Effect of Epoxy Volume Fraction on the Stiffness of Nb 3 Sn Rutherford Cable Stacks

For the optimization of Nb 3 Sn superconducting accelerator magnet design and assembly parameters the stress-strain behavior of the coils needs to be known. We have measured the stiffness of Nb 3 Sn Rutherford cable stacks with different epoxy volume fraction. The cable stack stiffness is strongly dependent on the load direction. The highest stiffness of about 95 GPa is measured in axial direction, as predicted by the rule of mixtures. In transverse load direction the stiffness is stress dependent, and about half of the axial stiffness. As expected the stiffness of the cable stacks increases with decreasing epoxy volume fraction. The stiffness of a conductor block extracted from an already cold tested 11 T dipole coil is comparable to that of a ten-stack sample with similar epoxy volume fraction.