Abstract
After approximately ten years of research and development (R&D), Matsumoto-Ohtsuka (MO)-type flanges have been practically applied on a large scale to the vacuum beam pipes of the SuperKEKB, a particle accelerator under construction since 2010. The MO-type flanges are expected to effectively and reliably mitigate the problems related to electromagnetic waves that have been typically observed in high-intensity accelerators. Approximately 4700 MO-type flanges made of a copper or an aluminum alloy have been newly manufactured for the beam pipes and the bellows chambers of the SuperKEKB. All the beam pipes are baked at 150℃ before being installed into the KEKB tunnel. Approximately 2300 flanges have been used in the baking procedure until mid-November, 2014, and the percentage of leaks at the first fastening was approximately 2-3% on average. After the installation in the tunnel, the beam pipes are connected with bellows chambers. Approximately 3800 flanges have been used so far. The percentage of leaks after the connection procedure was 10% at an early stage, but was then reduced to less than 5% on average after revising the procedure. It was found that the sealing property is very sensitive to scratches or traces of machining on the sealing surface. Once these issues are under control, however, the flange is able to serve as a reliable connection for the accelerator beam pipes.
