EFFECT OF PIN DISTRIBUTION ON DC VOLTAGE-CURRENT CHARACTERISTICS OF A SUPERCONDUCTING FOIL IN THE PRESENCE OF A SMALL AC FIELD

To show that the distribution of the pinning force in a superconducting foil exerts a significant influence upon the dc voltage-current characteristic in the presence of a low-frequency ac magnetic field, observation was carried out in a foil sample with a surface-pinning layer made by evaporating a material with a higher critical current. As a result, a noticeable shoulder appeared in the dc voltage curve, as has been found in some foil samples. Theoretical expressions of the dc voltage are also derived from the critical-state model and the results show satisfactory agreement with experimental data. This provides the possibility of obtaining the pin distribution profile in a superconducting ribbon by observation of dc voltages. © 1979 IOP Publishing Ltd.