Nb3Sn research and development in the USA – Wires and cables

We summarize the status of Nb3Sn development in the USA. The US conductor development program (CDP), initiated in 1999, has resulted in commercial wires that carry more than 3 kAmm−2 at 12 T and 4.2 K. These high current Nb3Sn wires have successfully been cabled and used in accelerator magnets that achieved record magnetic fields. This article describes the CDP, its achievements, and the manufacturers involved. We discuss low magnetic field instability in magnets that re-emerged through the use of very high current density Nb3Sn wires, and solutions that address these stability problems. It is shown how cabling of high current wires is a balance between edge deformation and mechanical stability of the cable, and an empirical cable recipe is described. The article concludes with an outlook for possible future methods to optimize, and further increase, the current carrying capacity in Nb3Sn at medium magnetic fields. The article describes how record current density Nb3Sn wires have to be implemented in accelerator type magnets, to achieve magnetic fields that approach the performance limitations of Nb3Sn.