Operational domain estimation of a gamma-ray spectrometer for deuterium–tritium fusion power measurement at ITER

Abstract ITER will be equipped with two types of diagnostics for fusion power measurement in deuterium–tritium plasmas: neutron flux monitors and neutron cameras, both absolutely counting the 14 MeV neutrons emitted by the D(T, 4 He)n reaction. The radial gamma-ray spectrometer (RGRS), though, has recently been considered as an additional fusion power diagnostic, detecting 17 MeV gamma-rays emitted by the radiative D(T, 5 He) γ channel of the DT reaction. This work describes the RGRS performance by determining the upper limit of its operational domain, strictly correlated with the expected background intensity and resulting between 2.6 ⋅ 10 17 neutrons per second and 3.2 ⋅ 10 18 neutrons per second. Based on this assessment, design optimization are introduced to fit the RGRS performances to the ITER requirements for safety-relevant fusion power measurements, for which the required operational range is between 2.4 ⋅ 10 19 neutrons per second and 3.2 ⋅ 10 20 neutrons per second. The expected different energy ranges covered by signal and background are exploited with the employment of a proper gamma-ray attenuator, allowing to widen and shift the RGRS operational domain toward the most relevant, high power plasma scenarios.