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  • Articles  (76)
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  • 1
    Electronic Resource
    Electronic Resource
    Optical fiducials for x-ray streak cameras at LLE (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2189-2191 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The incorporation of an optical timing fiducial onto a time-resolved x-ray streak record permits one to precisely relate the x-ray emission to the incident laser pulse. At the Laboratory for Laser Energetics, our approach to recording fiducials is twofold. In addition to recording the x-ray emission on a bifurcated photocathode, we also streak the incident laser light at 351 nm, which is scattered from the target and an independent signal at 4ω0 (264 nm), which is derived by frequency quadrupling a tiny fraction of the OMEGA laser driver output. The signal at 4ω0 is transported through the vacuum wall to the streak camera photocathode via fiber optics. A 200-A(ring) aluminum layer on mica is utilized for the UV sensitive photocathode. We will present examples and further details of this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138727
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray diagnosis of high-density compression of Ar-filled polymer shell targets (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1851-1851 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Time-resolved x-ray diagnosis is the only practical approach at present to examining the change of fuel and shell conditions during the final stages of compression of laser fusion targets. Time-resolved spectroscopy of lines emitted by the fuel or shell elements can provide information about the time history of the density, temperature, and integrity of the target. We report on time-integrated and time-resolved x-ray measurements of compressed polymer shell targets filled with Ar, or mixtures of Ar/Kr, directly irradiated by the 24-beam 2-kJ, UV (351-nm) OMEGA laser. These include x-ray photography, time-resolved and spaced-resolved x-ray spectroscopy, and x-ray diode measurements. Picosecond x-ray spectroscopy of the K shell emission from Ar has been studied, and detailed modeling and Spark Broadening analysis of the H-like and He-like line emission made. The results are compared with predictions of hydrodynamics code simulations of the implosions. From this analysis, a consistent history of the density and temperature of the compressed target is inferred. This work was supported by the U.S. DOE Office of Inertial Fusion under agreement No. DE-FC08-85DP40200 and the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140083
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  • 3
    Electronic Resource
    Electronic Resource
    Time-resolving x-ray diagnostics for ICF (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1854-1859 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray streak cameras, which can be coupled to a large variety of spectroscopic or imaging devices, provide an important research tool for studying laser fusion plasmas. Generally, several of these instruments are deployed simultaneously on a given experiment to furnish a comprehensive data set of the x-ray emission spectrum and target hydrodynamics. Of particular importance is the ability to do quantitative analysis with the data set. This allows meaningful comparisons to be made with simulations. The sophistication of the hydrodynamic and atomic physics codes is such that qualitative analysis is insufficient. Various simple parameters in these codes are bench-marked against experimental measurements before more detailed calculations are performed. As in all diagnostic systems the range of linear response must be well defined. In this article we will discuss some of the constraints inherent in streak camera systems and how they affect the acquisition and analysis of the experimental results. Examples illustrating our current capabilities for diagnosing experiments on the OMEGA laser fusion facility will be presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140088
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical modeling of effects of power imbalance on irradiation nonuniformities (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 5036-5043 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the importance of various sources of power imbalance of the 24 beam OMEGA laser system in contributing to laser irradiation nonuniformity. Long spatial wavelength irradiation nonuniformities on target are investigated numerically by adapting existing uniformity codes to incorporate time-dependent density and temperature profiles. The analysis shows that power imbalance due to slightly detuned (≤100 μrad) frequency conversion crystals and small differences in the ultraviolet (UV)-transport losses (ΔE/E≤5%) makes only a modest contribution to the overall nonuniformity. However, power imbalance from pulse shape distortion was found to create substantial irradiation nonuniformity on the target early in the implosion. The predictions of the present analysis were verified by an experiment in which a well controlled power imbalance was applied. Good agreement was found between the experimentally observed core positions and those predicted by the simulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347091
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental and numerical study of thermal transport in 24-beam ultraviolet irradiation of spherical targets (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 969-977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of thermal transport experiments using spectral-line signature and ion expansion measurements has been performed in spherical geometry using the 24 UV-converted beams of the Omega laser system at the Laboratory for Laser Energetics of the University of Rochester. Comparison with previous experiments employing only six beams shows a much better agreement in the mass ablation rate, when using 24 beams, between experimental results obtained from charge collectors and code simulations using a flux limiter of 0.1. The influence of nonuniformities in the irradiation, x-ray line reabsorption, and ionization time lag (non-LTE effects) were studied with the help of a collisional-radiative model. These processes were found to alter the falloff rates (determined mainly by the radical profile of the temperature) of the relative x-ray line intensity with overcoat thickness. With these effects included, agreement between calculated and measured burnthrough curves is greatly improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343000
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  • 6
