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

The lateral critical current density (Jc) distribution in high-temperature superconducting tapes is determined with a new experimental method. With this method it is possible to determine a Jc-profile in a non-destructive manner. The experiment utilizes the strong suppression that occurs in the critical current (Ic) 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 Ic of the entire tape. By moving this field gradient along the tape it is possible to observe the spatial variations in Jc. For a quantitative analysis of the critical current density a deconvolution of the measured Ic-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 Jc is determined for two different types of superconducting tape.