Fabrication of Beryllium Capsules with Copper-Doped Layers for NIF Targets: A Progress Report

The sputtering of beryllium (Be) has been used at LLNL for nearly 30 years in the fabrication of laser targets. Several years ago the prospect of using sputtering to fabricate spherical Be capsules for National Ignition Facility (NIF) targets began to be explored and a basic strategy was developed that involved sputtering down onto plastic mandrels bouncing in a pan. While this appears to be very straightforward in principle, in practice sputtering has been used almost exclusively to make thin films (< 1 micron) on flat substrates. Thick films pose a significant challenge for sputtering while materials on spherical substrates are essentially unexplored. More recently, based on computational results, the point design for the first NIF ignition target capsule was specified as a Be capsule with Cu-doped layers of specific thickness, each layer with a different concentration of copper. While the work described here was motivated by the need to make these layered capsules, progress has been made in developing a more complete metallurgical understanding of the materials that are fabricated and the relationship between the sputter processing and microstructure of these spherical samples.