5T級 Bi-2223 超伝導コイルの通電損失の評価

Abstract

This study considers a method to evaluate AC transport current losses in Bi-2223 superconducting coils through integrating local external field losses of stacked, taped wires over the winding part of the coils. We measured the transport current losses of two kinds of pancake superconducting coils of Bi-2223 Ag-sheathed tapes, which were composed of 8 or 16 doublepancake (DP) coils, at 0.008 and 0.04 Hz. We also measured the AC external field losses of short specimens of six-layer Bi-2223 wires in both perpendicular and parallel field configurations using a method based on saddle-shaped pickup coils. The approximate local external field loss was calculated as the sum of perpendicular and parallel field losses of the short specimen. In the calculation, a demagnetization effect was considered in order to introduce the geometrical situation of winding in the coil, in addition to the distributions of the perpendicular and parallel magnetic-field components. The comparison between the experimental results of the transport current loss and the numerical results revealed that there is good agreement in the lower amplitude region of the transport current, and deviation in the higher amplitude region. The former finding indicates that this method is applicable as a general means to estimate the transport current losses in superconducting coils. The latter finding suggests that the effects of the transport current may cause significant changes to the AC loss properties of the superconducting coils.