Free-surface mhd flows as a potential tool for high heat flux removal in fusion applications

We consider liquid-metal free-surface flows subject to a strongmagnetic field, including film, droplet and jet flows, as potential means to remove high heat fluxes of (5-15).106 W/m2 or larger in fusion applications. These considerations are partially based on the earlier experimental studies of free-surface flows performed in the Tokomak-3 reactor in the city of Shatura, Russia. We also review recent studies of free-surface MHD flows and those of 1980-1990 on the implementation of free-surface flows in several industrial applications rather than fusion, such as semi-levitation metallurgical devices, hot dip coating of hard metals and metallization, and MHD atomization and granulation of liquid metals. As shown, all free-surface flows in a strong magnetic field suffer with MHD instabilities. To mitigate this critical issue under the fusion reactor conditions, we propose a new MHD-controlled film-flow device called the "in-and-out honeycomb" to be used as a plasma-facing component. The two main ideas of the proposed concept are: 1) to create a "short" flow with the minimum distance between the flow inlet and the drain channels to decrease the area, where surface instability can develop, and to minimize the surface temperature, and 2) to apply a special surface retaining electromagnetic force. Due to the strong retention effect, the flow can be oriented at almost any angle, including vertical and horizontal upside down orientations. In this paper, we introduce a pre-conceptual design and describe R&D plans, including physical experiments and modelling. Also, first numerical results computed with a 2D MHD code are presented, which demonstrate stable free-surface behaviours once this special retaining force is applied.