Single-Beam Smoothing Requirements for Wetted-Foam, Direct-Drive NIF Ignition Target Designs

Wetted-foam, direct-drive target designs are a path to high-gain experiments on the National Ignition Facility (NIF). Previous studies have shown that reduction of single-beam nonuniformity is central to target performance of designs incorporating solid CH ablators.\footnote{ P. W. McKenty\textit{ et al}., Phys. Plasmas \textbf{8}, 2315 (2001).} It has also been shown that at 1 MJ, even a wetted-foam target with a low IFAR and low acceleration-phase instability requires a minimum of two-dimensional (2-D) smoothing by spectral dispersion (SSD)\footnote{ S. Skupsky\textit{ et al}., J. Appl. Phys. \textbf{66}, 3456 (1989).} for ignition.\footnote{ T. J. B. Collins\textit{ et al}., Phys. Plasmas \textbf{14}, 056308 (2007).} We show the results of 2-D simulations indicating that this is also the case for 1.5-MJ, wetted-foam, direct-drive NIF target designs. Some possible avenues for single-beam smoothing in the absence of 2-D SSD will be briefly presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement DE-FC52-92SF19460.