An investigation of cylindrical liner Z-pinches as drivers for converging strong shock experiments

• Main Author: Burdiak, Guy Christopher
• Other Authors: Lebedev, Sergey
• Published: Imperial College London 2013
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568039

A cylindrical liner z-pinch configuration has been used to drive converging radia- tive shock waves into different gases. Experiments were carried out on the MAGPIE (1.4 MA, 250 ns rise-time) pulsed-power device at Imperial College London [1]. On application of the current pulse, a series of cylindrical shocks moving at typical velocities of 20 km s-1 are consecutively launched from the inside liner wall into an initially static gas- ll. The drive current skin depth calculated prior to resis- tive heating was slightly less than the liner wall thickness and no bulk motion of the liner occurred. Axial laser probing images show the shock fronts to be smooth and azimuthally symmetric, with instabilities developing downstream of each shock. Evidence for a radiative precursor ahead of the first shock was seen in laser inter- ferometry imaging and time-gated spatially resolved optical spectroscopy. In addition to investigating the shock waves themselves, the timing of the shocks was used together with their trajectories to gain insight into launching mechanisms. This provided information on the response of the liner to the current pulse, which is useful for the benchmarking of magneto-hydrodynamics (MHD) codes. A new load voltage diagnostic provided evidence for two phase transitions occurring within the liner wall. The voltage probe was also fielded on various other z-pinch loads for measurements of energy deposition and inductance. The response of magnetically thick liners was found to differ significantly from the case where the liner wall was thin with respect to the initial skin depth of the current. In the later case the evolution of the liner is dominated by the ablation of plasma much like during the ablation phase of a wire array z-pinch.