Simplified method to determine absolute ac-loss values of superconducting tapes for varying sample geometries

The measurement of energy dissipation in superconducting high T(c) tapes in an external ac-field is of major concern for their technical application at 50 Hz. The widely used technique is based on the measurement of the magnetization loop which is proportional to the dissipated energy. Since the proportionality constant depends on the geometry of the sample and of the pick-up coils used, calibration of the system is necessary. A convenient way is the calibration with a calorimetric measurement which however leads, at 77 K, to the problem of long thermal time constants. It requires furthermore a special preparation of the sample which must be thermally insulated from the cooling bath. This paper gives a simple relationship between the sample geometry and the calorimetric calibration factor, empirically deduced from measurements on tapes and stacks of tapes with rectangular cross sections. The accuracy of the method is within about +/- 10%, which is sufficient for most technical applications.