Developments in NIF Beryllium Capsule Design

Recent beryllium capsule designs have focussed on the lower temperatures and laser powers expected before the NIF laser reaches its full capability, 192 beams, 500TW, and 1.8MJ. First, several new designs are given with peak radiation temperatures for 250 to 280 eV. A 250eV design uses 2% oxygen dopant instead of 0.9% copper. Second, a radiography study of planar joints in S200D beryllium using a Cu, Au, Ag, Al, or Au/Cu braze quantified the diffusion away from the joint. LASNEX calculations show that Cu joint perturbations grow to large enough amplitude to preclude ignition. However by allowing the copper to diffuse twice as far as in these experiments (e.g. by holding at braze temperature longer), the joint calculates to be acceptable, and the capsule gives full yield. Aluminum diffuses extremely far from the joint, almost uniformly in the sample. Third, a capsule with a high Z shell and beryllium ablator calculates to ignite. As expected its ignition threshold is lower, about 70% of the implosion velocity for a capsule like the Be330. The extra tamping of DT bum by a 6 μm tungsten shell increases the yield from 17 to 32 MJ. The capsule radiates 3 MJ of this yield as X-rays. Unfortunately the capsule is more sensitive to DT ice roughness than the Be330 design, failing at 0.6μm roughness.