Characteristics of soft x-ray spectra from ultra-fast micro-capillary discharge plasmas*

The efficient generation of high aspect ratio (e.g. 300:1) plasma columns ionized to very high degrees of ionization (e.g. Ni-like Xenon) by an ultrafast current pulses of moderate amplitude in ~micro-capillary channels is of interest for fundamental plasma studies and for applications such as the generation of discharge-pumped soft x-ray lasers. Spectra and simulations for plasmas generated in 500 um alumina capillary discharges driven by 35-40 kA current pulses with 4 ns rise time were obtained 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 and Si (from injected SiH$_{4})$ are ionized to the H-like and He-like stages. He-like spectra containing the resonance line significantly broaden by opacity, the intercombination line, and Li-like satellites are analyzed and modeled. For Xenon discharges, the spectral lines from the Ni-like transitions the 3d$^{9}$4d(3/2, 3/2)$_{\mathrm{J=0}}$ to the 3d$^{9}$4p(5/2, 3/2)$_{\mathrm{J=1}}$ and to 3d$^{9}$4p(3/2, 1/2)$_{\mathrm{J=1}}$ are observed at gas pressures up to 2.0 Torr.