Studies of Al and W wire array z-pinches, and the role of ``magnetic bubbles'' in energy deposition at 1 MA Cobra generator

Implosions of cylindrical arrays with eight 12.5 $\mu $m Al or 5.1 $\mu $m W wires were studied on the 1MA, 100-150 ns rise time COBRA generator. X-ray and EUV detectors, time-gated cameras, spectrometers, backlighters and electrical diagnostics were used. Total radiation yields$_{ }$of 2.8 and 3.7 kJ, and total radiated powers of 15 GW and 25 GW were measured for Al and W, respectively. The keV yield for W arrays was lower than for Al. The Al spectra have shown T$_{e}$ from 200 eV to 300 eV. X-ray spectra from W arrays included very weak spectral features that were compared with results from W/Mo X-pinch experiments. Relatively uniform plasma columns (life-time 5-10 ns) were observed on time-gated images during the initial implosion stage for both Al and W. Studies of the possible role of ``magnetic bubbles'' on energy deposition were initiated based on the plasma resistance compared with the nonlinear resistance predicted by theory, total radiation yield, and the time-gated and backlighting images. This work was sponsored by NNSA through DOE Coop. Agreement DE-F03-02NA00057 and in part by the DOE/ NNSA under UNR grant DE-FC52-01NV14050.