Stainless flange bonded to niobium tube and simple aluminum sealing

We have successfully used indium sealing for super-conducting (sc) RF cavities for a long time. Indium sealing has high reliability, but several problems: cavity contamination by indium fragments and too soft to self-standing so on. These problems bring performance degradation of sc cavity to the final horizontal cavity assembly. We need other simpler sealing to establish the degradation free final assembly. As a simple sealing instead of indium, we have developed aluminium sealing, which uses an aluminium ring 1mm wide and 1mm thick. The kind of ring can be easily made cutting by EDM or stamping out of 1mm aluminium sheet. For reliable aluminium sealing, we have developed stainless flange bonded to niobium tube in order to get higher hardness of the flange. We successfully used HIP technology to bond the stainless tube and the niobium tube. We made leak tight tests of the bonding with thermal cycle from 750degC to 1.5K for 3 times, and confirmed leak tightness. The aluminium sealing was also successfully tested with super-leak. In this paper, we will present the R and D and results. (author)