Improving the Reproducibility of the Radial Argon Concentration in Beryllium Shells

Abstract

Sputter coating of beryllium on spherical mandrels has been used at Lawrence Livermore National Laboratory and at General Atomics to produce graded, copper doped beryllium shells. While these coatings have consistent microstructure and acceptable void content, different coaters produced different results with respect to argon implantation. Each individual system met the requirements for argon implantation, but the deviation from one system to another and from run to run exceeded the variability requirements as specified by the National Ignition Facility target design requirements. We redesigned the fixturing within one system to improve reproducibility. Then, we reconfigured the coaters so that the vertical and lateral alignments of the shells under the gun varied <1 mm between systems. After this process, the systems were able to produce beryllium capsules with radial argon profiles that met specifications and were consistent from run to run and from system to system. During this process we gained insight into the beryllium coating process. The radial argon variation was shown to be dependent on sputter target thickness. We also found that the argon content in the shells was extremely dependent on the position of the shells with respect to the gun.