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  • 1990-1994  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Evaluating the accuracy of optical-streak-camera sweep rates using uncertain data (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4322-4326 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A number of optical streak cameras are routinely operated for experiments at the Lawrence Livermore National Laboratory Nova laser facility. We report results from a study of the accuracy and reproducibility of the sweep rate. The sweep rates, measured using a 3 GHz pulse generator, vary by ±1.3% rms for data collected routinely over a several month period. Using statistical analysis, we develop an analytic model describing the effect of noise on our measurement technique in order to estimate the actual variation in the sweep rate. Numerical simulations of the effect of noise on the uncertainty of our measurement technique show close agreement with the model. By applying this model, we estimate that the sweep rate is reproducible to at least ±1.2%, and that the measurement technique contributes ±0.5% uncertainty. Other data are presented which support this estimate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143731
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Intensity scaling and saturation of stimulated Raman forward scattering (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1985-1996 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intensity scaling of stimulated Raman forward scattering has been measured in preformed laser-produced plasmas. It was found that predictions based on linear convective theory were consistent with the amount of scattered light measured when the laser intensity was less than about 1×1015 W/cm2. No increase in the amount of scattered light was found for higher intensities. The measured saturation level is compared to several nonlinear models: pump depletion, coupling to Langmuir and ion-acoustic waves, ponderomotive detuning, wave breaking, and particle trapping. It is found that saturation models based on ponderomotive detuning and on coupling to Langmuir and ion-acoustic waves are consistent with the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870654
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Structural features of Alberta oil sand bitumen and heavy oil asphaltenes (1992)
    s.l. : American Chemical Society
    Energy & fuels 6 (1992), S. 83-96 
    Details
    ISSN: 1520-5029
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ef00031a013
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Nonlinear laser–matter interaction processes in long-scale-length plasmas (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2232-2240 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper reports on nonlinear laser–plasma interaction experiments using long-scale-length plasmas produced by the 24-beam OMEGA laser system operating at 351 nm. The experiments were carried out with distributed phase plates (DPP's) in all beams and with and without smoothing by spectral dispersion (SSD). Most of the beams were used to create a large preformed plasma, which had gradient scale lengths of ≤800 μm at electron densities below a quarter of the critical density nc and temperatures in excess of 1 keV. One of the beams, the "interaction beam,'' was timed independently and tightly focused to intensities ∼1015 W/cm2. All beams had pulse durations of ∼0.6 nsec. The interaction processes studied were mainly Raman scattering and the two-plasmon decay (TPD) instability as evidenced by its characteristic 3/2-harmonic emission. Details of the Raman and 3/2-harmonic spectra are presented. Evidence was found for the TPD instability close to its Landau cutoff density at ∼ 0.2nc. Raman emission was narrow-band and observed only from densities 〈 0.2nc. For late timings of the interaction beam, the Raman emission appeared to originate from near the peak of the density profile, but for earlier timings it appeared to come from densities a factor of 2 below the calculated peak. Application of SSD affected the 3/2-harmonic emission only slightly, but it strongly reduced the Raman emission. A discussion is given of some models that attempt to explain these observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860191
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental studies of stimulated Raman scattering in reactor-size, laser-produced plasmas (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1473-1478 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the results of experiments designed to provide information regarding the scaling of the stimulated Raman scattering (SRS) instability in long-scale-length, inertial- confinement-fusion-reactor-size plasmas are described. Reactor-scale plasma conditions were experimentally simulated by exploding thin CH foils with nine beams of the Nova laser [Rev. Sci. Instrum. 57, 2101 (1986)]. Using a one-dimensional hydro model, the target and irradiation parameters were chosen to produce the largest-possible scale length plasma consistent with the energy and pulse width capabilities of Nova. The SRS emissions, driven by both the nine plasma-production beams and a tightly focused and delayed tenth beam, were recorded using an angularly resolved photodiode array and a temporally resolved optical spectrometer. These measurements verified the production of a reactor-size plasma (L/λ ≈ 5000) and indicated that the absolute levels of SRS backscatter detected in the present experiments have not increased relative to those measured in previous experiments despite a calculated sevenfold increase in the plasma density-gradient scale length. Inverse bremsstrahlung absorption of the scattered light is believed to be the dominant mechanism for this apparent saturation and, in this parameter regime, may enhance the effective thermal coupling between the incident laser and plasma densities below 0.15ncrit where absorption of the incident laser light is typically weak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859714
