The Impact of the Cable Insulation Thickness Tolerances on LHC Dipole Coil Size

The variation of coil size in LHC dipoles often exceeds its specified value of ±30 µm and in order to keep coil pre-stress in allowed range, up to date ~10% of the magnets have been collared with non-nominal shims. The use of non-nominal shims is not favourable for dipole field quality as it increases the random multipoles. In this paper we present the analysis performed on the measured size of cable insulation and we demonstrate their impact on coil dimensions. Finally, the dimensional data of three main coil components: cable, insulation and copper wedges were collected for 90 magnets and analysed together with the data of coil size measurements. A good correlation between the coil size and its component dimensions was found.