Non-Destructive Measurement of Electrical Conductivity in Thin-Film Nb coated Cu for SRF Cavities using Planar Eddy Current Sensors

Abstract A novel contactless method for measuring the electrical conductivity of thin-film niobium (Nb) superconductors is presented. The impedance of the planar eddy current sensors is measured with thin film Nb-coated targets and Cu-only targets. The difference in resistance ∆ R is a function of the film’s conductivity. Experiments identified a distinct minimum in ∆ R with and without the Nb film on copper (Cu) substrates across various frequencies. Conductivity was calculated using a theoretical model. The impedance of the planar eddy current sensors was measured at room and liquid nitrogen temperatures, with Nb-coated Cu targets deposited using DC magnetron sputtering. The method observed a temperature-dependent frequency shift in minimum ∆ R , indicating the conductivity changes. A Python simulation model was used to calculate the conductivity from the measured impedance data. There was a 26% difference from experimental conductivity values. This non-destructive, contactless approach offers a promising means to assess thin-film superconductor conductivity.