Characteristics of multifilamentary wires for a.c. use developed by the bronze process using diffusion barrier techniques

Abstract

Nb 3 Sn multifilamentary superconducting wires for a.c. use were developed by the bronze method using Cu diffusion barrier techniques. To reduce a.c. losses, the filament diameter was designed to be less than 0.5 µm and the final resistivity of the bronze matrix was increased using a Cu alloy diffusion barrier with the addition of Si and Mn elements around the filaments. As a result, interfilamentary proximity coupling could be prevented until a filament spacing of 0.3 µm and hysteresis losses for the wires reached lower values, from 1.75 kJ m −3 to 12.18 kJ m −3 at a magnetic field amplitude of 0.5 T under controlled reaction heat treatment. The perpendicular resistivity of the matrix between the filaments estimated from the coupling loss was about 2.5 × 10 −8 m, which was considerably less than the resistivity value of the matrix estimated after the reaction. This was thought to be due to an extreme reduction in Sn concentration between the filaments. Furthermore, a small a.c. coil was fabricated by winding a stranded cable fabricated in this way. The a.c. loss of the coil at 50 Hz in a central magnetic field of 0.5 T was 178 kW m −3 and the a.c. quench current at 50 Hz was 195 A, which is about 10% lower than the critical current on the load line. This degradation was due to the temperature rise in the cable caused by a.c. loss.

Morphology and Structure of Diffusion Layers in Nb₃Sn-Based Superconductors of Different Geometry

“…Commercial fabrication of the Nb 3 Sn superconducting composites of long lengths is presently performed by three approaches: the bronze route [19][20][21], the internal-tin route [22][23][24][25][26][27] and the powder in tube (PIT) approach [28][29][30].…”

Electromagnetic properties of proximity-induced superconductivity for matrices with different penetration lengths in NbTi multifilamentary wires

“…It was pointed out that the excessive hysteresis loss is mainly caused by interfilamentary coupling due to the proximity effect [4,5]. In order to suppress this coupling, it is known that there are two effective means: the reduction of the mean free path of Cu matrix by adding Ni or Si element, or the destruction of Cooper pairs due to localized magnetic moment by adding Mn element [6,7]. In previous papers [8][9][10], the interfilamentary proximity coupling behaviours of NbTi multifilamentary wires with Cu or CuMn matrices were studied quantitatively by measuring the twist-pitch l p dependence of magnetization.…”