High Resolution Surface Resistance Studies

CERNs Quadrupole Resonator enables sub-nΩ-resolution measurements of the surface resistance. Much more information about the RF performance is accessible compared to regular cavity measurements. In this contribution we show that the surface resistance decreases for low cooling rates. The design of the Quadrupole Resonator allows us to exclude the formation of niobium hydrides, the efficacy of the magnetic shielding and thermal currents as possible causes. We find that the expulsion of the residual ambient magnetic field as the cause of the reduction of the surface resistance is consistent with our results.