thesis

Experimental Studies of the Interaction of Radiatively Cooled Supersonic Plasma Jets with Ambient Plasma

Abstract

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.Open Acces

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