Etude de la matière dense et tiède à l'aide de diagnostics X - Applications aux intérieurs planétaires

Abstract : With the recent discovery of many exoplanets, modelling the interior of these celestial bodies is becoming a fascinating scientific challenge. In this context, it is crucial to accurately know the equations of state and the macroscopic and microscopic physical properties of their constituent materials in the Warm Dense Matter regime (WDM). Moreover, planetary models rely almost exclusively on physical properties obtained using first principles simulations based on density functional theory (DFT) predictions. It is thus of paramount importance to validate the basic underlying mechanisms occurring for key planetary constituents (metallization, dissociation, structural modifications, phase transitions, etc…) as pressure and temperature both increase. In this thesis, we were interested in two materials that can be mainly found in the Earth-like planets: silica, or SiO2, as a model compound of the silicates that constitute the major part of their mantles, and iron, which is found in abundance in their cores. These two materials were compressed and brought to the WDM regime by using strong shock created by laser pulses during various experiments performed on the LULI2000, JLF, GEKKO XII and LCLS laser facilities. In order to penetrate this dense matter and to have access to its both ionic and electronic structures, we have probed silica and iron with X-ray diagnostics, such as time-resolved X-ray Absorption Near Edge Structure (XANES) and time-resolved X-ray diffraction. In parallel with these experiments, we performed quantum molecular dynamics simulations based on DFT at conditions representative of the region investigated experimentally so as to extract the interesting physical processes and comprehend the limits of the implemented models. In particular, these works allowed us to highlight the metallization processes of silica in temperature and the structural changes of its liquid in density, as well as to more constrain the melting curve of iron at very high pressures.
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Adrien Denoeud. Etude de la matière dense et tiède à l'aide de diagnostics X - Applications aux intérieurs planétaires. Physique [physics]. Ecole Polytechnique, 2014. Français. ⟨tel-01093197⟩

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