Nb3Sn Accelerator Magnets: The Early Days (1960s–1980s)

Abstract

Since Nb 3 Sn became available in the form of relatively long tapes in the early 1960s, it was considered for high-field magnets thanks to its high upper critical magnetic field and critical temperature. This chapter is a review of the effort accomplished by the community in the first 25 years of development of Nb 3 Sn accelerator magnets, and an attempt to understand why it took so long before this technology became successful. IntroductionDiscovery and major advancements in the understanding and development of practical type II superconductors in the 1950s and 1960s made it possible to employ them in superconducting magnets, particularly, in accelerator magnets used for steering charged particle beams. The superconducting properties of Nb 3 Sn were discovered in the early 1960s, and soon it was available in form of tapes (or ribbons) produced by the surface diffusion process. Shortly afterwards an alternative concept based on solid-state diffusion was introduced. This principle has been used since the 1970s to fabricate Nb 3 Sn composite wires by the so-called bronze route. In 1974 the internal tin (IT) process was developed, which allowed overcoming the limitation of the bronze method to reach a high critical current density J c due to the limited content of tin in bronze. The availability of IT composite wires eventually proved to be a key asset for high-field Nb 3 Sn magnet research and development (R&D) for accelerators. The year-by-year history of Nb 3 Sn wire development can be found in Foner and Schwartz (1981).