This paper presents a diagnostic system, gamma-ray alpha-particle monitor (GRAM), for continuous monitoring of deuterium–tritium fusion α-particles in the MeV energy range escaped from the plasma to the first wall. The diagnostic is based on the detection of γ-rays produced in nuclear reactions. The reactions 9Be(α,nγ)12C and 10B(α,pγ)13C have been selected. For that purpose, Be- or 10B-target is placed on the first wall, where the alphas are expected to be mostly lost. Striking the target, the lost alphas generate specific γ-rays, if their energy Eα > 1.5 MeV. To measure this γ-ray emission, the target should be in the field of view of a collimated detector, which is protected from neutrons and background gammas. The calibrated detector could deliver absolute values of the lost α-particle flux with a temporal resolution depending on intensity of losses. A high-performance γ-ray spectrometer with a novel architecture, GRITER, is proposed to be used in GRAM. It consists of a stack of the optically isolated high-Z fast scintillators with independent signal readout. GRITER is supposed to be operated at count-rates substantially exceeding the capability of a single crystal detector of the same size. The GRAM diagnostic system consists of two identical spectrometers, which measure both γ-rays due to α-particle loss and γ-ray background ensuring reliable data in a harsh reactor environment. GRAM could be tested during the non-DT plasma operation monitoring lost DD fusion products, neutral beam heating D-ions (ED > 0.5 MeV) and ICRF accelerated H- and 3He-ions through the detection of γ-rays resulting from nuclear reactions. The use of GRAM on JET and ITER, including events with extremely high loss rates, is discussed.
'Burning plasma' diagnostics for the physics of JET and ITER