Comparison and analysis of Hall probe scanning, magneto-optical imaging and magnetic knife measurements of Bi-2223/Ag tape

Magneto-optical (MO) imaging, Hall probe measurements and the magnetic knife method were used for sample quality studies of multi-core Bi-2223/Ag tape with a columnar 60-filament structure made by the TIRT (tape in rectangular tube) process. While the magneto-optical imaging was made at 25 K and without transport current, Hall probe and magnetic knife measurements were performed for the sample carrying a direct current at 77 K. The MO image recorded at 25 K and external field 30 mT has shown non-uniform flux distribution in the three filament columns. 2D field profiles were analysed by the finite element method assuming ideal filament homogeneity. B-z(x) was computed analytically with an assumption that current density flows straight through the cross-section of the filament columns. The best agreement of computed profiles with measured ones is achieved for equal currents flowing in all filament zones. According to the magnetic knife measurements, current density is lowest in the centre column, but in this method the magnetic self-field is hardly influencing the current distribution. A better understanding of such experimental differences is obtained with 3D modelling. Three different cases of meandering transport current were studied computationally in order to explain the measured results. Finally, we discuss the advantages and drawbacks of the methods used and present how they can together produce the most complex information.