Particle description of the electron diffusion region in collisionless magnetic reconnection

The present study clarifies the dissipation mechanism of collisionless magnetic reconnection in two-dimensional system based on particle dynamics. The electrons are accelerated without thermalization in the electron diffusion region, carry out the meandering oscillation, and are ejected away from the X-line. This electron behavior not only generates the electron inertia resistivity based on the particle description, but also it can be the origin of the electron viscosity resulting in the off-diagonal pressure tensor term in the generalized Ohm's law near the X-line. We derive an analytical profile for the electron pressure tensor term and confirm that the profile is consistent with the particle-in-cell simulation. The present results demonstrate that the magnetic dissipation due to the electron viscosity in the fluid picture is equivalent to that due to the inertia resistivity in the particle description. It is also suggested that the width of the electron current sheet is on the order of the electron inertia length in the case without electron scattering and thermalization, while it is expected that the width is broadened if the electron scattering occurs in the current sheet.