Development of bakeable seals for large noncircular ports on the Tokamak Fusion Test Reactor

Abstract

The Tokamak Fusion Test Reactor (TFTR), being constructed at the Princeton Plasma Physics Laboratory, has a total of 60 large ports of rectangular and racetrack shape that must be equipped with demountable seals. The largest port is a rectangle about 0.74×0.89 m. Seals must be compatible with a 10−8 Torr base pressure, be bakeable to 250°C, and be capable of remote demounting and resealing. A literature search and initial experiments showed that conventional commercially available sealing approaches were not useful, partly because of the large sizes and the noncircular shapes. Successful tests were made with ’’Helicoflex’’ seals. These seals consisted of a helical Inconel wire, surrounded by a stainless steel jacket that is covered with a soft metal, and were compressed between flat flange surfaces. General results were: a silver covering performed better than aluminum; with a smooth flange surface, higher compression produced better results; and performance was improved by striations produced in flange surfaces along the direction of the seal axis.