Status of cryogenic layering for NIF ignition targets

Recent advances in cryogenic layering include improved surface roughness characterization of many layers formed using 'slow-cool' and 'rapid-cool' protocols. At 0.25 K below the melt, slow-cooled layers meet the NIF smoothness requirement. However, at 1.5 K below the melt grain-boundary misalignments dominate the layer roughness and cause it to exceed the smoothness specification. Rapid-cool of the layer to 1.5 K below the melt shows promise for meeting the ignition requirements. Much of the current research effort is aimed at characterizing the onset of roughness during rapid cooling and determining the scale of the resulting roughness