Gamma-ray diagnostics of D-T fusion reactions

The development of D-T fusion-energy sources requires intimate and precise measurement of fusion-burn conditions in reactor-development experiments. Some of the limitations inherent in presently available diagnostics based on massive particle emissions can be overcome by measuring fusion-generated high-energy gamma rays. Although gamma-ray intensities are low, gamma rays offer diagnostic advantages of dispersion-free propagation and low intrinsic backgrounds. This paper describes two detector systems developed to study D-T fusion reactions by measuring the associated 16.7-MeV gamma-ray emissions. The first system is a Compton-recoil spectrometer and features good energy resolution of the 16.7-MeV photons. This system uses a sector-magnet spectrometer to isolate electrons forward-scattered by the high-energy gamma rays. The second system is a threshold Cerenkov detector and features a higher net sensitivity. A chamber filled with CO2 gas acts as a Cerenkov medium for electrons scattered by the 16.7-MeV photons. The gas pressure is adjusted so that electrons scattered by photons having energies less than 16.7 MeV do not have sufficient energy to generate Cerenkov light in the gas