The Study of Nb3Sn Phase Formation Process in Multifilamentary Superconductors for High-Magnetic-Field Systems

Recent investigations of the connection between the microstructure and the properties of Nb₃Sn superconductors produced by the bronze method, for the large ITER magnets, have enabled us to develop wire fabrication technologies and to manufacture large quantities of such material that met all the technical requirements. The next stage is to study the possibility of increasing the critical current properties in a wide range of magnetic fields with the aim to apply them in the next generation of magnetic systems. In this study, the superconducting phase formation process, its structure, and the composition and critical properties of various layouts of Nb₃Sn wire used under magnetic fields of 12-16 T have been investigated. It is shown that the intermetallic compound structure heavily depends on the grain structure of niobium filaments produced by multiple deformation of the composite wire with intermediate heat treatments. It is concluded that the improvement of the superconducting phase structure and the increase in current-carrying capability of wire in high magnetic fields are possible by the fine grain structure of initial niobium filament and an increase in the tin content of the bronze matrix.