Sub-micro-Tesla Magnetic Shielding Design for Cryomodules in the High-gradient Program at CERN

In the framework of the High-Gradient R\&D; program at CERN a cryomodule, consisting of four superconducting 5-cell cavities, has been designed. In order to reduce flux trapping in the surface of the superconductor and to minimize Q degradation during a quench, highly effective magnetic shielding is needed. The solution proposed includes cold and warm passive shielding enhanced by four compensating coils. In this paper the magneto-static simulation results are presented illustrating different design considerations that led to a final design. Finally the shielding ability of the vacuum vessel is investigated experimentally through ambient magnetic field measurements.