Imaging plate (IP) is a phosphor which has image storage capability. Because of its immunity to electric-magnetic-interference, IP's have been used in various laser-plasma experiments as a detector ...for X-ray imaging and electron spectroscopy. IP's are sensitive to most of ionizing radiations. Response of IP's to X-ray, gamma-ray, and charged particle exposure has been reported. However its intrinsic response to neutron exposure has not been understood clearly. In order to assess expected performance of IP's in harsh neutron background environment of the National Ignition Facility, it is crucial to understand IP's sensitivity to 14MeV neutrons. We exposed absolutely calibrated IP's to known neutron flux at OMEGA laser facility. Comparison of experimental results and Monte Carlo simulations will be reported.
Recent work has shown that it is possible to explain many discrepancies in experimental data on shock melting using a nucleation theory for the formation of the liquid phase. The model predicts that, ...during dynamic loading, solid material may persist into the equilibrium liquid regime, which may be equivalent to superheating of several tens of percent above the static melt temperature. The previous theory can be recast as a transition rate from solid to or from liquid, as a function of the instantaneous state. We have applied this model to the interpretation of shock wave experiments on beryllium. The data are compared with simulations performed with an equation of state incorporating an explicit melt curve, with and without the rate-dependent model.
Peak core temperature is an important measure of implosion performance, and will be a critical diagnostic of ignition implosion performance at the National Ignition Facility because peak temperatures ...must attain high values in order to form the hot-spot spark that ignites the main mass of deuterium-tritium fuel. We plan to measure peak core temperatures, resolved in space and time, using a gated pinhole camera that differentially filters the individual images in different continuum x-ray bands. Ross pair analysis allows the temperature profile to be measured directly. We describe the technique, the various challenges that include x-ray scattering, Abel inversion of noisy images that do not have perfect two-dimensional symmetry, calibrations, and background suppression, and we discuss how we expect to meet these challenges.
Summary form only given. The HED 2-Shock implosion campaign was developed on the National Ignition Facility as a relatively robust and well-beha ved nearly one-dimensional, low convergence, symmetric ...platform by employing a very high foot temperature and a large case-to-capsule (hohlraum-to-capsule) ratio. The results of these experiments investigating capsule implosion phenomena such as interface hydrodynamic mixing, convergence effects, and shape effects are being used for the validation of hydro-c odes and to develop a systematic understanding of performance degradation mechanisms. A sequence of experiments was initially completed to tune the 2-Shock implosion round, with little shape swing from in-flight to stagnation. Then, hohlraum size and hohlraum gas fill were systematically changed to study the effect on shape and symmetry evolution. Details and results of these experiments are described.
The Trident laser at Los Alamos was used to impart known and controlled shocks in various materials by launching flyer plates or by irradiating the sample directly. Materials investigated include ...copper, gold, NiTi, SS316, and other metals and alloys. Tensile spall strength, elastic-plastic transition, phase boundaries, and equation of state can be determined with small samples. Using thin samples (0.1-1.0 mm thick) as targets, high pressure gradients can be generated with relatively low pressures, resulting in high tensile strain rates (10 exp 5 to 10 exp 8 s exp -1 ). Free surface and interface velocities are recorded with point- and line-imaging VISARs. The flexible spatial and temporal pulse profiles of Trident, coupled with the use of laser-launched flyer plates, provides capabilities which complement experiments conducted using gas guns and tensile bars. These samples spalled at high strain rates will be compared with samples spalled at lower strain rates to elucidate mechanisms for the initiation the initiation and growth of spall.
Shock waves were induced in single crystals of beryllium, by direct illumination using the TRIDENT laser at Los Alamos. The velocity history at the surface was measured using a line-imaging VISAR, ...and transient x-ray diffraction (TXD) records were obtained with a plasma backlighter and x-ray streak cameras. At lower pressures, the VISAR records exhibited an elastic precursor followed by a plastic wave and spall. At higher pressure, the velocity records showed a two-wave structure suggesting a phase change, then at the highest pressure a single broad wave suggesting a shock directly into the high pressure phase. The rocking curves of the crystals were typically about 2 degrees wide, so analysis of the TXD records is complicated by the relatively large amount of blurring. However, the Bragg record of the shocked 002 peak clearly indicates a smaller lattice parameter at higher pressure. In the shots where polymorphism seemed to appear in the VISAR record, additional lines appeared in the Bragg record, and new lines also appeared within the field of view of the Laue camera. These results are consistent with a new quantum mechanical equation of state for beryllium, which suggests that the hexagonal to body-centered cubic transition occurs at approx40 GPa on the principal Hugoniot.
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