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  • 1
    Electronic Resource
    Electronic Resource
    Ablation front Rayleigh–Taylor growth experiments in spherically convergent geometry : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2033-2039 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments were performed on the Nova laser [E. M. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)], using indirectly driven capsules mounted in cylindrical gold hohlraums, to measure the Rayleigh–Taylor growth at the ablation front by time-resolved radiography. Modulations were preformed on the surface of Ge-doped plastic capsules. With initial modulation amplitude of 2–2.5 μm, growth factors of about six in optical depth were seen, in agreement with simulations using the radiation hydrocode FCI2 [G. Schurtz, La fusion thermonucleaire inertielle par laser, edited by R. Dautray et al. (Eyrolles, Paris, 1994), Vol. 2]. With initial modulation amplitude of 0.5 μm and a longer drive, growth factors of about 100–150 in optical depth were seen. Comparable planar experiments showed growth factors of about 40 in optical depth. Analytical models predict the observed growth factors. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874024
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  • 2
    Electronic Resource
    Electronic Resource
    Exploring the limits of the National Ignition Facility's capsule coupling : The 41st annual meeting of the division of plasma physics of the american physical society (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2092-2098 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The original ignition "point designs" (circa 1992) for the National Ignition Facility (NIF) [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, 755 (1994)] were made energetically conservative to provide margin for uncertainties in laser absorption, x-ray conversion efficiency and hohlraum-capsule coupling. Since that time, extensive experiments on Nova [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)] and Omega [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] and their related analysis indicate that NIF coupling efficiency may be almost "as good as we could hope for." Given close agreement between experiment and theory/modeling, one can credibly explore target enhancements which couple more of NIFs energy to an ignition capsule. These include using optimized mixtures of materials to reduce x-ray wall losses, slightly reduced laser entrance holes, and laser operation strategies which increase the amount of energy one can extract from NIF. It is found that 3–4× increases in absorbed capsule energy appear possible, providing a potentially more robust target and ∼10× increase in capsule yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873913
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  • 3
    Electronic Resource
    Electronic Resource
    Three-dimensional HYDRA simulations of National Ignition Facility targets : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2275-2280 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of a targets designed for the National Ignition Facility (NIF) are simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. [M. Marinak et al., Phys. Plasmas 5, 1125 (1998)] In simulations of a cylindrical NIF hohlraum that include an imploding capsule, all relevant hohlraum features and the detailed laser illumination pattern, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser light is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics mirror the results from an axisymmetric simulation. A NIF capsule simulation resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of anomalous low mode growth driven by nonlinear mode coupling. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1356740
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetization processes in Co–Cr submicron samples: Hall measurements and micromagnetic simulations : 38th Annual Conference On Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5508-5510 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetization reversal of Co–Cr with perpendicular anisotropy is studied by anomalous Hall effect measurements and by micromagnetic simulations. In a measured hysteresis loop of a 300 nm×300 nm sample (consisting of approximately 40 columns of Co–Cr), discrete jumps are observed, together with a more or less continuous change in magnetization, the latter with both positive and negative sign. The continuous and discrete parts of the hysteresis loop are separated to extract micromagnetic information from the anomalous Hall measurement. The discrete jumps are attributed to parts of columns that switch irreversibly, the continuous magnetization change is attributed to reversible rotation, partly of volumes with in-plane anisotropy. These assumptions are checked by means of a micromagnetic model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355671
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  • 5
    Electronic Resource
    Electronic Resource
    A simple time-dependent analytic model of the P2 asymmetry in cylindrical hohlraums : 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. 2137-2143 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple time-dependent analytic view factor model for the P2 asymmetry in cylindrical hohlraums is presented. The model includes the effects of hohlraum wall motion, time-varying hohlraum wall albedo and time-varying hohlraum-to-capsule diameter. The results of the model compare well with predictions from two-dimensional radiation hydrodynamics computer simulations and with time-resolved hohlraum symmetry data obtained at the Nova laser facility [J. T. Hunt and D. R. Speck, Opt. Eng. 28, 461 (1989)] and Omega laser facility [J. M. Sources, R. L. McCrory, C. P. Verdon et al., Phys. Plasmas 3, 2108 (1996)]. The model is also extended to the more complicated but relevant case of a multiple-ring cylindrical hohlraum illumination geometry, the baseline scheme for the National Ignition Facility [J. A. Paisner, J. D. Boyes, S. A. Kumpan, and M. Sorem, ICF Quart. 5, 110 (1995)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873465
