The effect of precursor plasma flow on foam targets in wire array z-pinch experiments

Previous experiments have demonstrated that the slow ablation rate of material from wire arrays results in the formation of a precursor plasma stream bombarding the axis [1]. This could have major repercussions for the centrally located foam targets used in dynamic and static walled hohlraum configurations on the Z facility at Sandia National Laboratory (SNL) [2]. Experiments to characterise the effect of precursor plasma flow on foam targets were carried out on the MAGPIE generator at Imperial College. The TPX foam used is similar in size and density to foam used in the experiments at SNL. Diagnostics included: x-pinch backlighter; x-ray framing cameras; diamond PCDs; laser shadowgraphy and interferometry; optical streak photography. Backlighter results suggested that the foam was compressed at a rate consistent with experimental estimates of the momentum of the bombarding plasma streams. Laser probing images, however, showed expansion of low density plasma from the foam surface that exhibited structure similar to an m=0 instability. Side-on XUV and x-ray imaging showed axially modulated emission from the foam.