Impact of multi-species physics and cross-beam-energy-transfer in near vacuum hohlraum simulations

Inertial confinement fusion (ICF) experiments performed on the National Ignition Facility have found that low density hohlraum fill improves laser coupling, reduces hot electron generation, and increases laser propagation to the hohlraum wall. However, the ability of rad-hydro codes to model the P2/P0 capsule symmetry at these lowest densities (He fill = 0.03 mg/cc) has historically been poor. This makes the design process at these densities problematic and motivates the use of He fill >0.15 mg/cc. The disagreement was previously attributed to multi-species (MS) physics; but it was not possible to simulate this until recently. This work utilizes rad-hydro simulations with a novel MS fluid physics package to investigate the source of the P2 asymmetry. Surprisingly, we find that MS physics alone makes only slight modifications to P2 symmetry. However, the use of an inline cross-beam-energy-transfer (CBET) package dramatically increases P2 of the capsule to a more prolate implosion; an effect that is amplified by the MS physics package. Understanding the details of MS and CBET physics in hohlraums is thus shown to be important in the development of predictive ICF modeling, especially in realizing the potential of low-fill hohlraums.