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  • 1
    Electronic Resource
    Electronic Resource
    Four-frame gated optical imager with 120-ps resolution (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1457-1460 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we describe the operation and applications of a framing camera capable of four separate two-dimensional images with each frame having a 120-ps gate width. Fast gating of a single frame is accomplished by using a wafer image intensifier tube in which the cathode is capacitively coupled to an external electrode placed outside of the photocathode of the tube. This electrode is then pulsed relative to the microchannel plate by a narrow (120-ps), high-voltage pulse. Multiple frames are obtained by using multiple gated tubes which share a single bias supply and pulser with relative gate times selected by the cable lengths between the tubes and the pulser. A beam-splitter system has been constructed which produces a separate image for each tube from a single scene. Applications of the framing camera to inertial confinement fusion experiments are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139687
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  • 2
    Electronic Resource
    Electronic Resource
    Fluorescence measurements of the M-band photon emission from a laser-irradiated gold disk (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1476-1478 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Gold M-band x rays with energies above the sulfur K edge of 2.472 keV create sulfur Kα fluorescence with a quantum efficiency of 8.1%. The sulfur fluorescer was a 600×1500-μm rectangle about 1100 μm from the gold plate. It was 25 μm of C6H4S plastic shielded by 50 μm of beryllium. The absolute brightnesses of both the M-band spectrum and of the fluorescence line were measured by separate spectrographs. The spectrograph measuring the fluorescence did not have a direct line of sight to the hot gold. These measurements were made with 3512-A(ring) laser light irradiating the gold plate for 1 ns over a number of intensities between 2×1014 and 1015 W/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139692
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of a high-magnification x-ray microscope on Nova (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1852-1852 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have implemented a Wolter-type x-ray optic in a high- (22×) magnification microscope on Nova. We report on the on-line characterization of this system and show results from the several types of experiments performed. The point spread function, contrast transfer function at selected spatial frequencies, x-ray throughput, alignment accuracy, and field of view have all been measured as configured for Nova experiments. Such characterization may be used to remove the degradation introduced by the instrument. This work was performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140085
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  • 4
    Electronic Resource
    Electronic Resource
    Conversion efficiencies from laser-produced plasmas in the extreme ultraviolet regime (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2251-2258 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conversion efficiency of spectral emission from laser-irradiated solid targets was investigated for short wavelength source development. The plasma brightness was quantified using absolutely calibrated detectors for 20 materials and spectra were obtained between 50 and 200 A(ring). Laser parameters such as wavelength, pulse length, intensity, and spot size were systematically varied to establish a comprehensive database for source optimization. Qualitative differences in the underlying dominant emission features as a function of atomic number and laser wavelength were observed that accounted for the relatively high spectral conversion efficiencies produced. In the specific case of Sn, a conversion efficiency greater than 0.8%/eV has been observed in the technologically important region of λ=134.0 A(ring) using a laser intensity of 1–2×1011 W/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361149
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  • 5
    Electronic Resource
    Electronic Resource
    X-ray radiographic imaging of hydrodynamic phenomena in radiation-driven materials—Shock propagation, material compression, and shear flowf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1662-1668 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One- and two-dimensional, time-resolved x-ray radiographic imaging at high photon energy (5–7 keV) is used to study shock propagation, material motion and compression, and the effects of shear flow in solid density samples which are driven by x-ray ablation with the Nova laser. By backlighting the samples with x rays and observing the increase in sample areal density due to shock compression, the trajectories of strong shocks (∼40 Mbars) in flight are directly measured in solid density plastic samples. Doping a section of the samples with high-Z material (Br) provides radiographic contrast, allowing a measurement of the shock-induced particle motion. Instability growth due to shear flow at an interface is investigated by imbedding a metal wire in a cylindrical plastic sample and launching a shock in the axial direction. Time-resolved radiographic measurements are made with either a slit-imager coupled to an x-ray streak camera or a pinhole camera coupled to a gated microchannel plate detector, providing ∼10 μm spatial and ∼100 ps temporal resolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870668