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Near-forward scattering of laser lightf| (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2596-2602 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Near-forward scattering of laser light in a plasma, in regimes relevant to future inertial-confinement-fusion (ICF) experiments, has been investigated experimentally. The intensity scaling of stimulated Raman scattering (SRS) forward scattering at one angle was measured from a low-Z plasma. It was found that the intensity threshold and scaling were consistent with convective theory. Forward SRS saturated at a relatively low intensity. In a second experiment using Ti plasmas, absolutely calibrated, time-resolved stimulated Brillouin scattering (SBS) spectra from up to seven different angles were measured simultaneously. It was found that the angular dependence of the scattered energy was qualitatively consistent with convective theory. The spectra provided the first evidence of near-forward SBS. Contrary to previous estimates, near-forward SBS was shown to be more efficient than oblique backscattering and may be an important effect for ICF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860696
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Multiple-angle, time-resolved spectroscopy of scattered light from laser-produced plasmas (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5205-5205 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new instrument at the NOVA laser facility has been developed to measure absolute levels of scattered light at up to seven angles simultaneously from laser-produced plasmas. The multiple-angle time-resolving spectrometer (MATRS) both temporally (t=120 ps) and spectrally (λ=1 A(ring)) resolves light scattered from the plasma at or near the laser wavelength. MATRS has been used to study parametric instabilities in plasmas pertinent to laser fusion. Measurement of the angular dependence of the scattered light from these processes will provide a clear test of convective theory. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143430
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    An experimental investigation of refraction-induced distortions in harmonic-light images of laser-produced plasmas (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3630-3634 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the results of a simple experiment designed to study refraction-induced distortion of images of narrow-band-light-emitting regions in a laser-produced plasma are described. Source regions were formed by relaying the image of a backlit pinhole array into the plasma (25 μm-diam. pinhole; 30-ps, 0.25-μm backlighter beam). Images of these source regions were recorded on film and compared with and without plasma present. Refraction effects, evidenced by translation of the apparent pinhole locations and blurring of the pinhole spots, are compared for different plasma sizes and for different delays of the backlighter pulse with respect to the plasma-production laser pulse. These results were then compared with expectations based on numerical raytraces through a plasma-density profile derived from a hydrodynamic simulation of our exploding-foil plasma. The significance of these results in the imaging of harmonic and half-harmonic light as a plasma-density diagnostic is discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345316
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  • 9
    Electronic Resource
    Electronic Resource
    Production of very large, sub-tenth-critical plasmas for laser-fusion research (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2898-2905 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The development of a plasma environment that is appropriate for the study of low-gain processes in laser-fusion plasmas is reported. These plasmas have long scale lengths, low densities, and no quarter-critical or critical-density surfaces. The plasmas were created by two-sided irradiation of CH foils with 15 kJ of 351 nm laser light. When the peak electron density in the plasma had decayed to about 2×1020 cm−3, the parabolic density profile was estimated to have a full width at half-maximum of 3 mm and the electron temperature was estimated to be 1 keV. Probe lasers of different wavelengths were used to measure the peak electron density via stimulated scattering processes and odd half-harmonic generation. Sufficiently accurate modeling of the laser-irradiation conditions led to improved agreement between the experiment and two-dimensional (2-D) computer simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859923
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Erratum: "Narrow Raman spectra: The competition between collisional and Landau damping'' [Phys. Fluids B 1, 2217 (1989)] (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1709-1709 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859589
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    Paper (German National Licenses)
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