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Des plasmas stellaires aux plasmas de laboratoire : Application aux mesures d'opacité dans les domaines X et XUV

Abstract : The general context of this thesis is the one of radiative properties of high energy density matter. Energy densities involved (>1011 J/cm3) implies that a large part of energy exchange goes through radiation-matter interactions. My studies deal with spectral opacity, a fundamental parameter for modelling stellar interiors and constitute a propitious observable to experimental tests of theoretical descriptions of hot and dense plasmas physics. My PhD activities are centred on the experimental study of opacities of plasmas at local thermodynamic equilibrium for temperature conditions of a few tens eV (a few 100 000 K) and a few mg/cm3 in matter density. Plasmas are obtained in conditions as homogenous as possible using the radiative heating of a laser-irradiated cavity. Heating is provided though a laser beam of high energy (100-300 J) and with relatively long pulse duration of a few nanosecond. For such measurements we could benefit from the LULI (Laboratoire pour l'Utilisation des Lasers Intenses) lasers configuration coupling the nanosecond beam with a picosecond one used to perform on a short duration the measurement of the plasma transmission. The use of short pulse laser to produce a short time radiography beam was a first achievement for this kind of experience. In the spectral range of keV photons, absorbing transitions 2p − 3d or 3d − 4f of elements of moderate or high atomic number have been probed. They present absorption structures which shape results mainly of the competition between spin-orbit splitting and statistical broadening effects. It appeared that this competition depend strongly on the atomic number Z. Thus for similar plasma parameters we explored opacities of Iron, Nickel, Copper and Germanium (Z of about 30) in a first series of measurement and the one of Barium, Samarium and Gadolinium (Z of about 60) in a second campaign. Stellar astrophysics necessitate as well to measure precisely and in well-characterised condi- tions, opacities of the so-called "Iron-group" (Cr, Fe, Ni and Cu) in the XUV domain (50 − 200 eV). These opacities are at the origin of the excitation in stellar radiative envelops of pulsating stars, massive and of spectral type B for a temperature of the order of 200 000 K. In these conditions, Rosseland means show clear differences between computations used within the astrophysical community and do not allow to interpret oscillations and observed frequencies in a univocal fashion. To allow comparisons with spectral computation, I participated to the develop- ment of a new experimental scheme using two cavities which goal was to improve homogeneity of sample heating. Finally, I will show my analysis of plasma parameters for this specific setup. I analysed the case of the Nickel absorption measured for the first time in this spectral range. For each case I will present the analysis of the obtained results.
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Contributor : Guillaume Loisel <>
Submitted on : Friday, April 29, 2011 - 12:13:30 AM
Last modification on : Friday, October 23, 2020 - 4:45:57 PM
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  • HAL Id : tel-00579800, version 1



Guillaume Loisel. Des plasmas stellaires aux plasmas de laboratoire : Application aux mesures d'opacité dans les domaines X et XUV. Analyse de données, Statistiques et Probabilités []. Université Paris Sud - Paris XI, 2011. Français. ⟨tel-00579800⟩



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