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

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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.