Die Feinstruktur in Roentgenabsorptionsspektren stosskomprimierter dichter Plasmen. Eine theoretische Untersuchung

The main goal of this thesis is a comprehensive theoretical description of the extended X-ray absorption fine structure (EXAFS) in dense plasmas. This fine structure is based on the interference of the outgoing photoelectron wave with its reflected parts, due to the presence of the neighbouring atoms. The dependence on the distance of the neighbours leads to the use of EXAFS for density measurements. The results presented here are concerned with dense, strongly coupled plasmas, like they are currently produced with the help of shock wave experiments on high energy laser facilities. Typical densities for this kind of plasmas are around the solid state density, and temperatures are typically in the region of some eV. In solid state physics EXAFS has become a standard tool for structure analysis. The advanced theoretical formulation necessary to extend this method to dense plasmas is given in this text, esp. including the appropriate treatment of the short range order, i.e. ionic correlations. Furthermore, the mean free path for electrons moving in the plasma as well as the backscattering of the photoelectron wave on the neighbouring atoms has to be determined. For a given interaction potential the determination of the ionic correlations in the strongly coupled plasma can be done with the help of methods taken from statistical mechanics of fluids. First the effective interaction potential for the plasma ions is calculated in a quasimolecular approach, involving density functional theory in the Thomas-Fermi-approximation. The the Ornstein-Zernicke-relation is solved together with the Percus-Yevick-approximation as closure relation. This kind of approximation is tested by comparison with calculations based on the Hypernetted-Chain-approximation as closure relation as well as with results of Monte-Carlo-simulations. (orig.)130 refs.SIGLEAvailable from TIB Hannover: RN 5339(198) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman