Force pondéromotrice, champs magnétiques et hydrodynamique des plasmas produits par laser

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Abstract
Non linear effects deeply change the structure of a laser driven plasma flow. For high intensities, the radiation pressure should be taken into account. It acts through a ponderomotive force proportional to the electron density and to the gradient of the mean electric field energy density of the incident wave. Static magnetic fields originate from a term in the ponderomotive force which includes radiation absorption and whose curl is non zero. The basic properties of the structure are determined analytically in the absence of thermal conductivity and magnetic fields : steep density gradient close to the cut-off density, shelf at lower densities. The conditions of a steady state régime are set up. The isothermal case is specially investigated. It is shown that the cavities which are created in a motionless plasma may disappear due to the onset of a flow. Régions in which electromagnetic forces arising from the static field compensate the ponderomotive force are determined. The subsequent effects on the flow itself are studied