Exploring gradient layer sensitivities in double shell ICF designs*

Double shell designs for inertial confinement fusion (ICF) implosions are susceptible to hydrodynamic instabilities at their interfaces, which has led to the consideration of gradient density inner shells as a mitigation strategy. We employ the Eulerian radiation-hydrodynamics code xRAGE to examine these alternative inner shell density profiles comprised of mixtures of beryllium and tungsten to specifically characterize their stability and impact on performance. There is a yield hit in 1D simulations from incorporating gradient layers due to reduced efficiency of kinetic energy transfer between the shells, but improved stability in 2D simulations can offset this drawback. We perform a mode study to determine the sensitivity of different density gradients to each mode and to quantify feedthrough to the fuel-inner shell boundary. This motivates exploring alternative shell dimensions to exploit improved stability of the implosion, and a preliminary study is presented. The joint in the outer hemispherical shells also imprints onto the inner shell, and we measure the impact of this on the various inner shell profiles.