High-Volume and -Adiabat Capsule (HVAC) experiments using advanced hohlraums

Recent experiments using advanced hohlraums have demonstrated 20-30% energy coupling, or 300-500kJ, to capsules with diameters 2.5-3.4mm on the NIF (Ping et al. Nature Phys. 15, 138, 2019; Phys. Plasmas, 27, 100702, 2020; Nuclear Fusion, 2021). Such a high energy coupling efficiency makes it possible to explore a single-shell volume ignition scheme named HVAC,  where the entire DT fuel forms a large hot spot and the confinement is provided by the remaining ablator shell (P. Amendt et al., Phys. Plasmas 27, 122708, 2020). The advantages over the conventional central hot spot ignition include lower convergence requirement, higher adiabat to suppress instabilities, less conduction loss, longer confinement time, and more tolerance to defects. 2D simulations have shown promising performance in yield, symmetry and instability mitigation. A set of NIF shots has been planned and the initial experimental results will be presented. The prospect of HVAC as a complementary path toward ignition will also be discussed. This work was performed under the auspices of the US DOE by LLNL under contract number DEAC52- 07NA27344.