Abstract
Abstract. Spatial dimensions of the detailed structures of the electron diffusion region in anti-parallel magnetic reconnection were analyzed based on two-dimensional fully kinetic particle-in-cell simulations. The electron diffusion region in this study is defined as the region where the positive reconnection electric field is sustained by the electron inertial and non-gyrotropic pressure components. Past kinetic studies demonstrated that the dimensions of the whole electron diffusion region and the inner non-gyrotropic region are scaled by the electron inertial length de and the width of the electron meandering motion, respectively. In this study, we successfully obtained more precise scalings of the dimensions of these two regions than the previous studies by performing simulations with sufficiently small grid spacing (1∕16–1∕8 de) and a sufficient number of particles (800 particles cell−1 on average) under different conditions changing the ion-to-electron mass ratio, the background density and the electron βe (temperature). The obtained scalings are adequately supported by some theories considering spatial variations of field and plasma parameters within the diffusion region. In the reconnection inflow direction, the dimensions of both regions are proportional to de based on the background density. Both dimensions also depend on βe based on the background values, but the dependence in the inner region ( ∼ 0.375th power) is larger than the whole region (0.125th power) reflecting the orbits of meandering and accelerated electrons within the inner region. In the outflow direction, almost only the non-gyrotropic component sustains the positive reconnection electric field. The dimension of this single-scale diffusion region is proportional to the ion-electron hybrid inertial length (dide)1∕2 based on the background density and weakly depends on the background βe with the 0.25th power. These firm scalings allow us to predict observable dimensions in real space which are indeed in reasonable agreement with past in situ spacecraft observations in the Earth's magnetotail and have important implications for future observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.
Highlights
Magnetic reconnection is one of the most important energy transfer processes in space and laboratory plasmas, which converts magnetic energy to kinetic energy by changing the magnetic field topology (e.g., Birn and Priest, 2007; Yamada et al, 2010; Paschmann et al, 2013; Treumann and Baumjohann, 2015)
The topology change in the reconnection process takes place in a small-scale region called the diffusion region where plasmas are decoupled from the magnetic field
The initial parameters are similar to the ones employed in the Geospace Environmental Modeling (GEM) magnetic reconnection challenge (Birn et al, 2001; Pritchett, 2001)
Summary
Magnetic reconnection is one of the most important energy transfer processes in space and laboratory plasmas, which converts magnetic energy to kinetic energy by changing the magnetic field topology (e.g., Birn and Priest, 2007; Yamada et al, 2010; Paschmann et al, 2013; Treumann and Baumjohann, 2015). Kinetic simulations further demonstrated that near the center of the diffusion region (the reconnection X-point), EyEI is negligible and instead the non-gyrotropic term EyNG is dominant (e.g., Hesse and Winske, 1998; Pritchett, 2001) This non-gyrotropic pressure component is known to result from the electron meandering motion whose width can be described by a hybrid of the electron gyroradius and the magnetic field gradient scale (ρeLB )1/2 (e.g., Horiuchi and Sato, 1994; Kuznetsova et al, 1998; Hesse et al, 1999; Dorfman et al, 2008). We performed a series of fully kinetic particle-in-cell simulations changing the ion-to-electron mass ratio, the background plasma density and the electron temperature to measure the spatial dimensions of the whole diffusion region and the inner non-gyrotropic region under different conditions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
