Design and performance tests of gas circulation heating of JT-60U vacuum vessel

In the final stage of construction of the upgraded JAERI Tokamak-60 device (JT-60U), baking tests of the vacuum vessel were performed. The vessel torus was heated up to 300°C by means of the nitrogen gas circulation system and electric heaters mounted on the outboard solid wall of the vessel. The design of the gas flow channels inside the double-wall structure of the vessel was done based on flow model tests, fluid analysis, and flow network analysis. The results of the baking tests were satisfactory. In maintaining 300°C bake-out temperature, required heating power of the gas circulation system and outboard heaters was 520 kW and 50 kW, respectively. The temperature distribution over the vessel wall was within 300±30°C. It was also shown or suggested that heat-up and cool-down time is about 30 h. The baking test data have been reflected in operations for plasma experiments