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  • 1
    Electronic Resource
    Electronic Resource
    Fusion neutrons from the gas–pusher interface in deuterated-shell inertial confinement fusion implosions (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 768-774 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first measurements and numerical simulations of fusion neutrons from the gas–pusher interface of indirectly-driven inertial confinement fusion implosions have been performed using hydrogen-filled capsules made with a deuterated inner layer. Nonlinear saturation of the growth of hydrodynamic perturbations in high linear growth factor ((similar, equals)325) implosions was varied by adjusting the initial surface roughness of the capsule. The neutron yields are in quantitative agreement with the direct simulations of perturbation growth, and also with a linear mode superposition and saturation model including enhanced thermal loss in the mixed region. Neutron spectra from these capsules are broader than expected for the calculated ion temperatures, suggesting the presence of nonthermal broadening from mass motion during the fusion burn. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872761
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  • 2
    Electronic Resource
    Electronic Resource
    Neutron calibration for the FRX-C/LSM magnetic compression experiment (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1489-1493 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Neutron source strength and yield from field-reversed configurations have been measured in the FRX-C/LSM magnetic compression experiment using plastic scintillators, indium activation samples, and moderated rhodium activation counters. The calibration of these neutron detectors is complicated by the changing shape and position of the plasma and by the presence of the massive aluminum compression coils. The overall uncertainty in the neutron measurements is estimated to be 45%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142473
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Foam-buffered spherical implosions at 527 nm (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1379-1384 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Creation of a low density, high temperature plasma buffer between the absorption and ablation layers of a directly driven inertial confinement fusion implosion capsule has been proposed as a means to reduce "early time" imprint from laser nonuniformities. This thermal smoothing blanket might be created from a low density foam layer wrapped around the deuterium–tritium filled microballoon. Preliminary spherical implosion tests of this concept using a polystyrene foam layer surrounding a glass microballoon were performed at the Nova laser [Rev. Sci. Instrum. 57, 2101 (1986)], using a 527 nm drive wavelength. Comparison of capsule yield and imploded core symmetry showed promising improvements in overall target performance, relative to one-dimensional undegraded hydrodynamic simulations, when the foam-buffer layer was present. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872568
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  • 5
    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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  • 6
    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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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Colliding plasma neutron production at Trident : 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. 618-620 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Trident is a two-beam Nd:glass laser producing typically 100 J at 2ω in 2 ns pulses. Diffraction unlimited f/6 optics reduce the 20-cm-diam beams down to 100 μm diameter. The laser is capable of producing neutrons from D-D and D-T plasmas, and has demonstrated yields of 〉106 D-D neutrons from colliding plasma geometries. We have combined a previously existing neutron activation technique with two large photomultiplier tubes (PMTs) coupled to scintillators to produce a neutron measuring capability on Trident. In addition, we have coupled a time-of-flight compensated scintillator to a fast microchannel plate PMT to provide neutron energy resolution and hence the potential to measure ion temperatures through time-of-flight spread. The activation technique is sensitive to 〉105 neutrons per count in its present configuration. The PMT/scintillators have comparable sensitivities. The MCP/PMT/scintillator combination has 220 ps rise time with an order of magnitude less sensitivity. We will describe these detectors and the methods used to calibrate the individual detector sensitivities. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147756
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  • 9
    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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  • 10
    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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