Direct-Drive Measurements of Laser-Imprint--Induced Shock-Velocity Nonuniformities and Laser Imprint Mitigation

ORAL

Abstract

In laser-direct-drive inertial confinement fusion, nonuniformities in the laser drive caused by laser speckle and beam-to-beam intensity variations, as well as mass modulations in the target, can seed the Richtmyer--Meshkov and Rayleigh--Taylor hydrodynamic instabilities and adversely affect the compression of the imploding shell. The physical energy transfer of the laser-intensity modulations to the shock front, called laser imprint, depends strongly on the initial plasma formation. Perturbations in the velocity profile of a laser-ablation driven shock wave seeded by laser imprint were recorded using a 2-D high-resolution velocimeter. The measured results for experiments with one, two, and five overlapping beams incident on target demonstrate a reduction in long-wavelength (\textgreater 25-?m) perturbations with an increasing number of overlapping laser beams, consistent with theoretical expectations. These measurements are crucial to validate radiation-hydrodynamics simulations of laser imprint, since they highlight a threefold underestimation of the level of seeded perturbation when the microphysics processes for initial plasma formation such as multiphoton ionization are neglected.

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Authors

  • J. Peebles

    University of Rochester, Laboratory for Laser Energetics

  • S. X. Hu

    Laboratory for Laser Energetics, Laboratory for Laser Energetics, University of Rochester, University of Rochester

  • Wolfgang Theobald

    Laboratory for Laser Energetics, University of Rochester, Laboratory for Laser Energetics, U. of Rochester, Laboratory for Laser Energetics, University of Rochester, Laboratory of Laser Energetics

  • V. N. Goncharov

    Laboratory for Laser Energetics, University of Rochester, Laboratory for Laser Energetics, University of Rochester - LLE, Laboratory for Laser Energetics, University of Rochester, Laboratory for Laser Energetics, U. of Rochester, University of Rochester, Laboratory for laser Energetics, University of Rochester

  • N. Whiting

    Laboratory for Laser Energetics

  • Michael Campbell

    Laboratory for Laser Energetics, U. of Rochester, LLE, University of Rochester, Laboratory for Laser Energetics, University of Rochester - LLE, Laboratory for Laser Energetics, University of Rochester, Laboratory for Laser Energetics

  • Tom Boehly

    Laboratory for Laser Energetics

  • Sean Regan

    LLE, University of Rochester, Laboratory for Laser Energetics, University of Rochester - LLE, University of Rochester, Laboratory for Laser Energetics, U. of Rochester, Laboratory for Laser Energetics, University of Rochester, Laboratory for Laser Energetics

  • S. J. Ali

    Lawrence Livermore National Laboratory

  • Peter Celliers

    Lawrence Livermore National Laboratory

  • G. Duchateau

    University Bordeaux-CNRS-CEA