Surface Roughness Measurements of Beta-Layered Solid Deuterium-Tritium in Toroidal Geometries

New experiments in a NIF-scale toroidal cylinder have resulted in true shadowgraphs of the DT ice surface. The spectral analysis of the images summed over ℓ-modes 2 through 256 reveal that the surface roughness reaches values just below 1.0 μm at temperatures of 19 K and above. Summing only modes ℓ ≥10, the partial surface roughness is below 0.7 μm at 19.5 K. These results indicate that native beta-layering will be sufficient to meet the NIF requirements for DT ice surface finish for both Be and CH ablating shells.

The toroidal cylinder incorporates a linear heater along the cylindrical axis to test the concept of surface enhancement due to heat assisted beta-layering in DT. Additionally, with the use of this heater it is possible to symmetrize a pure D₂ layer.