Anisotropic Electron Fluid Closure Validated by in Situ Spacecraft Observations in the far Exhaust of Guide‐field Reconnection

Wetherton, Blake; Egedal, J.; Lê, A.; Daughton, W.

doi:10.1029/2020ja028604

Cited by 7 publications

(5 citation statements)

References 45 publications

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“…Thus this Φ ‖ is different with the acceleration potential derived from an analytical model on the electron anisotropy (Egedal et al, 2013;Le et al, 2009), which is present over large spatial scales in reconnection. This potential can effectively accelerate electrons along separatrices (Norgren et al, 2020) and modify the plasma density structures in guide-field reconnection (Wetherton et al, 2021). The relation between these two parallel potentials should be explored in the future.…”

Section: Discussion and Summarymentioning

confidence: 99%

Electron Dynamics in the Electron Current Sheet During Strong Guide‐Field Reconnection

Wang

Tang

et al. 2023

Geophysical Research Letters

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Magnetic reconnection is a fundamental process with explosive energy conversion from magnetic fields to plasmas and rapid reconfiguration of magnetic field lines. In general, the reconnecting magnetic fields do not have to be antiparallel, and an additional magnetic component known as the guide field (B g ) can appear in the direction perpendicular to the reconnecting plane. With the increase of B g , the guide field can gradually magnetize electrons in the central diffusion region (e.g., Le et al., 2013), resulting into the transition from antiparallel to guide-field reconnection (Swisdak et al., 2005). In guide-field reconnection, B g can cause the diamagnetic drift of the X-line, which may eventually suppress reconnection (e.g., Phan et al., 2013;Swisdak et al., 2003). The reconnection current sheet is deflected by the J L × B g force (J L is the current along the reconnecting direction, Goldman et al., 2011;Tang et al., 2022), and the Hall field structure is accordingly distorted (Eastwood et al., 2010). The reconnection electric field becomes parallel to the guide field in the vicinity of the X-line, which leads to the shift of the local energy conversion location to the magnetic field reversal points (Genestreti et al., 2017) and the significance of parallel energy dissipation (Wilder et al., 2018). In addition, this parallel electric field (E ‖ ) can accelerate electrons from one direction, and decelerate electrons from the other direction, forming a density cavity on one edge of the exhaust (Eastwood et al., 2018) and electron beams that are unstable for electron beamtype instabilities (e.g.,

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Section: Discussion and Summarymentioning

confidence: 99%

Electron Dynamics in the Electron Current Sheet During Strong Guide‐Field Reconnection

Wang

Tang

et al. 2023

Geophysical Research Letters

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“…( 2016 ) and Wetherton et al. ( 2021 ). We examine the electron distribution functions to understand the possible energization processes that worked on the electrons.…”

Section: Energization Of Electrons Associated With Flux Ropes and X‐l...mentioning

confidence: 96%

“…The full evolution of the electric and magnetic fields of the reconnection X-lines and flux ropes is impossible to obtain for our case. However, since particles were accelerated/interacted with the electric and magnetic fields, we may be able to 10 derive some information from the measured particles' distributions, similar to the analysis in Egedal et al (2016) and Wetherton et al (2021). We examine the electron distribution functions to understand the possible energization processes that worked on the electrons.…”

Section: Electron Distribution Functions and Parallel Electric Potentialmentioning

confidence: 99%

Properties and Acceleration Mechanisms of Electrons Up To 200 keV Associated With a Flux Rope Pair and Reconnection X‐Lines Around It in Earth's Plasma Sheet

et al. 2022

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The properties and acceleration mechanisms of electrons (<200 keV) associated with a pair of tailward traveling flux ropes and accompanied reconnection X‐lines in Earth's plasma sheet are investigated with MMS measurements. Energetic electrons are enhanced on both boundaries and core of the flux ropes. The power‐law spectra of energetic electrons near the X‐lines and in flux ropes are harder than those on flux rope boundaries. Theoretical calculations show that the highest energy of adiabatic electrons is a few keV around the X‐lines, tens of keV immediately downstream of the X‐lines, hundreds of keV on the flux rope boundaries, and a few MeV in the flux rope cores. The X‐lines cause strong energy dissipation, which may generate the energetic electron beams around them. The enhanced electron parallel temperature can be caused by the curvature‐driven Fermi acceleration and the parallel electric potential. Betatron acceleration due to the magnetic field compression is strong on flux rope boundaries, which enhances energetic electrons in the perpendicular direction. Electrons can be trapped between the flux rope pair due to mirror force and parallel electric potential. Electrostatic structures in the flux rope cores correspond to potential drops up to half of the electron temperature. The energetic electrons and the electron distribution functions in the flux rope cores are suggested to be transported from other dawn‐dusk directions, which is a 3‐dimensional effect. The acceleration and deceleration of the Betatron and Fermi processes appear alternately indicating that the magnetic field and plasma are turbulent around the flux ropes.

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“…Over the next decade, a major goal should be understanding how the basic mechanisms of particle energization scale up to large systems, particularly in low-β plasmas. Kinetic-scale simulations 238 and magnetospheric observations 215,239 found temperature changes ∆T of each component of the plasma during reconnection scale with the available upstream magnetic energy per particle ∆T ∝ B 2 /2µ 0 n, suggesting there are large fractional temperature changes in low-β plasmas. Similarly, simulation studies find the most significant acceleration of nonthermal particles in low-β regimes 156 .…”

Section: /35mentioning

confidence: 99%

Magnetic reconnection in the era of exascale computing and multiscale experiments

Ji,

Daughton,

Jara-Almonte

et al. 2022

Preprint

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Astrophysical plasmas have the remarkable ability to preserve magnetic topology, which inevitably gives rise to the accumulation of magnetic energy within stressed regions including current sheets. This stored energy is often released explosively through the process of magnetic reconnection, which produces a reconfiguration of the magnetic field, along with high-speed flows, thermal heating, and nonthermal particle acceleration. Either collisional or kinetic dissipation mechanisms are required to overcome the topological constraints, both of which have been predicted by theory and validated with in situ spacecraft observations or laboratory experiments. However, major challenges remain in understanding magnetic reconnection in large systems, such as the solar corona, where the collisionality is weak and the kinetic scales are vanishingly small in comparison to macroscopic scales. The plasmoid instability or formation of multiple plasmoids in long reconnecting current sheets is one possible multiscale solution for bridging this vast range of scales, and new laboratory experiments are poised to study these regimes. In conjunction with these efforts, we anticipate that the coming era of exascale computing, together with the next generation of observational capabilities, will enable new progress on a range of challenging problems, including the energy build-up and onset of reconnection, partially ionized regimes, the influence of magnetic turbulence, and particle acceleration.Website summary: Magnetic reconnection explosively releases stored magnetic energy in astrophysical plasmas. Thanks to advances in observations, exascale computing and multiscale experiments, it will be possible to solve outstanding physics problems, including the immense separation between global and dissipation scales, reconnection onset, and particle acceleration.

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Anisotropic Electron Fluid Closure Validated by in Situ Spacecraft Observations in the far Exhaust of Guide‐field Reconnection

Cited by 7 publications

References 45 publications

Electron Dynamics in the Electron Current Sheet During Strong Guide‐Field Reconnection

Electron Dynamics in the Electron Current Sheet During Strong Guide‐Field Reconnection

Properties and Acceleration Mechanisms of Electrons Up To 200 keV Associated With a Flux Rope Pair and Reconnection X‐Lines Around It in Earth's Plasma Sheet

Magnetic reconnection in the era of exascale computing and multiscale experiments

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