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of titanium laser-produced plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3792-3803 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The development of a plasma environment that is appropriate for the study of laser-plasma processes in laser-fusion plasma is reported. A material (titanium) with medium atomic number (Z) was used to provide x-ray measurements of radial and axial plasma symmetry as well as electron temperature. The electron density evolution was measured using stimulated scattering processes and odd half-harmonic generation from probe lasers of different wavelengths. The plasmas were created by two-sided irradiation of thin foils with 24 kJ of 351 nm laser light. When the peak electron density had decayed to about 4×1020 cm−3, the density profile was estimated to have a full width at half-maximum of 2 mm and the electron temperature was measured to be about 3 keV using K-shell spectroscopy. Two-dimensional computer simulations were found to reproduce some features of both electron density and temperature evolution. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871079
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  • 7
    Electronic Resource
    Electronic Resource
    Laser ionization and heating of gas targets for long-scale-length instability experiments (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1971-1984 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper examines the use of gas targets to create low- and mid-Z plasmas ≈3 mm in size at 5% to 10% critical density for green and blue light (ne≈2×1020 to 1021 cm−3) with an electron temperature of several keV. At sufficiently high intensities (≈1014 W/cm2) the gas is ionized and heated by a laser absorption wave propagating faster than the sound speed. For pulses under 2 ns, the bulk of the plasma remains stationary, resulting in efficient heating minimizing density and velocity gradients, which are particularly important for instability thresholds in nonuniform plasmas. The propagation of a laser absorption wave in a preionized plasma is derived analytically. Ionization resulting from multiphoton and electron avalanche processes is studied by numerical methods and dimensional analysis. This establishes the length and time scales over which an absorption wave can be observed. Computer simulations, using the lasnex code, are presented for several implementations of this concept, applicable to the relevant regime for inertial confinement fusion. These examples include a gas jet (≈3×1 mm in cross section), 3 to 4 mm diameter gas balloons, and gas puffs generated by exploding a foil with a low-energy prepulse (≈200 J).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870653
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamical compensation of irradiation nonuniformities in a spherical hohlraum illuminated with tetrahedral symmetry by laser beams (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2963-2975 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Indirect-drive inertial confinement fusion with laser beams requires focusing the beams through laser entrance holes (LEHs) onto the inside surface of the hi-Z case comprising the hohlraum. The problem is how to illuminate the hohlraum so that the x-ray flux upon the capsule is as highly symmetric as possible at all times. This approach involves putting four LEHs at the corners of an imaginary regular tetrahedron whose vertices lie on the spherical hohlraum and putting a multiple of three beams through each LEH. Strict tetrahedral symmetry is maintained, so that under any proper tetrahedral symmetry operation, beam cones map into beam cones and LEHs into LEHs. The radiation field can have no l=1, 2, or 5 spherical harmonic components. By using two sets of twelve beams with different pulse shapes, the single surviving l=3 and single surviving l=4 components of the radiation flux upon the capsule can be made to vanish at all times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870537
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  • 9
    Electronic Resource
    Electronic Resource
    Radiation drive in laser-heated hohlraums (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2057-2062 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nearly 10 years of Nova [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] experiments and analysis have lead to a relatively detailed quantitative and qualitative understanding of radiation drive in laser-heated hohlraums. Our most successful quantitative modeling tool is two-dimensional (2-D) LASNEX numerical simulations [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)]. Analysis of the simulations provides us with insight into the physics of hohlraum drive. In particular we find hohlraum radiation conversion efficiency becomes quite high with longer pulses as the accumulated, high-Z blow-off plasma begins to radiate. Extensive Nova experiments corroborate our quantitative and qualitative understanding. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872002
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  • 10
    Electronic Resource
    Electronic Resource
    Hydrodynamic expansion of exploding-foil targets irradiated by 0.53 μm laser light (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1089-1096 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An experiment is reported in which several diagnostics were used to study the hydrodynamic expansion of exploding-foil targets. The CH targets, 1–3 μm thick, were irradiated with 3–4 kJ of 0.53 μm laser light in 1 nsec pulses. The electron density was diagnosed using the transmission and scattering of light at the laser frequency, the scattering of light at 3/2 of the laser frequency, the spectrum of Raman-scattered light, the x-ray spectrum from doped targets, and the image of the ultraviolet bremsstrahlung emission from the plasma. The measurements were consistent with one another, but generally were not consistent with two-dimensional computer simulations. The targets burned through later and took longer after burnthrough to reach quarter-critical density than predicted. This discrepancy may be a consequence of excessive profile steepening caused by the local, heat-transport model used in the simulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858979
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