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  • 1
    Electronic Resource
    Electronic Resource
    Numerical modeling of effects of power imbalance on irradiation nonuniformities (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5036-5043 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the importance of various sources of power imbalance of the 24 beam OMEGA laser system in contributing to laser irradiation nonuniformity. Long spatial wavelength irradiation nonuniformities on target are investigated numerically by adapting existing uniformity codes to incorporate time-dependent density and temperature profiles. The analysis shows that power imbalance due to slightly detuned (≤100 μrad) frequency conversion crystals and small differences in the ultraviolet (UV)-transport losses (ΔE/E≤5%) makes only a modest contribution to the overall nonuniformity. However, power imbalance from pulse shape distortion was found to create substantial irradiation nonuniformity on the target early in the implosion. The predictions of the present analysis were verified by an experiment in which a well controlled power imbalance was applied. Good agreement was found between the experimentally observed core positions and those predicted by the simulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347091
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  • 2
    Electronic Resource
    Electronic Resource
    Review of indirect-drive ignition design options for the National Ignition Facility : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2164-2170 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several inertial confinement fusion (ICF) capsule designs have been proposed as possible candidates for achieving ignition by indirect drive on the National Ignition Facility (NIF) laser [Paisner et al., Laser Focus World 30, 75 (1994)]. This article reviews these designs, their predicted performance using one-, two-, and three-dimensional numerical simulations, and their fabricability. Recent design work at a peak x-ray drive temperature of 250 eV with either 900 or 1300 kJ total laser energy confirms earlier capsule performance estimates [Lindl, Phys. Plasmas 2, 3933 (1995)] that were based on hydrodynamic stability arguments. These simulations at 250 eV and others at the nominal 300 eV drive show that capsules having either copper doped beryllium (Be+Cu) or polyimide (C22H10N2O4) ablators have favorable implosion stability and material fabrication properties. Prototypes of capsules using these ablator materials are being constructed using several techniques: brazing together machined hemishells (Be+Cu), sputter deposition (Be+Cu), and monomer deposition followed by thermal processing (polyimide). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873467
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements of core and pusher conditions in surrogate capsule implosions on the OMEGA laser system : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1870-1879 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments have been carried out on the 60-beam, 30 kJ OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] as part of an integrated program to diagnose all phases of direct-drive capsule implosions. Laser-imprint levels and Rayleigh–Taylor growth rates associated with the spherical implosions have been inferred from planar-foil radiography experiments. In spherical targets, measurements of the combined effects of imprint and unstable growth at the ablation surface have been carried out using the burnthrough technique [J. Delettrez et al., Phys. Plasmas 1, 2342 (1994)]. Target behavior during the deceleration phase has been investigated using a series of surrogate cryogenic capsules in which the main fuel layer is represented by a Ti-doped CH shell and the hot spot is represented by an Ar-doped deuterium fill gas. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872858
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  • 4
    Electronic Resource
    Electronic Resource
    Self-consistent stability analysis of ablation fronts with large Froude numbers (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1402-1414 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear stability analysis of accelerated ablation fronts is carried out self-consistently by retaining the effect of finite thermal conductivity. Its temperature dependence is included through a power law (κ∼Tν) with a power index ν(approximately-greater-than)1. The growth rate is derived for Fr(very-much-greater-than)1 (Fr is the Froude number) by using a boundary layer analysis. The self-consistent Atwood number and the ablative stabilization term depend on the mode wavelength, the density gradient scale length, and the power index ν. The analytic formula for the growth rate is shown to be in excellent agreement with the numerical fit of Takabe, Mima, Montierth, and Morse [Phys. Fluids 28, 3676 (1985)] for ν=2.5 and the numerical results of Kull [Phys. Fluids B 1, 170 (1989)] over a large range of ν's. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871730
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  • 5
    Electronic Resource
    Electronic Resource
    Self-consistent stability analysis of ablation fronts in inertial confinement fusion (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2122-2128 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear stability analysis of accelerated ablation fronts is carried out self-consistently by retaining the effect of finite thermal conductivity. Its temperature dependence along with the density gradient scale length are adjusted to fit the density profiles obtained in the one-dimensional simulations. The effects of diffusive radiation transport are included through the nonlinear thermal conductivity (κ∼Tν). The growth rate is derived by using a boundary layer analysis for Fr(very-much-greater-than)1 (Fr is the Froude number) and a WKB approximation for Fr(very-much-less-than)1. The self-consistent Atwood number depends on the mode wavelength and the power law index for thermal conduction. The analytic growth rate and cutoff wave number are in good agreement with the numerical solutions for arbitrary ν(approximately-greater-than)1. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871664
