Modeling Composition Gradients in Planar Shock Experiments

We present results of planar shock experiments where acceleration pushes a less dense material into a more-dense one. Such an interface is Rayleigh-Taylor (RT) unstable and the instability growth is governed partly by the Atwood number gradient. The double shell inertial confinement fusion capsules have a foam spacer layer that pushes on an inner capsule composed of a beryllium tamper and a high-Z inner shell. We benchmark a planar shock experiment with beryllium/tungsten targets to assess our ability to match the shock velocity through the Be and W. One target had the normal bilayer construction of beryllium and tungsten in two distinct layers; the second target had the beryllium grading into tungsten with a quasi-exponential profile, motivated by the potential for reduced RT growth with the gradient profile. Simulations mimic the shock profiles for both targets and match the shock velocity to within 5%. These results validate the ability of our simulations to model double shell capsules with bilayer or graded layer Be/W inner shells, which are needed to design future experiments at the National Ignition Facility.