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

本研究是按照IFMIF（国际聚变材料辐照设施）目标的自由表面锂流动实验研究的思路进行的，从2000年开始进行，并处理由于磁场等外力引起的流动稳定化，这并不包括在IFMIF的研发范围内。在IFMIF设计中，流动是由离心力稳定的。然而，由于磁场对湍流的抑制作用是显著的，因此通过研究简单磁场的稳定化，为今后的设计提供一个选择是值得的。为锂自由表面测试回路设计了施加磁场的空芯线圈，并在线圈上安装了电源。安装了一些仪器来验证流动的稳定性。在流道下制备了超声波变送器，通过探测流道表面回波来考察流道的稳定性。机械波前仪和激光波前仪安装在通道上方。评价了磁场的稳定效果，估计了对磁场的需求。根据这些评价进行了实验，在氩气气氛下，自由表面流动速度最高可达13.6m/s。在0.029MPa和真空条件下分别可产生8.5m/s和4.3m/s的稳定流动。目测证实了波前是稳定的。波前的扰动也被记录在高速摄像机中。通过对视频图像的分析，发现波数谱几乎是随机的，没有观察到异常频率，即识别出任何特殊的不稳定性。从分析中还发现，表面波的速度可以由表面波的相互关系来计算。研究结果令人满意，对IFMIF的研发具有一定的指导意义。

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.