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  • 6
    Electronic Resource
    Electronic Resource
    The role of the Rayleigh–Taylor instability in laser-driven burnthrough experiments (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2342-2349 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments were conducted to confirm that the Rayleigh–Taylor instability is the main process controlling the burnthrough time in imploding spherical experiments. In these experiments the laser irradiates targets overcoated with a parylene layer, in which one or more thin signature layers of moderate- to high-Z material are embedded to signal the penetration of the heat front. Target parameters were varied to study the effect on the burnthrough time of changes to target acceleration, Atwood number, and ablation velocity. The effects of improved laser uniformity through the introduction of smoothing by spectral dispersion are also presented. The results agree well with those obtained from a multimode mix model. This suggests that burnthrough experiments can be used to measure improvements in laser-irradiation or target-fabrication uniformity and to test methods to mitigate the growth of the Rayleigh–Taylor instability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870631
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  • 7
    Electronic Resource
    Electronic Resource
    Nonlinear evolution of multimode Rayleigh–Taylor instability in two and three dimensions (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2465-2472 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear evolution of the Rayleigh–Taylor instability from multimode initial perturbations is studied by two complementary approaches. First, a statistical-mechanics bubble-merger model is presented, that enables determination of the late-time scaling properties based on single-mode and two-bubble interaction physics. The results for Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) bubble and spike front penetrations are given, as well as scaling laws for mixing under a time-dependent driving acceleration. The second approach is a modal model, in which nonlinear mode coupling and saturation are included in an equation for effective modes that describe the mixed region. The importance of mode coupling in the generation of large structure that dominates the late stage evolution, and the relative importance of long-wavelength components in the initial perturbation spectra on the late-stage evolution are studied. Finally, multimode RT instability in three dimensions is studied by both full-scale simulations and the modal model. The effect and late-stage memory loss of different aspect ratios in the initial perturbation are demonstrated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871476
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  • 8
    Electronic Resource
    Electronic Resource
    Self-consistent cutoff wave number of the ablative Rayleigh–Taylor instability (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3844-3851 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The cutoff wave number of the ablative Rayleigh–Taylor instability is calculated self-consistently by including the effects of finite thermal conduction. The derived cutoff wave number is quite different from the one obtained with the incompressible fluid (∇⋅v˜=0) or sharp boundary models, and it is strongly dependent on thermal conductivity (K∼Tν) and the Froude number (Fr). The derivation is carried out for values of ν(approximately-greater-than)1, Fr(approximately-greater-than)1, and it is valid for some regimes of interest to direct and indirect-drive inertial confinement fusion (ICF). The analytic formula for the cutoff wave number is in excellent agreement with the numerical results of Kull [Phys. Fluids B 1, 170 (1989)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871083
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  • 9
    Electronic Resource
    Electronic Resource
    High-speed gated x-ray imaging for ICF target experiments (invited) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4813-4817 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the use of gated microchannel-plate detectors as high-speed framing cameras in laser-driven inertial-confinement-fusion experiments. Using an array of pinholes to image the target, detectors capable of generating up to 16 individual frames with ∼90 ps resolution on a single laser shot are now in routine use. The detectors have been used to study the development of intentionally applied perturbations in laser-driven targets. In off-line tests new detectors have demonstrated time resolutions better than 40 ps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143571
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  • 10
    Electronic Resource
    Electronic Resource
    Growth rates of the ablative Rayleigh–Taylor instability in inertial confinement fusion (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1446-1454 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple procedure is developed to determine the Froude number Fr, the effective power index for thermal conduction ν, the ablation-front thickness L0, the ablation velocity Va, and the acceleration g of laser-accelerated ablation fronts. These parameters are determined by fitting the density and pressure profiles obtained from one-dimensional numerical simulations with the analytic isobaric profiles of Kull and Anisimov [Phys. Fluids 29, 2067 (1986)]. These quantities are then used to calculate the growth rate of the ablative Rayleigh–Taylor instability using the theory developed by Goncharov et al. [Phys. Plasmas 3, 4665 (1996)]. The complicated expression of the growth rate (valid for arbitrary Froude numbers) derived by Goncharov et al. is simplified by using reasonably accurate fitting formulas. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872802
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