Nb3Sn wire technology for high field superconducting magnet

Nb3Sn superconducting wires are widely used for high field superconducting magnets, and the NMR magnet is one of the most successful applications. In order to realize large Jc (critical current density), which is essential to high field superconducting magnets, several different types of production methods have been developed such as the bronze-route method, the powder-in-tube method and the internal tin method. This article first reviews those wire production methods and the technique for Jc value enhancement. After that, current developments in the large Jc Nb3Sn superconducting wire of Kobe Steel and Japan Superconductor Technology are described. The magnetic field dependence of Jc values in each manufacturing method is presented and the strong and weak points for the industrial usage of each manufacturing method are also described. An effective guideline for achieving the best superconducting magnet performance is discussed, optimizing the placement of Nb3Sn wire manufactured by each method. The proposed design concept uses PIT method wire for the innermost layer winding and IT method wire for outer layer winding. This idea could realize an NMR magnet with a high magnetic field and superior cost performance.