Comparison of Simulations to Measurements in Direct-Drive Energy Coupling Experiments on the National Ignition Facility*

Energy coupling is a critical determinant of implosion performance. In this talk, results from experiments that systematically study laser drive during different times of the laser pulse on the NIF are presented. Shock radiography using solid spheres is used to infer early-time coupling during the foot and rise to the main pulse. Since shocks decouple from the laser drive shortly after peak intensity, studying shock trajectories isolates the effect of laser drive during this time. Simulations that include the effects of non-local transport and CBET reproduce these trajectories very well for varying on-target intensities, though some uncertainties remain. Implosions are sensitive to coupling throughout the drive. Self-emission and backlit implosion trajectories will be presented for varying on-target intensities. Implications for direct-drive implosion performance will be discussed.