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  • 1
    Monograph available for loan
    Monograph available for loan
    Five-day mean 500 hPa height and mean sea level pressure fields for the Northern Hemisphere (1946-1977) (1983)
    Geneva : WMO
    Associated volumes
    Details Availability
    Call number: MOP Per 849(2)
    In: Long-range forecasting research publication series
    Type of Medium: Monograph available for loan
    Series Statement: Long-range forecasting research publication series 2
    Location: MOP - must be ordered
    Branch Library: GFZ Library
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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
    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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  • 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
    Convective gain of stimulated Brillouin scattering in long-scale length, two-ion-component plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 1073-1090 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear kinetic theory is developed for the convective amplification of stimulated Brillouin scattering in a plasma containing two distinct ion species. A computationally tractable expression for the gain coefficient Q is obtained by, first, restricting consideration to growth from the two possible weakly damped ion modes in the two-ion-species plasma and, second, invoking the two-mode approximation for ε−1, the ion response function, in the plasma. Furthermore, a practical procedure is presented for efficiently obtaining Q over the mesh of a large-scale hydrodynamic simulation of a laser-irradiated target. The theory and its application are demonstrated in the simulation of a simple gas target. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871763
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  • 6
    Electronic Resource
    Electronic Resource
    Convective threshold of stimulated Brillouin scattering in a two-ion plasma (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1682-1695 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The convective threshold of stimulated Brillouin backscatter (SBS) in a laser-irradiated plasma containing two distinct ion species is investigated over a wide range of plasma conditions and laser intensities. This investigation, carried out in the context of kinetic theory, is a generalization of a previous investigation of ion acoustic waves in a two-ion plasma, i.e., the unpumped system. The totality of SBS modes in the two-ion system is obtained using a numerical sweep through the complex-ω plane. The coupling of the electromagnetic pump wave to the plasma produces only one mode, in addition to the ion acoustic modes. Because this additional mode is not a normal mode of the plasma in the absence of the pump wave, it is called a quasimode. The SBS modes fall into three classes: (a) at least one and, at most, two modes that are weakly damped for sufficiently low laser intensity, reducing to the weakly damped ion acoustic modes as the pump strength vanishes; (b) an infinity of critically damped modes, most of which are relatively insensitive to the laser intensity; and (c) a single mode (quasimode), which may exhibit either growth or damping as laser intensity increases. The threshold laser intensity for convective SBS growth, the smallest intensity, where one of the modes ceases to be damped, ωI=0, may be associated with modes of classes (a), (b), or (c). The present study shows that the growing mode is not necessarily associated with the SBS modes obtained from fluid theory. A practical numerical procedure is presented for quickly determining the threshold intensity for SBS in a two-ion system for a given set of plasma parameters. The method is quite efficient and may be readily incorporated into large-scale hydrodynamic simulation codes to provide an assessment of SBS growth over the numerical mesh of the computation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871317
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  • 7
    Electronic Resource
    Electronic Resource
    An analytical and numerical investigation of ion acoustic waves in a two-ion plasma (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3542-3556 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ion acoustic dispersion relation for a plasma containing two distinct ion species is investigated over a wide range of plasma conditions. An approximate general analytic solution to the dispersion relation has been found, and is shown, by comparison to accurate numerical solutions of the individual modes, to be remarkably precise. This solution provides for the first time a systematic account of the totality of ion acoustic modes of the two-ion system. It has been found that ion acoustic modes consist of two types of modes: (a) at least one, and, at most, two weakly damped modes for which ||ωI/ωR||(very-much-less-than)1, and (b) an infinity of critically damped modes for which ωI/ωR(approximately-equal-to)−1. The critically damped modes are organized into two distinct categories: (a) modes for which ||ω||/k(approximately-greater-than)vF (vF is the thermal speed of the fast ion species); and (b) modes for which vS〈||ω||/k〈vF (vS is the thermal speed of the slow ion species). The critically damped modes with ||ω||/k(approximately-greater-than)vF are further organized into three distinct classes: (1) modes with phase speeds characterized by vF, (2) modes with phase speeds