Development of a Zero Rate Evaporation Cryogenic System for 200 MeV Proton Cyclotron

Based on the collaboration of ASIPP (Hefei, China)-JINR (Dubna, Russia) for proton therapy, a 200-MeV compact superconducting proton cyclotron project (SC-200 project) has been launched at ASIPP. The superconducting coil of the main magnet system for cyclotron is cooled by liquid helium. A zero rate evaporation cryogenic system has been designed and tested for the main superconducting magnet system. Three GM-cry coolers (40 W at 50 K, 1.5 W at 4.2 K) were worked as the cold source to cooling the thermal shield, a pair of high-temperature superconducting current leads (HTSCL) and liquid helium container. The test results show that the thermal shield and HTSCL can be cooler lower than 77 K, the heat load of the cryogenic system is less than 2.8 W. The detail design of the cryogenic system and test process will be described in the paper.