Including Measured Stimulated Brillouin Backscatter in Simulations of Experiments at the National Ignition Facility*

Inertial confinement fusion experiments at the National Ignition Facility use 192 laser beams to drive a hohlraum to produce x-rays, which in turn drive a capsule implosion leading to a fusion reaction. Stimulated Brillouin backscatter (SBS) is a laser-plasma instability that can cause a portion of incoming laser light to return out of the hohlraum without coupling to the hohlraum walls. While the impact of SBS on overall energetics is small in modern hohlraums, it can still have significant impacts on implosion shape, necessitating its inclusion in simulations and other modeling efforts.

In this talk, we detail a statistical modeling approach that automates the extraction of a smooth, non-negative SBS signal from about 66 SBS measurements across two types of diagnostics (DrDs and FABS). This smooth SBS signal is readily incorporated into simulations, as we demonstrate for several Hybrid-E experiments (most notably N210808). We show that including such SBS corrections to the incoming laser power can lead to significant (20-35%) shifts in predicted P2/P0 even with total SBS energy as small as 1-2% of incoming laser energy. We close by discussing the potential of such automated analysis to regularly assist future modeling efforts.

LLNL-ABS-851414