Experimental observation of hydrodynamic instability inhibition in a material and density gradient

Hydrodynamic instabilities are a significant degradation mechanism in Inertial Confinement Fusion experiments. These instabilities contribute to a loss of symmetry and an undesired intermixing between the fuel and the capsule that reduces the efficiency of the reaction. This effect is especially prominent at interfaces with sudden and large density changes, such as the surface of the heavy inner-shell in a double-shell capsule implosion. Theory suggests that the growth of these instabilities can be mitigated by replacing the sharp density jump with a smooth density gradient, but these models do not account for certain complex effects such as mixed opacities or equations-of-state.

This experiment compares instability growth between a density jump and a density gradient. A hohlraum is used to accelerate an Al ablator into pure Zr foils, Zr foils with a Be tamper, and density-gradient foils that consists of a linear material gradient of Be to Zr. We infer the growth of seed perturbations using x-ray radiography, and compare these results to 2D simulations performed with RAGE, an Eulerian radiation hydrodynamics code with Adaptive Mesh Refinement.