A simple method for measurement of ac losses in superconducting wires under configuration of a double-layer non-inductive coil

摘要

We measured AC losses in superconducting wires with NbTi fine filaments exposed to a transverse magnetic field of 60 Hz by a simple pickup coil. The samples have configuration of a double-layer non-inductive coil. Potential taps were attached to both terminals of the sample coil. In this configuration, the double-layer sample itself is a pickup coil to measure the AC loss. In this procedure, we can approximiately estimate and averaged Poynting's vector on the side surface between the two layers by means of signals from a pair of the potential taps and a pickup coil for the external magnetic field. For comparison, we measured the AC losses both by a conventional electromagnetic method with coaxial pickup coils and by a calorimetric one. In the latter method, we obtain an equivalent AC loss by calibrating the amount of vaporized helium gas. Experimental results of the AC losses coincide with each other among the three methods in a wide range of the amplitude of external magnetic field. We also measured a transport-current loss in the sample coil and had a good agreement with results from the calorimetric method. Furthermore, we discuss the applicability of the proposed method to more universal types of AC loss measurement.