Improving hohlraum efficiency at the National Ignition Facility with smaller cylinders

Recent inertial confinement fusion (ICF) experiments at the National Ignition Facility (NIF) have set records for fusion energy liberated in a laboratory setting, reaching burning plasma and near ignition conditions. Some of these experiments were conducted with the Hybrid-E cylindrical hohlraum platform, consisting of a 6.4 mm diameter hohlraum with 3.1 mm diameter “laser entrance holes” (LEH’s) driving a CVD diamond capsule of inner radius 1.05 mm. This work represents the next step in improving cylindrical hohlraum efficiency at NIF by placing the same sized capsule in a 6.2 mm diameter cylinder with 2.7 mm diameter LEH’s. This effectively increases the available x-ray drive energy by ~6% by reducing hohlraum losses. Novel beam pointing schemes are required to clear the smaller LEH and implosion symmetry control is accomplished using cross-beam energy transfer (CBET) via laser wavelength detuning (Δλ) between the inner and outer cones. Early tuning experiments and simulations with the radiation-hydrodynamic code HYDRA will be discussed.