Progress towards direct-drive wetted-foam implosions on the NIF and OMEGA*

Wetted foam direct-drive inertial confinement fusion (ICF) implosions offer the prospect of improved stability, mitigation of laser-plasma instabilities (LPI), and control over the convergence ratio to achieve high gain without the stringent requirements of solid fuel layering. Recent advancements in two-photon polymerization manufacturing of deterministic and reproducible foam targets have renewed interest in wetted foam as a path forward for ICF and inertial fusion energy. Dedicated experiments to study the physics of wetted-foam spherical targets have been conducted on the National Ignition Facility (NIF). First, implosion of 18-um thick, 3-mm diameter capsules filled with liquid D₂ demonstrated the feasibility of fielding these cryogenic targets while quantifying laser-energy coupling. A transition to lower coupling after the laser burned through the CH shell and into the D₂ matches expectations from radiation-hydrodynamics simulations and bounds the expected coupling in a wetted foam layer, which consists of a CH/D₂ mixture. Further experiments on NIF will diagnose energy coupling in a liquid D₂-filled CH capsule lined with a 135-um thick, 32 mg/cm³ foam. On OMEGA, foam-lined cone-in-shell experiments filled throughout with liquid D₂ are planned to diagnose energy coupling, LPI, and shock propagation in wetted-foam ablators. Preliminary results and plans for future experiments towards the implementation of wetted-foam implosions with interior vapor regions will be discussed