A recent satellite observation has revealed the presence of energy conversion in the separatrix region (SR) of magnetotail reconnection, driven by perpendicular components. We investigated this phenomenon by means of particle-in-cell simulations in two-dimensional (2D) and three-dimensional (3D) systems. Our result indicates that in the 2D simulation, energy conversion in the SR is dominated by parallel components, with the main influencing factor being the parallel electric field, which is not consistent with the observation. However, a case that is similar to the observation is found in the 3D simulation, suggesting that the observation result may be attributed to the 3D characteristics. Our findings provide a potential explanation for the satellite observation. ©2024 by Earth and Planetary Physics.

Most of the plasma fluid equations have employed the electrical resistivity to generate the magnetic dissipation required for magnetic reconnection to occur in collisionless plasma. However, there has been no clear evidence that such a model is indeed appropriate in the reconnection diffusion region in terms of the kinetic physics. The present study demonstrates that, using a large-scale 3D kinetic simulation and analytical analysis, the spatial distribution of the non-ideal electric field is consistent with the dissipation due to the viscosity rather than the resistivity, when electromagnetic (EM) turbulence is dominant in the electron diffusion region (EDR). The effective viscosity is caused by the EM turbulence that is driven by the flow shear instabilities leading to the electron momentum transport across the EDR. The result suggests a fundamental modification of the fluid equations using the resistivity in the Ohm's law. In contrast, for the 2D current sheet without significant turbulence activity, the non-ideal field profile does not obey the simple form based on the viscosity, so that further investigation is needed for a better description.

Magnetic reconnection is a natural energy converter that can have a significant impact on global processes in space, astrophysics, and fusion plasmas. Macroscopic modeling of reconnection is crucial in understanding the global responses to local kinetic processes. The key issue in developing the reconnection model is the description of the magnetic dissipation around the x-line to drive reconnection. In collisionless plasma, the dissipation can be generated by plasma turbulence through wave-particle interactions. However, the mechanisms to yield turbulence and dissipation in the reconnection current layer are currently poorly understood. In this study, we show, using three-dimensional particle-in-cell simulations, that the electron Kelvin-Helmholtz instability plays a primary role in driving intense electromagnetic turbulence leading to the dissipation and electron heating. We find that the ions hardly react to the turbulence, which indicates that the turbulence does not cause significant momentum exchange between electrons and ions resulting in electrical resistivity. It is demonstrated that the dissipation is mainly caused by viscosity associated with electron momentum transport across the current layer. The present results suggest a fundamental modification of the current magnetohydrodynamics models using the resistivity to generate the dissipation.

The Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

Using the K computer,we have performed plasma particle-in-cell simulations of 3D magnetic reconnection with the world’s largest scale,and have investigated plasma turbulence arising in the vicinity of the magnetic neutral line and its impact on the reconnection process.We found that the turbulence intensity and the power of the power spectrum density depend strongly on the computational domain size.This is because the larger domain size yields additional unstable modes with longer wavelength,leading to the change in the driving mechanism of turbulence.In accordance with plasma turbulence,the magnetic diffusion is enhanced,so that the current sheet is broaden.However,it is found that,contrary to the previous theory,the width does not increase beyond an upper limit and remains the electron-scale size.