An important component of the U.S. effort to achieve thermonuclear
ignition in 2010 on the National Ignition Facility is the development of
high quality 2 mm diameter spherical capsules to function as the ablator
and contain the cryogenic DT fuel. Three ignition capsule designs have
been developed, and detailed fabrication specifications for each design
have been established and placed under change control. A research program
with activities coordinated mainly between Lawrence Livermore, General
Atomics and Los Alamos is underway to demonstrate fabrication of capsules
meeting specifications. The point design for ignition campaigns beginning
in 2010 is a Cu-doped Be capsule that has a radial gradient in Cu dopant
level in the capsule wall. This capsule is being produced by sputter
deposition of Be and Cu onto either a hollow glow discharge polymer (GDP)
spherical mandrel or a solid spherical mandrel, followed by removal of the
mandrel and polishing of the capsule. A key goal in the U.S. is to
demonstrate fabrication of this capsule by the end of 2006. Two other
ignition capsule designs are also being developed as contingencies to the
point design. One contingency design is a GDP capsule that has a radial Ge
dopant level in its wall. This capsule is produced by co-deposition of Ge
and GDP onto a PAMS mandrel followed by thermal removal of the mandrel.
The second contingency design is a uniform Cu-doped Be capsule that is
fabricated from high purity fine grain Be0.3at.%Cu alloy using a precision
machining route followed by polishing. Ignition targets to be fielded in
2010 will be filled with DT fuel through a small fill hole. Laser drilling
capability has been developed and used to drill approximately 5 μm
diameter holes through capsule walls for DT filling. Characterization
methods necessary for characterizing capsules are being developed.