Microwave and Fast-Acting Valves and Vacuum Couplings for Accelerators

The high vacuum requirements of the Stanford Two-Mile Linear Electron Accelerator plus the radiation produced by electron acceleration have made it necessary to design special vacuum and isolation components. Two of these are special purpose valves capable of operating in a vacuum system at 10-8 torr, and the third is a group of quick-disconnect couplings used for component installation in the beam switchyard area of the accelerator. One valve is an all-metal, 50-megawatt, S-band microwave valve used to isolate an evacuated rectangular waveguide feed system from exposure to air during the replacement of a klystron drive tube for the accelerator. The valve is built with a remeltable indium seal which provides for leak rates on closure below 24 × 10-8 std. cc He/sec. The second valve is a fast-acting unit that was designed for beam axis application within the disk-loaded waveguide accelerator structure. This valve also has an indium seal that is remotely remeltable and has a measured closing time of nine milliseconds. The group of quick-disconnect couplings, which are 6, 10 and 12-inch pipe sizes, are remotely operable, non-elastomer couplings used in the vacuum chamber system of the beam switchyard. The radiation intensity in this area is sufficient to make elastomer seals impractical and to require that replacement of switchyard components be done quickly and remotely. Indium is also used as a reusable seal for these couplings and can be re-formed mechanically to extend seal life.