Stress- and Radiation-Induced Swelling in Plastic Capsules

The process of filling targets with D-T for cryogenic experiments on the OMEGA laser induces small-scale features on the inner surface of the plastic capsules. Each feature was a cluster of low-level domes (<0.1 m high) with individual lateral dimensions <5 m that collectively covered lateral dimensions of up to 300 m² . These features were observed only when a high radiation dose was combined with high stress in the plastic wall, as occurs when the capsules are permeation filled and transferred at cryogenic temperatures. No porosity or void structure was observed in or below these domes. It is speculated that the domes are a swelling caused by radiation-induced bond scission and chemical restructuring that reduces the plastic density in localized regions.