Advanced Composite Insulation Systems in Nb3Sn Superconducting Magnets for Accelerators: Electrical Characterization of Laminates at Cryogenic Temperatures

Abstract

The electrical insulation system in wind-and-react Nb3Sn superconducting magnets must be robust, such that it can sustain the mechanical stresses, high radiation doses, and thermal cycles involved in the operation of the magnets. The chosen cable insulation material, currently a thin layer of braided S2 Glass, must also withstand a high-temperature heat treatment in an inert atmosphere, required to develop the superconducting phase in the cable. To be braided, these fibres require sizing; however, the presence of organic components on the fibre surface can lead to the formation of conductive residue during the Nb3Sn heat treatment. In this study, the electrical properties of different fibre reinforced composite systems have been characterized by measuring dielectric properties. Techniques for fibre de-sizing have also been employed and compared for their suitability to the wind-and-react manufacturing process by using thermal analysis. The results of these tests are presented in this paper, providing an indication of how the design of composite insulation systems could be adapted to achieve improvements in magnet performance.