Rearrangement of liquid metal surface waves by a uniform transverse magnetic field

In the fusion engineering, the liquid metal flows are considered to be an alternative solution against the solid surface in designing the plasma facing components. However, it remains unclear about the magneohydrodynamics influences on the liquid metal flows due to the lacking of experimental observations that the limited measurement method for the opaque liquid metal film should be criticized. In the present study, a laser profilometer based on the laser triangulation technique is adapted to measure the thickness of liquid GaInSn film, while a visualization method is introduced to monitor the topography of the free surface, which is formed on a horizontal substrate in the presence of a uniform transverse magnetic field. We will firstly demonstrate the applicability of a laser profilometer by measuring the thickness of GaInSn in a container with a quasi-static or dynamic free surface, to validate that the result is in good agreement with theoretical data. Using the visualization method and the laser profilometer, the evolutions of free surface waves and the time-dependent film thickness across a fixed line are measured by varying the flow rate and the magnetic field continuously. It is found that, under the influences of transverse magnetic field, the free surface waves are strongly suppressed along the spanwise direction, leaving the surface waves to propagate in the streamwise direction. More quantitatively, the measured thickness of the free surface reveals that a moderate magnetic field tends to decrease the averaged value and the root mean square value of the film thickness fluctuations while a strong magnetic field will conversely increase them. Besides, the dominant fluctuation frequencies of surface wave are observed to decrease with the increase of magnetic intensity, indicating that greater suppression is induced on the motion of small waves by the transverse magnetic field.