Advanced inversion algorithm for current density reconstruction in REBCO tapes using a regularization-enhanced FFT approach

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Accurate reconstruction of current density distribution in superconducting materials is essential for understanding their fundamental properties and evaluating their electromagnetic performance. However, direct measurement of internal current density in these materials is virtually unfeasible. For rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes, the current distribution is typically inferred by measuring the normal component of the magnetic field above the sample surface and subsequently applying numerical inversion of the Biot–Savart law. Despite advances in electromagnetic inversion techniques, achieving both high accuracy and stability in the reconstruction results remains a significant challenge. To address these limitations, a novel mathematical algorithm integrating regularization methods with fast Fourier transform (FFT) was developed to accomplish the inversion of the Biot–Savart law using magnetic field normal component data. This approach not only preserves the computational efficiency of FFT-based methods, but also introduces intelligent automatic control of stability parameters through regularization. Furthermore, an iterative technique was incorporated to enhance the accuracy of the inversion process. Experiments were conducted using a custom-designed scanning Hall-probe microscopy system to measure the surface magnetic field of REBCO CC tapes, both without and with preset defects, under current-carrying conditions. The results demonstrate that the proposed current density inversion algorithm effectively mitigates the issue current of spillover into non-current-carrying regions, a common limitation of traditional inversion methods. Notably, the algorithm achieves high precision in reconstructing current densities near the boundaries between current-carrying and non-current-carrying domains. This advancement provides a robust foundation for the high-precision reconstruction of current density distributions in REBCO CC tapes, offering significant potential for improving the characterization and application of these materials.