Dual Coolant Liquid Metal Divertor Development

Fusion reactor divertors experience a combination of high heating, erosive plasma bursts, and irradiation which can lead to damage of crystal structures in metal components, surface recession, and contamination of the plasma. To address these issues, renewable molten lithium systems have been developed to protect the metal walls, assist in thermal management, and remove impurities from the plasma. These lithium systems show promise, but suffer from large magnetohydrodynamic pressure losses, heat flux limitations, and potential dryout of the liquid metal on the wall. Recently, a concept developed by a member of the proposal team was shown to perform well at heat fluxes of 3 MW/m2. The performance of these trenches may be improved by shortening the surface flow paths of the lithium from their current lengths (~60 mm) to the order of a millimeter, improving thermal performance, reducing magnetohydrodynamic and friction pressure losses, and suppressing instability formation. Reducing the channel length to this degree requires the channel dimensional scale to be of the order of a tenth of a millimeter - the microchannel regime. The proposer has developed a variety of microchannel cooling concepts for the aerospace and laser industries, providing thermal management solutions for laser diodes, gas turbine engines, and hypersonic vehicle components. These solutions employ intricately cooled metallic structures formed by stacking thin layers of etched metal foils and diffusion bonding them together. This approach can be used to create large molybdenum wall segments with a very fine array of trenches (~ >5x106 trenches per m2). This approach also allows integration of helium microchannel cooling, capable of dissipating high heat fluxes even at inlet temperatures higher than the saturation temperature of water. This creates a dual coolant thermal management system capable of accommodating steady-state heating up to 30 MW/m2. The major tasks proposed for the Phase I effort are: evaluate lithium wettability of small molybdenum structures, analytically evaluate and optimize subscale concept design, demonstrate fabrication of subscale (10 cm x 15 cm) concept design, demonstrate performance of the concept design through testing Solving the high heat flux engineering problems associated with plasma facing components is critical to the world’s 70+-year pursuit of achieving energy production via fusion reactions. The components must successfully contain the plasma, while at the same time extracting heat for power generation. The proposed approach may represent an enabling technology for divertors, and perhaps first wall structures, increasing reactor lifetime while promoting energy extraction from the plasma. It relies on proven technologies applied in an innovative way, reducing risk and maximizing the potential benefit to world energy production.