Analysis of conductor displacements in the coil of the LHC main dipole by speckle interferometry

Magnetic field quality in superconducting magnets mostly depends on the conductor position in operational conditions (under pressure, at 1.9 K). For the case of the LHC main magnets, the conductor layout must agree with the nominal design within less than 0.05 mm to met the field quality specifications. Finite element models are a numerical tool to forecast loads and deformations of mechanical structures, and can be used to evaluate conductor displacements. To verify the FEM response at room temperature, we made displacement measurements using speckle interferometer on a short sample of the dipole coils. Experimental results are compared with the numerical calculations, allowing a stringent test of the most critical features of the FEM (interfaces between different materials and coil properties).