Nb3Sn conductors for high energy physics and fusion applications

There are two basic approaches to internal-tin Nb3Sn conductor design. 1) M aintaining individually separated filaments after reaction and 2) allowing groups of filaments to bridge, while, at the same time ensuring that the ov erall size of the agglomerate is limited in order to control the effective filament diameter (d(eff.)) and losses. In this paper we discuss recent dev elopments in both of these conductor types. The strand for the Levitated Di pole Experiment (LDX) is illustrative of type 1, and the most significant d evelopment in this area is a react-and-wind conductor soldered into a coppe r channel. In category 2, conductors with higher current density capabiliti es have been made primarily for High Energy Physics applications, although they can also be used in small high field magnets. Many of these conductors have much higher losses than the other type. Some of the factors controlli ng piece length, critical current density (J(c)) and losses are discussed f or a series of different designs, filament sizes and compositions.