High Jc ybco superconductors prepared by the “powder melting process”

We have developed a model to calculate the response of the current distribution in disks and rings to a time dependent applied magnetic field. In the model the ring (or disk) is divided in concentric segments. The segments are assumed to be inductively coupled to each other and to the applied field. A time dependent magnetic field induces a finite electric field in the ring/disk. The induced currents wi11 then depend on the magnitude of the electric field and the current-voltage characteristic. The current-voltage characteristic is modelled by a nonlinear resistivity. The currents determined from AC magnetization measurements on rings and experimental I-V characteristics are compared with the results of our model. We find that we can easily reproduce the shape of the magnetization curves. However, the frequency dependence of the current in the rings shows a discrepancy. The experimental frequency dependence of the currents is much smaller than that expected on the basis of the I-V characteristics and the model calculations. A possible cause could be inhomogeneities in the sample, influencing the current distribution.