Flux-shaping configuration for improved triton burn up detection at the Divertor Tokamak Test facility

Abstract The measurement of 14 MeV neutrons in deuterium-deuterium plasmas provides insights into triton burn-up and confinement in magnetic fusion devices. At the Divertor Tokamak Test (DTT) facility, triton burn-up neutron yields will be measured by liquid scintillators and single-crystal diamond matrices, which are expected to face saturation-related issues due to low-energy neutron and gamma-ray interference. This work evaluates flux-shaping materials, such as borated polyethylene and lead, to enhance detector performance for the measurement of 14 MeV neutrons in the DTT mixed n/γ field. MCNP simulations are used to model neutron and gamma-ray transport through various material configurations and results show that a combination of a 30%-boron-loaded polyethylene slab followed by a layer of lead can effectively attenuate signals created by low-energy neutrons and gamma-rays while retaining the neutron flux above an energy threshold suitable for 14 MeV neutron measurements. Based on this, a modular configuration is proposed allowing the adjustment of material thicknesses between the different power scenarios of DTT to ensure a flat detector response. The proposed flux-shaping method allows for the insertion of different material combinations in front of each detector, which can extend its operational range by 1–3 orders of magnitude, to simultaneously cover with all three detectors the full spectrum of neutron yield scenarios anticipated at DTT.