The Spin-Plane Double Probe Electric Field Instrument for MMS

Hesse

et al. 2019

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Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.14–0.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the X‐line region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozen‐in condition.

Section: Mms Datamentioning

confidence: 99%

Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields

Chen

Hesse

et al. 2019

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“…The magnetic field is sampled at 128/s (Russell et al, 2016), and the electric field is sampled at 8192/s Lindqvist et al, 2016). The magnetic field is sampled at 128/s (Russell et al, 2016), and the electric field is sampled at 8192/s Lindqvist et al, 2016).…”

Section: Database and Observationmentioning

confidence: 99%

An Electron‐Scale Current Sheet Without Bursty Reconnection Signatures Observed in the Near‐Earth Tail

Nakamura

et al. 2018

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Observations of a current sheet as thin as the electron scale are extremely rare in the near‐Earth magnetotail. By measurement from the novel Magnetospheric Multiscale mission in the near‐Earth magnetotail, we identified such an electron‐scale current sheet and determined its detailed properties. The electron current sheet was bifurcated, with a half‐thickness of nine electron inertial lengths, and was sandwiched between the Hall field. Because of the strong Hall electric field, the super‐Alfvénic electron bulk flows were created mainly by the electric field drift, leading to the generation of the strong electron current. Inevitably, a bifurcated current sheet was formed since the Hall electric field was close to zero at the center of the current sheet. Inside the electron current sheet, the electrons were significantly heated while the ion temperature showed no change. The ions kept moving at a low speed, which was not affected by this electron current sheet. The energy dissipation was negligible inside the current sheet. The observations indicate that a thin current sheet, even as thin as electron scale, is not the sufficient condition for triggering bursty reconnection.

“…In MMS, magnetic fields are from Flux Gate Magnetometer , electric fields from double probes in the FIELDS suites Lindqvist et al, 2014;Torbert et al, 2014), and electron VDFs from Fast Plasma Investigation . In MMS, magnetic fields are from Flux Gate Magnetometer , electric fields from double probes in the FIELDS suites Lindqvist et al, 2014;Torbert et al, 2014), and electron VDFs from Fast Plasma Investigation .…”

Section: Comparison Between Theory and Mms Observationmentioning

confidence: 99%

Effect of the Reconnection Electric Field on Electron Distribution Functions in the Diffusion Region of Magnetotail Reconnection

Bessho

Chen

et al. 2018

Electron distribution functions in the electron diffusion region during symmetric magnetic reconnection are investigated by means of theory and fully kinetic simulations. Crescent‐like striations are formed in distribution functions in the velocity plane perpendicular to the magnetic field. Using an analytical current sheet, we solve the equation of motion for electrons, and derive the shape of a crescent distribution, as a function of the distance from the neutral line, field gradients, and the reconnection electric field. Each crescent is tilted in the velocity plane because of the acceleration by the reconnection electric field, and multiple stripes appear due to multiple meandering bounces. Applying the theory to distribution functions observed in Earth's magnetotail, we deduce the amplitude of the reconnection electric field.