Magnetic field studies in the ISAC-II cryomodule

The medium beta section of the ISAC-II heavy ion accelerator consists of five cryomodules each containing four quarter wave bulk niobium resonators and one superconducting solenoid. The 9 T solenoid is not shielded but is equipped with bucking coils to reduce the magnetic field in the neighbouring rf cavities. A prototype cryomodule has been designed and assembled at TRIUMF. The cryomodule vacuum space shares the cavity vacuum and contains a μ-metal shield, an LN2 cooled, copper, thermal shield, plus the cold mass and support system. Several cold tests have been done to characterize the cryomodule. Early operating experience with a high field solenoid inside a cryomodule containing SRF cavities will be given. The results include measurements of the passive magnetic field in the cryomodule. We also estimate changes in the magnetic field during the test due to trapped flux in the solenoid. Residual field reduction due to hysteresis cycling of the solenoid has been demonstrated.