Experimental Study of the Hall Effect and Electron Diffusion Region During Magnetic Reconnection in a Laboratory Plasma

Abstract

The Hall effect during magnetic reconnection without an external guide field has been extensively studied in the laboratory plasma of the Magnetic Reconnection Experiment (MRX) [Yamada et al., Phys. Plasmas 4, 1936(1997] by measuring its key signature, an out-of-plane quadrupole magnetic field, with magnetic probe arrays whose spatial resolution is on the order of the electron skin depth. The in-plane electron flow is deduced from out-of-plane magnetic field measurements.The measured in-plane electron flow and numerical results are in good agreement. The electron diffusion region is identified by measuring the electron outflow channel. The width of the electron diffusion region scales with the electron skin depth (∼ 8c/ω pe ) and the peak electron outflow velocity scales with the electron Alfvén velocity (∼ 0.11V eA ), independent of ion mass. The measured width of the electron diffusion region is much wider and the observed electron outflow is much slower than those obtained in 2D numerical simulations. It is found that the classical and anomalous dissipation present in the experiment can broaden the electron diffusion region and slow the electron outflow.As a consequence, the electron outflow flux remain consistent with numerical simulations. The ions, as measured by a Mach probe, have a much wider outflow channel than the electrons, and their outflow is much slower than the electron outflow everywhere in the electron diffusion region.

Electron Inflow Velocities and Reconnection Rates at Earth's Magnetopause and Magnetosheath

“…Similar investigations are conducted in the laboratory with MRX: Yamada et al (2018) observed the high out‐of‐plane velocity (v eM ) at the stagnation point of asymmetric reconnection; Ren et al (2008) observed outflow velocities at 0.11v eA , which are consistent with our measurements.…”

How anomalous resistivity accelerates magnetic reconnection

“…An interesting observation based on a set of particlein-cell (PIC) simulations is that the maximum Hall-reconnection rate seems universal and is independent of the mechanism that breaks the field lines 20,21 . Observations and laboratory experiments have discovered the Hall field and Hall current associated with fast collisionless magnetic reconnection 10,12 , but no direct experimental or observational evidence has been found to show that the rate is irrelevant to the dissipation mechanism [22][23][24][25] . On the other hand, observations of solar flares found that magnetic reconnection may commonly be turbulent as evidenced by the filamentary structure of magnetic field, non-thermal heating observed in X-ray, and coherent radio emissions that are likely results of electron two-stream instability [26][27][28] .…”

The solar wind electric field does not control the dayside reconnection rate

“…The Cassak‐Shay formulation has been successfully used to predict the measured reconnection outflow speeds at the magnetopause for a wide range of densities and magnetic field strengths in the magnetosheath and magnetosphere [ Walsh et al ., , ] at various IMF clock angles. In the symmetric‐plasma limit, the Cassak‐Shay equation reduces to the familiar Petschek formula for the fast reconnection rate R ~ 0.1 v A B that has been successfully tested in a variety of computer simulations in the Geospace Environmental Modeling (GEM) reconnection challenge [ Birn et al ., ; Otto , ; Shay et al ., ; Birn and Hesse , ] and tested against dayside reconnection measurements [ Fuselier et al ., ], magnetosheath reconnection measurements [ Phan et al ., ], and collisionless plasma laboratory experiments [ Yamada et al ., ; Ren et al ., ].…”