A Brief History of Backscatter on NIF*

In indirectly-driven inertial confinement fusion (ICF) experiments, understanding how the laser energy is transported and coupled into the hohlraum and capsule is critical for achieving ignition. Laser-plasma instabilities (LPI) play a major role in energy transport, implosion symmetry and nuclear fuel preheat, and have had a significant impact on ICF experiments carried out at the National Ignition Facility since the beginning of the ignition campaign in 2009. The primary LPIs at NIF are cross-beam energy transfer, which moves power between laser cones, and backscatter, in the form of stimulated Brillouin and Raman scattering (SBS and SRS). Precise measurement of the backscattered light will provide information about LPI and quantify the amount of energy that is coupled into the hohlraum. In this presentation we summarize the evolution of backscatter throughout years of operation at NIF and the various designs and platforms used for ICF experiments; we identify the key changes that have reduced backscatter and increased energy coupling into the target.