Theoretical optimization and experimental validation of a microchannel target for a high-current accelerator-driven neutron source

The High Brilliance neutron Source (HBS) project aims to develop a high-current accelerator-driven neutron source (Hi-CANS) to deliver high-brilliant neutron beams to a variety of neutron scattering instruments. One of the key components of such a facility is the target that generates neutrons from nuclear reactions between protons and atoms of the target material. Within the HBS project, a solid tantalum target with an innovative internal microchannel water-cooling structure was developed for a 70 MeV pulsed proton beam with a peak current of 100 mA, a duty cycle of 1.43% and an average power of 100 kW deposited on a surface area of 100 cm${}^2$. Known potential risks like blistering, sufficient heat dissipation and thermomechanical stresses have been consequently tackled during the development by optimizing the neutron-producing target accordingly. The first solid tantalum target with an internal microchannel water-cooling structure was manufactured and tested with a high-power electron beam. It was shown that a power of 1 kW/cm${}^2$ can be dissipated with the special microchannel cooling. In addition, a new target with an optimized microchannel structure was obtained from an iteration between particle transport simulations with FLUKA and thermomechanical simulations with ANSYS. Only 4.56% of protons accumulate in the neutron-producing tantalum and hence blistering issues are minimized. Additionally, a homogeneous heat deposition within the target was achieved minimizing strains and stresses. Steady-state and transient analysis on the cooling effect of the target in operation shows that the maximum temperature and heat flux could be kept in a safe range with the proposed microchannel structure. A prototype of the optimized target was manufactured via wire erosion and the tolerances were examined successfully with computed tomography. The maximum machining error is 0.2 mm and the effect on the target's lifetime is negligible, proving the optimized microchannel target is manufacturable and reliable.