405 research outputs found
Spacecraft Observations And Analytic Theory Of Crescent-Shaped Electron Distributions In Asymmetric Magnetic Reconnection
Supported by a kinetic simulation, we derive an exclusion energy parameter providing a lower kinetic energy bound for an electron to cross from one inflow region to the other during magnetic reconnection. As by a Maxwell Demon, only high energy electrons are permitted to cross the inner reconnection region, setting the electron distribution function observed along the low density side separatrix during asymmetric reconnection. The analytic model accounts for the two distinct flavors of crescent-shaped electron distributions observed by spacecraft in a thin boundary layer along the low density separatrix. Egedal, J; Le, A; Daughton, W; Wetherton, B; Cassak, P A; Chen, L -J; Lavraud, B; Trobert, R B; Dorelli, J; Gershman, D J; Avanov, L
The Force Balance of Electrons During Kinetic Anti-parallel Magnetic Reconnection
Fully kinetic simulations are applied to the study of 2D anti-parallel
reconnection, elucidating the dynamics by which the electron fluid maintains
force balance within both the electron diffusion region (EDR) and the ion
diffusion region (IDR). Inside the IDR, magnetic field-aligned electron
pressure anisotropy ( develops upstream of the
EDR. Compared to previous investigations, the use of modern computer facilities
allows for simulations at the natural proton to electron mass ratio
. In this high--limit the electron dynamics changes
qualitatively, as the electron inflow to the EDR is enhanced and mainly driven
by the anisotropic pressure. Using a coordinate system with the -direction
aligned with the reconnecting magnetic field and the -direction aligned with
the central current layer, it is well-known that for the much studied 2D
laminar anti-parallel and symmetric scenario the reconnection electric field at
the -line must be balanced by the and
off-diagonal electron pressure stress
components. We find that the electron anisotropy upstream of the EDR imposes
large values of within the EDR, and along the
direction of the reconnection -line this stress cancels with the stress of a
previously determined theoretical form for . The
electron frozen-in law is instead broken by pressure tensor gradients related
to the direct heating of the electrons by the reconnection electric field. The
reconnection rate is free to adjust to the value imposed externally by the
plasma dynamics at larger scales.Comment: Submitted to Physics of Plasmas, 11 October 202
Influence of the Lower Hybrid Drift Instability on the onset of Magnetic Reconnection
Two-dimensional and three-dimensional kinetic simulation results reveal the
importance of the Lower-Hybrid Drift Instability LHDI to the onset of magnetic
reconnection. Both explicit and implicit kinetic simulations show that the LHDI
heats electrons anisotropically and increases the peak current density. Linear
theory predicts these modifications can increase the growth rate of the tearing
instability by almost two orders of magnitude and shift the fastest growing
modes to significantly shorter wavelengths. These predictions are confirmed by
nonlinear kinetic simulations in which the growth and coalescence of small
scale magnetic islands leads to a rapid onset of large scale reconnection
Spacecraft observations and analytic theory of crescent-shaped electron distributions in asymmetric magnetic reconnection
Supported by a kinetic simulation, we derive an exclusion energy parameter
providing a lower kinetic energy bound for an electron to cross
from one inflow region to the other during magnetic reconnection. As by a
Maxwell Demon, only high energy electrons are permitted to cross the inner
reconnection region, setting the electron distribution function observed along
the low density side separatrix during asymmetric reconnection. The analytic
model accounts for the two distinct flavors of crescent-shaped electron
distributions observed by spacecraft in a thin boundary layer along the low
density separatrix.Comment: 6 pages, 3 figure
2D Reconstruction of Magnetotail Electron Diffusion Region Measured by MMS
Models for collisionless magnetic reconnection in near-Earth space are distinctly characterized as 2D or 3D. In 2D kinetic models, the frozen-in law for the electron fluid is usually broken by laminar dynamics involving structures set by the electron orbit size, while in 3D models the width of the electron diffusion region is broadened by turbulent effects. We present an analysis of in situ spacecraft observations from the Earth's magnetotail of a fortuitous encounter with an active reconnection region, mapping the observations onto a 2D spatial domain. While the event likely was perturbed by low-frequency 3D dynamics, the structure of the electron diffusion region remains consistent with results from a 2D kinetic simulation. As such, the event represents a unique validation of 2D kinetic, and laminar reconnection models.Peer reviewe
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