Investigation of free-surface fluctuations of liquid lithium flow for IFMIF lithium target by using an electro-contact probe

In the international fusion materials irradiation facility (IFMIF), 14 MeV neutrons will be generated by 40 MeV deuteron beam injection into a high-speed liquid lithium (Li) plane jet, flowing along a vertical concave wall in vacuum. The Li jet has to be stable to produce a stable neutron field, while a free surface flow is anticipated to be unstable. In order to ensure a reliable operation, a detailed knowledge of the Li flow is of conical importance. The experiment on the Li flow is conducted using the Li loop facility to qualify the magnitude of the surface oscillation. The test section of this loop, which is a 1/2.5 scale of the IFMIF design, produces a flat plane jet of 10 mm in depth and 70 mm in width with a free surface in the velocity range of up to 15 m/s. In the present study, a surface-detection apparatus called electro-contact probe, is employed. This apparatus allows us to measure the surface oscillation directly. By means of the electro-contact probe, the magnitude of the surface oscillation in this configuration was found to be in the range from 2.2 to 2.9 mm at the position of 175 mm downstream from the nozzle exit at a mean velocity of 15 m/s. This is the first time it was measured in detail. These values are considered to be improved in the case of the actual target of IFMIF. Estimation shows the present data of 2.9 mm could be transformed to be much smaller value, if the flow is free from the effect of surface wakes.