Surface Roughness Statistics and Temperature Step Stress Effects for D-T Solid Layers Equilibrated inside a 2 mm Beryllium Torus

Abstract

Solid D-T layers are equilibrated inside a 2 mm diameter beryllium toroidal cell at temperatures ranging from 19.0 K to 19.6 K, using the beta-layering process. Each experimental run consisted of multiple cycles of rapid- or slow-freezing of the initially liquid D-T charge. Each of these freeze cycles was followed by a lengthy period of beta-layering equilibration, which was terminated by melting the layer. The temperature was changed in discrete steps at the end of some equilibration cycles in an attempt to simulate actual ICF target conditions. High-precision images of the D-T solid-vapor interface were analyzed to yield the surface roughness σrms as a sum of modal contributions. Results show an average σrms. of 1.3 ± 0.3 μm for layers equilibrated at 19.0 K and show an inverse dependence of σrms on equilibration temperature up to 19.525 K. Inducing sudden temperature perturbations lowered σrms to 1.0 ± 0.05 μm.