Effect of the magnetic field and current orientation on the splashing of liquid metal free surface of fusion reactor PFCs

In future tokamak nuclear fusion devices, the development of suitable plasma facing materials is considered to be one of the great challenges. Liquid metal, instead of conventional solid materials, has been proposed as a potential solution to plasma facing components (PFCs) for future nuclear fusion reactors, and it can solve the problems that most fusion reactors are facing. The splashing of liquid metal into the fusion plasma is a big problem because of the implementation of liquid metal PFCs in fusion reactors. An experiment involving the splashing of liquid metal has been developed under a strong magnetic field and electric field to imitate the interaction between plasma electric current and PFCs of liquid metal in fusion reactors. The current direction is perpendicular or parallel to the magnetic field direction. The influences of Kelvin-Helmholtz (KH) instability are experimentally observed and quantitatively analyzed on the magneto-electricity-driven liquid metal free surface. Processes of liquid metal splashing in the rectangular chamber are recorded by a high-speed camera. When the Lorentz force is upward and the external magnetic field and liquid thickness are constant, the liquid metal splashing from the liquid metal free surface when the external current exceeds the critical value. Critical current presents as almost inverse proportional functions with the magnetic field variation for different liquid thicknesses. In the experiment, the instability is characterized by the dimensionless numbers Bond number, Bd, determined from the importance of gravitational forces compared to surface tension forces, and the Hartmann number, Ha, determined from the intensities of the imposed magnetic field. Multiple linear regression models of the critical current density are summarized which indicates that the magnetic field and current's influence determine the splashing critical point of liquid metal under the condition of multi-field coupling.