A Configurationally-Resolved-Super-Transition-Arrays method for calculation of the spectral absorption coefficient in hot plasmas

Abstract

A new method, 'Configurationally-Resolved-Super-Transition-Arrays', for calculation of the spectral absorption coefficient in hot plasmas is presented. In the new method, the spectrum of each Super-Transition-Array is evaluated as the Fourier transform of a single Complex Pseudo Partition Function, which represents the exact analytical sum of the contributions of all constituting unresolved transition arrays sharing the same set of one-electron solutions. Thus, in the new method, the spectrum of each Super-Transition-Array is resolved down to the level of the (unresolved) transition arrays. It is shown that the corresponding spectrum, evaluated by the traditional Super-Transition-Arrays (STA) method [A. Bar Shalom, J. Oreg, W.H. Goldstein, D. Shvarts and A. Zigler, Phys. Rev. A 40, 3183 (1989)], is just the coarse grained Gaussian approximation of the Configurationally-Resolved-Super-Transition-Array. A new computer program is presented, capable of evaluating the absorption coefficient by both the new configurationally resolved and the traditional Gaussian Super-Transition-Arrays methods. A numerical example of gold at temperature 1keV and density 0.5 gr/cm^{3}, is presented, demonstrating the simplicity, efficiency and accuracy of the new method.