Anisotropy of the Critical Current in Technical Superconductors: Methods of Analysis and Application Examples

Abstract

The study of critical current anisotropy with respect to the direction of the external magnetic field is fundamental for optimizing the design of superconductor-based devices, particularly magnetic systems in controlled fusion facilities. This article provides a concise critical overview of modern methods for analyzing the angular dependence of the critical current in technical superconductors, with a focus on second-generation high-temperature superconducting (HTS) tapes. These methods are grounded in three previously proposed models: scaling, vortex path, and anisotropic pinning. Experimental results of angular dependence studies for HTS-2 tapes with varying chemical compositions are presented. Several distinctive features are highlighted, including the nontrivial effect of rare earth element substitution in the HTS composition on the pinning landscape, peak asymmetry, and critical current dependence on the Lorentz force direction. The analytical methods discussed are then applied to the experimental data. The quality of model approximations was evaluated using the coefficient of determination, adjusted for the number of fitting parameters. The analysis reveals fundamental differences in the interpretation of features of angular dependences depending on the chosen model. It is concluded that no universal approach exists to reasonably interpret observed features while linking them to the defect structure of HTS materials. This highlights a significant gap in current understanding of superconducting electromagnetic behavior and underscores the need for further research.