Beta-Layering in Foam-Lined Surrogate IFE Targets

Solid deuterium-tritium (the symbol DT is used here to represent the equilibrium mixture of 50% deuterium and 50% tritium, having the molecular composition: 25% D₂, 50% deuterium tritide molecules, and 25% T₂) (DT) is nucleated from DT-wetted foam and subsequently forms a uniform layer by the beta-layering phenomenon. Compared to DT frozen on smooth metal surfaces, the surface roughness of the inner-lying pure DT solid-vapor interface is substantially lower at all modal values higher than ~10, possibly due to the small-grain-size polycrystalline nature of the solid. For thick layers, deleterious effects are observed, notably the formation of DT-rich vapor voids in the foam matrix and the subsequent propagation of these voids into the pure solid DT layer.