Al and W Wire Array Implosions and Energy Deposition on the 1-MA COBRA Generator

Implosion characteristics of cylindrical arrays of aluminum (Al) or tungsten (W) wires with low number of wires were studied on the 1-MA 100-150-ns current rise time COBRA generator at Cornell University using X-ray/extreme ultraviolet detectors, time-gated cameras, spectrometers, and electrical diagnostics. Total radiation yields E_T of 2.8 and 4.1 kJ were measured for Al and W, respectively. The yield above 0.75 keV for W arrays was lower than for Al. Al spectra imply T_e of 250-280 eV. X-ray spectra in the 2-3-keV range from W arrays showed only very weak spectral lines. A relatively uniform precursor plasma column was observed on time-gated images in the initial implosion phase for both Al and W. Rapid radiation cooling of W plasmas after precursor plasma formation leads to a decrease of plasma T_e before the stagnation phase of the implosion. No evidence of the increased energy deposition that could be associated with the single-shell or closed toroidal magnetic structures models was found