Using Secondary DT Neutrons to Infer Fuel Convergence and Areal Density Asymmetries in NIF Implosions

Brandon Lahmann


Tuesday, September 17, 2019



PSFC Student Seminars

In deuterium-filled inertial confinement fusion (ICF) implosions, DD-tritons can undergo secondary fusion reactions with the thermal deuterium plasma to create secondary DT neutrons. On the National Ignition Facility (NIF), both the primary reactions (via DD-neutrons) and the secondary DT neutrons are routinely measured from several lines of sights using neutron time of flight (nTOF) spectrometers. The ratio of these secondary and primary reactions are used to infer the areal density (ρR) and the convergence of the fuel region. Additionally, the shape of the secondary DT neutron spectra can be used to infer the final asymmetry of the imploded capsule. Convergences inferred using x-ray imaging techniques are consistently larger than those inferred by this secondary DT neutron technique. These apparent discrepancies are not currently understood, but potential explanations are discussed. This work is supported in part by the U.S. Department of Energy and Lawrence Livermore National Laboratory.