X-ray spectroscopy of z-pinches in implosions of wire arrays with combined materials

Abstract

Time-resolved laser-probe diagnostics and gated x-ray imaging of star-like wire array z-pinch implosions have shown implosion characteristics that are more stable than those of other types of wire arrays on the Zebra generator. Here, we study the plasma conditions achieved in star-like wire arrays implosions using time-integrated and spatially-resolved x-ray spectroscopy. To this end, spectroscopic data have been recorded along a line of sight perpendicular to the z-pinch axis using a convex KAP crystal spectrometer, with a spectral resolution power of 350 in a series of shots performed at the Nevada Terawatt Facility. The target loads were star-like wire arrays comprised of 9 to 15 wires, 7.6–25 microns in diameter each, and driven by the Zebra pulsed-power accelerator. The wire array material combined aluminum with wires made out of titanium, stainless steel, and tungsten. The implosion dynamics in wire arrays was observed with laser probing at wavelengths of 532 and 266 nm and time-gated x-ray pinhole camera. The spectroscopic analysis focuses on the K-shell emission of aluminum, but the total energy radiated in soft and K-shell x-rays was also measured. The observed aluminum K-shell spectra show line transitions in Li-, He- and H-like Al ions; analysis of the spectra using detailed collisional-radiative atomic kinetics and radiation transport calculations yields electron temperature and density in the plasma. We discuss the plasma conditions achieved for several types of star-like wire array configurations, and its connection with soft and K-shell radiated energy.