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  • 6
    Electronic Resource
    Electronic Resource
    A comparison of three-dimensional multimode hydrodynamic instability growth on various National Ignition Facility capsule designs with HYDRA simulations (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 1125-1132 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three similar cryogenic ignition capsule designs for the National Ignition Facility [J. Lindl, Phys. Plasmas 2, 3933 (1995)] are analyzed to determine surface roughness specifications required to mitigate the growth of hydrodynamic instabilities. These capsule utilize brominated plastic, polyimid and copper-doped beryllium ablator materials respectively. Direct three-dimensional numerical simulations with the HYDRA radiation hydrodynamic code [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)] examine the growth of multimode perturbations seeded by roughness on the outer ablator and inner ice surfaces. The simulations, which showed weakly nonlinear behavior for optimized surfaces, were carried through ignition and burn. A three-dimensional multimode perturbation achieves somewhat larger amplitudes in the nonlinear regime than a corresponding two-dimensional simulation of the same rms amplitude. The beryllium and polyimid capsules exhibit enhanced tolerance of roughness on both the ice and ablator surfaces. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872643
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  • 7
    Electronic Resource
    Electronic Resource
    Three-dimensional simulations of Nova high growth factor capsule implosion experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2070-2076 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Capsule implosion experiments carried out on the Nova laser [E. M. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)] are simulated with the three-dimensional HYDRA radiation hydrodynamics code [NTIS Document No. DE-96004569 (M. M. Marinak et al. in UCRL-LR-105821-95-3)]. Simulations of ordered, near single mode perturbations indicate that structures which evolve into round spikes can penetrate farthest into the hot spot. Bubble-shaped perturbations can burn through the capsule shell fastest, in which case they cause even more damage. A simulation of a capsule with a multimode perturbation of moderate amplitude shows spike amplitudes evolving in good agreement with a saturation model during the deceleration phase. The presence of sizable low mode asymmetry, caused either by drive asymmetry or perturbations in the capsule shell, can dramatically affect the manner in which spikes approach the center of the hot spot. Three-dimensional coupling between the low mode shell perturbations intrinsic to Nova capsules and the drive asymmetry is found to be important, bringing the simulated neutron yields into closer agreement with the experimental values. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872004
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  • 8
    Electronic Resource
    Electronic Resource
    Reduced scale National Ignition Facility capsule design (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3708-3713 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we describe the design and simulated performance characteristics of an indirectly-driven inertial confinement fusion capsule which utilizes only 900 kJ of laser energy and 250 TW of laser power from the National Ignition Facility (NIF) [Paisner et al., Laser Focus World 30, 75 (1994)]. This intentional reduction in laser performance from the nominal NIF specifications of 1.8 MJ and 500 TW results in lowering the hohlraum x-ray drive temperature from 300 eV to 250 eV. These energy and radiation temperature reductions are believed to define a "lower bound" on the successful implosion of an ignition capsule. This reduced scale capsule has a beryllium ablator containing a radially varying copper dopant, and a cryogenic solid deuterium–tritium fuel layer surrounding a cavity filled with equilibrium vapor pressure gaseous deuterium and tritium. Two-dimensional simulations predict ignition and propagated burn from this capsule when either Rayleigh–Taylor instability or time-dependent drive asymmetry effects are included. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873086
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  • 9
    Electronic Resource
    Electronic Resource
    Modeling of Nova indirect drive Rayleigh–Taylor experiments (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3652-3661 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth due to the Rayleigh–Taylor (RT) instability of single-wavelength surface perturbations on planar foils of brominated CH [CH(Br)] and fluorosilicone (FS) was measured. The foils were accelerated by x-ray ablation with temporally shaped drive pulses. A range of initial amplitudes (a0) and wavelengths (λ) have been used. This paper focuses upon foils with small a0/λ, which exhibit substantial growth in the linear regime, and are most sensitive to the calculated growth rate. The CH(Br) foils exhibit slower RT perturbation growth because opacity differences result in a larger ablation velocity and a longer density scale length than for FS. Tabulated opacities from detailed atomic models, OPAL [Astrophys. J. 397, 717 (1992)] and super transition array (STA) [Phys. Rev. A 40, 3183 (1989)] were employed. Unlike previous simulations which employed the average atom (XSN) opacity treatment, parameter adjustments to fit experimental data no longer appear necessary. Nonlocal thermodynamic equilibrium (NLTE) effects do not appear to be important. Other variables which may affect the modeling, such as changes of the equation of state and radiation drive spectrum, were also examined. The current calculational model, which incorporates physically justified choices for these calculational ingredients, agrees with the Nova single wavelength RT perturbation growth data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870900
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  • 10
    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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