    Electronic Resource
    Electronic Resource
    Direct-drive laser-fusion experiments with the OMEGA, 60-beam, 〉40 kJ, ultraviolet laser system (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2108-2112 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: OMEGA, a 60-beam, 351 nm, Nd:glass laser with an on-target energy capability of more than 40 kJ, is a flexible facility that can be used for both direct- and indirect-drive targets and is designed to ultimately achieve irradiation uniformity of 1% on direct-drive capsules with shaped laser pulses (dynamic range (approximately-greater-than)400:1). The OMEGA program for the next five years includes plasma physics experiments to investigate laser–matter interaction physics at temperatures, densities, and scale lengths approaching those of direct-drive capsules designed for the 1.8 MJ National Ignition Facility (NIF); experiments to characterize and mitigate the deleterious effects of hydrodynamic instabilities; and implosion experiments with capsules that are hydrodynamically equivalent to high-gain, direct-drive capsules. Details are presented of the OMEGA direct-drive experimental program and initial data from direct-drive implosion experiments that have achieved the highest thermonuclear yield (1014 DT neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser-fusion experiments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871662
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  • 7
    Electronic Resource
    Electronic Resource
    Production and characterization of hot, long-scale-length laser plasmas (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 432-449 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental data and hydrodynamic simulation results are presented for long-scale-length plasmas produced by the multibeam OMEGA fusion laser, with (approximately-less-than)1.5 kJ on target at wavelength 351 nm. The appropriately time-delayed beams from this system allow the production of millimeter-sized plasmas with (approximately-greater-than)1 keV electron temperatures maintained over extended periods of time ((approximately-greater-than)1 nsec). The two-dimensional plasma expansion and the temporal evolution of the electron temperature and density are found to be in very good agreement with simulations. The plasma thus produced forms an excellent tool for investigating laser–plasma interaction processes under conditions relevant to future laser-fusion reactor targets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860294
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of direct-drive-implosion core conditions on OMEGA with time-resolved Ar K-shell spectroscopy (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1357-1365 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct-drive-implosion core conditions have been characterized on the 60-beam OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system with time-resolved Ar K-shell spectroscopy. Plastic shells with an Ar-doped deuterium fill gas were driven with a 23 kJ, 1 ns square laser pulse smoothed with 1 THz smoothing by spectral dispersion (SSD) and polarization smoothing (PS) using birefringent wedges. The targets are predicted to have a convergence ratio of ∼15. The emissivity-averaged core electron temperature (Te) and density (ne) were inferred from the measured time-dependent Ar K-shell spectral line shapes. As the imploding shell decelerates the observed Te and ne increase to 2.0 (±0.2) keV and 2.5 (±0.5)×1024 cm−3 at peak neutron production, which is assumed to occur at the time of the peak emissivity-averaged Te. At peak compression the ne increases to 3.1 (±0.6)×1024 cm−3 and the Te decreases to 1.7 (±0.17) keV. The observed core conditions are close to those predicted by a one-dimensional hydrodynamics code. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456530
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  • 9
    Electronic Resource
    Electronic Resource
    Two-channel, elliptical analyzer spectrograph for absolute, time-resolving time-integrating spectrometry of pulsed x-ray sources in the 100–10 000-eV region (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 1537-1552 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new spectrographic system has been developed and calibrated in this laboratory for the absolute spectrometry of high-intensity pulsed x-ray sources in the 100–10 000-eV region. This spectral region is analyzed with fixed elliptically curved crystals and molecular or sputtered-or-evaporated multilayers of 2d values in the 3–160-A range. Twin channels are utilized for simultaneous time-integrated photographic recording and for time-resolved x-ray streak camera recording. Absolute calibrations of the elliptical analyzers, of the photographic film, and of the gold and CsI transmission photocathodes have been made using monoenergetic, cw laboratory x-ray sources. The overall transmission characteristics of the spectrograph have also been determined. The instrument has been designed for mounting through a pneumatically controlled high-vacuum valve onto a 4-in. port of a 1-m-diameter source chamber and includes an appendage, high-vacuum, sputter-ion prepumping station. The initial dynamic testing and application of this new spectrographic system has been on the University of Rochester's LLE 24 laser beam OMEGA source facility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138150
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  • 10
    Electronic Resource
    Electronic Resource
    Spectroscopic analysis of Ar-doped laser-driven implosions : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 755-757 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In a series of experiments performed at the Laboratory for Laser Energetics plastic microballoons filled with DD and doped with small amounts of Ar were imploded using the Omega laser system. Time-resolved K-shell Ar spectra were simultaneously recorded using two spectrographs (SPEAXS and flat-crystal). We focus on the analysis of the He-β line and its associated Li-like satellites. The density and temperature sensitivity of this composite spectral feature has been studied previously [R. C. Mancini et al., Rev. Sci. Instrum. 63, 5119 (1992)]. Here, we use it as a diagnostic. Modeling results take into account the built-in density and temperature dependence characteristic of the level populations and broadening properties of these transitions; in addition, we also consider the effects of ion dynamics and opacity. To check the consistency of our analysis we include in the model the He-γ and Ly-β lines. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146532
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