Studying shape transfer of low-mode deformations in Double Shell capsule implosions

We present numerical studies of Double Shell capsule implosions to understand the transfer of low-mode perturbations from the ablator to the inner shell. Double Shells are composed of a low-Z ablator (or outer shell) and a high-Z inner shell which encloses the fuel. During the implosion, the outer shell collides with the inner shell, setting it in motion. The latter then compresses the fuel to densities and pressures that are sufficiently high for volumetric ignition. However, asymmetry sources from the hohlraum radiation and capsule fabrication can result in low-mode deformations of the ablator. During shell collision, these can imprint on the inner shell affecting implosion symmetry and capsule performance.

We determine shape transfer and growth of low-modes on the inner shell during implosion and evaluate their observability with NIF’s Advanced Radiographic Capability (ARC). For this, we perform 2D implosion simulations of capsules that include low-mode ablator deformations. We then create synthetic radiographs to determine whether the deformations on the inner shell can be captured with ARC-level backlighting. Finally, we test different initial perturbations and target dimensions, as well as, ablator surface roughness on the visibility of effects on the inner shell with ARC.