Wire Contact Resistance Effects in a Multiwire Z-Pinch

Summary form only given. Investigations of the effect of initial wire contact-resistance on wire ablation dynamics are being conducted. Experiments utilize a 120 kV, 20 kA pulser with 140 ns rise-time, which drives a two-wire z-pinch load. Diagnostics for the experiment include laser shadowgraphv, streak camera images, and time-gated ICCD visible-UV wavelength spectroscopy. Both aluminum and stainless steel wires of 19-30 mum diameter have been studied. UM wire holders utilize slots and weights similar to those employed on Sandia´s Z-Machine. Both precision DC-AC low current measurements and 20 kA pulsed experiments have been performed and compared. Typical wire contact resistances for this wire-holder design account for more than 85 percent of the total resistance of the load. Variations in contact resistance between two wires were observed for wires strung in a nearly identical fashion. DC experiments have shown that initial differences in the contact resistance between two wires results in one wire continually drawing more current than the other. Streak camera images with 20 kA pulses have shown that the wire with lower contact resistance draws more current prior to wire explosion, and that the wire drawing greater current exhibits a higher plasma expansion velocity. In a large number wire array, a difference in plasma expansion velocities between wires might be expected to lead to a non-uniform plasma shell, which would negatively affect plasma implosion dynamics. Ongoing experiments are aimed at characterizing the relationship between plasma expansion velocity and contact resistance between wires using both streak camera images and laser shadowgraphy. Spectroscopic measurements will examine variations in plasma temperature between the two plasmas. Methods will be explored to reduce variations in wire contact resistance, as well as to reduce the overall contact resistance of the wires.