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Abstract
In this dissertation we present studies of non-MHD effects, the Hall effect and magnetic fluctuations, during magnetic reconnection in the laboratory plasma of the Magnetic Reconnection Experiment (MRX). The Hall effect is studied 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 calculated from out-of-plane magnetic field measurements. The measured in-plane electron flow and predictions from numerical simulations 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, and the electron outflow velocity scales with the electron Alfvén velocity. In contrast to simulations, the presence of classical and anomalous dissipation broadens the electron diffusion region and slows the electron outflow. The electron outflow flux is independent of the width of the electron diffusion region. 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. The separatrices are identified by tracing the ridges of the measured quadrupole field. The angle between the two separatrices defines the aspect ratio of the ion diffusion region, which shows a positive correlation with the aspect ratio of the electron diffusion region. Further measurements show that, in the collisionless regime, the Hall effect balances the reconnecting electric field at the electron diffusion region edge and correlates with the measured effective resistivity. Magnetic fluctuations and the quadrupole field are simultaneously measured in the diffusion region during collisionless magnetic reconnection. The presence of both non-MHD effects shows that the development of plasma turbulence, a three-dimensional feature, does not disrupt the generation of the quadrupole field, a two-dimensional feature. Time-frequency analysis shows that these magnetic fluctuations have spectral peaks around the lower-hybrid frequency. The time characteristics of the fluctuations reveal their impulsive nature. The location of peak fluctuations is found to be at the current sheet center at three different positions along the outflow direction.
