Fielding Of An Imaging Visar Diagnostic At The National Ignition Facility Nif PDF Download

The National Ignition Facility (NIF) requires diagnostics to analyze high-energy density physics experiments. As a core NIF early light diagnostic, this system measures shock velocities, shock breakout times, and shock emission of targets with sizes from 1 to 5 mm. A 659.5 nm VISAR probe laser illuminates the target. An 8-inch-diameter fused silica triplet lens collects light at f/3 inside the 33-foot-diameter vacuum chamber. The optical relay sends the image out an equatorial port, through a 2-inch-thick vacuum window, and into two VISAR (Velocity Interferometer System for Any Reflector) interferometers. Both streak cameras and CCD cameras record the images. Total track is 75 feet. The front end of the optical relay can be temporarily removed from the equatorial port, allowing for other experimenters to use that port. 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. Along with special coatings on the mirrors, cutoff filters reject the NIF drive laser wavelengths and pass a band of wavelengths for VISAR, for passive shock breakout light, or for thermal imaging light (bypassing the interferometers). Finite Element Analysis was performed on all mounting structures. All optical lenses are on kinematic mounts, so that the pointing accuracy of the optical axis can be checked. A two-color laser alignment scheme is discussed.