Numerical and Experimental Study of Critical Currents of YBa2 Cu3 O7–δ Coils With and Without Magnetic Substrates

It has been shown that the substrate magnetism of YBCO tapes affects the critical current, but the role of substrate magnetism in the local critical current of the YBCO coils still needs further study. The purpose of this paper is to improve the accuracy of the current numerical model of critical current and to investigate the effect of the substrate layer magnetism on the local critical current of YBCO coils. To improve the accuracy of the present model, the contribution of the self-magnetic field to the anisotropy of the critical current and the reduction of the critical current density near the edge of the tape are considered in the finite element model (FEM). The effect of substrate magnetism on the critical current of YBCO coils is investigated experimentally and numerically, and the mechanism is clarified. It can be found that the critical current obtained by the four-lead method for a multi-turn coil is not the arithmetic average of the critical current per turn. And the magnetic flux density on the surface of coils wound by YBCO tapes with magnetic substrate is much higher than that of coils wound by tapes with non-magnetic substrate, but the magnetic flux density on the YBCO layer inside the tape is smaller. Additionally, the critical current per turn of the coil with magnetic substrate is more uniformly distributed compared with that the coil with non-magnetic substrates. The critical current model of YBCO coils developed in this paper can provide a reference for the design and optimization of HTS devices.