ダブルパンケーキコイルで構成した種々のコイル配置に用いる多重HTS テープ導体の電流分布一様化

Abstract

Multi-laminated HTS tape conductors wound into double-pancake (DP) coils are planned to be used widely in the production of large superconducting coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is not homogeneous because of the different inductances of all the tapes. Non-uniform current distribution should be avoided because it causes increased AC loss and decreased critical current in the conductor. Transposition of these tapes at the innermost or outermost layer of the coil so as to arrange the tapes symmetrically is effective for inducing homogeneous current distribution. However, geometrically, this method does not result in perfect symmetry of the conductor for tapes with more than double-lamination and restricts the coil arrangement. In this paper, we analyze the current distribution in the tape conductor using an electrical circuit model, and then discuss how to obtain homogeneous current distribution in multi-laminated HTS tape conductors wound into DP coils for various coil arrangements. We propose a new method to obtain uniform current distribution by adjusting gaps between HTS tapes in the conductor, and apply this method to tapes laminated four times and wound into solenoid coils and a toroidal coil. In this paper, the solenoid coils are composed of two or three DP coils and the toroidal coil is composed of eight unit coils made of a single DP coil. The homogeneous current distribution in the multi-laminated HTS tapes for the arbitrary solenoid coil and toroidal coil composed of multiple DP coils can be obtained by symmetrical transposition at the middle of the unit coil and insertion of appropriate additional thickness between tapes.