Distribution and characterization of screening current and induced field in HTS quasi-isotropic and simply stacked strands

With the development of the second-generation high temperature superconducting tapes (2G HTS tapes), there have been several high current-carrying conductors proposed by different groups. However, since the conductors are generally stacked by 2G HTS tapes with a high aspect ratio, the perpendicular AC magnetic field can induce the screening current on the wide surface of tapes, then generates a magnetic field during the process of excitation and demagnetization, which affect the spatial uniformity and temporal drift as well as field quality in HTS magnets. In this paper, as potential conductors can be used in fusion magnets, the screening effect characteristics of quasi-isotropic strand (Q-IS) and simply stacked strand (SSS) are performed numerically and experimentally. We plot the penetration diagrams of the screening current for both strands under applied changing vertical magnetic field. The dependence of the screening current induced field (SCIF) on the amplitude of the external magnetic field is analyzed, the SCIF hysteresis loop is obtained. We also discuss the spatial distribution of SCIF for both strands. It is shown that SCIF of Q-IS has quasi-isotropic distribution and considerable amplitude reduction comparing with the SSS. The study provides a valuable reference for the application of Q-IS in superconducting magnets, especially nuclear fusion magnets.