Low-recycling liquid-metal "divertorlets" concept for heat exhaust in divertors of fusion reactors

Liquid metal flows are promising for heat exhaust in divertors of fusion devices and continuous operation at the reactor scale [1]. Fast flows are intended to remove all of the heat captured by liquid metals, but they have risk of splashing and formation of liquid-metal pileups due to intense MHD drag [2]. Slow flows may suffer liquid metal evaporation for the increased exposure time of the liquid metal to the plasma.

The divertorlets concept is a liquid-metal alternative for heat exhaust in divertors that combines advantages of fast and slow flows: (1) reduced MHD drag as it operates in the slow-speed regime and (2) small exposure time of the liquid metal to the plasma [3] to avoid overheating. The divertorlets concept offers continual flow mixing, ensuring a fresh plasma-facing surface of liquid metal, making it compatible with a low hydrogen recycling scenario when operating with liquid lithium. The divertorlets consists of slats that create adjacent vertical channels with direction-alternating flow. A radial electric current is applied to the divertorlets and with a toroidal magnetic field, a Lorentz force (jxB) is produced in the liquid metal, driving the flow around the slats.

Performance of a divertorlets prototype was tested. Agreement between theory, simulations and experiments was attained with |B| < 0.3 T and allowed projections at the reactor scale. Power requirements of a divertorlets system in ITER/DEMO-like reactor are less than 5% of the expected power outputs of such devices. Moreover, heat-exhaust capacities for divertorlets are estimated to improve significantly through the minimization of flow-path length, even above 10 MW/m^2.

[1] E. Kolemen, et al., Nucl. Mater. Energy, 19, 524-530 (2019)

[2] A. Fisher, et al., Nucl. Mater. Energy, 25, 100855 (2020)

[3] F. Saenz, et al., Nucl. Fusion, 62(8), 086008, (2022)