Grain-induced perturbations, decompression, and mixing in numerical simulations of imploding high-density-carbon cylindrical shells in planned OMEGA experiments*

The granular structure of chemical-vapor-deposition high-density carbon (HDC) material is believed to induce perturbations leading to potentially serious effects on the performance of ICF targets employing such material[1]. In preparation for experiments examining the effect of various grain sizes in HDC, we are carrying out simulations of laser-driven DT-filled cylindrical HDC shells composed of microscale or nanoscale grains, using the xRAGE code and the Mazinisin laser-deposition model. We follow the prescription of Davidovits et al. [1] in preserving the measured mean density and density variance of HDC when it is infeasible to resolve the actual size of grain structures. The simulations show that grains seed strong perturbation growth, leading to shallow, long-scale-length density gradients at the ablation surface, in stark contrast to the steep density gradient seen in non-granular material. Grains lead to much higher densities of carbon driven to the axis during peak fusion burn, compared to non-granular material. We are also beginning simulations of granular HDC indirect-drive spherical NIF capsules, and will compare their behavior to simulations of similar but non-granular capsules.

1. S. Davidovits, C. R. Weber, and D. S. Clark, Phys. Plasmas 29, 112708 (2022)