Fabrication and Metrology Challenges in Making Thin, Hollow, Silver Spherical Halfraum Targets for EPEC Experiments on the National Ignition Facility

Energy partitioning, energy coupling (EPEC) is one of the new experimental platforms being investigated at the National Ignition Facility (NIF) to provide valuable data for national security applications. The EPEC target is a 7-m-thick silver spherical halfraum driven by a single NIF quad. This paper will describe the fabrication of the hollow spherical target, starting with the selection of the mandrel, the single-point diamond turning process used to achieve the desired thickness, and the final processing to remove the mandrel. Also discussed will be the metrology technique, X-ray opacity, used to determine the wall thickness and wall uniformity and how this nondestructive technique was benchmarked by two destructive characterization techniques, dual focused ion beam and scanning electron microscope, for wall thickness determination.