Plasma dynamics in aluminium wire array Z-pinch implosions

The wire array Z-pinch is the world's most powerful laboratory X-ray source. An achieved power of #approx#280TW has generated great interest in the use of these devices as a source of hohlraum heating for inertial confinement fusion experiments. However, the physics underlying how wire array Z-pinches implode is not well understood. This thesis presents the first detailed measurements of plasma dynamics in wire array experiments. The MAGPIE generator, with currents of up to 1.4MA, 150ns 10-90% rise-time, was used to implode arrays of 16mm diameter typically containing between 8 and 64 15#mu#m aluminium wires. Diagnostics included: end and side-on laser probing with interferometry, schlieren and shadowgraphy channels; radial and axial streak photography; gated X-ray imaging; XUV and hard X-ray spectrometry; filtered XRDs and diamond PCDs; and a novel X-ray backlighting system to probe high density plasma. It was found that the plasma formed from the wires consisted of cold, dense cores, which ablated producing hot, low density coronal plasma. After an initial acceleration around the cores, coronal plasma streams flowed force-free towards the axis, with an instability wavelength determined by the core size. At #approx#50% of the implosion time, the streams collided on axis forming a precursor plasma which appeared to be uniform, stable, and inertially confined. The existence of core-corona structure significantly affected implosion dynamics. For arrays with <64 wires, the wire cores remained in their original positions until #approx#80% of the implosion time before accelerating rapidly. At 64 wires a transition in implosion trajectories to 0-D like occurred indicating a possible merger of current carrying plasma close to the cores - the cores themselves did not merge. During implosion, the cores initially developed uncorrelated instabilities that then transformed into a longer wavelength global mode of instability. The study of nested arrays (2 concentric arrays, one inside the other) has shown sharpening of the X-ray pulse in different modes of implosion. By limiting the current entering the inner array, a 'current transfer' mode was isolated. Here the majority of current initially flowed through the outer array, accelerating it towards the axis. Upon passing the stationary inner array, current switched from the outer to the inner, resulting in a rapid implosion of the inner array. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN042436 / BLDSC - British Library Document Supply CentreGBUnited Kingdo