Measurement of transient flow characteristics of target flow in water experiment for IFMIF

International Fusion Material Irradiation Facility (IFMIF) is the facility generating the high flux and high energy neutrons to develop fusion reactor materials. In IFMIF, high-speed liquid lithium (Li) jet is used as the target irradiated by deuteron beams. Since the Li jet must flow with high velocity for heat removal, it is important to research on the Li flow characteristics. These researches have been aimed toward the steady-state Li flow characteristics. On the other hand, in the actual IFMIF, it is also necessary to clarify transient flow characteristics at start and stop of the system for the operation. In this study, water experiment to obtain them at start and stop is thus conducted. Water can be substituted for liquid Li as the target, because the kinematic viscosity of the Li at operation temperature in IFMIF is nearly equal to that of water at normal temperature and pressure. Flow patterns of the water jet at test section which consists of a two-staged contraction nozzle, a vertical concave flow channel are observed by laser probe method and high-speed video camera. As a result, the flow pattern at start and stop was successfully observed. The flow at stop became stable by venting gas.