Fabrication of the 320-CM-OD all-ceramic ZT-40 torus

The fabrication of the ZT-40 torus, a large complex all-ceramic toroidal plasma containment vessel, is described. Several glass sealants covering the temperature range of 500 to 1300°C, were developed and used to “braze” segments of the torus together, sapphire windows to the torus and the required pump-out and diagnostic ports to the ceramic vacuum vessel. Designs of window seals were developed that allowed sealing of the sapphire windows in a vertical position with minimum sealing glass flow.