Implosion dynamics and radiation output of wire-array z-pinches on the cobra pulsed-power generator

Experimental results are presented which characterize the implosion dynamics and subsequent radiation output of wire-array Z-pinches on the 1-MA, 100-ns rise-time COBRA pulsed-power generator. Diagnostics fielded include an optical streak camera, a time-gated XUV framing camera, a laser shadowgraph system, filtered time-integrated pinhole cameras, an X-ray focusing spectrometer with spatial resolution (FSSR), a load voltage monitor, a Faraday cup, a bolometer, silicon diodes and diamond photoconducting detectors (PCDs). The load geometries investigated include hollow cylindrical arrays ranging from 4 to 16 mm in diameter, and consisting of 8, 16, or 32 wires of either tungsten (W), aluminum (Al), or Invar. The data produced by the entire suite of diagnostics are analyzed and presented to provide an overall picture of implosion dynamics and timing on COBRA. In particular, data fitting to various implosion trajectory models, as well as X-ray pulse shape dependencies on various loads and implosion characteristics are presented and discussed. From this study, it was determined that by moving the stagnation time earlier (i.e., before the peak in the driving load current, where dI/dt is positive), the total X-ray yield is increased by ~1.5-2times on COBRA. From bolometer measurements, we recorded ~10 kJ of total X-ray energy, which is a conversion efficiency of -10% for the 100-kJ discharge of a typical COBRA pulse. Load scaling for an earlier stagnation time was accomplished by dropping to a smaller initial array diameter (i.e., 4 mm) and using smaller initial wire diameters (i.e., 5-mum W; 12-mum Al). The use of fine wire and a small array diameter also allowed for enough wires and a tight enough wire-spacing to provide good implosion uniformity (i.e., 16 wires on a 4-mm array diameter for 785-mum wire spacing).