INTERPRETATION OF HOT AND DENSE ABSORPTION-SPECTRA OF A NEAR-LOCAL-THERMODYNAMIC-EQUILIBRIUM PLASMA BY THE SUPER-TRANSITION-ARRAY METHOD

The super-transition-array model is shown to be a very convenient tool for the interpretation of near-local-thermodynamic-equilibrium hot and dense plasmas. Specifically, we interpret here the absorption spectra of the CH-Ni-CH foil experiment performed at Lawrence Livermore National Laboratory using the backlighter technique. In this experiment a laminar foil composed of 200-Angstrom Ni with 1000-Angstrom CH on both sides was radiatively heated by the x-ray continuum from a nearby gold plasma and was backlit by the x-ray continuum from a distant gold plasma that could be time delayed with respect to the heating pulse. This setup was designed to achieve a uniform density and heating of the Ni middle layer. It is found that the Ni absorption features depend very weakly on the density of the foil but are quite sensitive to the foil temperature. Remarkably good agreement between the theory and the experiment is obtained for the Ni 2p-3d spectrum. The detailed features indicate that the plasma temperature-is confined to a narrow range between 14 and 18 eV, demonstrating that the foil design, aiming to create a homogeneous Ni plasma, was successful. These results represent an alternative temperature diagnostic for high-Z plasma.