Developments in nif beryllium capsule design

Recent beryllium capsule designs have focussed on the lower temperatures an d laser powers expected before the NIF laser reaches its full capability, 1 92 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 dop ant 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 diff usion away from the joint. LASNEX calculations show that Cu joint perturbat ions grow to large enough amplitude to preclude ignition. However by allowi ng the copper to diffuse twice as far as in these experiments (e.g. by hold ing at brats temperature longer), the joint calculates to be acceptable, an d the capsule gives full yield. Aluminum diffuses extremely far from the jo int, almost uniformly in the sample. Third, a capsule with a high Z shell a nd beryllium ablator calculates to ignite. As expected its ignition thresho ld is lower, about 70% of the implosion velocity for a capsule like the Be3 30, The extra tamping of DT burn by a 6 mu m tungsten shell increases the y ield from 17 to 32 MJ. The capsule radiates 3 MJ of this yield as X-rays. U nfortunately the capsule is more sensitive to DT ice roughness than the Be3 30 design, failing at 0.6 mu m roughness.