Reaction rate determination by t(d,g)5He gamma-ray measurements in plasmas approaching ignition: challenges and synergies between inertial and magnetic confinement fusion

In inertial confinement fusion (ICF) experiments the reaction rate is one of the key parameters to assess the plasma performance and is usually determined by measurements of the 14 MeV neutron emission. As the plasma approaches ignition conditions, however, the 14 MeV neutrons experience significant energy degradation by scattering in the plasma, which makes the number of those unscattered no longer proportional to the fusion rate. Under these conditions, measurements of 17 MeV gamma-rays born from the 105 less likely t(d,g)5He reactions could be used instead. In magnetic confinement fusion (MCF), on the other hand, the plasma is always transparent to neutron propagation, but there is here need to have at least two independent methods to determine the fusion power for nuclear licensing of the power plant. This, similarly to ICF, makes t(d,g)5He gamma-ray measurements a potential choice. In this work, we describe the challenges that must be faced to determine the fusion power from t(d,g)5He gamma-ray measurements in ICF and MCF. These range from the development of absolutely calibrated detectors to aspects of the reaction cross sections and are both tackled by a recently approved project in the context of MCF. Proof of principle experiments in forthcoming deuterium-tritium MCF campaigns will be also discussed.