SELF-FIELD MEASUREMENTS AND CURRENT DISTRIBUTION IN CERAMIC SUPERCONDUCTORS

We report on self-field measurements and calculation procedures which have yielded a methodology for the determination of critical current d ensity distributions in superconductors. Axial components of the self- field, generated by polycrystalline superconductors of different geome tries and composition, have been measured at grid points in planes abo ve the sample. The measurements were made with a precision custom-desi gned and computer-controlled x-y scanning assembly at liquid-nitrogen temperature, using a Hall probe or a superconducting magnetic-field se nsor developed in our laboratory. A method for calculating current dis tributions based on inverse matrix and iteration procedures has been d eveloped for flat samples of arbitrary shape. The method makes possibl e the evaluation of persistent current patterns in thin superconductin g samples, using experimental field data and ''inverted'' matrix equat ions relating currents and fields.