Hybrid baking system for the vacuum vessel of the Spanish stellarator TJ-II

The vacuum vessel of the TJ-II is bakeable at 150°C in order to provide a good base pressure (10^-8 mbar). A hybrid baking system has been chosen, using a combination of electrical heaters and induction heating by currents in toroidal coils of TJ-II. The induction heating is used to bake the rings and the groove of the vacuum vessel, while the electrical heaters heat the external part of the sectors and ports. The high density of temperature sensors ensures the uniformity of the baking process during the long baking cycles. This paper deals with the development and test of this hybrid baking system and concentrates on its design, construction, commissioning and operation