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Instabilités hydrodynamiques : Application à l'astrophysique de laboratoire et diagnostics X à haute résolution

Abstract : During the 20th century, the development of high power laser enabled scientist to reach a regime known as High Energy Density (HED), where matter is carried under extreme conditions. This allow the development of a new discipline: the laboratory astrophysics. This discipline aims to reproduce, in the laboratory, conditions similar to those observed in astrophysics, for instance in planet or star interiors, during cataclysmic phenomena.This thesis corresponds to an experimental and numerical study of hydrodynamic instabilities, which can be found in such situations. These instabilities affect the evolution of astrophysical objects and hinder their observation. Here, we will focus on the Rayleigh-Taylor (RTI) and the Richtmyer-Meshkov (RMI) instabilities. The first one does arise when a high density fluid is lying above a low density one. The second can be seen as a special case of the first, where the force responsible for the motion of the instability is linked to a shock wave. In astrophysics, both instabilities can be found in supernovae remnants, which are composed of the matter ejected during the death (explosion) of massive stars. They can also be found in inertial confinement fusion, and are responsible of the failure of ignition.In this thesis, we will show the results of experiments on those instabilities carried on LULI2000 (Palaiseau, France), GEKKO XII (Osaka, Japan), and SACLA (Japan) facilities. Thanks to these experiments, we observed directly and reconstructed the evolution of the RTI from its linear phase, early in time, up to its turbulent phase, late in time. We proceeded to a parametric study of the RTI, where we varied classical parameters: the wavelength modulation, the density ratio (Atwood number). Therefore, this constitutes a complete experimental study of the RTI with hitherto unseen results. Especially our observation of the turbulence with an unprecedented resolution in this regime (HED).To complete this experimental study, simulations were performed using FLASH, a magneto-hydrodynamic code developed by the FLASH centre (University of Chicago). These simulations allowed us to design our experiments and to analyse and understand our results.Concurrently, we developed a new high resolution X-ray radiography diagnostic. This diagnostic is based on a LiF crystal used as a detector. We proceed to the characterisation of this diagnostic on the SOLEIL synchrotron (spectral response, change in resolution...). This allowed us to use this diagnostic as our main detector on a SACLA experiment, which results on a sub-micron spatial resolution and to a temporal resolution of 10 fs.
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Submitted on : Tuesday, March 2, 2021 - 1:01:28 AM
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  • HAL Id : tel-03155653, version 1

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Gabriel Rigon. Instabilités hydrodynamiques : Application à l'astrophysique de laboratoire et diagnostics X à haute résolution. Physique des plasmas [physics.plasm-ph]. Institut Polytechnique de Paris, 2020. Français. ⟨NNT : 2020IPPAX020⟩. ⟨tel-03155653⟩

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