We have directly measured, for the first time, the Nb3Sn and Cu loading strains and stresses in 11 T dipole coil segments upon compressive loading using neutron diffraction. For this purpose a 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 Heinz Maier-Leibnitz FRM II neutron source. The neutron diffraction data suggests that the magnet coil wound of Rutherford type cables can be considered as a fibre reinforced composite material. In the axial load direction the load is mainly carried by the Nb3Sn filaments and the composite stiffness can be estimated by the rule of mixtures assuming iso-strain conditions in all composite constituents. Under transverse compression the fully annealed Cu provides an isotropic pressure around the Nb3Sn filaments. The transverse load stresses in the Cu and Nb3Sn are similar, indicating iso-stress behaviour of the coil constituents under transverse compression. The broadening of the Nb3Sn diffraction peaks above critical stress values indicates reversible and irreversible Nb3Sn loading stress effects.

Nb3Sn magnets are presently build for the HL-LHC accelerator upgrade and are developed for the Future Circular Collider (FCC) study. The knowledge of the Nb3Sn strain state distribution in these magnets is required in order to predict their ultimate performance limit. We have measured the Nb3Sn residual strain distribution in an 11 T dipole accelerator magnet coil. Ambient temperature Nb3Sn strain maps across 11 T dipole coil cross sections were acquired by means of fast high energy synchrotron X-ray diffraction. Using complementary neutron diffraction measurements the Nb3Sn residual strain and stress was measured in the four largest conductor blocks of a massive 11 T dipole coil segment.

The Nb3Sn 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 Nb3Sn 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 Nb3Sn and Cu loading strain was measured in situ by neutron diffraction under monotonic and cyclic compressive loading. Socalled ten-stack samples composed of Nb3Sn Rutherford type cable with different impregnation, and coil blocks extracted from a 11 T dipole short model coil were investigated.