Cold K-shell emission from the implosion of brass planar wire arrays and X-pinches performed at the 1-MA zebra generator at UNR

Abstract

Summary form only given. Understanding the time evolution of the cold K-shell lines will help elucidate the nature of electron beams interacting with plasmas in Z- and X-pinches. Experiments using brass (70% copper, 30% zinc) planar wire arrays and x-pinches on the 1-MA Zebra generator at the University of Nevada, Reno were done to capture the emission of cold K-shell radiation. The diagnostic suite included time-integrated spatially resolved spectrometers capturing L-shell and K-shell spectra using a KAP crystal and a LiF crystal, respectively, time-integrated and time-gated pinhole imaging, PCD, XRD, Si-diode signals, a Ni bolometer, a faraday cup, and laser shadowgraphy. In particular, the cold K-shell lines from the wire material (1.39-1.54 Å) were recorded using a time-gated spatially integrated spectrometer with a LiF crystal. These cold K-shell lines originate from inner shell transitions of lower ionization stages of copper and zinc. Contrary to expectations, experimental intensity ratios of the copper to zinc Kα lines from time-gated spectra did not conform to their abundance in brass (0.7/0.3), but instead varied in time over the x-ray pulse. In order to explain this data, properties of the plasma and electron beam need to be considered. It will be demonstrated that opacity alone cannot be responsible for the discrepancy in the observed cold Kα ratios from their abundance in brass. Understanding the copper and zinc cold K-shell line intensities in time from inner shell ionization cross sections, high energy electron beams, and radiation physics will be highlighted. Results from non-LTE kinetic models of copper and zinc are also discussed. The experimental observations and modeling of brass x-pinches and planar wire arrays will be compared and contrasted.