In recent years, properties of high temperature superconducting (HTS) tapes, especially in-field performance and mechanical strength, have been continuously improved. The HTS tapes have been widely used for high field (>20 T) magnet researches and there are several technical challenges including field attenuation of an HTS magnet by screening currents induced within the HTS tapes. Several publications reported that the screening currents, induced by penetration of self magnetic fields into 2 HTS tapes within an HTS magnet, weakened a field constant of the HTS magnet. The result may demonstrate that the screening current changes an overall current density distribution in HTS tapes and, as a consequence, the generated magnetic field. Therefore, it is necessary to investigate the screening current distribution in an HTS tape. This paper reports numerical simulation of the screening current distribution in an HTS tape of high field magnets using 2D finite element method with the E-J characteristic of the HTS tape taken into account. Self magnetic field distribution and its orientation to the HTS tape are also considered to compute critical currents and locally generated electric fields, two key components to figure out the distribution of screening currents.
Abstract-In recent years, many toroidal HTS-SMES consisting of some superconducting element coils have been investigated and designed. In stable operation, the electromagnetic force applying to the superconducting element coils maintains balance because of the toroid structure and the same transport current of each superconducting element coil. However, if one of the superconducting element coils transitioned into a resistive state, the balance of the electromagnetic force would be broken down, and then the huge electromagnetic force would work onto the superconducting element coils. The huge electromagnetic force may overturn the superconducting element coils, and consequently a large accident occurs. However, the behavior of the overturning electromagnetic force after the transition of some superconducting element coils into the resistive state has been not yet well investigated. For the design of the HTS-SMES magnet, it is, therefore, necessary to investigate the overturning electromagnetic force on the design stage. We have developed a simulation code to investigate the behavior of the overturning electromagnetic force on the toroidal HTS-SMES system after the transition of one superconducting element coil into the resistive state. The magnetic field and the circuit analysis are coupled and solved in the developed simulation code.Index Terms-Electromagnetic force, HTS-SMES, magnetic field simulation, superconducting magnet.
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