Total fusion yield measurements using deuterium–tritium gamma rays

Abstract

The deuterium–tritium (DT) fusion reaction, D(T,γ)5He, has a rare (4.2 ×10−5) branching ratio that releases a ∼16 MeV gamma ray instead of the more common 14.1 MeV fusion neutron. These fusion gamma rays can be used as a complementary source of measuring the net fusion yield of experiments. Fusion gamma rays have the advantage of having negligible Doppler broadening, being isotropic and less down-scattered compared to fusion neutrons. At the National Ignition Facility, the DT fusion gamma rays are measured by the Gamma Reaction History diagnostic that thresholds to only measure >10 MeV gamma rays. After removing a ∼12% contribution from neutron capture interactions in deuterium, D(n,γ)T, and carbon, 12C(n,γ)13C, the deviation between GRH measurements and neutron-based yield measurements has been reduced to 10%. Further improvements are needed for detailed physics comparison.