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>

scholarly journals Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space

Science ◽  
2018 ◽  
Vol 362 (6421) ◽  
pp. 1391-1395 ◽  
Author(s):  
R. B. Torbert ◽  
J. L. Burch ◽  
T. D. Phan ◽  
M. Hesse ◽  
M. R. Argall ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Magnetospheric Multiscale ◽  
Energy Conversion Process ◽  
Spatial Dimensions ◽  
Reconnection Site ◽  
Plasma Measurements ◽  
Inflow Conditions ◽  
Fast Reconnection

Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth’s magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth’s magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.

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>

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 Bursty emission of whistler waves in association with plasmoid collision

2017 ◽  
Vol 35 (4) ◽  
pp. 885-892 ◽  
Author(s):  
Keizo Fujimoto
Keyword(s):  
Magnetic Field ◽  
Electron Temperature ◽  
Magnetic Reconnection ◽  
High Energy ◽  
Temperature Anisotropy ◽  
Whistler Waves ◽  
High Energy Electrons ◽  
Parallel Direction ◽  
Short Time ◽  
Particle Energization

Abstract. A new mechanism to generate whistler waves in the course of collisionless magnetic reconnection is proposed. It is found that intense whistler emissions occur in association with plasmoid collisions. The key processes are strong perpendicular heating of the electrons through a secondary magnetic reconnection during plasmoid collision and the subsequent compression of the ambient magnetic field, leading to whistler instability due to the electron temperature anisotropy. The emissions have a bursty nature, completing in a short time within the ion timescales, as has often been observed in the Earth's magnetosphere. The whistler waves can accelerate the electrons in the parallel direction, contributing to the generation of high-energy electrons. The present study suggests that the bursty emission of whistler waves could be an indicator of plasmoid collisions and the associated particle energization during collisionless magnetic reconnection.

scholarly journals First Resolved Observations of the Demagnetized Electron-Diffusion Region of an Astrophysical Magnetic-Reconnection Site

2012 ◽  
Vol 108 (22) ◽  
Author(s):  
J. D. Scudder ◽  
R. D. Holdaway ◽  
W. S. Daughton ◽  
H. Karimabadi ◽  
V. Roytershteyn ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Diffusion Region ◽  
Electron Diffusion ◽  
Reconnection Site

scholarly journals Electron pitch angle distribution during magnetic reconnection diffusion region observations in the Earth's magnetotail

2012 ◽  
Vol 30 (1) ◽  
pp. 109-117 ◽  
Author(s):  
A. L. Borg ◽  
M. G. G. T. Taylor ◽  
J. P. Eastwood
Keyword(s):  
Magnetic Reconnection ◽  
Electron Flux ◽  
Diffusion Region ◽  
Angle Distribution ◽  
Ion Diffusion ◽  
Electron Field ◽  
Outflow Region ◽  
The Magnetic Field ◽  
Case Basis ◽  
Magnetotail Current Sheet

Abstract. The Earth's magnetosphere provides an excellent laboratory for magnetic reconnection research. In particular, the magnetotail current sheet that is formed between the interface of the similar Northern and Southern Hemispheres of the magnetotail provides a relatively stable symmetric reconnection configuration that can be used to study basic aspects of the reconnection process. Of particular importance is the manner in which electrons are processed by the reconnection. Simulations and satellite data analyses of the ion diffusion region have suggested that the fluxes of electrons in the inflow regions of reconnection are greater in the directions parallel and anti-parallel to the magnetic field (field-aligned) whereas the electron flux in the outflow region is distributed more isotropically. However, this has only been studied experimentally on a case-by-case basis. In this paper, we investigate this claim by analyzing the degree of bulk electron field alignment in the outflow and inflow regions during encounters of the magnetic reconnection ion diffusion region by the Cluster spacecraft in the years 2001–2006. We demonstrate that while the median electron flux in the inflow region is indeed more field aligned than in the outflow region during some ion diffusion region encounters, the variation of the signature across events is so large that it cannot be said to be a general feature of magnetic reconnection in the Earth's magnetotail.

scholarly journals A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet

2009 ◽  
Vol 27 (1) ◽  
pp. 395-405 ◽  
Author(s):  
K. G. Tanaka ◽  
K. Haijima ◽  
M. Fujimoto ◽  
I. Shinohara
Keyword(s):  
Electron Temperature ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Time Scale ◽  
Large Scale ◽  
Saturation Level ◽  
Small Island ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
A Current

Abstract. How to trigger magnetic reconnection is one of the most interesting and important problems in space plasma physics. Recently, electron temperature anisotropy (αeo=Te⊥/Te||) at the center of a current sheet and non-local effect of the lower-hybrid drift instability (LHDI) that develops at the current sheet edges have attracted attention in this context. In addition to these effects, here we also study the effects of ion temperature anisotropy (αio=Ti⊥/Ti||). Electron anisotropy effects are known to be helpless in a current sheet whose thickness is of ion-scale. In this range of current sheet thickness, the LHDI effects are shown to weaken substantially with a small increase in thickness and the obtained saturation level is too low for a large-scale reconnection to be achieved. Then we investigate whether introduction of electron and ion temperature anisotropies in the initial stage would couple with the LHDI effects to revive quick triggering of large-scale reconnection in a super-ion-scale current sheet. The results are as follows. (1) The initial electron temperature anisotropy is consumed very quickly when a number of minuscule magnetic islands (each lateral length is 1.5~3 times the ion inertial length) form. These minuscule islands do not coalesce into a large-scale island to enable large-scale reconnection. (2) The subsequent LHDI effects disturb the current sheet filled with the small islands. This makes the triggering time scale to be accelerated substantially but does not enhance the saturation level of reconnected flux. (3) When the ion temperature anisotropy is added, it survives through the small island formation stage and makes even quicker triggering to happen when the LHDI effects set-in. Furthermore the saturation level is seen to be elevated by a factor of ~2 and large-scale reconnection is achieved only in this case. Comparison with two-dimensional simulations that exclude the LHDI effects confirms that the saturation level enhancement is due to the ion anisotropy effects, while the LHDI effects shorten the overall time scale significantly. The results imply that the ion temperature anisotropy is one of the key properties that enable large-scale magnetic reconnection to develop in a super-ion-scale current sheet.

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
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