Measuring Energy Balance in Inertial Confinement Fusion from Nuclear Reaction History*

Nuclear Reaction History measurements are a critical quantity for understanding performance in Inertial Confinement Fusion (ICF) implosions.  Historically these measurements have been conducted by measuring the D(T,γ [16.74 MeV])⁵He reaction with diagnostics such as the Gamma Reaction History diagnostic (GRH) and Gas Cherenkov Detector (GCD) on the National Ignition Facility (NIF).  DT fusion gamma emission is commonly used for nuclear reaction history measurements as it does not suffer from Doppler broadening from the thermal motion of ions seen in neutron-based measurements and offers the potential for < 10ps temporal resolution.  Simple analytic models of a static burning DT mass have been developed that include alpha heating and radiative losses.  When applied to the reaction history curve measurements, the models provide information including time-resolved ion temperature, and the timing of the onset of ignition. Deviations from the model indicate the presence of PdV gains or losses (Where P is pressure and dV is the change in volume) dominating the progression of the burn.  These models may enable a greater degree of understanding energy gain/loss mechanisms in ICF implosions and the evolution of thermonuclear burning plasmas through a combination of reaction history curves with other measurements such as ablator and pusher trajectories.  The analytical models for the static burning mass regime will be presented along with the methodologies for applying the models to reaction history curves and associated diagnostic challenges.