Triumf Cyclotron Vacuum System Upgrade and Operational Experience

The replacement of the 30-year-old Philips cryogenerator with a modern LINDE-1630 helium refrigerator is an important component of TRIUMF’s ongoing 500 MeV cyclotron refurbishing program. Two 10.7 m long cryopanels are cooled with liquid helium rather than with 17 K helium gas, as was the case with the cryogenerator. This has increased the pumping speed and, respectively, improved the vacuum in the approximately 100 m cyclotron tank. Additionally, the thermal shield, previously cooled with helium gas, is now cooled with liquid nitrogen. These changes have resulted in increased reliability of the cyclotron vacuum system and, consequently, longer operation periods without maintenance. The new refrigeration unit was commissioned in September 2007. The results from over one year of operational experience are discussed. Also, data on hydrogen cryopumping is presented. INTRODUCTION The prior cryogenerator [1] used for TRIUMF’s cyclotron was replaced with a modern helium refrigerator. The helium refrigerator liquefies helium for use in cooling the cryopanels, essential for maintaining adequate vacuum in the cyclotron. Figure 1 depicts the cryogenic systems and transfer lines in their current state. Installation of this new helium refrigerator has resulted in improvements in cyclotron vacuum, since the cryopanels can now be cooled with liquid helium, compared to the prior system which used cold helium gas. This has also improved the cyclotron reliability and increased the time between cryopanel defrosts. The new system has undergone several tests to quantify the resulting improvements as well as to confirm continued performance. Tests have included measurements of the pumping speed of the cyclotron cryopanels and measurements of the helium refrigerator’s cooling power and liquefaction rate. The results from these tests are presented below. Figure 1: Cyclotron Cryogenic System Diagram. Paper presented at PAC 09, 23rd Particle Accelerator Conference, Vancouver May 4-8 TR-PP-09-0