Etude expérimentale et théorique de la structure électronique de l'aluminium en conditions extrêmes par spectroscopie d'absorption X

La matière en conditions extrêmes appartient au régime de la Warm Dense Matter qui se situe à la frontière entre le régime plasma dense et le régime de la matière condensée. Son comportement est encore mal connu et mal décrit. En effet, sa description théorique est très complexe et il est difficile de générer cet état de matière en laboratoire pour obtenir des données expérimentales pouvant valider les modèles. Ce travail de thèse a pour objectif d'étudier la structure électronique de l'aluminium en conditions extrêmes par le diagnostic de la spectroscopie d'absorption X. Expérimentalement l'aluminium a été porté dans des conditions de fortes densités et fortes températures jusque-là inexplorées. Par ailleurs, une source X capable de sonder l'aluminium sous choc a été générée. Deux spectromètres X ont permis l'acquisition des spectres d'absorption de l'aluminium dans ces conditions et des diagnostics optiques ont permis de déduire les conditions de densité et de température de l'aluminium de façon indépendante. En parallèle, des calculs ab initio ont été réalisés pour obtenir des spectres d'absorption dans les mêmes conditions afin de les comparer aux spectres expérimentaux. Du point de vue théorique, l'objectif était de valider les méthodes de calcul des spectres d'absorption X dans ce régime de fortes densités et fortes températures en analysant les modifications du flanc d'absorption. Le diagnostic de l'absorption X a également été utilisé pour étudier le phénomène physique de la transition métal-non métal qui a lieu à basse densité (densité < densité du solide). Cette transition peut alors être étudiée par les changements de la structure électronique du système étudié.Matter in extreme conditions belongs to Warm Dense Matter regime which lays between dense plasma regime and condensed matter. This regime is still not well known, indeed it is very complex to generate such plasma in the laboratory to get experimental data and validate models. The goal of this thesis is to study electronic structure of aluminum in extreme conditions with X-ray absorption spectroscopy. Experimentally aluminum has reached high densities and high temperatures, up to now unexplored. An X-ray source has also been generated to probe highly compressed aluminum. Two spectrometers have recorded aluminum absorption spectra and aluminum density and temperature conditions have been deduced thanks to optical diagnostics. Experimental spectra have been compared to ab initio spectra, calculated in the same conditions. The theoretical goal was to validate the calculation method in high densities and high temperatures regime with the study of K-edge absorption modifications. We also used absorption spectra to study the metal-non metal transition which takes place at low density (density < solid density). This transition could be study with electronic structure modifications of the system.PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Laser shock experiments on metallic glasses: From the Newton's pendulum to spallation process

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Courbes d'Hugoniot de verres métalliques ZrCuAl sous choc laser et évolution de la limite à rupture avec la vitesse de déformation

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Courbes d'Hugoniot de verres métalliques ZrCuAl sous choc laser et évolution de la limite à rupture avec la vitesse de déformation

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Laser shock experiments on metallic glasses: From the Newton's pendulum to spallation process

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Laser shock experiments on metallic glasses: From the Newton's pendulum to spallation process

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Ab initio calculation of x-ray absorption of iron up to 3 Mbar and 8000 K

International audienceUsing ab initio simulations within the generalized gradient approximation, we calculate x-ray absorption near edge spectra (XANES) at the iron K edge throughout the high-pressure phase diagram and up to extreme density and temperature conditions that are representative of the Earth's inner core (up to 3 Mbar and 8000 K). We show that XANES spectra near the Fe K edge exhibit clear signatures for the different high-temperature, high-pressure phases of iron. This suggests that XANES spectroscopy might be used to resolve ongoing controversies regarding both the high-pressure melting curve of iron and the nature of the solid phases undergoing melting up to several Mbar. In contrast to diffraction measurements, it also offers a severe constraint for density functional theory predictions of the transport properties of iron by providing direct information on the electronic structure of iron at these extreme conditions

Publisher's Note: ``Temperature and electron density measurements on laser driven radiative shocks'' [Phys. Plasmas 13, 010702 (2006)]

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Experimental and numerical studies of radiative shocks

International audienceThis paper deals with radiative shocks from both theoretical and experimental viewpoints. First, experimental results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI) at high (E&tilde;400-800 J) energies are presented. The modeling of these phenomena is mainly performed through numerical simulations (1D and 2D calculations). We compare simulations given by several radiative hydrodynamics codes and discuss numerical methods employed. The lateral radiative looses are examined. A major point for discussion is the physical data (EOS, ionization, opacities) included in these codes. It is shown that the radiative precursor length depends on the dimensionality of codes and on the opacities employed. Additional quantities (temperature of the shock, electron density in the precursor) are also calculated and good agreement is obtained with the experimental data

Density and Temperature Measurements on Laser Generated Radiative Shocks

International audienceThis paper presents some recent measurements on radiative shocks generated in a xenon gas cell using high power laser. We show new results on temperature and electronic density, and on radial expansion of the shock at various initial conditions (laser energy and gas pressure). The data obtained are compared with one-dimensional and two-dimensional hydro simulations