Simulation of the current dynamics in a superconductor induced by a small permanentmagnet: application to the magnetoscan technique

Abstract

The magnetoscan is a rather new technique for investigating local inhomogeneities of large bulkhigh-Tc superconductors. Local (shielding) currents, which are induced by a small permanentmagnet slightly above the sample surface, generate a magnetic field that is recorded by aHall probe. We report on a theoretical analysis of such a three-dimensional system usingnumerical simulations to calculate the current dynamics during a magnetoscan.The magnetoscan signal is analysed for different experimental setups and different criticalcurrent densities of the superconductor. We show that the shape of small defects(∼1 mm in size) is almost exactly displayed, even if the radius of the permanent magnet is muchlarger than the defect size. The critical current density of larger inhomogeneities can bedirectly determined at the sample surface, if all details of the experimental setup areknown. Different aspects of how to improve the experimental resolution are discussed.