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  • 1
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Implosions of direct-drive, deuterium–tritium (DT) gas-filled plastic capsules are studied using nuclear diagnostics at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. In addition to traditional neutron measurements, comprehensive sets of spectra of deuterons, tritons, and protons elastically scattered from the fuel and shell by primary DT neutrons ("knock-on" particles) are, for the first time, obtained and used for characterizing target performance. It is shown with these measurements that, for 15-atm DT capsules with 20-μm CH shells, improvement of target performance is achieved when on-target irradiation nonuniformity is reduced. Specifically, with a two-dimensional (2D) single-color-cycle, 1-THz-bandwidth smoothing by spectral dispersion (SSD), plus polarization smoothing (PS), a primary neutron yield of ∼1×1013, a fuel areal density of ∼15 mg/cm2, and a shell areal density of ∼60 mg/cm2 are obtained; these are, respectively, ∼80%, ∼60%, and ∼35% higher than those achieved using 0.35-THz, 3-color-cycle, 2D SSD without PS. (In determining fuel areal density we assume the fuel to have equal numbers of D and T.) With full beam smoothing, implosions with moderate radial convergence (∼10–15) are shown to have ρR performance close to one-dimensional-code predictions, but a ratio of measured-to-predicted primary neutron yield of ∼0.3. Other capsules that are predicted to have much higher radial convergence (3.8-atm DT gas with 20-μm CH shell) are shown to have ρRfuel∼3 mg/cm2, falling short of prediction by about a factor of 5. The corresponding convergence ratios are similar to the values for 15-atm capsules. This indicates, not surprisingly, that the effects of mix are more deleterious for high-convergence implosions. A brief comparison of these moderate- and high-convergence implosions to those of similar deuterium–deuterium (D2) gas-filled capsules shows comparable hydrodynamic performance. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 3558-3566 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent spectroscopic analysis of charged particles generated by fusion reactions in direct-drive implosion experiments at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] show the presence of low-mode-number asymmetries in compressed-capsule areal density (ρR) at the time of fusion burn. Experiments involved the acquisition and analysis of spectra of primary (14.7 MeV) protons, from capsules filled with deuterium and helium-3, and secondary (12.6–17.5 MeV) protons, from cryogenic deuterium capsules. The difference between the birth energy and measured energy of these protons provides a measure of the amount of material they passed through on their way out of a capsule, so measurements taken at different angles relative to a target provide information about angular variations in capsule areal density at burn time. Those variations have low-mode-number amplitudes as large as ±50% about the mean (which is typically ∼65 mg/cm2); high-mode-number structure can lead to individual pathlengths through the shell that reach several times the mean. It was found that the observed ρR asymmetries are often similar for contiguous implosions, but change when the laser beam energy balance is significantly changed, indicating a direct connection between drive symmetry and implosion symmetry. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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