Electromagnetic properties of the new conductor, with controlled twist angles, developed to break the existing upper limit of superconducting coil performance and optimization of its design

本研究的目的是通过阐明新型超导导体的基本电磁特性，通过控制扭转角，打破现有超导线圈的性能限制，为实现超导器件做出贡献。研究结果表明：(1)高横截面长径比的NbTi/Cu单片导体具有预期的高性能；(2)将通过提高横截面长径比来提高导体性能的设计方法应用于临界温度约为39K的MgB_2，实际表明MgB_2带的性能得到了提高。(3)为了提高卷绕式超导线圈的性能，提出了卷绕式超导线圈的新设计方法。从理论上说明了该方法的价值。(4)从CIC型导体的测试导体上取下Bi-2223带（高温超导带）组成的转置并联电缆。测量了局部电压沿电缆轴线的分布。从而澄清了观察到导体临界电流减小的原因。(5)完成了电流容量为1kA级的电流互感器的制作，以评价高温超导大导体的电磁特性。电流互感器第二回路的交流输运电流幅值达到880 A。用波印亭矢量法测量了往返导线的交流损耗。实际证明了该测量系统的有效性。

The purpose of this study is to contribute to realise the superconducting devices by clarifying the fundamental electromagnetic properties of the new superconducting conductor, with controlled twist angles, developed to break the existing performance limit of superconducting coils. The results of this study are as follows: (1) It was actually shown that NbTi/Cu monolithic conductors with high aspect ratio of cross-sections have the expected high performances (2) The design method to increase the performances of the conductors by increasing its aspect ratio of cross-section was applied to MgB_2, which has the high critical temperature of about 39K and it was actually shown that the performances of MgB_2 tapes increase. (3) In order to increase the performances of the superconducting coil wound with the tape conductors, the new design method of the coil was proposed. The value of this method was theoretically shown. (4) The transposed parallel cable composed of Bi-2223 tapes (high temperature superconducting tapes) was taken from the test conductor of CIC type conductors. The distributions of local voltages along the cable axis were measured. As a result, the causes of observation of decreasing the critical currents on the conductors were clarified. (5) The fabrication of the current transformer with current capacities of 1kA class was finished to evaluate the electromagnetic properties of high temperature superconducting large conductors. Moreover, the amplitude of ac transport currents in the 2nd circuit of current transformer was achieved to 880 A. The ac losses in the round-trip conductors were measured by Poynting vector method. The validity of the measuring system was actually shown.