Ｂｉ‐２２２３系転位型ケーブル導体用丸線の開発

Abstract

Ag-sheathed Bi-2223 round strands for high-temperature superconducting (HTS) transposed cable conductors were developed. The critical current density (Jc) at 77K, 0T reached 2.5×108A/m2 in a short-length sample and 1.6×108A/m2 in a 50m-long sample. Several analyses were done to evaluate the basic properties of round strands, such as Bi-2223 volume fraction and crystal alignment, and magnetic field dependence of the Jc. Bi-2223 volume fraction was determined by magnetic susceptibility measurement using a SQUID magnetometer. It was confirmed that the Bi-2223 volume fraction was closely correlated with Jc. The crystal alignment was observed by SEM in the cross section of the round strand. It was found that the crystal alignment angle decreased with increasing Jc. The outgrowth feature of the crystals was also found to be decreased in the high-Jc sample. The crystal alignment angle in the longitudinal direction of the round strand was determined by two different Jc-B curves, in which magnetic fields were applied parallel and perpendicular to the longitudinal directions. An assumption was employed in the analysis that Jc was suppressed only by the c-axis component of the applied magnetic field. It was also found that the crystal alignment angle in the longitudinal direction of the round strand was decreased with increasing Jc.