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

The transport properties of superconductors are commonly characterized by m eans of a 4-probe measuring technique and the critical current is determine d on a certain criterion for the electrical field. An alternative method to investigate the transport properties is to measure the magnetic response o f a superconductor in a changing magnetic field. This magnetic technique ha s the interesting advantage that it can be used to investigate long lengths of (insulated) conductor. A detailed analysis is made to develop a reliabl e measuring procedure for this new test facility. The magnetic response of a superconductor is modeled in a description for an infinitely long tape wi th a rectangular cross-section and an arbitrary voltage-current relation. T he calculated magnetic profiles, in space and time, are compared with exper imental results at 77K. 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 re lation can be reconstructed based on the frequency dependence of the magnet ic response.