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  • 1
    Electronic Resource
    Electronic Resource
    Nuclear diagnostics for the National Ignition Facility (invited) : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 773-779 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The National Ignition Facility (NIF), currently under construction at the Lawrence Livermore National Laboratory, will provide unprecedented opportunities for the use of nuclear diagnostics in inertial confinement fusion experiments. The completed facility will provide 2 MJ of laser energy for driving targets, compared to the approximately 40 kJ that was available on Nova and the approximately 30 kJ available on Omega. Ignited NIF targets are anticipated to produce up to 1019 DT neutrons. In addition to a basic set of nuclear diagnostics based on previous experience, these higher NIF yields are expected to allow innovative nuclear diagnostic techniques to be utilized, such as neutron imaging, recoil proton techniques, and gamma-ray-based reaction history measurements. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319356
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  • 2
    Electronic Resource
    Electronic Resource
    A sensitive neutron spectrometer for the National Ignition Facility : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 846-849 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We are developing a sensitive neutron spectrometer for the National Ignition Facility laser at Livermore. The spectrometer will consist of a 1020 channel single-neutron-interaction time-of-flight detector array fielded 23 m from the neutron-producing target. It will use an existing detector array together with upgraded electronics for improved time resolution. Measurements of neutron yield, ion and electron temperatures, and density-radius product are all possible under certain conditions using one-, two-, or three-step reaction processes. The locations of the most important potential sources of scattered neutron backgrounds are determined as the first step in designing collimation to reduce these backgrounds. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323242
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  • 3
    Electronic Resource
    Electronic Resource
    Interpretation of neutron time-of-flight signals from current-mode detectors : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 610-613 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Neutron time-of-flight (nToF) signals from current-mode neutron detectors are often used to determine burn-averaged ion temperature from ICF targets because the spread of the neutron energy distribution is a function of the temperature of the reacting ions. The measured signal will, however, be a convolution of the actual neutron signal, the detector response, and the response of the recording system. In addition, scattered neutrons will arrive at the detector later than unscattered neutrons, further broadening the signal. The ion temperature derived from nToF data depends strongly on the functions used to fit the data or the methods utilized to unfold the neutron energy spectrum. A functional form based on known and measured properties of the detectors is used to fit the integral of the time-of-flight signal, allowing ion temperature derivations from targets with lower neutron yield than previously possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147763
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  • 4
    Electronic Resource
    Electronic Resource
    Experimental configuration of direct drive cylindrical implosions on the OMEGA laser : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 471-475 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Details about the cylindrical implosions using direct-drive irradiation on the OMEGA Laser facility are provided. The experimental configuration, including orientation, construction, and mounting of the targets is described. An attempt to characterize the modulation transfer function of the primary x-ray framing camera diagnostic results in insufficient exposure contrast but relative agreement with other determinations. The x-ray intensity of the titanium backlighter driven by the 2.5-ns-linear ramp of the laser beams is described, and the relative intensity on film is compared to similar Nova experiments. The parallax effects of different length marker layers of high-opacity dichloropolystyrene are measured, resulting in the conclusion that the marker layer length should be matched to the laser drive illumination profile. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149480
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  • 5
    Electronic Resource
    Electronic Resource
    Measurements of neutron spectra from Nova targets : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 607-609 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have measured neutron spectra from targets on the Nova laser. The three basic classes of targets are (1) directly driven capsules with ablative or exploding pushers, (2) indirectly driven imploding capsules with various hohlraum drives, capsule thicknesses, capsule fill pressures, and hohlraum gas fills, and (3) gas-filled hohlraums containing deuterated gas mixtures. In many capsule implosions, the neutron spectra are significantly broader than predictions of fusion-reaction-weighted ion temperatures from simulations. For implosions of deuterated capsules filled with H2, the observed spectra are consistent with the predicted combination of thermal and motional broadening. For normal capsules filled with D2, we conjecture that implosion asymmetries may induce fluid motion within the compressed fuel which contributes to the measured spectral width, but not the fusion reactivity, and which is not included in the simulations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147665
