High-Resolution Optical Measurements of Surface Roughness for Beta-Layered Deuterium-Tritium Solid Inside a Re-Entrant Copper Cylinder

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Abstract
A high-resolution optical imaging system and custom-designed image analysis software are used to make surface roughness measurements for deuterium-tritium (D-T) solid layers, equilibrated inside a 2-mm-inside-diameter re-entrant copper cylinder. Several experiments are performed that yield D-T layer thicknesses of between 75 and 139 µm, with equilibration temperatures between 17.4 and 18.8 K. A 1024-× 1024-pixel charge-coupled-device imaging camera, coupled with a Maksutov-Cassegrain long-range microscope, produces a 2.5-µm (single-pixel) image resolution. The error function fitting of the image analysis data produces submicron resolution of the layer interior surface finish. The length scale for the cylinder inner bore is just over 6 mm, and the final layer surface roughness for this length ranges from 3- to 1.7-µm root-mean-square. The feasibility is being explored of using these highly uniform and smooth D-T solid layers inside future targets for inertial confinement fusion reactors to produce surface finishes that will meet target design requirements for the National Ignition Facility. Techniques for improving the D-T solid layer surface finish are examined, limitations of the current D-T cell configuration and fuel mix are discussed, and cell configurations for future experiments are described.