The role of a detailed configuration accounting (DCA) atomic physics package in explaining the energy balance in ignition-scale hohlraums

摘要

In 2009 the National Ignition Campaign (NIC) gas-filled/capsule-imploding hohlraum energetics campaign showed good laser-hohlraum coupling, reasonably high drive, and implosion symmetry control via cross-beam transfer. There were, however, discrepancies with expectations from the standard simulation model including: the level and spectrum of the Stimulated Raman light; the tendency towards pancake-shaped implosions; and drive that exceeded predictions early in the campaign, and lagged those predictions late in the campaign. We review here the origins/development path of the " high flux model" (HFM). The HFM contains two principal changes from the standard model: 1) It uses a detailed configuration accounting (DCA) atomic physics non-local-thermodynamic-equilibrium (NLTE) model, and 2) It uses a generous electron thermal flux limiter, f=0.15, that is consistent with a non-local electron transport model. Both elements make important contributions to the HFM's prediction of a hohlraum plasma that is cooler than that predicted by the standard model, which uses an NLTE average atom approach, and a value of f=0.05 for the flux limiter. This cooler plasma is key in eliminating most of the discrepancies between the NIC data and revised expectations based on this new simulation model. The HFM had previously been successfully deployed in correctly modeling Omega Laser illuminated gold sphere x-ray emission data, and NIC empty hohlraum drive. However, when the HFM was first applied to this energetics campaign, the model lacked some credibility/acceptance compared to the standard model, because it actually worsened the discrepancy between the observed hohlraum drive for the 1. MJ class experiments performed late in the campaign and the revised expectation of higher drive based on the HFM. Essentially, the HFM was making a prediction that the laser-hohlraum coupling was less than that assumed at that time. Its credibility was then boosted when a re-evaluation of the laser light losses from the hohlraum due to laser plasma interactions matched its prediction.