Continuous recording of the transport properties of a superconducting tape using an AC magnetic field technique

The transport properties of superconductors are commonly characterized by means of a 4-probe measuring technique and the critical current is determined on a certain criterion for the electrical field. An alternative method to investigate the transport properties is to measure the magnetic response of a superconductor in a changing magnetic field. This magnetic technique has the interesting advantage that it can be used to investigate long lengths of (insulated) conductor. A detailed analysis is made to develop a reliable measuring procedure for this new test facility. The magnetic response of a superconductor is modeled in a description for an infinitely long tape with a rectangular cross-section and an arbitrary voltage-current relation. The calculated magnetic profiles, in space and time, are compared with experimental results at 77 K. It is demonstrated that the magnetic signal can be used to monitor the quality of a long length of tape (>500 m) with a high accuracy. Additionally it is shown that the shape of the voltage-current relation can be reconstructed based on the frequency dependence of the magnetic response.