Feasibility study of gamma-ray spectroscopy for the determination of the fusion power at the SPARC tokamak

SPARC is a high-field, compact tokamak aiming to obtain a fusion gain Q>1 in Deuterium-Tritium (DT) plasmas for the first time in a magnetic confinement fusion reactor. Fusion power measurement is a key diagnostic requirement. In this work we present a scoping study of a gamma-ray spectrometer for the determination of the fusion power at SPARC. Measurements are based on the detection of the 16.7 MeV and ∼ 14 MeV gamma-rays produced by the weak secondary channel T(D,γ)5He of the DT fusion reaction, whose branching ratio has been recently measured at the JET tokamak. Starting from the numerical calculation of the DT gamma source and a first evaluation of the sources of background radiation, we determine the fusion power range where measurements are possible at SPARC. We find that the fusion power can be determined in the broad range of 0.2 MW to 140 MW, when different neutron and gamma-ray attenuators are employed depending on the operational conditions. Potential additional applications of the gamma-ray detector scoped in this work are also briefly discussed.