A protocol for mapping transport current density of REBCO-coated conductor by magneto-optical imaging

Abstract

The measurement of transport current density is significant for investigations on improving the properties of REBa2Cu3O7−x (REBCO, where RE refers to rare-earth elements)-coated conductors (CCs). In this work, a protocol for mapping the transport current density of CC by magneto-optical imaging (MOI) is presented. A calibration method is developed based on the non-linear physical governing function for the MOI indicator, in which only two parameters are determined, i.e. the anisotropic magnetic field BA , and cMs , which is the multiplication of the constant c related to the thickness of the MOI indicator and the spontaneous magnetization Ms . The experimental results also showed that they were independent of the optical measure condition but dependent on temperature, making this calibration method comparative among different utilizers. The numerical results clearly manifested that the selected window size of the magnetic field around a long superconducting tape is closely related to the error of the reconstructed current density. A large window size of the magnetic field is needed to precisely reconstruct the transport current density. For actual MOI testing, a practical approach to extend the magnetic field data outside the MOI window was realized by fitting with a power function according to Ampere’s law, through which the false current density outside the sample is automatically suppressed to a large extent. On this basis, the mapping of the transport current density in the CC sample was achieved. It is believed that this work will improve MOI for a more precise measurement of the transport current density for long superconducting strips.