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  • 6
    Electronic Resource
    Electronic Resource
    Neutron time-of-flight signals from expanding or contracting spherical sources : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 614-617 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The width of the energy distribution of fusion-produced neutrons is often used as an indication of the temperature of the reacting ions. The Doppler broadening of the neutron energy is due to the center-of-mass velocity of reacting ion pairs and is characterized by the ion temperature for a Maxwellian distribution of ions with zero collective velocity. If there is bulk fluid motion or turbulence characterized by a velocity on the order of the ion thermal speed, a significant additional broadening may be introduced. Suggestions of this phenomenon have been observed for two classes of laser targets. The first is a "gas bag" target, in which a deuterated hydrocarbon gas is contained in a thin spherical membrane and illuminated uniformly. The second target is an ICF capsule with a deuterated plastic inner layer. In both cases, measured neutron energy distributions were wider than expected from theoretical ion temperatures and if interpreted as indicative of the ion temperature, are inconsistent with the neutron yields observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147666
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Production of enhanced pressure regions due to inhomogeneities in inertial confinement fusion targets : 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. 2007-2013 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that regions of enhanced pressure have been produced in targets with indirect radiation drive in planar and cylindrically convergent geometry through the interaction between the flows caused by target inhomogeneities and the main target drive. Design calculations for National Ignition Facility (NIF) [J. A. Paisner et al., Laser Focus World 30, 75 (1994)] targets with beryllium ablators formed by bonded hemi-shells [D. C. Wilson et al., Bull. Am. Phys. Soc. 43, 1667 (1998)] indicate that related behavior produces a seed perturbation in the ablator which can in some cases lead to the suppression of ignition. From simulation and analysis of the NIF problem in the planar geometry analog, a scaling for the perturbation, which should be useful for validation of the behavior with lower energy drive and smaller-scale geometries, is derived. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874022
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  • 9
    Electronic Resource
    Electronic Resource
    Rayleigh–Taylor spike evaporation (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4156-4162 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-based experiments have shown that Rayleigh–Taylor (RT) growth in thin, perturbed copper foils leads to a phase dominated by narrow spikes between thin bubbles. These experiments were well modeled and diagnosed until this " spike" phase, but not into this spike phase. Experiments were designed, modeled, and performed on the OMEGA laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] to study the late-time spike phase. To simulate the conditions and evolution of late time RT, a copper target was fabricated consisting of a series of thin ridges (spikes in cross section) 150 μm apart on a thin flat copper backing. The target was placed on the side of a scale-1.2 hohlraum with the ridges pointing into the hohlraum, which was heated to 190 eV. Side-on radiography imaged the evolution of the ridges and flat copper backing into the typical RT bubble and spike structure including the " mushroom-like feet" on the tips of the spikes. RAGE computer models [R. M. Baltrusaitis, M. L. Gittings, R. P. Weaver, R. F. Benjamin, and J. M. Budzinski, Phys. Fluids 8, 2471 (1996)] show the formation of the " mushrooms," as well as how the backing material converges to lengthen the spike. The computer predictions of evolving spike and bubble lengths match measurements fairly well for the thicker backing targets but not for the thinner backings. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1386802
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic-fusion data acquisition at Los Alamos (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1913-1914 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Controlled Thermonuclear Research (CTR) division uses a single software package to acquire data from hundreds of CAMAC recorders. For the past five years, this package has been used by all experiments, both manual and computer controlled. A variety of signals are stored in transient digitizers and other memories. The computer retrieves the data and applies an efficient compression algorithm before storing it on disk. The physicist can plan his next shot from the acquired data even as the rest is read. The readout is list directed with device, amplifier, and time-base types and their settings selected by the physicist. A new experiment may be set up in minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138793
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