Turbulence and Particle Acceleration in Collisionless Magnetic Reconnection: Effects of Temperature Inhomogeneity across Pre-reconnection Current Sheet

Abstract

Magnetic reconnection is an important process in various collisionless plasma environments because it reconfigures the magnetic field and releases magnetic energy to accelerate charged particles. Its dynamics depend critically on the properties of the pre-reconnection current sheet. One property in particular, cross-sheet temperature inhomogeneity, which is ubiquitous throughout the heliosphere, has been shown to increase reconnection outflow speed, energy conversion efficiency, and secondary island formation rate using two-dimensional particle-in-cell simulations. Here we expand upon these findings, considering two cases with a long, thin current sheet, one with homogeneous temperature and one with inhomogeneous temperature across the current sheet. In the inhomogeneous temperature case, numerous secondary islands form continuously, which increases current sheet turbulence (well-developed cascade power spectra) at large wavenumbers. Current density, energy conversion, dissipation, and acceleration of high-energy particles are also enhanced relative to the homogenous temperature case. Our results suggest that inhomogeneous temperature profiles, which are realistic, need to be incorporated into studies of turbulence and particle acceleration in collisionless magnetic reconnection.

Particle‐In‐Cell Simulations of Electrostatic Solitary Waves in Asymmetric Magnetic Reconnection

“…(2019), Lu, Angelopoulos, et al. (2019) found that the strong temperature inhomogeneity in a current sheet further increases reconnection outflow speed, causing numerous secondary islands to be formed continuously at reconnection X‐lines. Secondary islands have also been observed by satellites in different regions (Wang et al., 2010, 2016).…”

Reconnection from a turbulence perspective

“…On the other hand, the role of turbulence associated with reconnection has received significant scrutiny. Reconnection is known to generate several secondary instabilities (e.g., 7,12,25,49 and references therein) which themselves have been shown to generate energy spectra with power laws consistent with a turbulent cascade 26,31,37 . Turbulent fluctuations in the plasma flowing into the reconnection region have been found to affect the process of reconnection 30 , and even amplify the reconnection rate 23 .…”

Magnetohydrodynamic With Embedded Particle‐In‐Cell Simulation of the Geospace Environment Modeling Dayside Kinetic Processes Challenge Event

“…The PSDs of the ideal‐MHD (orange lines) and Hall‐MHD (green lines) simulations are also plotted for comparison, and neither of them shows the −2.8 slope. The evolution of the small‐scale secondary magnetic islands is another mechanism that produces a power law spectrum (Lu et al, 2019). Since our simulation does not capture small‐scale reconnections in the magnetosheath (Phan et al, 2018) and the secondary islands along the magnetopause are not produced frequently, the PSDs in Figure 4 are not likely related to the secondary magnetic islands.…”