Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616738
Title: Experimental study of plasma implosion dynamics in a two-stage wire array Z-pinch configuration
Author: Khoory, Essa
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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Abstract:
This thesis presents results from experiments of a two-stage wire array Z-pinch configuration carried out on the MAGPIE generator ( ~ 1.4MA in ~ 250ns) at Imperial College, London. This configuration preconditions the load wires (heating and expanding wires into columns of gas) before allowing the full current to rapidly switch into the load. The preconditioning effect of cylindrical Al wire array loads of different wire numbers and wire thicknesses were investigated from density analysis of laser interferometry. It was found that thicker wires expand to larger diameters than thinner wires in the preconditioning phase. The 30μm wire expanded to a diameter of 3.7±0.4mm while the 10μm wire expanded to a diameter of 1.6±0.4mm in ~ 170ns after current start. Experiments were also conducted on a single Al wire load of different thicknesses. Again thicker wires expanded to a larger diameter. This uniform column of Al gas on axis showed a high degree of azimuthal symmetry. The fast current switch into the load drives a snowplough implosion with an implosion time of ~ 25-30ns with no apparent development of Rayleigh-Taylor instability. It was observed at stagnation that the expansion the m=1 MHD instability into a helical structure was responsible for the main X-ray pulse. A cylindrical plasma ‘shell’ was formed by preconditioning an array of large wire number and a small inter-wire separation causing the expanding wires to merge before the current switch time. The shell imploded in a 0D manner with no ablation phase and no trailing mass left behind as in standards wire arrays. Implosion of the ‘shell’ was susceptible to R-T instability. Analysis of this instability growth estimated an initial effective perturbation of ~ 1-2μm on the preconditioned wires surface prior to implosion.
Supervisor: Lebedev, Sergey Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.616738  DOI: Not available
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