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  • 1
    Electronic Resource
    Electronic Resource
    Shock structuring due to fabrication joints in targets (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3327-3336 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of copper-doped beryllium ablators on National Ignition Facility [J. A. Paisner et al., Laser Focus World 30, 75 (1994)] targets, in place of plastic, can require the bonding together of hemispheres with a joint of differing composition. Indirect drive experiments have been conducted on the Nova laser [J. L. Emmet, W. F. Krupke, and J. B. Trenholme, Sov. J. Quantum Electron. 13, 1 (1983)], and the resulting shock structuring compared with code simulations. It is concluded that one of the available codes, the RAGE code [R. M. Baltrusaitis et al., Phys. Fluids 8, 2471 (1996)] provides useful insight into the effect of joints. This code is then employed to obtain a physical picture of the shock front nonuniformity in terms of a secondary rarefaction and an oblique shock interacting with the main shock that propagates in the absence of the joint. A simple analysis reinforces this picture.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873572
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  • 2
    Electronic Resource
    Electronic Resource
    Moderate-convergence inertial confinement fusion implosions in tetrahedral hohlraums at Omega (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2594-2603 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A highly uniform thermal x-radiation field for indirect-drive inertial confinement fusion implosions may be obtained by irradiating a four-hole, tetrahedral geometry, spherical hohlraum with all 60 Omega laser beams. Implosion studies and calculations [J. M. Wallace et al., Phys. Rev. Lett. 82, 3807 (1999)] indicate a drive uniformity comparable to that expected for the National Ignition Facility [J. A. Painser et al., Laser Focus World 30, 75 (1994)]. With 60 beams distributed over the cavity wall, tetrahedral hohlraums have a natural insensitivity to power balance and pointing errors. Standard, smooth Nova capsules imploded with this drive indicate that moderate convergence-ratio implosions, Cr∼18, have measured-neutron yield to calculated-clean-one-dimensional-neutronyield ratios similar to those previously investigated using the comparatively poor drive uniformity of Nova cylindrical hohlraums. This may indicate that a nonsymmetry-related neutron yield degradation mechanism, e.g., hydrodynamic mixing of cold, dense ablator material with the hot-spot region or some combination of nonsymmetry effects, is dominating in this Cr regime. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874101
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  • 3
    Electronic Resource
    Electronic Resource
    Observation of reduced beam deflection using smoothed beams in gas-filled hohlraum symmetry experiments at Nova (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 1609-1613 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Execution and modeling of drive symmetry experiments in gas-filled hohlraums have been pursued to provide both a better understanding of radiation symmetry in such hohlraums and to verify the accuracy of the design tools which are used to predict target performance for the National Ignition Facility (NIF) [J. Lindl, Phys. Plasmas 2, 3933 (1995)]. In this paper, the results of a series of drive symmetry experiments using gas-filled hohlraums at the Nova laser facility [C. Bibeau et al., Appl. Opt. 31, 5799 (1992)] at Lawrence Livermore National Laboratory are presented. A very important element of these experiments was the use of kineform phase plates (KPP) to smooth the Nova beams. The effect of smoothing the ten Nova beams with KPP phase plates is to remove most of the beam bending which had been observed previously, leaving a residual bending of only 1.5°, equivalent to a 35 μm pointing offset at the hohlraum wall. The results show that the symmetry variation with pointing of implosions in gas-filled hohlraums is consistent with time integrated modeling. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873982
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  • 4
    Electronic Resource
    Electronic Resource
    Indirect drive experiments utilizing multiple beam cones in cylindrical hohlraums on OMEGA : 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. 1960-1965 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current plans for time-dependent control of flux asymmetry in the National Ignition Facility [J. A. Paisner, J. D. Boyes, S. A. Kumpan, and M. Sorem, "The National Ignition Facility Project," ICF Quart. 5, 110 (1995)] hohlraums rely on multiple beam cones with different laser power temporal profiles in each cone. Experiments with multiple beam cones have begun on the Omega laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at the University of Rochester. In addition to allowing symmetry experiments similar to those performed on Nova [A. Hauer et al., Rev. Sci. Instrum. 66, 672 (1995)], the Omega facility allows multiple beam cones to be moved independently to confirm our ability to model the resulting implosion image shapes. Results indicate that hohlraum symmetry behaves similarly with multiple rings of beams as with a single ring, but with the weighted beam spot position used to parametrize the beam pointing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872866
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  • 5
    Electronic Resource
    Electronic Resource
