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 (NIF) 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 talk I will show how backscatter light is measured at the NIF using the Full Aperture Backscatter System (FABS), Near Backscatter Imager (NBI), Scattered Light Time-history Diagnostic (SLTD) and the Drive Diagnostic (DrD).
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and the NSF-DOE Partnership in Plasma Science under Grant 1803874.
Nuno Lemos is a staff-scientist with the NIF & Photon Science group at the Lawrence Livermore National Laboratory (LLNL) whose research is focused on laser plasma interactions. He received his PhD in Plasma Physics in 2013 (IST-Portugal) and was a post-doctoral fellow at UCLA before joining LLNL. His research is focused on laser plasma interaction with short (fs-ps) and long (ns) laser pulses. In the short laser pulse interactions, he has established himself as a crucial contributor on the production and characterization of x-ray, electrons and ions beams, in particular high-energy x-ray sources generated through laser wakefield acceleration. In the long laser pulse regime, he has made key contributions to the inertial confinement fusion program by identifying key energy loss mechanisms due to laser plasma interactions as well as developed and utilized optical backscatter diagnostics for experiments on NIF.