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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 36 (1964), S. 133-138 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1737-1739 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The final stages in the compression of microencapsulated DT fueled ICF targets require detailed characterization for meaningful comparison with predictions of hydrodynamic codes. The determination of such parameters as the fuel and shell areal densities, the average ion temperature, and the impact of implosion nonuniformities in high-density target implosions present a strong challenge. We describe several approaches utilizing the self-generated neutrons to diagnose these conditions, including neutron spectrometry, neutron activation of tracer gas and shell materials, and neutron scattering techniques. The importance of making simultaneous measurements of several core parameters to limit ambiguity in interpretation is discussed.
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  • 3
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of gas-filled, plastic-shell implosions has significantly improved with advances in on-target uniformity on the 60-beam OMEGA laser system [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)]. Polarization smoothing (PS) with birefringent wedges and 1-THz-bandwidth smoothing by spectral dispersion (SSD) have been installed on OMEGA. The beam-to-beam power imbalance is ≤5% rms. Implosions of 20-μm-thick CH shells (15 atm fill) using full beam smoothing (1-THz SSD and PS) have primary neutron yields and fuel areal densities that are ∼70% larger than those driven with 0.35-THz SSD without PS. They also produce ∼35% of the predicted one-dimensional neutron yield. The results described here suggest that individual-beam nonuniformity is no longer the primary cause of nonideal target performance. A highly constrained model of the core conditions and fuel–shell mix has been developed. It suggests that there is a "clean" fuel region, surrounded by a mixed region, that accounts for half of the fuel areal density. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 211 (1966), S. 396-398 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] At Socorro, the pressure disturbance was recorded with two hot-wire pressure transducers and also with three seismographs. The seismographs were not compensated for pressure changes and thus were not of much interest to this report. At the Mountain Laboratory, the pressure wave was recorded with a ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5036-5043 
    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
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2122-2128 
    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.
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  • 7
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: OMEGA, a 60-beam, 351 nm, Nd:glass laser with an on-target energy capability of more than 40 kJ, is a flexible facility that can be used for both direct- and indirect-drive targets and is designed to ultimately achieve irradiation uniformity of 1% on direct-drive capsules with shaped laser pulses (dynamic range (approximately-greater-than)400:1). The OMEGA program for the next five years includes plasma physics experiments to investigate laser–matter interaction physics at temperatures, densities, and scale lengths approaching those of direct-drive capsules designed for the 1.8 MJ National Ignition Facility (NIF); experiments to characterize and mitigate the deleterious effects of hydrodynamic instabilities; and implosion experiments with capsules that are hydrodynamically equivalent to high-gain, direct-drive capsules. Details are presented of the OMEGA direct-drive experimental program and initial data from direct-drive implosion experiments that have achieved the highest thermonuclear yield (1014 DT neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser-fusion experiments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 4665-4676 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear growth rate of the Rayleigh–Taylor instability is calculated for accelerated ablation fronts with small Froude numbers (Fr(very-much-less-than)1). The derivation is carried out self-consistently by including the effects of finite thermal conductivity (κ∼Tν) and density gradient scale length (L). It is shown that long-wavelength modes with wave numbers kL0(very-much-less-than)1 [L0=νν/(ν+1)ν+1 min(L)] have a growth rate γ(approximately-equal-to)(square root of)ATkg−βkVa, where Va is the ablation velocity, g is the acceleration, AT=1+O[(kL0)1/ν], and 1〈β(ν)〈2. Short-wavelength modes are stabilized by ablative convection, finite density gradient, and thermal smoothing. The growth rate is γ=(square root of)αg/L0+c20k4L20V2a−c0k2L0Va for 1(very-much-less-than)kL0(very-much-less-than)Fr−1/3, and γ=c1g/(Vak2L20)−c2kVa for the wave numbers near the cutoff kc. The parameters α and c0−2 mainly depend on the power index ν; and the cutoff kc of the unstable spectrum occurs for kcL0∼Fr−1/3(very-much-greater-than)1. Furthermore, an asymptotic formula reproducing the growth rate at small and large Froude numbers is derived and compared with numerical results. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1402-1414 
    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.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2465-2472 
    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.
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