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Description
It has been already revealed that for no-insulation (NI) HTS coils during transient charge and discharge, biased transport current concentrates on the coil terminals, which is closer to the power supply and is less affected by azimuthal current delay effect caused by turn-to-turn current. However, the 3D current density distribution, which considers the terminal effect, is still unclear. Based on 3D polygon-anisotropic-resistivity (PAR) model, this paper finds that during charging process, the terminals of the coil, compared to other parts of the coil, exhibits not only excessive positive (i.e., in same direction with transport current) current densities, but also significant negative current densities. Correspondingly, during discharge process, the terminals compared with other parts, exhibits not only excessive negative current densities, but also significant positive current densities. The excessive screening current effect on coil terminals indicates higher risk of local mechanical damage and is instructive to magnet design and operations.
