Towards a more universal understanding of radiation drive in gas-filled hohlraums

We have found that radiation-hydrodynamic calculations that use the high flux model assumptions [1] can accurately predict the radiation drive produced by a laser-heated hohlraum under certain conditions, but can not predict drive over a broad range of parameters (pulse energy, hohlraum gas fill density, hohlraum case-to-capsule ratio). In particular, the model is accurate for ∼7 ns long laser pulses used to implode capsules with high density carbon (HDC) ablators in hohlraums with helium fill gas densities of 0-0.6 mg/cc. By systematically varying the gas fill density from 0 to 1.6 mg/cc we found that the agreement with drive begins to diverge for fills > 0.85 mg/cc. This divergence from the model coincides with the onset of measureable SRS backscatter. In this same set of experiments the radiation drive symmetry inferred from the imploded shape of a gas-filled capsule is not predicted with this model. Finally, several possible fixes to the model to reduce the observed discrepancies are considered.