Cooling-Induced Deformation of Polystyrene Spherical Shells

We carried out experiments on cooling-induced deformation (CID) of inertial-fusion fuel capsules. Polystyrene spherical shells were used as test samples. In the experiments, approximately 90 shells were cooled using liquid nitrogen and observed with an optical microscope. Pictures of each shell were recorded at 0°C and −190°C, and they were compared with each other. About a half of the tested shells showed CID, where the maximum deformation was in the order of 1% of the shell radius. Although the polystyrene shells were fabricated by a density-matched emulsion method using both hand-shaken microencapsulation and triple-orifice droplet-generator techniques, we recognized no significant difference in deformation characteristics between these two techniques. The observed CID showed poor reproducibility. We tried annealing in order to prevent CID, but no apparent improvement was recognized.