Studies on the stabilization of high-speed surface flow of liquid metal lithium by magnetic field

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This study was planned on the lines of the experimental study of the free-surface lithium flow for the IFMIF (International Fusion Material Irradiation Facility) target, held from the year 2000, and treating the stabilization of the flow due to external force such as magnetic field, which was not included in the scope of the IFMIF R&D. In the IFMIF design, the flow is stabilized by centrifugal force. It is, however, worthwhile to have an option for future desing by studying the stabilization with simple magnetic field because the turbulent suppression effect of magnetic field is signficant.An air-core coil to apply magnetic field was designed for the lithium free-surface test loop, and power supplies were equipped with the coil. Some instruments were installed to verify the stability of the flow. An ultrasonic transmitter was prepared under the flow channel to investigate the stability by sounding echoes from the surface. Mechanical and laser wavefront meters were mounted above the channel. Stabilization effect of magnetic field was evaluated and the requirement for the magnetic field was estimated as well.Experiments were done according to these evaluation, the free-surface flow of 13.6m/s at maximum was achieved under argon atmosphere. It was also achieved to generate stable flow of 8.5m/s at 0.029MPa, and 4.3m/s at vacuum. The wavefront was cofirmed to be stable by visual observation. THe perturbation of the wavefront was also recorded into a high-speed video camera. As the result of analyzing the video image, it was found that the wave-number spectrum was almost randon and no anomalous frequency was observed, that is, any particular instability was recognized. From the analysis, it was also found that the speed of surface wave was able to calculate from the cross correlation of the wave.It is concluded that the results are satisfactory and will contribute to the R&D of IFMIF.