Characterizing instability mitigation and preheat effects in gradient inner shells for double shell designs

While double shell designs offer many advantages for inertial confinement fusion (ICF) implosions, they are susceptible to hydrodynamic instabilities at their interfaces. We employ the Eulerian radiation-hydrodynamics code xRAGE to explore alternative inner shell density profiles – using gradients comprised of beryllium and tungsten – and to specifically characterize their stability and impact on performance. First, we examine the preheat expansion of the different inner shells using a drive that has been constrained by measured preheat; we measure the density gradient length scale seen prior to shell collision as a function of initial profile, as this will impact stability. We next 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. Certain engineering features – such as the joint in the outer hemispherical shells – also can imprint onto the inner shell, and we measure the impact of this on the various inner shell profiles. Finally, a complementary graded layer campaign at OMEGA is discussed, and future directions – including observable metrics – are given.



*This work conducted under the auspices of the U.S. DOE by LANL under contract 89233218CNA000001.