    Symmetry experiments in gas-filled hohlraums at NOVA (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2022-2028 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Understanding drive symmetry in gas-filled hohlraums is currently of interest because the baseline design of the indirect drive ignition target for the planned National Ignition Facility uses a gas-filled hohlraum. This paper reports on the results of a series of experiments performed at the Nova laser [C. Bibeau et al. Appl. Opt. 31, 5799 (1992)] facility at Lawrence Livermore National Laboratory with the goal of understanding time-dependent drive symmetry in gas filled hohlraums. Time-dependent symmetry data from capsule implosions and reemission targets in gas-filled hohlraums are discussed. Results of symmetry measurements using thin wall gas-filled hohlraums are also discussed. The results show that the gas is effective in impeding the motion of the wall blowoff material, and that the resulting implosion performance of the capsule is not significantly degraded from vacuum results. The implosion symmetry in gas differs from vacuum results with similar laser pointing indicating a shift in beam position on the hohlraum wall and hotter drive at the capsule's poles than at the equator. A theory has been proposed to explain the observed shift as a plasma physics effect: beam steering due to filamentation and transverse plasma flows. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871999
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  • 6
    Electronic Resource
    Electronic Resource
    X-ray spectroscopy of high-energy density inertial confinement fusion plasmas (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3328-3336 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Analysis is presented of K- and L-shell spectra obtained from Ar and Xe dopants seeded into the fuel region of plastic capsules indirectly imploded using the Nova laser. Stark broadening measurements of the n=3-1 lines in H- and He-like Ar (Ar Ly-β and He-β, respectively) are used to infer fuel electron density, while spatially averaged fuel electron temperature is deduced from the ratio of the intensities of these lines. Systematic variations in Ar spectral features are observed as a function of drive conditions. A spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data. It is shown that correct modeling of the x-ray emission requires a proper treatment of the coupled radiative transfer and kinetics problem. Continuum lowering effects are shown not to affect diagnostic line ratios, within the confines of a simple model. A recently developed diagnostic based on fitting measured line profiles of Ar He-β and its associated dielectronic satellites to theory is shown to provide a simultaneous measure of electron temperature and electron density. L-shell Xe spectroscopy is under development as an electron temperature and electron-density diagnostic. Density and temperature sensitive ratios of spectral features each consisting of many lines have been identified. Observed Xe spectra from imploded cores show the same qualitative behavior with temperature, as predicted by model calculations of Xe emission spectra. Stark broadening of Ne-like Xe 4-2 lines appears viable as an electron density diagnostic for Ne∼1025 cm−3 and is under continuing investigation. (Based on the invited paper 8I3 at the 1992 APS/DPP annual meeting [Bull. Am. Phys. Soc. 37, 1553 (1992)].)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860964
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  • 7
    Electronic Resource
    Electronic Resource
    Collision and interpenetration of plasmas created by laser-illuminated disks (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 979-988 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Supersonic, counterstreaming plasmas were produced by ablating plasma from the inside surfaces of two parallel disks made of aluminum and magnesium, respectively, with a 0.53 μm laser at an intensity of 1014 W/cm2 for 1.3 nsec. Diagnostics included holographic interferometry, a time-integrated x-ray pinhole camera and a gated x-ray crystal spectrograph with imaging slits. The plasmas interpenetrate for the first half of the laser pulse but stagnate once the electron density exceeds 5×1020 cm−3. Spectroscopic measurements suggest a coronal electron temperature of ∼800 eV and an ion temperature of ∼15 keV in the stagnated plasma. The observations are in good agreement with a two ion fluid model of interpenetrating plasmas in which the dominant slowing down process is ion–ion collisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860114
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  • 8
    Electronic Resource
    Electronic Resource
    K- and L-shell x-ray spectroscopy of indirectly driven implosions (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. 5017-5021 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Time-resolved x-ray spectroscopy is used to study the implosion of indirectly driven inertial confinement fusion capsules on the Nova laser. Through the use of high-Z dopants (Ar and Xe) in the fuel, measurements of the peak temperature, from emission line ratios, and density, from line broadening, are obtained. These measurements indicate peak electron temperatures of ∼1–1.6 keV and electron (and deuteron) densities in the range of 1.0–2.0×1024 cm−3, depending on the type of laser drive used. The higher densities are achieved on targets that are driven with a shaped laser drive that allows a more isentropic compression of the fuel. Emission from high-Z pusher dopants have also been studied. These dopants can provide information on pusher conditions and can be used to study mix at the pusher fuel interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143477
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  • 9
    Electronic Resource
    Electronic Resource
    Density and temperature diagnostic based on the Ar He β line and associated Li-like satellites : 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. 5119-5121 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have modeled the temperature and density dependence of the Li-like satellites of the Ar He β line by performing NLTE kinetic modeling of level populations in conjunction with Stark broadening calculations. Composite line profiles are computed including resonance and satellite line transitions that have built-in the temperature and density dependence characteristic of the level populations and Stark broadening of these transitions. These synthetic spectra can be used to analyze experimental data, providing a simultaneous diagnostic of temperature and density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143458
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