Modeling Lessons from the Build-A-Hohlraum Campaign

Radiation-hydrodynamic simulations of indirect-drive inertial confinement fusion (ICF) targets are not able to adequately predict the implosion time and shape of the capsule. Peak neutron production routinely is predicted to occur roughly ~400 ps earlier than measured representing, and simulated implosion shape is much more prolate than observed. Due to a lack of predictive simulations, calibrated models have been developed which discard roughly 20% of the incident laser energy to tune to experimental measurements but such models are not expected to scale. In order to narrow the list of possible hypotheses that can explain modeling discrepancies, the Build-A-Hohlraum campaign at the National Ignition Facility (NIF) was executed which started at the simplest possible hohlraum and incrementally added features present in ignition designs. This talk will summarize the key results from the campaign: the impact of external hardware on the relative drive-deficit as observed by two independent lines-of-sight and the consistent overprediction of x-ray flux in the 2-4 keV range. The latter issue can be addressed through the use of an opacity multiplier for energies > 1.8 keV.