Analysis of remnant field detected by hall sensors above superconductor tape

This paper describes various approaches to the analysis of the remnant field arising from the current distribution in superconductor tape. This is of use as a quality control technique when it is important that the superconducting tape has a homogenous current distribution across its width. Superconducting tape is exposed to a magnetic field perpendicular to its surface, inducing currents within the tape. The magnetic field produced by these induced currents can then be measured to assess the distribution of the currents. This paper discusses three techniques to analyze the remnant field in superconducting tape viz. (i) analytic inversion of the Biot-Savart law (ii) computation of the local perpendicular field gradient across the tape and (iii) a least squares fit of the measured magnetic field data to a critical state model. Defects are detected as disruptions to the current distribution calculated for a uniform superconductor. Gradient computation offers a quick way to compare the quality of the samples.