Superconducting Nb 3Sn joints by chemical vapour deposition

Abstract

Nb 3Sn is an A15 superconductor with high critical current density in high magnetic fields, e.g. 200 000 A cm −2 at 10 T and 4.2 K. Unfortunately, A15 intermetallics are brittle and difficult to manufacture in defect-free lengths for large superconducting coils. This paper describes a chemical vapour deposition (CVD) process which deposits Nb 3Sn on to prespliced Nb 3Sn substrates to form a superconducting joint between two superconductive sections. The CVD-deposited material has very fine grain structure (probably less than 0.2μm), a T c of between 16.2 and 17.8K (in zero field) and a critical current density of greater than 500 000 A cm −2 at 5 T. In addition, the CVD layer definitively bridged the gap between two spliced superconductors, increasing the current capacity at 5 T from a baseline capacity of 66 A mm −1 on the original material to greater than 80 A mm −1 after a CVD Nb 3Sn coating of 3.5μm per side had been applied.