On the dependence of Reaction-in-flight (RIF) neutron production upon ion-stopping power models in Inertial Confinement Fusion

Reaction-in-Flight (RIF) neutrons are generated with energies up to 30-MeV by knock-on deuterium and tritium ions undergoing DT fusion. The knock-on ions are generated from elastic scatting from 14-MeV neutrons or nuclear elastic scattering of 3.5-MeV alpha particles. The production of RIF neutrons depends on the energy loss of the knock-on ions as they traverse an igniting plasma. In this work, we present a semi-analytic model for the RIF neutron spectrum which accounts for the plasma geometry. Currently, this model is applied to Los Alamos' campaign to achieve volumetric ignition via double-shell implosions. The semi-analytic model was used to understand the effect of uncertainties in ion-stopping power model on the RIF neutron spectrum in a Bayesian framework. This model extends previous semi-analytic RIF neutron models and enables a reconstruction of the burning plasma conditions using the primary (~14-MeV), down-scatter (10-12 MeV), and RIF (>20 MeV) neutron yield measurements. Applying the model to interpret RIF neutron spectra emitted from hot-spot ignition geometries will also be discussed.