Opacity of iron, nickel, and copper plasmas in the x-ray wavelength range: Theoretical interpretation of2p−3dabsorption spectra

Abstract

This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm(3). The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code SCO and with the fine-structure atomic physics codes HULLAC and FAC. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code RCG has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by SCO. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code SCRIC. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the Δn=0 absorption in medium-Z plasmas for astrophysical applications.

Theoretical interpretation for 2p−ndabsorption spectra of iron, nickel, and copper in X-ray range measured at the LULI2000 facility

“…In the iron case, it has been shown [5] that, ignoring the configurations with a 3p open subshell, the 2p − 3d structure at a temperature T ∼ 20 eV as calculated by HULLAC is composed of wellseparated components, in contradiction with the prediction from the SCO code and with the experiment. The list of configurations is given in Table 1.…”

“…[4,5]. Let us mention here that the 2p − 3d splitting partially appears in the LULI data though less than expected.…”

“…A presentation of the LULI campaign on X-ray opacities of iron, nickel, copper, and germanium, as well as details about the theoretical models used have been published elsewhere [4,5].…”

“…A previous analysis [5] identified the most probable cause for this as being inhomogeneities in the sample temperature, density, or thickness.…”

“…The recent experiment performed on the LULI2000 facility [4] aimed at checking a similar effect at fixed T but varying the atomic number Z: at T ∼ 20 eV, the 2p − 3d splitting is expected to vanish when Z decreases from 29 (Cu) to 26 (Fe). To describe this experiment, several models have been used and compared [5]: a statistical analysis with the superconfiguration code SCO [6], detailed-level accounting approaches using either HULLAC [7] or FAC [8] packages, the mixed approach SCO-RCG [9] combining the SCO approach with a detailed line analysis based on Cowan's code, and the collisional-radiative code SCRIC [10] suited to characterize the non-local-thermodynamic-equilibrium effects. It turned out that HULLAC a e-mail: michel.poirier@cea.fr This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.…”