Papers by Author: Yuichi Nakamura

Abstract: Ag-sheathed Bi2223 composite tapes with interfilamentary resistive barriers were successfully fabricated by using a powder-in-tube (PIT) method and their AC loss properties at 77 K are evaluated. The mixture of Ca2CuO3 and 30 wt% Bi2212 was used as the barrier material for tape fabrication to make an electromagnetic decoupling between the filaments. The barrier layers formed on all surfaces of hexagonal monocore wires by a dip-coating method, and several pieces of the coated wires were stacked and inserted into an Ag tube. Subsequently, the composites deformed into tape shape and subjected to a standard process consisting of a flat rolling and sintering. Degradations in the Jc values at 77 K and self-field by introducing the barriers were estimated to be at most 15%. The transverse resistivity and AC loss properties under AC external magnetic fields for the barrier tapes were examined and compared with those for the tape without barriers. The results showed that an introduction of Ca2CuO3 barriers was effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field. The fabrication of the barrier tapes on the order of several meters, together with the uniformity of superconducting properties along a length direction has been also presented.

Abstract: We fabricated Ag-sheathed Bi2223 composite tapes with interfilamentary resistive barriers by using powder-in-tube (PIT) method and evaluated their AC loss characteristics at 77 K. The mixture of Ca2CuO3 and 30 wt% Bi2212 are used as the barrier material for tape fabrication. The barrier layers were coated on all surfaces of the hexagonal monocore wires. Then, several pieces of the coated wires were stacked and inserted into an Ag tube, and the composites were deformed into tape shape. By introducing the barrier layers between the filaments, the Jc values at 77 K and self-field are degraded about 15%. The loss measurements under AC parallel transverse magnetic field were systematically performed, as a function of field amplitude and frequency. The loss properties in the barrier tape were compared with those in the tape without barriers. The results indicated that introducing Ca2CuO3 barriers is effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field. We also present the fabrication of the barrier tapes on the order of several meters, together with the uniformity of superconducting properties along a length direction.