Experimental and numerical investigations of operational parameters of TRIUMF’s cyclotron cryogenic system

Abstract

TRIUMF houses the world’s largest cyclotron built in 1972. The cyclotron accelerates H− ions up to 520 MeV. Proton beams are extracted from the cyclotron by using stripping foils converting H− ions to H+ ions. High availability of the 520 MeV proton beams is a vital part of TRIUMF’s scientific program. Vacuum tank of the cyclotron is ≈ 100 m3 chamber operating at 1 × 10−8 Torr pressure during beam production. The vacuum is achieved through the use of turbo pumps, cryopumps and cryopanels. The cryopanels are a form of a distributed cryopump that does the major portion of pumping. The cryogenic system of cryopanels went through an extensive upgrade from B-20 Stirling cycle cryo-refrigerators to Linde-1630 helium liquefier. Open-loop liquid nitrogen circulation was introduced for cryopanels 80 K shield. Operational costs associated with procurement of liquid nitrogen triggered the search for alternative configurations of cryogenic support for cryopanels. This paper presents the results of TRIUMF’s evaluation for possible upgrades of the existing cryogenic system, as well as experimental and numerical investigations of its operational parameters.