Mechanical Characterization of Nb3Sn Cable Insulation Systems Used for HL-LHC Accelerator Magnets at Ambient Temperature

The performance of accelerator magnets is strongly relying on the dielectric strength and mechanical robustness of the insulation system. This is in particular relevant for the current development of high field superconducting Nb 3 Sn magnets with the insulation system made from resin-impregnated glass fibres. During the assembly and operation at cold temperature, this insulation system is exposed to high mechanical compressive and shear stresses. The focus of the study was the investigation of the mechanical shear strength of the insulation composite. The experimental tests have been performed at room temperature, determining the mechanical strength and the failure mechanisms of the cable insulation system. Within this test the inter-laminar shear strength (ILSS) and non-standardized combined shear compressive strength were determined. The test sample preparation was based on the manufacturing procedures and materials used in the series fabrication for the CERN HL-LHC Nb 3 Sn coils. The individual insulation systems are varying in the S2-glass yarn density, the sizing, and the fibre volume fraction. Furthermore, the presence of mica insulation on the mechanical strength has also been studied. This paper describes the applied measurement procedures used during the test campaign, and presents the relevant measurement results, identifying the mechanical limitations of the insulation system.