Advancing Compression in Large-Scale HDC-Based Ablator Implosions Through Modified Drive and Capsule Profiles

Target gain greater than unity has been achieved for the first time in inertial fusion experiments [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)]. However, the fuel burn-up fraction remains at only about one-fourth of ideal estimates due to limited areal density, indicating the potential for greater gain through increased compression. Efforts to enhance compression using high-density carbon (HDC) ablator implosions have been hindered by hydrodynamic instability growth.

Recently, a series of experiments at the National Ignition Facility [Spaeth et al., Fusion Science and Technology 69, 25 (2016)] using a gently ramped "SQ-n" pulse [Clark et al., Physics of Plasmas 29, 052710 (2022)] and a modified HDC ablator profile has resulted in the highest areal densities achieved to date, with up to a 30% increase in compression, attributed to reduced fuel-ablator mixing and lower adiabat compared to previous designs. [Tommasini et al., Physical Review Research 5, L042034 (2023)]

Here, we report on applying this design to larger-scale implosions, using a 1050 µm inner radius capsule in a 6.4mm x 11.2mm hohlraum, to test the physics and the limits of compression of the combination of the ramped pulse and the modified ablator profile on DT fuel in the burn-wave propagation regime. The results suggest a significant potential for increasing fuel areal density in larger-scale implosions, as predicted by simulations. This marks a significant advancement in efforts to achieve much higher gains.