Optimization of a LaBr 3 scintillation detector for high-energy gamma-ray diagnostics in the HL-3 tokamak

Abstract To meet the high-energy gamma-ray diagnostic requirements for future D-T discharge experiments on the HL-3 tokamak, this study proposes the development of a LaBr 3 detector with wide dynamic range and high energy resolution, inspired by the SiPM-coupled LaBr 3 detectors reported by the Joint European Torus (JET) team. However, such detectors exhibit a fundamental trade-off between the linearity of energy response and energy resolution when detecting high-energy gamma rays due to SiPM saturation effects. To address this limitation, we systematically investigate the combined impact of SiPM array nonlinearity on energy linearity and resolution. The study employs SPADs size and photon collection efficiency (modulated via neutral density (ND) filters) as independent variables, with energy linearity and resolution as dependent metrics. Experimental configurations combined SiPM arrays of varying SPADs sizes with ND filters of different optical densities (OD). An LED source simulated the equivalent light intensity of 12 MeV gamma-ray interactions with the crystal to quantify the nonlinearity of the SiPM. The performance of the LaBr 3 detector was also evaluated using standard gamma sources: 137 Cs (0.662 MeV), 22 Na (0.511 MeV, 1.274 MeV), 60 Co (1.173 MeV, 1.332 MeV), 54 Mn (0.834 MeV), 152 Eu (0.344 MeV, 1.408 MeV) and an Am-Be neutron source (4.4 MeV). Results demonstrate that increasing SPADs density and reducing photon collection efficiency effectively both improve energy response linearity. The experimental results indicate that the HL-3 project can utilize the Hamamatsu S13360 SiPM array with 25 μm SPADs pitch coupled with a LaBr 3 scintillator, thereby attaining an optimal equilibrium between energy linearity and resolution.