scholarly journals On the electron diffusion region in asymmetric reconnection with a guide magnetic field

2016 ◽  
Vol 43 (6) ◽  
pp. 2359-2364 ◽  
Author(s):  
Michael Hesse ◽  
Yi‐Hsin Liu ◽  
Li‐Jen Chen ◽  
Naoki Bessho ◽  
Masha Kuznetsova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Guide Magnetic Field

Micro-scale tearing mode turbulence in the diffusion region during macro-scale evolution of turbulent reconnection

2021 ◽  
Author(s):  
Takuma Nakamura ◽  
Hiroshi Hasegawa ◽  
Tai Phan ◽  
Kevin Genestreti ◽  
Richard Denton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Conversion ◽  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Efficient Energy ◽  
Micro Scale ◽  
Island Evolution ◽  
Macro Scale ◽  
Scale Evolution

<p>Magnetic reconnection is a key fundamental process in collisionless plasmas that explosively converts magnetic energy to plasma kinetic and thermal energies through a change of magnetic field topology in an electron-scale central region called the electron diffusion region. Past simulations and observations demonstrated that this process causes efficient energy conversion through the formation of multiple macro-scale or micro-scale magnetic islands/flux ropes. However, how these different spatiotemporal scale phenomena are coupled is still poorly understood. In this study, to investigate the turbulent evolution of magnetic reconnection, we perform a new large-scale fully kinetic simulation of a thin current sheet considering a power-law spectrum of initial fluctuations in the magnetic field as frequently observed in the Earth’s magnetotail. The simulation demonstrates that during a macro-scale evolution of turbulent reconnection, the merging of macro-scale islands results in reduction of the rate of reconnection as well as the aspect ratio of the electron diffusion region. This allows the repeated, quick formation of new electron-scale islands within the electron diffusion region, leading to an efficient energy cascade between macro- and micro-scales. The simulation also demonstrates that a strong electron acceleration/heating occurs during the micro-scale island evolution within the EDR. These new findings indicate the importance of non-steady features of the EDR to comprehensively understand the energy conversion and cascade processes in collisionless reconnection.</p>

In situ spacecraft observations of structured electron diffusion regions during magnetic reconnection

2020 ◽  
Author(s):  
Giulia Cozzani ◽  
Alessandro Retinò ◽  
Francesco Califano ◽  
Alexandra Alexandrova ◽  
Yuri Khotyaintsev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Energy Conversion ◽  
Magnetic Reconnection ◽  
Rapid Heating ◽  
Energy Transition ◽  
Field Measurements ◽  
Low Noise ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Point Analysis

<p>Magnetic reconnection is a fundamental energy conversion process in plasmas. It occurs in thin current sheets, where a change in the magnetic field topology leads to rapid heating of plasma, plasma bulk acceleration and acceleration of plasma particles. To allow for magnetic field reconfiguration, both ions and electrons must be demagnetized. The ion and electron demagnetization  take place in the ion and electron diffusion regions respectively, in both cases at kinetic scales. For the first time, Magnetospheric Multiscale (MMS) spacecraft observations, at inter-spacecraft separation comparable to the electron inertial length, allow for a multi-point analysis of the electron diffusion region (EDR). A key question is whether the EDR has a homogeneous or patchy structure. </p><p>Here we report MMS observations at the magnetopause providing evidence of inhomogeneous current densities and energy conversion over a few (∼ 3 d<sub>e</sub>) electron inertial lengths suggesting that the EDR can be structured at electron scales. In particular, the energy conversion is patchy and changing sign in the vicinity of the reconnection site implying that the EDR comprises regions where energy is transferred from the field to the plasma and regions with the opposite energy transition, which is unexpected during reconnection. The origin of the patchy energy conversion appears to be connected to the large v<sub>e,N</sub> ∼ v<sub>e,M</sub> directed from the magnetosphere to magnetosheath. These observations are consistent with recent high-resolution and low-noise kinetic simulations of asymmetric reconnection. Patchy energy conversion is observed also in an EDR at the magnetotail, where the inter-spacecraft separation was ∼ 1 d<sub>e</sub>. Electric field measurements are different among the spacecraft suggesting inhomogeneities at the electron scale. However, in this case the current density appear homogeneous in the EDR suggesting that the structuring may be sourced from a different kind of electron dynamics in the magnetotail.</p>

scholarly journals Identification of the Electron-Diffusion Region during Magnetic Reconnection in a Laboratory Plasma

2008 ◽  
Vol 101 (8) ◽  
Author(s):  
Yang Ren ◽  
Masaaki Yamada ◽  
Hantao Ji ◽  
Stefan P. Gerhardt ◽  
Russell Kulsrud
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Laboratory Plasma ◽  
Electron Diffusion

scholarly journals The influence of resistivity gradients on shock conditions for a Petschek reconnection geometry

2016 ◽  
Vol 34 (4) ◽  
pp. 421-425
Author(s):  
Christian Nabert ◽  
Karl-Heinz Glassmeier
Keyword(s):  
Magnetic Field ◽  
Necessary Conditions ◽  
The Other ◽  
Diffusion Region ◽  
Two Dimensional ◽  
Characteristic Velocity ◽  
Magnetohydrodynamic Equations ◽  
One Dimensional ◽  
The Magnetic Field ◽  
Alfven Velocity

Abstract. Shock waves can strongly influence magnetic reconnection as seen by the slow shocks attached to the diffusion region in Petschek reconnection. We derive necessary conditions for such shocks in a nonuniform resistive magnetohydrodynamic plasma and discuss them with respect to the slow shocks in Petschek reconnection. Expressions for the spatial variation of the velocity and the magnetic field are derived by rearranging terms of the resistive magnetohydrodynamic equations without solving them. These expressions contain removable singularities if the flow velocity of the plasma equals a certain characteristic velocity depending on the other flow quantities. Such a singularity can be related to the strong spatial variations across a shock. In contrast to the analysis of Rankine–Hugoniot relations, the investigation of these singularities allows us to take the finite resistivity into account. Starting from considering perpendicular shocks in a simplified one-dimensional geometry to introduce the approach, shock conditions for a more general two-dimensional situation are derived. Then the latter relations are limited to an incompressible plasma to consider the subcritical slow shocks of Petschek reconnection. A gradient of the resistivity significantly modifies the characteristic velocity of wave propagation. The corresponding relations show that a gradient of the resistivity can lower the characteristic Alfvén velocity to an effective Alfvén velocity. This can strongly impact the conditions for shocks in a Petschek reconnection geometry.

Reconstruction of the electron diffusion region

2016 ◽  
Vol 121 (5) ◽  
pp. 4279-4290 ◽  
Author(s):  
B. U. Ö. Sonnerup ◽  
H. Hasegawa ◽  
R. E. Denton ◽  
T. K. M. Nakamura
Keyword(s):  
Diffusion Region ◽  
Electron Diffusion
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