Neutron Time-of-Flight based Reaction-in-Flight Fusion Measurements at the National Ignition Facility (NIF)

At Inertial Confinement Fusion (ICF) facilities, such as the National Ignition Facility (NIF), the deuterium-tritium (D-T) reaction is a top candidate for demonstrating ignition. The primary products of the reaction include neutrons and alpha particles. The reaction-in-flight (RIF) neutron spectrum results from up-scattered deuterons and tritons that gain energy through elastic scattering with the fusion products (n, a) and then undergo fusion reactions. Stopping power losses in the fuel affect the RIF spectrum and therefore make it sensitive to the conditions of the hot-spot and fuel shell. RIF spectra are sensitive to key properties of the fuel such as the mix fraction, quantum degeneracy of the cold fuel, the fuel adiabat, as well as the alpha stopping range. The NIF hosts a suite of neutron time-of-flight (nToF) detectors at five different line-of-sight locations. These spectrometers can span over six orders of magnitude in dynamic range to measure both the primary D-T fusion and RIF spectra. This work will discuss recent progress towards nToF based RIF measurements as well as its implications in providing a better understanding of implosion performance at the NIF.