Measurement of the Gamma-Ray-to-Neutron Branching Ratio for the Deuterium-Tritium Reaction in Magnetic Confinement Fusion Plasmas

At present, magnetic confinement fusion devices rely solely on absolute neutron counting as a direct way of measuring fusion power. Absolute counting of deuterium-tritium gamma rays could provide the secondary neutron-independent technique required for the validation of scientific results and as a licensing tool for future power plants. However, this approach necessitates an accurate determination of the gamma-ray-to-neutron branching ratio. The gamma-ray-to-neutron branching ratio for the deuterium-tritium reaction H3(H2,γ)He5/H3(H2,n)He4 was determined in magnetic confinement fusion plasmas at the Joint European Torus in predominantly deuterium beam heated plasmas. The branching ratio was found to be equal to (2.4±0.5)×10-5 over the deuterium energy range of (80±20) keV. This accurate determination of the deuterium-tritium branching ratio paves the way for a direct and neutron-independent measurement of fusion power in magnetic confinement fusion reactors, based on the absolute counting of deuterium-tritium gamma rays.