Theoretical interpretation of X-rays photo-absorption in medium-Z elements plasmas measured at LULI2000 facility

Abstract We analyzed the spectra of X-ray transmission through radiatively heated medium- Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2 p – nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2 p –3 d transitions except in the germanium case. In the wavelength range of the 2 p –2 d , n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2 p –3 d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2 p –3 d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.