Experimental Demonstration Of The Reduced Expansion Of A Laser-Heated Surface Using A Low Density Foam Layer, Pertaining To Advanced Hohlraum Designs With Less Wall-Motion

The ablative expansion of laser-heated materials is important for determining how hohlraum cavities can be utilized for inertial confinement fusion. The utility of a low-density foam layer to reduce the density of the expanding heated hohlraum wall is demonstrated in a series of experiments on the National Ignition Facility. X-ray radiography measurements of the expanding foam-lined Au wall in low aspect-ratio cylindrical geometry are used to compare the impact of Au-doped CH and Ta(2)O(5)foams between 10 and 40 mg/cc on the wall expansion. HYDRA Simulations are used to estimate the x-ray transmission at the 1/4 n(c)surface, which is important in understanding the absorption of laser light by the plasma. These demonstrate for the first time that a foam layer reduces the expansion of a hohlraum-like target and illustrate that the interplay between the expanding foam plasma and the shock reflected by the hohlraum wall is critical in optimizing foam-liner parameters to achieve the maximum time for a symmetric drive on a capsule.