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Magnetic reconnection exhausts in the solar wind

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Title: Magnetic reconnection exhausts in the solar wind
Authors: Mistry, Rishi
Item Type: Thesis or dissertation
Abstract: The restructuring of magnetic fields in plasmas through the process of magnetic reconnection is important in laboratory experiments, magnetospheres and many astrophysical systems. In-situ observations of reconnection processes in the near-Earth environment provide an excellent opportunity to probe the physics of magnetic reconnection. In the solar wind, reconnection between interplanetary magnetic fields accelerates and heats solar wind plasma, generating large exhaust structures which may be intercepted by spacecraft. In this thesis solar wind reconnection exhausts are probed using in-situ measurements from multiple spacecraft. A statistical survey of 188 exhausts is used to determine their average properties and show that the plasma density and temperature of the reconnection exhaust depends on the plasma beta and reconnection guide field. Whilst the ion temperature is found to depend on the plasma Alfv\'en speed (as has been previously demonstrated), we show that this scaling is more tenuous in the presence of strong guide fields. Comparisons of measurements between multiple spacecraft for three different events shows that the structure of the reconnection current sheet changes with increasing distance downstream of the reconnection site. Additionally, measurements of solar wind exhausts often differ considerably between different events. We show that much of this variability may be attributed to different inflow region conditions, the magnetic shear angle and the distance downstream of the X-line at which the exhaust is observed. In addition to their average properties, less frequently observed properties of reconnection exhausts are presented. Hall physics is observed for the first time in solar wind exhausts, which is confirmed through quantitative comparisons with an appropriately scaled fully kinetic particle-in-cell simulation. These measurements indicate that narrow regions of kinetic physics can persist thousands of ion inertial lengths downstream of the reconnection site. Additionally, multi-spacecraft measurements are used for a case study event to reveal the small-scale three dimensional structure of a reconnection exhaust, indicating that whilst exhausts may be planar on large scales, they may also exhibit small scale structure.
Content Version: Open Access
Issue Date: Oct-2016
Date Awarded: Feb-2017
URI: http://hdl.handle.net/10044/1/46008
DOI: https://doi.org/10.25560/46008
Supervisor: Eastwood, Jonathan
Horbury, Timothy
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses



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