Optical and X-ray observations of multi-wire z-pinch experiments

Summary form only given, as follows. An important question associated with z-pinch implosion experiments using fine wire arrays concerns the effect on the implosion of the plasma formed around and between the wires during the expansion phase. Heating and expansion occurs early on in the pulse, before the current is so high (>10 kA/wire) that the global magnetic fields are strong enough to initiate the implosion. We report on our initial results to study the dynamics of plasma expansion and inter-wire merging as well as the early stages of implosion. The intent of the work is to better understand how the wire material is swept away from the initial wire positions by the global magnetic field forces. Our experiments were conducted using Cornell´s XP pulsed power generator (450 kA peak current, 100 ns) and an LC current pulser (4.5 kA peak current, 10 A/ns rise rate). Multi-wire arrays (2-8 wires) driven by currents ranging from 1 kA/wire to 100 kA/wire were studied. Consequently, both the expansion and early implosion regimes could be investigated. We used W, Al, and Ag wires, 1 cm in length, and 7.5-25 mm in diameter. Plasma densities were measured using both a shearing interferometer (l=532 nm) and X-ray backlighting. The optical interferometer was especially useful for observing relatively low electron densities present during plasma formation, expansion and inter-wire merging. X-ray backlighting was used to image the high density wire cores and the relatively high density merged plasma that occurred late in the expansion phase. Some X-ray imaging was also possible during the early stages of implosion.