Update on Germanium-Doped CH Capsule Production for NIF: Scale-Up Issues and Current Yields

Abstract

A germanium-doped CH capsule is one of the capsule designs for the National Ignition Facility. Eight batches were made to evaluate yields and reproducibility for production. When larger batches (more than 20 capsules) were made, numerous nanometer-height domes, together with many nanometer-sized seeds and micrometer-sized beads, were observed on the capsule surface. These domes originate from abrasion-induced nanometer-sized seeds. Large batch sizes tend to slide as cohesive groups that enhance friction and abrasion. Limiting the batch size to 15 capsules prevented formation of nanometer-height domes. Roughly 80% of the capsules from 15 capsule batches meets the surface roughness specification, and 85% meets the isolated defect specification. The wall thickness and outer diameter yields, currently at 58% and 28 to 40%, respectively, are affected by variables that will be discussed. The average concentrations of the two Ge-doped layers are 0.77 and 0.50 at.%, with standard deviations of 0.15 at.%. The overall Ge-doping yield, with both layers within the most recent tolerance specification of ±0.2 at.%, is 20%. The best overall yields of 15 shell batches are currently 40 to 55%. The yield-limiting factors are wall-thickness accuracy and high mid-mode in outer surface power spectra.