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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1801-1803 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Experiments to obtain time-resolved, soft-x-ray emission from laser-driven plasmas are succinctly described. The spectra (0.19 keV ≤ hν ≤ 1.3 keV) at various times have been deconvolved and energy integrated to obtain time-resolved yields from Au disk targets. The temporal profiles of the total thermal x-ray output power follow the overall laser temporal shape but do not show the high-frequency fluctuation observed in the laser pulse. The behavior of the ratio of the instantaneous x-ray yields over the laser absorption is studied. The studies were done at the LLNL Nova laser facility. Single pulses and pulses in "picket fence'' configuration were used to heat the gold targets.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we report the results of experiments that compare the x-ray emission from a laser spot in a radiation-filled hohlraum to that from a similar laser spot on a simple disk target. The studies were done using the Nova laser facility [J. D. Lindl, Phys. Plasmas 2, 3933 (1995)] in its 0.35 μm wavelength, 1 ns square pulse configuration. Focal spot intensities were 2–3.5×1015 W/cm2. X-ray images measured x-ray conversion in a hohlraum and from an isolated disk simultaneously. A laser spot inside a hohlraum emitted more x rays, after subtracting the background emission from the hohlraum walls, than a spot on a disk. Numerical models suggest the enhanced spot emission inside the hohlraum is due to an increase in lateral transport relative to the disk. Filamentation in the hohlraum will also increase the spot size. The models agree fairly well with the results on spot spreading but do not explain the overall increase in conversion efficiency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 3477-3484 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments to study the angular dependence of laser-light absorption in long-scale-length, planar plasmas are reported. Flat-topped, 1 nsec pulses of 0.35 μm laser light, with up to 2.5 kJ at average laser intensities of 3×1013 to 6×1015 W/cm2, were used to irradiate thick, gold targets at angles of incidence of 0° to 〉50°. The scattered light was measured using a number of diagnostics, and the absorption was inferred from these measurements. The absorption decreased somewhat with increasing laser intensity, typically remaining above 90% for laser intensities below 1015 W/cm2, and was very weakly dependent upon the angle of incidence. Modeling of the reflected light was used to constrain the properties of the plasma and of the reflecting mechanism. No simple model of a single mechanism is consistent with all aspects of the data.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two-dimensional, time resolved x-ray imaging is a principal technique used to study hot plasmas produced in laser heated targets. It can be used to study laser energy deposition within the irradiation spot, the spatial and temporal dependence of laser to x-ray conversion efficiency, electron transport and density profiles, mass ablation rates as well as x-ray driven implosions in inertial confinement fusion experiments. We have successfully developed a new soft x-ray framing camera which will allow us to record two-dimensional images at different times almost simultaneously. It is a broadband diagnostic (100 eV≤Δhν≤400 eV) having three channels which can obtain x-ray images at four different times from laser driven targets. Its current configuration includes one 500 eV, one 1.0 keV, and one ∼2.5 keV channels. The two low energy channels resulted from pairing transmission filters to grazing x-ray mirrors. Other channel options can be implemented easily to measure other x-ray energies. Four different striplines coated on a microchannel plate are gated at different times. Each strip records three different images taken nearly simultaneously, one image per channel. The result is 12 x-ray images on film, four images per channel taken at four different times, with a nominal resolution of approximately 100 ps per image. The diagnostic's spatial resolution is approximately 10 μm. We have already fielded this new instrument during x-ray conversion experiments, using both low and high Z targets driven by 1–2 ns, "flattop'' laser pulses. We will show the details of the instrument design and sample results from conversion experiments.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The indirect drive method of inertial confinement fusion uses a high-Z radiation case to convert energy from high-powered laser beams to x rays which implode fusion capsules. Experiments have been performed on the Nova laser to characterize the x-ray production in high-Z cavities for studying the efficiency for x-ray production using two methods for characterization. One method measures the shock velocity produced in low-Z materials by the radiation. The shock velocity is measured by observing the optical signal from the rear of a stepped or continuously varying thickness of Al placed over a hole in the cavity wall. The other method measures the reradiated x-ray flux from the cavity wall viewing through a hole in the cavity. Both methods have been shown to provide a consistent characterization of the x-ray drive in the cavity target. © 1995 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: High-Z, laser heated hohlraums can be made thick enough to contain thermal radiation, yet thin enough to let out x rays 〉∼6 keV produced by hot, relatively dense blow-off plasma. We use such "thin wall hohlraums" to observe the physical location of hot, dense, laser produced hohlraum plasmas. This technique has allowed us to come to some understanding of laser transport/deposition, plasma stagnation, and bulk plasma filling. © 1997 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: Gated, microchannel-plate-based (MCP) framing cameras have been deployed worldwide for 0.2–9 keV x-ray imaging and spectroscopy of transient plasma phenomena. For a variety of spectroscopic and imaging applications, the angular sensitivity of MCPs must be known for correctly interpreting the data. We present systematic measurements of angular sensitivity at discrete relevant photon energies and arbitrary MCP gain. The results can been accurately predicted by using a simple two-dimensional approximation to the three-dimensional MCP geometry and by averaging over all possible photon ray paths. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1935-1939 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments investigating the pulse-width dependence of thermal x-ray conversion efficiencies (hν〈1.5 keV) in laser-heated gold plasmas are described. The results show that the instantaneous ratio of the emitted x-ray flux to the laser energy deposition rate increases throughout a 4-ns laser pulse. The studies were carried out using single arms of the 10-beam Nova laser facility. The irradiance was ∼4–5×1014 W/cm2 in the target plane as we varied the laser pulses' FWHM from 2 to 4 ns. The laser pulses were nominally flat-topped and contained between 1 and 2 kJ of (1)/(3) μm light. Time-resolved plasma radiation was monitored with a broadband, streaked x-ray spectrograph that has a roughly 30-ps time resolution and channels that are roughly 100–150 eV wide. One-dimensional numerical models run with the lasnex code produce a conversion efficiency that is nearly constant throughout the laser pulse. We discuss various approximations made in the one-dimensional models and conclude that none of them are a likely explanations for the increase of conversion efficiency with time. A preliminary two-dimensional model of a disk heated by a 3-ns pulse shows that the conversion efficiency increases throughout the pulse. The increase is due to soft x rays emitted from outside the laser spot. Further experiments and modeling will be carried out to assess these two-dimensional effects.
    Type of Medium: Electronic Resource
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