Surface Resistance of Superconductors in the Presence of a DC Magnetic Field: Frequency and Field Intensity Limits

We revisit the classical rigid-fluxon model which describes the effect of an applied magnetic flux on the RF surface resistance of a superconductor and discuss explicit formulations for a few limit cases. As an application, we discuss the role of magnetic flux on the enhanced surface resistance of RF accelerating cavities based on niobium, depending on its material properties. We also assess the conditions for the use of high-temperature superconductors for carrying the beam image RF currents in future high-energy circular hadron colliders such as the future circular collider being studied at CERN.