Saturn Designs for Small Proton-Backlighter Targets at the National Ignition Facility

Small exploding-pusher capsules with D$^{\mathrm{3}}$He fill are ideal sources for high-resolution proton radiography for many high-energy-density experiments at the National Ignition Facility (NIF). However, the laser energy that can be delivered to these capsules is currently limited by the need to minimize laser blowby---unabsorbed laser light passing by the target into opposing beam ports with the potential of damaging laser optics. This issue arises because it is logistically convenient to leave the indirect-drive phase plates in place. Saturn targets,\footnote{R. .S. Craxton and D.W. Jacobs-Perkins, Phys. Rev. Lett. \textbf{94}, 095002 (2005).} in which the capsule is surrounded by a toroidal plastic ring, promise to remove the energy limitation by blocking blowby light, permitting a brighter proton source. A design has been developed using the 2-D hydrodynamics code \textit{SAGE}\footnote{R. S. Craxton and R.L. McCrory, J. Appl. Phys. \textbf{56}, 108 (1984).} for a ring that can be used to block the laser blowby for target diameters from 440 to 866 $\mu $m and drive beams from any of the NIF quads. Full-power NIF beams can be safely used. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.