1998 年 41 巻 10 号 p. 841-845
It needs to make low ultimate pressure to decrease impurities in a plasma in a nuclear fusion device. Baking technique is very effective method to decrease outgassing rate from first walls and inner surface of the vacuum vessel. However, in such large vacuum vessel, e.g. JT-60, the non-uniform heating and the deformation due to thermal expansion might be very important problems. The baking technique of JT-60 is described. Two baking systems were applied to JT-60 to solve the problem of non-uniform heating. One is a circulation system of the hot nitrogen gas which is located between the inner and outer skins of the double-skin structured vacuum vessel. The other is an electric heater which apply the thick of the vessel. In order to prevent the deformation, the difference of temperature was as small as possible. By both the baking at 300°C and the conditioning such as discharge cleaning, the ultimate pressure was achieved 7.9 × 10-7 Pa.