X-ray spectra from exploded-wire plasmas

Abstract

X-ray line spectra were collected from exploded (Al to U) wire plasmas produced by ${10}^{12}$-W pulse discharges of high-energy electrons in the Gamble II generator. High-ionization states were found in these spectra that provided new spectroscopic data. The Ne- and Ni-like isoelectronic sequences involving $L$- and $M$-shell transitions were extended to high-atomic-number elements, Ag and Au, respectively. The correlation of spectra and x-ray pinhole images revealed that the high-temperature emission emanates from small ( 75 \ensuremath{\mu}m), high-density pinched regions with plasma temperatures of 1-2 keV (based on the coronal model). Other x-ray emission arises from cool-plasma (50-200 eV) regions associated with the flaring structure as seen in x-ray-pinhole images. In addition to low-temperature thermal x-ray emission from the flare regions, energetic electrons produce nonthermal inner-shell spectral lines. As the atomic number increases, the relative intensity of the cool plasma to high-temperature thermal emission increases systematically for isoelectronic sequences involving $K$-, $L$-, and $M$-shell transitions. The plasma characteristics determined from the distribution of ionization states in the exploded-wire spectra correlate well with those from other high-energy-density generating devices, namely the vacuum spark and plasma focus.