Residual Magnetic Field Inside the Superconducting RF Cavity Shield

Magnetic shielding is used to reduce ambient magnetic field surrounding superconducting RF cavities in order to decrease surface resistance and achieve high quality value. The tolerance of the residual magnetic field can be as low as 0.1 μT. Therefore, it is necessary to choose a proper shielding material to reduce the magnetic field to within permissible range. In this paper, field measurements are carried out using a flux gate sensor inside the magnetic shield for the superconducting RF test facility nine-cell cavity system. The measurement results at room and cryogenic temperatures are reported. A modeling method for the actual structure of the shield is developed, and the simulation results are compared with the measured results.