Étude théorique et numérique de l'expansion dans le vide d'un plasma créé par laser : cas d'une fonction de distribution des électrons bi-Maxwellienne

Abdourahmane Diaw 1
1 Interaction Laser Plasma
CPHT - Centre de Physique Théorique [Palaiseau]
Abstract : A comprehensive theory is developed to describe the expansion of a plasma into vacuum with a two-temperature electron distribution function (a " cold " and a " hot " electron population). In the first part, the characteristics (amplitude, position, microscopic structure, etc.) of the rarefaction shock which occurs in the plasma when the hot- to the cold-electron temperature ratio is larger than 9.9 are investigated with a semi-infinite plasma; i.e., an infinite source of particles and energy. Asymptotic expressions of the quantities of the flow are established in the limit of large temperature ratios. The behavior of the plasma structure is specified for different regimes of flow. The effects of the rarefaction shock on the ion acceleration are briefly discussed. The numerical simulations performed with a 1-D hybrid code are compared to the results of the analytical model. In the second part, we study the expansion into a vacuum of a thin-foil with a 1-D kinetic code. Conversely to the semi-infinite model, the electron distribution function does no stay bi-Maxwellian in time, but its dynamic is governed by Vlasov equation. The results of this code are used to explain the heating of the cold electrons, for a sufficiently large hot- to cold-electron density ratio. An expression of the cold temperature, during the acceleration of the rarefaction wave towards the center of the foil, is established. The maximum temperature gain is estimated in terms of the initial plasma parameters. For low values of the hot- to cold-electron density ratio, we evidence a global cooling of electrons over different time scales and then a reduction of the effective amplitude of the rarefaction shock.
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Abdourahmane Diaw. Étude théorique et numérique de l'expansion dans le vide d'un plasma créé par laser : cas d'une fonction de distribution des électrons bi-Maxwellienne. Physique des plasmas [physics.plasm-ph]. Ecole Polytechnique X, 2013. Français. ⟨pastel-00789762⟩

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