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  • 1
    Electronic Resource
    Electronic Resource
    Hydrodynamic target response to an induced spatial incoherence-smoothed laser beam (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2640-2651 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One of the critical elements for high-gain target designs is the high degree of symmetry that must be maintained in the implosion process. The induced spatial incoherence (ISI) concept has some promise for reducing ablation pressure nonuniformities to ≈1%. The ISI method produces a spatial irradiance profile that undergoes large random fluctuations on picosecond time scales but is smooth on long time scales. The ability of the ISI method to produce a nearly uniform ablation pressure is contingent on both temporal smoothing and thermal diffusion. In the start-up phase of a shaped reactorlike laser pulse, the target is directly illuminated by the laser light and thermal diffusion is not effective at smoothing residual nonuniformities in the laser beam. During this period in the laser pulse, the target response is dominated by the initial shock generated by the laser pulse and the results indicate that this first shock can be the determining factor in the success or failure of the implosion process. The results of numerical simulations of several target/laser pulse designs which were investigated in an attempt to mitigate the impact of the initial shock structure stemming from the early temporal phase of an ISI-smoothed laser beam are presented. It is shown that "foamlike'' layers, multiple laser wavelengths, and shallow angles of incidence can sharply reduce the perturbation level stemming from the first shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859976
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of the Rayleigh–Taylor instability in colliding, ablatively driven laser foils (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3485-3493 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper reports results from a series of numerical simulations of a pair of independently accelerated rectilinear foils in the presence of the ablative Rayleigh–Taylor (RT) instability on the laser-side surfaces. The foil thickness and laser intensity are chosen to be in the range relevant to high-gain inertial fusion pellets, with 80 μm thick plastic (CH) foils accelerated toward each other from a separation distance of 650 μm by a 1/4 μm laser beam with an intensity of 3×1014 W/cm2. At early times the foils are physically well separated from one another, and evolve independently in a way that is fully consistent with the previously studied evolution of ablatively RT unstable planar targets [Gardner et al., Phys. Fluids B 3, 1070 (1991)]. Subsequently, pressure builds up in the region between the foils, causing them to decelerate. This stabilizes the RT growth on the laser sides, while driving the RT instability on the inner sides. For thin foils, laser-side RT bubbles become rapidly growing inner surface RT spikes which mix and coalesce as the foils are pressed together.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859726
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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