Plasma formation and seeding of Rayleigh-Taylor instabilities in wire array z-pinches

Summary form only given, as follows. X-ray radiography with high temporal (/spl sim/1 ns) and spatial (/spl sim/20 /spl mu/m) resolution was used to study implosion dynamics of while array Z-pinch in experiments on the 1.4 MA, 240 ns MAGPIE facility. Comparison of laser probing and X-ray radiography data shows that the plasma formed from the wires has a heterogeneous structure, with a low density corona surrounding the dense wire cores. Non-uniform sweeping of the coronal plasma by the global J/spl times/B force from the wires towards the array axis produces both mass perturbations in the wire cores and a precursor column on the axis. The spatial scale of these perturbations, which act as seeding for the global m=0 mode of the Rayleigh-Taylor instability, is determined by the size of wire cores (0.25 mm for Al and 0.1 mm for W). A qualitative change in the implosion dynamics (transition to D-like implosion trajectory) was observed in Al arrays when the ratio of inter-wire gap to the wire core size decreased to /spl sim/3. This probably explains the existence of "critical" inter-wire gap, below which a significant rise in X-ray power was observed in experiments at Sandia National Lab. Experimental data on "nested" wire array implosions will be presented, which show significant sharpening of the X-ray pulse in different dynamic modes of the interaction between the two arrays.