainly studied in two-dimensional systems, but it is interesting to study three-dimensional effects where the patchy and turbulent reconnection can dynamically occur. This study explores the effects of three-dimensional relativistic reconnection on a pair plasma with the guide magnetic field, utilizing three-dimensional (3D) PIC simulations. The results indicate that the decrease in nonthermal particle production is smaller in 3D guide-field reconnection compared to 2D. More importantly, contrary to general expectation, 3D reconnection is capable of maintaining a hard nonthermal energy spectrum even in the presence of a strong guide magnetic field.