Robust Capsule and Fill Tube Assemblies for the National Ignition Campaign

The National Ignition Facility (NIF) tuning and ignition capsules will be gas filled through a laser precision drilled hole with a fill tube attached. To field these targets, several physics and assembly requirements must be met. These requirements drive the morphology of the final capsule and fill tube assembly (CFTA). Unexpectedly, they have also driven the need for a fill tube-transition tube subassembly, which is significant in the extra time required for fabrication. We have implemented engineering solutions that allow successful fabrication, testing, and transportation of CFTAs. During fabrication the fill tube is vertically inserted into both the transition tube and capsule, it is adhered with a low-viscosity adhesive, and there is a gap between mating surfaces. Nitrogen backpressure is flowed through the transition tube to prevent wicking of adhesive into the fill tube and to prevent partial restriction of flow or plugging. A nitrogen purge has also been implemented to displace atmospheric oxygen, which would otherwise absorb into the adhesive surface, truncate the polymerization process, and lead to a partially cured joint. Prior to transportation, the CFTA must complete a series of testing that simulates final assembly and NIF conditions: (a) helium leak test at room temperature, (b) helium leak test at liquid nitrogen temperature, (c) pressure test, and (d) X-ray fluorescence testing. The CFTA is transported in a custom device that provides vital support for the fill tube-to-capsule interface.