Overview We report on the progress since January, 1998, in preparing polymer mandrels by microencapsulation for NIF scale ICF capsules that meet the required symmetry and surface finish requirements. During that time we successfully completed our FY98 DOE TDF4.1 milestone of improving the mandrel low mode to meet NIF requirements. A number of batches of 2 mm microencapsulated poly(amethylstyrene) shells have been produced with mode 2 out-of-rounds of less than 2 urn. Detailed characterization

more »

... r these and other batches is presented. We have found that the key to reducing mode 2 out-of-round is the density matching of the composite oil/inner core water microencapsulated shell preform to the supporting bath. Density matching of the inner core water to the oil phase seems to be less important, perhaps because core centering is accomplished by other physical means. Shell roughness over the very important mode 10 to 100 region is still too high by at least a decade in power, and work aimed at improving this is the task for FY99. In addition to basic sphericity results we also report on a number of experiments designed to elucidate the fundamental scientific issues. In most cases the experiments reported are but starting points that will be followed up during FY99. Lastly we note that no effort has been placed on optimizing the overcoating and thermal decomposition steps, which must follow the successful microencapsulation step. Based upon GA's experience with smaller scale shells we are hopeful that these steps will not degrade capsule symmetry and surface finish. This question should be answered at least in part during FY99 as GA begins to supply finished 2 mm CH mandrels for the polyimide and Be ablator development work.