Calorimetric ac-loss measurement of high Tc-tapes at 77 K, a new measuring technique

Abstract

A method is described for calorimetric ac-loss measurements of high T c-tapes at 77 K. It is based on a technique approved at 4.2 K for conventional superconducting wires which allows a very easy and precise loss measurement in parallel or perpendicular external field orientation. The slight temperature increase of the sample in an ac-field, thermally insulated from the liquid nitrogen bath, is used as a measure of losses. The thermal insulation is provided by a material of low thermal conductivity, no vacuum vessel is used. Simultaneously the sample magnetization can be measured. All necessary sensors are incorporated in the sample holder allowing a rapid sample change. The combination of the calorimetric method at 77 K with the easier magnetization measurement allows to determine the ac-losses in a wide frequency and amplitude range of the external ac-field. The main part of data is obtained by the magnetization measurement while the calorimetric measurement is used for calibration.