Innovative Surfaces for Controlled Flow of Liquid Metal

The potential economic, environmental, and strategic benefits associated with the development of fusion energy are numerous. However, application of fusion technology cannot be realized until advanced materials are developed that allow operation under the high heat flux conditions necessary for cost-competitive electric energy generation. Bathing the wall of a fusion reactor plasma-facing component in a liquid metal such as lithium, gallium, or tin is a viable approach for accommodating continuous heat flux levels exceeding 10 MW/m2, and it is also the preferred approach for removing hydrogen isotopes. Stabilizing the liquid film is the key challenge, which will be addressed through the use of a microtextured surface. In previous work, Ultramet developed high temperature microtextured tungsten and rhenium coatings consisting of thousands of high aspect ratio pyramids per square millimeter that are compatible with lithium, gallium, and tin, and whose effectiveness in wicking molten lithium has been demonstrated even in the presence of strong body forces. Because of the safety issues surrounding lithium, this project will focus on adapting and optimizing this wicking technology for use with gallium and tin. The coatings will be deposited by chemical vapor deposition CVD), and the height, population density, and morphology of the pyramids will be varied to optimize the wetting properties, which will be measured and quantified by exposing the coatings to molten gallium or tin. Heat transfer and fluid flow characteristics will be modeled. If necessary, micron-thick films of other materials can be applied to the textured surface to improve wetting. The effects of dendrite morphology on the fluid flow and wetting behavior of liquid gallium and liquid tin will be characterized, the effects of surface tension and dendrite morphology on the ability of the coating to prevent dryout due to MHD effects will be modeled, and the heat and mass transfer characteristics of a dendrite-enhanced, liquid metal-coated plasma-facing component will be characterized. Nuclear fusion offers a replacement for increasingly scarce fossil fuel energy sources. Alternatives to fossil fuels e.g. wind, solar, geothermal) cannot generate sufficient energy to meet current needs. Fusion, with its low generation of radioactive waste, is ideal for large-scale energy production. Practical application is absolutely dependent on the development of advanced materials as well as innovative designs.