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  • 1990-1994  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Induced spatial incoherence effects on the convective Raman instability (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 910-919 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the induced spatial incoherence method of laser beam smoothing on the convective Raman instability in an underdense inhomogeneous plasma has been studied. It is found that only for bandwidths comparable to, or greater than, the time-averaged homogeneous growth rate, is there significant smoothing effect resulting in a reduction of the backscattered radiation. However, for narrow bandwidths the backscattered radiation computed in the presence of hot spots created by the echelons, turns out to be significantly less than the levels observed in the Naval Research Laboratory experiments. We argue that a combination of three-dimensional effects and filamentation may account for the observed level of enhanced scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860941
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of bandwidth on the convective Raman instability in inhomogeneous plasmas (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2882-2888 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of bandwidth on the convective amplification of the Raman instability in the underdense, inhomogeneous plasma is investigated. For the case when the homogeneous growth rate γ0(very-much-less-than)Δω, where Δω is the bandwidth, it is shown both analytically and numerically that there is no effect of bandwidth on the convective amplification. The reduction in the homogeneous growth rate due to the bandwidth is compensated for by an increase in the interaction region such that the convective amplification is unaffected. For γ0(approximately-greater-than)Δω there is a statistical enhancement in the amplification factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859921
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of induced spatial incoherence on the absolute Raman instability (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 776-780 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical and analytical study of the Raman instability in a homogeneous plasma is presented in which the pump has been modeled to include the effects of broad bandwidth and the induced spatial incoherence (ISI) method of beam smoothing. For a time-averaged homogeneous growth rate γ¯0 and a bandwidth σ, there is a significant reduction in Raman backscattering when σ(approximately-greater-than)2γ0, for γ¯20 near threshold intensity. However, for γ¯20 very large compared to the threshold, neither ISI nor bandwidth affects Raman scattering.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859873
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    Paper (German National Licenses)
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  • 4
    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
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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