A new experimental method to determine the local critical current density in high-temperature superconducting tapes

The lateral critical current density (J(c)) distribution in high-temperature superconducting tapes is determined with a new experimental method. With this method it is possible to determine a J(c)-profile in a non-destructive manner. The experiment utilizes the strong suppression that occurs in the critical current (I-c) when a perpendicular magnetic field is applied to a Bi-2223 tape. A perpendicular magnetic field with a strong gradient that passes through zero is applied to a tape, to select a zone where the perpendicular field is small. This magnetically selected zone then determines the I-c of the entire tape. By moving this field gradient along the tape it is possible to observe the spatial variations in J(c). For a quantitative analysis of the critical current density a deconvolution of the measured I-c-profile with the system response is required. The local superconducting area is obtained from an optical micrograph of the tape cross-section. Finally a position dependent J(c) is determined for two different types of superconducting tape. (C) 2000 Elsevier Science B.V. All rights reserved.