Superconducting rf cavity in a dc magnetic field

摘要

A superconducting (SC) rf cavity has been operated in the presence of an external magnetic field up to 2.4 kG. Measurements on the 48.5hyphen;MHz cavity were performed at 4.2 K. The external field was produced by an unshielded 60hyphen;kG superconducting solenoid 5.8 cm from the cavity. No degradation of cavityQwas observed for fields on the outer surface of the cavity up to 1240 G. This result is consistent with no flux penetration of the cavity surface for fields up to the first critical field of niobium at 4.2 K, and shows that strong focusing elements with large fringing magnetic fields may be placed immediately next to Nb SC accelerating structures without causing performance degradation.