Radiation hydrodynamics with backscatter and beam spray in gas filled hohlraum experiments at the National Ignition Facility

Abstract

Several experiments using either CO 2 or propane gas filled halfraums [i.e. hohlraums with a single laser entry hole (LEH)] have been shot at the National Ignition Facility (NIF) in a joint LosAlamos/Livermore collaboration. The experiments have been modeled by the Lasnex code. The possibility of beam spray due to filamentation of the incident laser beam is assessed through simulations which parametrically decrease the f-number of the beam at times of high intensity. The uncertainty in heat transport is evaluated through parametric variations in the electron thermal flux limit (fe). Each calculation in the resulting two parameter set is post-processed to simulate outputs which can be compared with Dante detector results for the soft X-ray flux through the LEH, and gated, framed images of hard X-rays (FXI) through the hohlraum side walls. Simulations which well match the data for both gases indicate that the laser energy is penetrating the gas filled hohlraum even towards the end of the pulse. This suggests that the gas fill is useful in keeping the hohlraum open to laser energy throughout the pulse.