Characterization of Embedded Spheres in Opaque Foams

This paper concerns the methods that were used to build an imbedded sphere in foam target for use on Omega to test theories of astrophysical jets. The core of the target is comprised of a titanium slab that is driven through a titanium washer into a low-density foam with an imbedded sphere. The critical dimension that needed to be known was the location of the center of the sphere with respect to the drive region. Initially, attempts were made to fabricate the sphere imbedded foam precisely, however the foam changed dimensionally during the drying phase of fabrication. The dimensional changes observed were often as large as the specified tolerances, so the foams required post fabrication characterization. Optical characterization of the foams weren't accurate enough and radiography was required for precision characterization. Once characterized, the sphere needed to be placed in the specified target geometry correct to an accuracy of ±25 m. The radiography images were imported into a CAD program and these images were used to assemble the target precisely. The methods used provided a well-characterized target with a good build.