scholarly journals Localized and Intense Energy Conversion in the Diffusion Region of Asymmetric Magnetic Reconnection

2018 ◽  
Vol 45 (11) ◽  
pp. 5260-5267 ◽  
Author(s):  
M. Swisdak ◽  
J. F. Drake ◽  
L. Price ◽  
J. L. Burch ◽  
P. A. Cassak ◽  
...  
Keyword(s):  
Energy Conversion ◽  
Magnetic Reconnection ◽  
Diffusion Region

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>

MMS observations of electron firehose fluctuations in the magnetic reconnection outflow

2021 ◽  
Author(s):  
Giulia Cozzani ◽  
Yuri Khotyaintsev ◽  
Daniel Graham ◽  
Mats André
Keyword(s):  
Energy Conversion ◽  
Electron Temperature ◽  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Temperature Anisotropy ◽  
Plasma Dynamics ◽  
Background Magnetic Field ◽  
Outflow Region ◽  
Reconnection Site

<p>Plasma waves and instabilities driven by temperature anisotropies are known to play a significant role in plasma dynamics, scattering the particles and affecting particle heating and energy conversion between the electromagnetic fields and the particles. Among these instabilities, the electron firehose instability is driven by electron temperature anisotropy T<sub>e,</sub> > T<sub>e,perp</sub> (with respect to the background magnetic field) and produce nonpropagating oblique modes. </p><p>Magnetic reconnection is characterized by regions of enhanced temperature anisotropy that could drive instabilities - including the electron firehose instability - affecting the particle dynamics and the energy conversion of the process. Yet, the electron firehose instability and its role in the reconnection process is still rather unexplored, especially with in situ measurements. </p><p>We report MMS observations of electron firehose fluctuations observed in the exhaust region of a reconnection site in the magnetotail. The fluctuations are observed in the Earthward outflow relatively close (less than 2 d<sub>i</sub> distance) to the electron diffusion region (EDR). While the characteristics of the fluctuations are compatible with oblique electron firehose fluctuations, the associated firehose instability threshold is not exceeded in the interval where the fluctuations are observed. However, the threshold is exceeded in the EDR. The wave analysis in the EDR suggests that the firehose instability could be active at the reconnection site. We suggest that the firehose fluctuations observed in the outflow region may have been originated at the EDR, where the electron temperature anisotropy exceeds the threshold values, and then advected in the outflow region.</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

Formation of non-thermal electron velocity distribution functions in kinetic magnetic reconnection

2021 ◽  
Author(s):  
Xin Yao ◽  
Patricio A. Muñoz ◽  
Jörg Büchner
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Field Strength ◽  
Magnetic Reconnection ◽  
Electron Beams ◽  
Distribution Functions ◽  
Electron Velocity ◽  
Diffusion Region ◽  
Electron Velocity Distribution ◽  
Velocity Distribution Functions

<div> <div>Magnetic reconnection can convert magnetic energy into non-thermal particle energy in the form of electron beams. Those accelerated electrons can, in turn, cause radio emission in environments such as solar flares. The actual properties of those electron velocity distribution functions (EVDFs) generated by reconnection are still not well understood. In particular the properties that are relevant for the micro-instabilities responsible for radio emission. We aim thus at characterizing the electron distributions functions generated by 3D magnetic reconnection by means of fully kinetic particle-in-cell (PIC) code simulations. Our goal is to characterize the possible sources of free energy of the generated EVDFs in dependence on an external (guide) magnetic field strength. We find that: (1) electron beams with positive gradients in their parallel (to the local magnetic field direction) distribution functions are observed in both diffusion region (parallel crescent-shaped EVDFs) and separatrices (bump-on-tail EVDFs). These non-thermal EVDFs cause counterstreaming and bump-on-tail instabilities. These electrons are adiabatic and preferentially accelerated by a parallel electric field in regions where the magnetic moment is conserved. (2) electron beams with positive gradients in their perpendicular distribution functions are observed in regions with weak magnetic field strength near the current sheet midplane. The characteristic crescent-shaped EVDFs (in perpendicular velocity space) are observed in the diffusion region. These non-thermal EVDFs can cause electron cyclotron maser instabilities. These non-thermal electrons in perpendicular velocity space are mainly non-adiabatic. Their EVDFs are attributed to electrons experiencing an E×B drift and meandering motion. (3) As the guide field strength increases, the number of locations in the current sheet with distributions functions featuring a perpendicular source of free energy significantly decreases.</div> </div>

scholarly journals ViDA: a Vlasov–DArwin solver for plasma physics at electron scales

2019 ◽  
Vol 85 (5) ◽  
Author(s):  
Oreste Pezzi ◽  
Giulia Cozzani ◽  
Francesco Califano ◽  
Francesco Valentini ◽  
Massimiliano Guarrasi ◽  
...  
Keyword(s):  
Plasma Physics ◽  
Magnetic Reconnection ◽  
Spatial Scales ◽  
Collisionless Plasma ◽  
Low Noise ◽  
Numerical Code ◽  
Small Scale ◽  
Diffusion Region ◽  
Plasma Dynamics ◽  
Algorithm Efficiency

We present a Vlasov–DArwin numerical code (ViDA) specifically designed to address plasma physics problems, where small-scale high accuracy is requested even during the nonlinear regime to guarantee a clean description of the plasma dynamics at fine spatial scales. The algorithm provides a low-noise description of proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov equation in phase space. Maxwell equations for the electric and magnetic fields are reorganized according to the Darwin approximation to remove light waves. Several numerical tests show that ViDA successfully reproduces the propagation of linear and nonlinear waves and captures the physics of magnetic reconnection. We also discuss preliminary tests of the parallelization algorithm efficiency, performed at CINECA on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations of a non-relativistic fully kinetic collisionless plasma and it is expected to provide relevant insights into important problems of plasma astrophysics such as, for instance, the development of the turbulent cascade at electron scales and the structure and dynamics of electron-scale magnetic reconnection, such as the electron diffusion region.

scholarly journals Spatial dimensions of the electron diffusion region in anti-parallel magnetic reconnection

2016 ◽  
Vol 34 (3) ◽  
pp. 357-367 ◽  
Author(s):  
Takuma Nakamura ◽  
Rumi Nakamura ◽  
Hiroshi Haseagwa
Keyword(s):  
Electric Field ◽  
Magnetic Reconnection ◽  
Real Space ◽  
Diffusion Region ◽  
Electron Mass ◽  
Plasma Parameters ◽  
Electron Diffusion ◽  
Background Density ◽  
Spatial Dimensions ◽  
Inner Region

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.

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