Numerical Investigation of Thermo-Fluid Dynamics in a High-Speed Lithium Jet under Ion Beam Irradiation for Fusion Neutron Sources

A high-speed liquid lithium (Li) jet with a free surface is being developed as a beam target for fusion neutron sources. The Li jet flows vertically along a concave flow channel, while its free surface is exposed to an ion beam. The internal pressure of the Li jet increases due to centrifugal force, thereby providing a temperature margin up to the boiling point. Since experiments simulating beam-on-target (BoT) operation are extremely difficult without actual facilities such as A-FNS and IFMIF-DONES, it is desirable to evaluate the behavior of the Li target during BoT operation through numerical simulations. For this purpose, we have been developing BoT simulation models; however, previous models still had several limitations in representing actual operating conditions. In this study, an ion-beam energy deposition model is newly introduced into three-dimensional two-phase flow simulations based on the volume of fluid (VOF) method, and BoT simulations of the Li jet are conducted using large-eddy simulation (LES) as the turbulence model. The results are compared with those of the ELTL experiment, analytical calculations, and our previous simulations. In addition, the surface fluctuation characteristics of the Li jet and the correlation between vortex structures and heat transfer within the Li jet are clarified. The findings provide important insights and recommendations for the operation of full-scale facilities.