Simulations of high-mode Rayleigh-Taylor growth in NIF ignition capsules

Near the pusher/fuel interface in the NIF indirect drive ignition capsule, the cold dense fuel can reach higher density than the material accelerating it. Unlike the outer surface where ablative stabilization is important, Rayleigh-Taylor (R-T) growth at this interface is stabilized only by the density gradient, plasma viscosity and mass diffusion. Highly resolved 2D and 3D HYDRA simulations of capsules seeded with a representative surface spectrum up to modes similar to 2000, with only gradient stabilization, indicate for our earlier design ("Rev 1")(1) a final mix width > 30 mu m, resulting in > 10% Be in the outer similar to 25% of the DT fuel. No degradation in the capsule neutron yield is observed. Simulations indicate that the R-T growth at this interface can be significantly reduced by increasing the Cu fraction in the Be ablator. This optimization is a key feature in our new designs ("Rev 2").