Improving the Yield of Target Quality OMEGA Size PAMS Mandrels by Modifying Emulsion Components

Poly(-methylstyrene) (PAMS) shells are made by microencapsulation and used in the fabrication of a large variety of targets for the inertial confinement fusion (ICF) program. Although this process has previously been developed into production mode, the yield of shells with acceptable sphericity and wall uniformity in the OMEGA size range (800-1000 m) has been poor (~ 18%). We have made improvements in the yield of these shells by modifying the composition of the outer water solution (W2) in the microencapsulation emulsion. This improvement was achieved by increasing the concentration of Poly Vinyl Alcohol (PVA) from 0.3% to 1.0% and an addition of 0.1% Poly Acrylic Acid (PAA). These modifications were aimed at increasing the interfacial surface tension in the emulsion but also appear to have played a role in density matching the components in the PAMS emulsion. These modifications improved the out of round (OOR) and non-concentricity (NC) of the PAMS mandrels resulting in as increase in the yield of target quality batches based on these basic criteria from 18% to over 80%. Meanwhile, the vacuole content and the surface finish of the PAMS shells were not adversely affected by these changes.