Current Prepulse Effect on Wire Array Core Temperature, Ablation Dynamics and x-ray Emission on 1-MA ZEBRA

Summary form only given. The effect of current prepulse on wire array core temperature on the 1-MA z-pinch installation ZEBRA was investigated using current, light emission, 4-channel laser shadowgraphy, visible ICCD camera and PCD/XRD diagnostics. A vacuum flashover switch reduced the original ~250ns prepulse on ZEBRA to as short as ~50ns. Shortened prepulse increases the initial current rate through the individual wires and this in turn leads to more energy deposited into the wire cores (higher temperature) at breakdown. Shorter current prepulse also improved the axial homogeneity for deposited energy. Better axial homogeneity of deposited Joule energy improves the axial symmetry of precursor plasma and reduces its typically observed m=l instability. Reduction of the precursor instability results in the generation of a single X-ray pulse rather than the multiple pulses observed for unstable precursor. Multi-frame shadowgraphy shows that discrepancy in the initial wire-electrode contacts results in differences in energy deposition and ablation from wire to wire. Keeping similar contacts for all wires in the array is critical for azimuth ablation uniformitv. Shortening the current prepulse using a flashover switch results in an increase of light emission peak and wire core temperature. Core temperature rises from ~800K to ~1100K and finally to ~3100K. at moment of breakdown. Moment t=0 corresponding to the beginning of main current pulse.