Closed Lithium Cycle Concept in the DEMO-FNS Tokamak with a Sectioned Divertor

The organization of the plasma–wall interaction remains an urgent problem for long-term operation of a tokamak with an intense thermonuclear fusion reaction. The concept of a lithium cycle and the design of a sectioned divertor for the Demonstration Fusion Neutron Source (DEMO-FNS) tokamak are proposed. The parameters are estimated, and requirements for the components of the lithium cycle are formulated. Technical solutions for the lithium cycle flow rate ≅10 g/s are selected. It is estimated that 0.1-µm liquid lithium layer on the surface of the first wall can protect its solid coating. On the basis of a simple model, it is shown that, at a wall temperature of 200–300°C, a thickness of 0.1 µm can be achieved in ≅1 min. The film can reach quasi-stationary values of 13–15 µm in 3–4 h. Above 340°C, the film does not form because of the increase in the thermal evaporation of lithium. The wall temperature of 700°C of the divertor section with the lithium pool is chosen so that lithium deuteride and lithium tritide do not form in it. They can form in the liquid metal lithium protective layer of the wall at temperatures less than 300°C. In order to significantly reduce the explosion and fire hazard when working with hot liquid lithium, it is proposed to increase the size of the DEMO-FNS divertor section with the lithium pool by 2 to 3 times, which may allow the transition from water to helium coolant.