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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 606-610 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fast protons (approximately-greater-than)1 MeV have been observed on the 60-beam, 30 kJ OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] at an intensity I(similar, equals)1015 W/cm2 and a wavelength λ=0.35 μm. These energies are more than 5 times greater than those observed on previous, single-beam experiments at the same Iλ2. The total energy in the proton spectrum above 0.2 MeV is ∼0.1% of the laser energy. Some of the proton spectra display intense, regular lines which may be related to ion acoustic perturbations in the expanding plasma. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2578-2584 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent work has resulted in the first high-resolution, spectroscopic measurements of energetic charged particles on OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 496 (1997)]. Energy spectra of charged fusion products have been obtained from two spectrometers, and have been used to deduce various physical quantities in imploded capsules. In this paper the first use of 14.7 MeV deuterium–helium3 (D–3He) proton spectra for diagnosing shell areal density (ρR) and fuel ion temperature (Ti) is discussed. For thick-plastic shell capsules, shell areal densities between 20 and 70 mg/cm2 and ion temperatures between 3 and 5 keV have been determined. The spectral linewidths associated with such capsules are found to be wider than the doppler widths. This effect, the focus of future study, is the result of ρR evolution during the burn; or is the result of an extended burn region; or results from nonuniformities in the shell. For thin-glass shell capsules, the spectral linewidths are dominated by the doppler width, and ion temperatures between 10 and 15 keV were determined. These measurements have been also compared and contrasted with the results from neutron measurements and from one-dimension hydrodynamic simulations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 5106-5117 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectral measurements have been made of charged fusion products produced in deuterium + helium-3 filled targets irradiated by the OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Comparing the energy shifts of four particle types has allowed two distinct physical processes to be probed: Electrostatic acceleration in the low-density corona and energy loss in the high-density target. When the fusion burn occurred during the laser pulse, particle energy shifts were dominated by acceleration effects. Using a simple model for the accelerating field region, the time history of the target electrostatic potential was found and shown to decay to zero soon after laser irradiation was complete. When the fusion burn occurred after the pulse, particle energy shifts were dominated by energy losses in the target, allowing fundamental charged-particle stopping-power predictions to be tested. The results provide the first experimental verification of the general form of stopping power theories over a wide velocity range. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Spectrometry of the neutron emission is discussed as a probe of the fuel ion velocity distribution in tokamak plasmas where the instrumental energy calibration allows determination of Doppler shifts on an absolute scale or relative to the emission of thermal plasma conditions. Such Doppler shifts have been measured for plasmas of different heating methods at the Joint European Torus (JET) using a neutron spectrometer of the magnetic proton recoil (MPR) type. The principles of the MPR spectrometer as a rotation diagnostic are discussed together with the results obtained for the JET plasmas. The development potential of neutron spectrometry as a rotation diagnostic at the accuracy level of ±1 km/s for toroidal and poloidal rotation is projected, especially, for use on burning plasma tokamaks. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The first magnetic proton recoil type neutron spectrometer has been put to use for diagnosing tokamak plasmas of high neutron yield rates (the range Yn=1015–6×1018 n/s). The spectrometer principles along with the diagnostic installation are presented. Performance and diagnostic capabilities are illustrated based on results obtained at Joint European Torus. The implications for neutron spectrometry diagnostics on the next step tokamak for burning plasmas (Yn→1022 n/s) are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Spectrometry of the neutron emission has been used to probe the nonthermal features of the fuel ion velocity distributions in tokamak plasmas, especially, those arising from auxiliary heating. The first time resolved measurements are reported from the use of the new magnetic proton recoil (MPR) spectrometer in observations of deuterium–tritium plasmas at JET with strong ion cyclotron resonance heating. Results from preliminary analysis data are presented and compared with simulated neutron emission spectra based on the assumptions of a thermal plasma (a single Maxwellian ion distribution) or anisotropic Maxwellians with parallel and perpendicular temperatures, beside their relative amplitudes. The diagnostic results attained are also used to assess the diagnostic capabilities and the potential for use of MPR based diagnostics on burning plasma tokamaks. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high resolution neutron spectrometer, based on the magnetic proton recoil (MPR) technique, is under construction for use on JET. It is designed for the planned high power DT experiments to make use of the very high neutron fluxes (up to a few times 1010 n/cm s) obtainable at vantage points close to the plasma. This will be used to operate at highest possible neutron count rates (Cn) to facilitate plasma measurements of maximum (statistical) accuracy without need of excessive integration times. The JET experimental conditions will permit operation in the MHz range (Cn≤0.5 MHz compared to Cn≤10 MHz on ITER). Prototype tests are planned to be performed with the MPR spectrometer besides diagnostic studies of the JET plasmas. We will describe the principles of the spectrometer and the research plans. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The principles and operation at Joint European Torus (JET) of the first magnetic proton recoil (MPR) spectrometer for measurement of fusion neutron spectra are described. Some technical aspects of the instrument are discussed, including energy calibration and monitoring system. Data from the recent experimental campaign with tritium at JET are presented as examples of the MPR's diagnostic abilities. It is shown that the spectrometer is a flexible and versatile instrument, capable of delivering high-quality data on a number of plasma parameters. In particular, the observation of the so-called α knock-on effect in neutron emission spectroscopy is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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