Single-mode Rayleigh–taylor Growth-rate Measurements

106 LLE Review, Volume 71 Understanding the growth of perturbations due to hydrodynamic instabilities is important to the design of direct-drive targets for the National Ignition Facility (NIF). Direct-drive inertial confinement fusion (ICF) has the potential to be more efficient than indirect-drive ICF; however, there is the potential for greater growth of hydrodynamic instabilities due to the lower ablation velocities, which will prevent a NIF target from igniting. The primary instability of concern is the Rayleigh– Taylor (RT) instability, where a less dense fluid “supports” a more dense fluid and as such merits a thorough investigation. Direct-drive targets are subject to the RT instability twice during an ICF target implosion: first during the ablative acceleration phase of the implosion and second when the deceleration phase begins core assembly. Target imperfections and laser-irradiation nonuniformities act as amplitude seeds for the acceleration RT instability, while interior target imperfections and feedthrough of the ablation surface growth to the fuel–pusher interface act as amplitude seeds for the deceleration RT instability.