Low-Velocity Shock Ignition on the NIF

Shock ignition (SI)\footnote{R. Betti\textit{ et al.}, Phys. Rev. Lett. \textbf{98}, 155001 (2007).} has been proposed as a low-energy alternative path to ignition on the National Ignition Facility (NIF). Previously, a polar-drive SI capsule and pulse design was presented\footnote{K. S. Anderson\textit{ et al.}, Phys. Plasmas \textbf{20}, 056312 (2013).} for the NIF at a velocity of $3.05 \times 10^{7}$ cm/s---substantially higher than the velocities of typical SI designs ($\sim$2.4 to 2.7 $\times$ 10$^7$ cm/s). The motivation for the higher velocity was to improve margin in 1-D simulations. This target was shown to be sufficiently stable in 2-D simulations to the various sources of nonuniformity anticipated on the NIF, being most sensitive to imprinted perturbations from laser speckle. This paper reports on lower-velocity SI designs aimed at reducing the in-flight aspect ratio, thereby decreasing sensitivity to laser imprint. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.