characterized by vFvS/(square root of)v2F−v2S, and (3) modes with phase speeds characterized by vS. The critically damped modes with vS〈||ω||/k〈vF belong to a single class, and are characterized by vS. Generally, it is found that there are one, or, at most, two modes with relatively small damping, while most of the remaining modes are too strongly damped to be physically realized. It has also been found possible to maximize the ion acoustic damping in a two-ion plasma by a judicious choice of the relative ion concentrations. More specifically, an admixture of the lighter ion species will maximize the damping coefficient over a wide range of plasma conditions. This is important for certain gas-filled, inertial-fusion targets of current interest, where it is desirable to minimize the stimulated Brillouin backscatter process by maximizing the damping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870889
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  • 8
    Electronic Resource
    Electronic Resource
    Weibel instability with constant driving source (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1579-1586 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method has been developed for performing numerical particle-in-cell simulations of the Weibel instability in which the driving anisotropy is held constant. With the method, the instability is computed to grow to saturation in a well-behaved manner. Initially, growth is in close agreement with the predictions of linear theory. Subsequently, the growth rate falls below linear-theory predictions as magnetic fields grow to substantial levels. And finally, the instability reaches saturation, after which a steady state is established. A single mode comes to dominate the magnetic field at late times in the simulations. This is the mode identified in linear theory as the most rapidly growing. The method has been employed to investigate the importance of the Weibel instability in laser-produced plasmas. It is found that, because of saturation, the fields do not grow sufficiently to affect heat flow (ωcτ〈1) in the overdense plasma. In the near-critical underdense plasma, the fields would have, at most, marginal influence for shorter wavelength irradiation (λL≤0.25 μm) but possibly substantial influence at longer wavelengths (λL≥1 μm).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859677
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  • 9
    Electronic Resource
    Electronic Resource
    Self-focusing and filamentation of laser light in high Z plasmas (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 1249-1272 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Self-focusing and filamentation of short wavelength laser light in high Z plasmas of interest to laser fusion are discussed. It is found that self-focusing behavior is very dependent on the details of the characteristics of the laser beam, the plasma conditions, and the energy transport processes. Laser light absorption and self-focusing are strongly competitive processes. At. 0.26 μm wavelength the collisional absorption is often so great that there is no intensity amplification of the beam despite the fact that strong self-focusing is present. Wide variations are found in laser light penetration, affected by several factors. Diverging optics reduce the likelihood of self-focusing. Large scale length density gradients have little effect on focusing behavior. The self-focusing behavior is very dependent on beam shape. Large scale hot spots can have a significant effect on whole beam self-focusing early in the pulse. The behavior of small scale hot spots can be qualitatively different than the standard picture. The calculations indicate that small scale hot spots do not achieve a steady state in some cases. Sound waves cause chaotic interactions among neighboring hot spots. It is found that sub-beam size structures are also generated when nonlocal thermodynamic equilibrium (non-LTE) radiation and atomic physics are used in the calculations. The nature of the heat flux and thermoelectric magnetic field generation are examined with a kinetic model. Stimulated Raman backscattering levels in self-focused light are significantly reduced for short wavelengths and high Z plasmas Landau damping plays an important role in determining the Raman levels. Implications for suprathermal electron production, symmetric illumination, x-ray conversion efficiency, and laser light absorption are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866754
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  • 10
    Electronic Resource
    Electronic Resource
    Collisional effects on the Weibel instability (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1085-1088 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of electron Rutherford scattering on the Weibel instability are investigated using the implicit plasma simulation code venus [J. Comput. Phys. 46, 271 (1982); 63, 434 (1986)]. Collisions decrease the Weibel growth rate below the collisionless value, in agreement initially with simple linear theory. Likewise, collisions decrease the saturation level, in agreement with a magnetic trapping mechanism. When the collision rate exceeds the collisionless Weibel growth rate, the instability is suppressed altogether. The results provide benchmarks for analysis of proposed short-wavelength laser-fusion schemes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866305
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