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Title: Experimental studies of the interaction of radiatively cooled supersonic plasma jets with ambient plasma
Author: de Grouchy, Philip William Legeyt
ISNI:       0000 0005 0733 3841
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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We present the design, development and characterisation of an experimental platform for studying astrophysically relevant plasma jet interactions with ambient plasma. Jet and ambient plasmas are formed during the z-pinch discharge of a 1.4MA, 240ns current pulse delivered by Imperial College London's MAGPIE generator. Jets are of centimetre length and microsecond lifetime but have sufficiently large Reynolds and Péclet numbers (> 10,000) to permit well-scaled comparison with non-magnetised astrophysical jets, including the bipolar outflows of protostars. Jet densities are of order 10e19 particles per cubic centimetre, and density ratios (jet density/ambient density) between 1 and 10, are demonstrated. Jets are formed by ablation of micrometer thickness aluminium (Al) or tungsten (W) wires arranged in the conical or radial wire array z-pinch geometries. Ambient plasmas are formed during the same current pulse by ablation of wires in the cylindrical wire array geometry, or the surface of a 14 micrometre thickness, 40mm diameter aluminium foil. Leading shock features launched by conical wire array jet material into foil-driven plasmas demonstrate effective adiabatic indices of 1.4 and 1.2 for Al/Al and W/Al interactions respectively. Radial wire arrays are observed to drive higher Mach number interactions than those of conical wire arrays, with upstream Mach numbers M > 3.5 and M > 1.7 respectively. Instability growth is observed during radial wire array jet experiments along the leading shocks and jet edges, on timescales typical of Rayleigh-Taylor and Kelvin-Helmholtz instabilities under our experimental conditions. This work complements and extends current numerical modelling of non-magnetised astrophysical jet propagation, and offers a body of controlled, repeatable experimental data for future code validation work.
Supervisor: Lebedev, Sergey Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral