X-ray spectroscopy and imaging of combined x-pinches with W wires at university-scale 1 MA pulsed power devices

Summary form only given. X-pinches composed of two different wire materials (Mo and W; Al and W) generated using the 1 MA pulsed power Zebra at University of Nevada, Reno (UNR) and COBRA at Cornell University (CU) provide unique information about implosion and radiation characteristics of different materials in one shot. In particular, combined X-pinches with W wires produce better quality M-shell W spectra than X-pinches or wire arrays made using W only, which makes them extremely valuable for development of M-shell W diagnostics on the SNL-Z generator for ICF applications. Specifically, planar loop (at UNR) and twisted (at CU) configurations of X-pinch loads with Mo and W wires have been studied. Both configurations produce X-ray spectra applicable for plasma diagnostics with more intense M-shell W radiation from twisted and with strong gradients in axially resolved spectra from planar-loop X-pinches. An analysis of L-shell Mo spectra indicates the existence of two radiation sources in radially resolved spectra with Te~900 eV, Ne~1021 cm-3, and a fraction of hot electrons f=0.05-0.1. A single radiation source with similar parameters is observed in axially resolved spectra from planar-loop X-pinches. Planar-loop X-pinches with Al and W wires have been produced on the UNR Zebra. For almost all combined X-pinches on both devices, the image size decreases with decreasing wavelength and PCD signals show multiple bursts. Time-gated as well as time integrated images indicate the presence of radiation from energetic electrons. Comparison of results for combined X pinches with Mo and W wires to those with Al and W wires indicates larger sources of K-shell Al and Mg radiation (Al lines are optically thick); similar plasma parameters from M-shell W and L-shell Mo plasmas which differ from K-shell Al and Mg plasmas; and overlapping of diagnostically important spectral features (more with Mo and less with Al). The application of the present results to the experiments with wir- arrays from W and Mo (or Al) wires is discussed