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 understand better 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 strain was measured in situ by neutron diffraction under monotonic and cyclic compressive loading. So-called ten-stack samples composed of Nb$_{3}$Sn Rutherford type cable with different impregnation, and coil blocks extracted from a 11 T dipole short model coil were investigated.