Ionization of Xenon to the Nickel-Like Stage and Beyond in Micro-Capillary Plasma Columns Heated by Ultrafast Current Pulses

Abstract

Homogeneous plasma columns with ionization levels typical of MA discharges were created by rapidly heating gas-filled 520 µm diameter channels with ns rise-time current pulses of unusually low amplitude, 40 kA. These conditions allow the generation of high aspect ratio (eg. > 300:1) plasma columns with very high degrees of ionization (e.g. Ni-like Xenon) of interest for soft x-ray lasers below λ = 10 nm. Spectra and simulations of plasmas generated in 520 µm diameter alumina capillaries driven by 35–40 kA current pulses with 4 ns rise time were obtained for discharges in Xenon and Neon discharges. The first shows the presence of lines corresponding to ionization stages up to Fe-like Xe. The latter show that Al impurities from the walls are ionized to the H-like and He-like stages. He-like Al spectra containing the resonance line significantly broaden by opacity, the intercombination line, and Li-like satellites are analyzed. For Xenon discharges, the spectral lines from the Ni-like transitions the 3d⁹4d (3/2, 3/2)_J = 0 to the 3d⁹4p(5/2, 3/2)_J = 1 and to 3d⁹4p(3/2, 1/2)_J = 1 are observed.