Stimulated Brillouin Scatter Reduction using Borated Gold Hohlraums on the National Ignition Facility

New target platforms for indirect drive ignition on NIF are being introduced to improve capsule and hohlraum performance. A number of these targets show increased Stimulated Brillioun Backscattering (SBS) late in the laser pulse on the outer cone beams. This scattering reduces the laser power available for x-ray drive in an ignition hohlraum as well as poses a damage risk to the laser optics. We observe a factor of 5 reduction in the SBS power from outer cone beams by doping the Au hohlraum wall with 1.5 $\mu$m layer of 40{\%} Boron in Au. The experiment used a room temperature Neopentane-filled ignition scale hohlraum and a 1 MJ, 370 TW laser pulse. The measured SBS backscatter from the outer cone beams on NIF is quantified temporally and spectrally. Comparing the measurements between a pure Au and a AuB hohlraum show approximately a 5x reduction in SBS power. Simulations show that the reduction is in the hohlraum wall plasma. A continuation of this study will extend the duration of the laser pulse to measure the time-dependence of the outer beam SBS. Experimental results from these experiments and detailed simulation results will be presented.