Abstract: In accelerator-based boron neutron capture therapy (BNCT) device, the Li target is commonly employed for neutron production. However, the lifetime of Li target is significantly reduced due to the high heat load deposition. Consequently, the target capable of withstanding high heat load is critical for ensuring stable operation of BNCT device. A liquid Li target module which is capable of withstanding heat fluxes exceeding 30 MW/m² in vacuum environment is designed in this paper. The module can maintain the liquid Li temperature below the safe threshold of 600 K even under irradiation by a 50 kW high-energy proton beam. The key components of the liquid Li target module include a nozzle, a concave back plate, a collection tank and heating wire. The effect of nozzle width, Li flow rate, and concave back-plate radius on the high-heat-flux removal capability of the module were simulated. The results demonstrate that, with liquid Li film thickness increasing from 1.2 mm to 2.3 mm as nozzle width increases from 1.5 mm to 3.0 mm, the surface temperature rise decreases from 82 K to 52 K. Furthermore, no significant further improvement in the heat removal capability of the target is observed when the nozzle width is increased beyond 3.0 mm. While increasing the liquid Li flow rate from 7 m/s to 14 m/s reduces the maximum temperature rise from 91 K to 46 K, the reduction in temperature rise gradually diminishes. When decreasing the concave back-plate radius from 500 mm to 250 mm, the maximum temperature rise of liquid Li decreases from 77 K to 43 K. Compared to a flat-plate structure, the concave design can effectively improve the uniformity and stability of the Li film. These findings provide valuable guidance for the engineering implementation of liquid Li targets and offer a feasible approach for ensuring stable operation of boron neutron capture therapy systems.

Key words: liquid Li target, heat load, neutron source, boron neutron capture therapy