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

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.