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Theses

Génération et transport des électrons rapides dans l'interaction laser-matière à haut flux.

Abstract : The general context of this study is the Inertial Confinement for thermonuclear controlled fusion and, more precisely, the Fast Igniter (FI). In this context the knowledge of the generation and transport of fast electrons is crucial. This thesis is an experimental study of the generation and transport of fast electrons in the interaction of a high intensity laser (>= 10 19 W/cm2) with a solid target. The main diagnostic used here is the transition radiation. This radiation depends on the electrons which produce it and thus it gives important information on the electrons: energy, temperature, propagation geometry, etc. The spectral, temporal and spatial analysis permitted to put in evidence the acceleration of periodic electron bunches which, in this case, emit a Coherent Transition Radiation (CTR). During this thesis we have developed some theoretical models in order to explain the experimental results. We find this way two kinds of electron bunches, emitted either at the laser frequency (w0), either at the double of this frequency (2w0), involving several acceleration mechanisms: vacuum heating / resonance absorption and vxB, respectively. These bunches are also observed in the PIC simulations. The electron temperature is of about 2 MeV in our experimental conditions. The electrons are emitted starting from a point source (which is the laser focal spot) and then propagate in a ballistic way through the target. In some cases they can be re-injected in the target by the electrostatic field from the target edges. This diagnostic is only sensitive to the coherent relativistic electrons, which explains the weak total energy that they contain (~ few mJ). The CTR signal emitted by those fast electrons is largely dominating the signal emitted by the less energetic electrons, even if they contain the major part of the energy (~ 1 J).
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Submitted on : Wednesday, July 28, 2010 - 10:39:24 AM
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Horia Popescu. Génération et transport des électrons rapides dans l'interaction laser-matière à haut flux.. Physique [physics]. Ecole Polytechnique X, 2005. Français. ⟨pastel-00001799⟩

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