Quick Shot

Laser-fusion experiments employ cryogenically cooled targets that each contain a shell of solid hydrogenic fuel. The interior surface of the hydrogenic fuel (referred to as a “layer”) is required to be very smooth to prevent perturbations from magnifying and spoiling target performance. Layering spheres are used to create these precisely layered cryogenic targets. They rely on a uniform layering-sphere temperature and beta heating from tritium decay within the shell to create spherical isotherms around the target. The new layering sphere (shown above) has the design features that are needed to fill the target with D₂ (and DT) through a 10-µm-diam tube. This layering-sphere assembly required three months of thermal analysis to design and was manufactured in-house within a three-week period. The performance of the new design is being tested in the Cryogenic Fill-Tube Test Facility in the Target Fabrication area. The immediate goal of these experiments is to control the thickness of a deuterium fuel-layer in the capsule to within ±1 µm of the desired value. Future experiments with DT (planned for 3QFY17) will determine if the design is adequate to form a uniformly thick ice layer.