Removal of the Mandrel from Beryllium Sputter Coated Capsules for NIF Targets

The choice of the mandrel material has a significant bearing on the properties of the sputter-coated beryllium shell needed for NIF targets. Here, we present our work on screening four mandrel materials, their impact on the Be shell and issues related to their subsequent removal. Beryllium shells sputter deposited on hollow glow discharge polymer or GDP spheres met most of the target specifications. However, they had greater opacity due to partial oxidation of the Be during the GDP burnout step. Poly (-methyl styrene), silicon and nickel beads were explored as alternative mandrels but were plagued with problems such as cracking of the Be shell or incomplete removal. The most promising approach was a two-step coating process mediated by a thin 6m Be mandrel that is made using GDP.