Experiments on the high-speed liquid lithium flow with free surface were conducted using the lithium circulation loop at Osaka University for the International Fusion Materials Irradiation Facility (IFMIF). The test section of the loop has a contraction nozzle which is 1/2.5 scale of IFMIF and produces a flat plane jet of 70mm width and 10mm thickness. In this study, velocity measurements on the liquid lithium flow were performed to develop a diagnostics system in view of its application on the IFMIF lithium target. The measurement invokes the Particle Image Velocimetry (PIV) technique. PIV is based on the statistical correlation of image subregions to determine the local flow velocity distribution. On the other hand, in this study, the local lithium flow velocity distribution was measured by tracking intensity patterns of the surface waves generated on the flow. Therefore, the measurable velocity consisted of the surface velocity and phase speed of the surface waves. As a result of the experiment, the surface-wave velocity was successfully measured.
