Insulation systems for Nb3Sn accelerator magnet coils manufactured by the wind & react technique

Superconducting dipole and quadrupole magnets for particle accelerators and storage rings usually rely on saddle-shaped coils wound from Rutherford-type cables. When using Nb₃Sn, the small radii of curvature of coil ends impose that the winding be performed with un-reacted conductors and that the heat treatment needed for Nb₃Sn compound formation be applied on the whole coil upon winding completion. This results in very stringent requirements on the cable insulation system, which must be able to sustain the high-temperature cycle while retaining its mechanical strength and avoiding the formation of deleterious carbon compounds. Furthermore, it is also desirable to integrate the insulation system as a means of conferring a rigid shape to the manufactured coils, in order to ease subsequent handling and assembly and to protect the brittle material. We review here how various accelerator magnet R&D programs around the world are presently dealing with these issues.