Processes setting the structure of the electron distribution function within the exhausts of anti-parallel reconnection

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

doi:10.1063/1.4972135

Cited by 13 publications

(23 citation statements)

References 29 publications

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“…(2015) and Egedal et al. (2016) both showed how those crescent distributions manifest themselves at higher and higher electron energies as an observer moves away from the EDR in the exhaust. Moving further from the EDR in the strengthening and lower‐curvature local B‐fields of the exhaust, electrons at higher energies remagnetize and experience betatron heating (Egedal et al., 2016); while such betatron heating should be stochastic in gyrophase, it is also proportional to electrons' initial energy and thus of potentially important significance for electrons at these relativistic energies.…”

Section: Discussionmentioning

confidence: 96%

“…we know was the case here for the energetic electrons in question. In such reconnecting field topologies, the resulting meandering electron distributions are expected to exhibit complex yet coherent structures (e.g., "triangles" or "crescents") in the electron distributions within the exhaust immediately adjacent to an active EDR (e.g., Shuster et al, 2015;Egedal et al, 2016;Chen et al, 2016). Such distributions have also been observed in the lower-energy electron distributions within and adjacent to EDRs (e.g., Burch (Egedal et al, 2016); while such betatron heating should be stochastic in gyrophase, it is also proportional to electrons' initial energy and thus of potentially important significance for electrons at these relativistic energies.…”

Section: Accepted Articlementioning

confidence: 99%

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Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Tracers of a Complex Magnetic Topology and Evidence of Localized Acceleration

Turner

Cohen

Bingham

et al. 2021

Geophysical Research Letters

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Magnetic reconnection is a fundamental physical process affecting plasmas from laboratory experiments to astrophysical environments (Hesse & Cassak, 2020; Zweibel & Yamada, 2009). Reconnection involves the explosive reconfiguration of magnetic field topologies, in which two previously unconnected field lines break apart and reconnect to each other. The reconnection itself takes place at very small scales, corresponding to thermal electron kinetic scales (e.g., several to ∼10 s of km in Earth's magnetosphere [Burch & Phan, 2016]), in a location referred to as the electron diffusion region (EDR) that lies at the intersection of an "X-line" in the magnetic topology (by "topology" we mean an instantaneous snapshot of the time-varying, 3-dimensional spatial configuration of magnetic field-lines). During reconnection, which is an energy conversion process in plasma physics, energy stored in the magnetic field is transferred to the particles in the plasma. That energy transfer results in kinetic motion manifested as outflow jets from the reconnection site, plasma heating, and acceleration of suprathermal energetic particles. The electron-scale physics and microscopic nature of reconnection have recently been illuminated in unprecedented detail by NASA'

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Section: Discussionmentioning

confidence: 96%

Section: Accepted Articlementioning

confidence: 99%

Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Tracers of a Complex Magnetic Topology and Evidence of Localized Acceleration

Turner

Cohen

Bingham

et al. 2021

Geophysical Research Letters

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“…Remagnetization causes pitch angle mixing of accelerated particles, 55 gyrotropization, and heating due to betatron effect. 19,55 The remagnetization jet is likely formed by accelerated meandering particles superimposed on a population of inflowing electrons that follow noncrossing Speiser orbits which dominate outside the inner and outer EDRs. 54 The substructures within the full electron demagnetization region continue to evolve after t ¼ 21.768 ( Fig.…”

Section: Edr Structure and Length Measuresmentioning

confidence: 99%

Inner and outer electron diffusion region of antiparallel collisionless reconnection: Density dependence

et al. 2019

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We study inflow density dependence of substructures within electron diffusion region (EDR) of collisionless symmetric magnetic reconnection. We perform a set of 2.5D particle-in-cell simulations which start from a Harris current layer with a uniform background density n b. A scan of n b ranging from 0:02 n 0 to 2 n 0 of the peak current layer density (n 0) is studied keeping other plasma parameters the same. Various quantities measuring reconnection rate, EDR spatial scales, and characteristic velocities are introduced. We analyze EDR properties during quasisteady stage when the EDR length measures saturate. Consistent with past kinetic simulations, electrons are heated parallel to the B field in the inflow region. The presence of the strong parallel anisotropy acts twofold: (1) electron pressure anisotropy drift gets important at the EDR upstream edge in addition to the E Â B drift speed and (2) the pressure anisotropy term Àr Á P ðeÞ =ðneÞ modifies the force balance there. We find that the width of the EDR demagnetization region and EDR current are proportional to the electron inertial length $d e and $d e n 0:22 b , respectively. Magnetic reconnection is fast with a rate of $0:1 but depends weakly on density as $n À1=8 b. Such reconnection rate proxies as EDR geometrical aspect or the inflow-to-outflow electron velocity ratio are shown to have different density trends, making electric field the only reliable measure of the reconnection rate.

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“…Ring-beam EVDFs satisfy the condition ∂ f /∂ v ⊥ > 0. Fully filled ring beam distributions have indeed been obtained by kinetic magnetic reconnection simulations 47,48 . In observations, however, partially filled rings were more often to be found, which is called perpendicular crescent-shaped EVDFs or electron crescents.…”

Section: Introductionmentioning

confidence: 86%

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

Yao¹,

Muñoz²,

Büchner³

2021

Preprint

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<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&#215;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>

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Processes setting the structure of the electron distribution function within the exhausts of anti-parallel reconnection

Cited by 13 publications

References 29 publications

Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Tracers of a Complex Magnetic Topology and Evidence of Localized Acceleration

Characteristics of Energetic Electrons Near Active Magnetotail Reconnection Sites: Tracers of a Complex Magnetic Topology and Evidence of Localized Acceleration

Inner and outer electron diffusion region of antiparallel collisionless reconnection: Density dependence

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

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