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· 1944
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· 1921
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· 2004
The National Ignition Facility (NIF) requires diagnostics to analyze high-energy density physics experiments. A VISAR (Velocity Interferometry System for Any Reflector) diagnostic has been designed to measure shock velocities, shock breakout times, and shock emission of targets with sizes from 1 to 5 mm. An 8-inch-diameter fused silica triplet lens collects light at f/3 inside the 30-foot-diameter vacuum chamber. The optical relay sends the image out an equatorial port, through a 2-inch-thick vacuum window, and into two interferometers. A 60-kW VISAR probe laser operates at 659.5 nm with variable pulse width. Special coatings on the mirrors and cutoff filters are used to reject the NIF drive laser wavelengths and to pass a band of wavelengths for VISAR, passive shock breakout light, or thermal imaging light (bypassing the interferometers). The first triplet can be no closer than 500 mm from the target chamber center and is protected from debris by a blast window that is replaced after every event. The front end of the optical relay can be temporarily removed from the equatorial port, allowing other experimenters to use that port. A unique resolution pattern has been designed to validate the VISAR diagnostic before each use. All optical lenses are on kinematic mounts so that the pointing accuracy of the optical axis can be checked. Seven CCD cameras monitor the diagnostic alignment.
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· 2005
In-situ x-ray diffraction was used to study the response of single crystal iron under shock conditions. Measurements of the response of [001] iron showed a uniaxial compression of the initially bcc lattice along the shock direction by up to 6% at 13 GPa. Above this pressure, the lattice responded with a further collapse of the lattice by 15-18% and a transformation to a hcp structure. The in-situ measurements are discussed and results summarized.
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· 1930
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· 1930
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· 1964
This report describes the investigations conducted during a program to investigate the applicability of endfire, dielectric radiating elements in easily transportable satellite communications antenna arrays. Investigations of the applicability of these elements as primary feeds for lenses and reflectors are also described. The program has provided a new and workable theory that is applicable to a wide range of element sizes and materials and has resulted in the development of the Foamrod Antenna which has an order of magnitude greater gain than conventional end-fire dielectric elements. An Array Design Plan was written which describes an array equivalent to a thirty foot diameter parabolic antenna. For a feasibility model, a 16-element array was designed for electrical performance equivalent to a 15 foot diameter paraboloid. In the area of feeds for reflector antennas, some promising results have been obtained.