Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb 3 Sn Rutherford Cable Stacks

The Nb 3 Sn superconductor in accelerator magnets must resist high mechanical stresses. In order to better understand the effect of the coil impregnation system on the stresses exerted on the strain-sensitive Nb 3 Sn superconductor, we have measured the elastic strain evolution in the conductor constituents under externally applied loads. For this purpose, a dedicated load frame that enables rotation of the sample load axis with respect to the neutron scattering geometry was installed in the Stress-Spec beamline at the neutron source Heinz Maier-Leibnitz FRM II. The Nb 3 Sn- and Cu-loading strains were measured in situ by neutron diffraction under monotonic and cyclic compressive loading. So-called ten-stack samples composed of Nb 3 Sn Rutherford type cables with different impregnation and coil blocks extracted from an 11 T dipole short model coil were investigated.