Spectroscopy and implosion dynamics of low wire number nested arrays on the 1 MA COBRA generator

Low wire number nested array Z-pinch experiments have been carried out with wires made of aluminum, stainless steel (uniform), and combinations of these two materials (mixed) on the 1 MA COBRA generator at Cornell University [J. D. Douglass, J. B. Greenly, D. A. Hammer et al., in Proceedings of the 15th IEEE International Pulsed Power Conference (IEEE, Piscataway, NJ, 2005)]. The outer array consisted of eight wires, whereas the inner array had four or eight wires. The 10 mu m Al wires were alloy 5056 and the 6.25 mu m stainless steel wires were alloy SS304. The diagnostic suite included fast-x-ray and extreme ultraviolet (EUV) detectors, a time-gated x-ray pinhole camera, x-ray spectrometers, and laser shadow imaging. The main focus was made on the spectroscopic study of plasma evolution after the main x-ray burst though the data from photoconducting detector (PCD) and EUV signals over the whole period of current, and in addition laser shadowgraphy images before the main x-ray burst were analyzed. Modeling of the time-gated spectra recorded after the main x-ray burst indicates that the electron temperature Te either follows the PCD signals and peaks at times of the second (and the third if present) x-ray burst or has the higher value at the first frame (closest to the main x-ray burst), then slightly changes and increases at the last frame, which coincides with the second maximum of the current. It was also found that the values of Te never drop below 150 eV, and the EUV signal remains intense even when the PCD signal is almost zero. (C) 2008 American Institute of Physics.