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Title: Experimental study of reverse shock structure in magnetised high energy density plasma flows driven by an inverse wire array Z pinch
Author: Suttle, Lee
ISNI:       0000 0004 5349 4331
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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The thesis reports on the design and data from a new experimental platform, which uses the supersonic ablated plasma flow from an inverse wire array z pinch to create a highly diagnosed interaction geometry for studying magnetised reverse shocks. The flow (v~10^7cm/s, Ms~4-5) is generated with a frozen in magnetic field (B~1-2T, ReM~100) at a level sufficient to affect the structure of the shocks created by its collision with a stationary planar obstacle. In addition to the expected accumulation of stagnated plasma material in a thin, high density (strong shock) layer at the obstacle surface, a separate detached shock-like transition is also observed upstream of the obstacle, first observed at a distance ~c/wpi. Measurements of the reverse shock profile from Thomson scattering, interferometry, and local magnetic field probes, show that this 'sub-shock' feature displays unusually small discontinuities in the plasma properties (velocity, density, temperature) despite the high Mach numbers of the flow. Analysis shows that this feature, which is weakly collisional during its formation phase, appears to be a consequence of the pile-up of magnetic flux brought by the flow, which accumulates at the obstacle surface and acts on the magnetised electrons of the flow. An apparent discrepancy between the field strength measured at the sub-shock and the magnetic pressure required to support it against the ram pressure of the flow is addressed towards the end of the thesis. Preliminary results using a newly fielded Faraday rotation diagnostic to measure the field distribution within the reverse shock structure suggests that a pressure balance is achieved via the generation of current loops within the region, which locally enhance the field strength. Future work is set out for continued investigation, including improvements to the diagnostic, and a proposal to adapt the wire array setup to study magnetic reconnection in colliding plasma flows.
Supervisor: Lebedev, Sergey Sponsor: Engineering and Physical Sciences Research Council ; Department of Energy (U.S.)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available