Nb3Sn accelerator magnet development around the world

During the past 30 years superconducting magnet systems have enabled accelerators to achieve energies and luminosities that would have been impractical if not impossible with resistive magnets. By far, NbTi has been the preferred conductor for this application because of its ductility and insensitivity of Jc to mechanical strain. This is despite the fact that Nb₃Sn has a more favorable Jc vs. B dependence and can operate at much higher temperatures. Unfortunately, NbTi conductor is reaching the limit of it usefulness for high field applications. Despite incremental increases in Jc and operation at superfluid temperatures, magnets are limited to approximately a 10 T field. Improvements in conductor performance combined with future requirements for accelerator magnets to have bore fields greater than 10 T or operate in areas of large beam-induced heat loads now make Nb₃Sn look attractive. Thus, laboratories in several countries are actively engaged in programs to develop Nb₃Sn accelerator magnets for future accelerator applications. A summary of this important research activity is presented along with a brief history of Nb₃Sn accelerator magnet development and a discussion of requirements for future accelerator magnets.