Status of the cyclotron vacuum system at TRIUMF

The world's largest cyclotron was built at TRIUMF in 1972 and commissioned to full energy in 1974 [Harwood VJ, Yandon JC. TRIUMF Design Note, TRI-69-7, 1969 [1], Blakely RG, Moore RW, Harwood VJ. TRIUMF Design Note, TRI-69-9, 1969 [2]]. The cyclotron accelerates negatively charged hydrogen ions up to 500 MeV, and protons are produced by inserting a stripping foil in the beam which removes two electrons from each negatively charged hydrogen ion and allows the remaining bare protons to be channeled out of the accelerator. By making these protons strike different kinds of targets, intense beams of neutrons, pions and muons can also be created, thus making possible many different experiments. The volume of the cyclotron vacuum tank is about 100 m3 and operates at 2×10−8 Torr pressure during beam production. Most of the vacuum is achieved by cryopumping with a B-20 cryogenerator and six cryopumps. The B-20 is a Stirling cycle refrigerator, which supplies helium gas at 16 and 70 K to the cryopanels in the tank. The tank is also equipped with two turbo pumps. The vacuum system went through a few modifications during more than 30 years of operation. This paper presents the status of the cyclotron vacuum system and discusses the latest upgrades.