Impact of Magnetic Permeability of the Collars and Warm-cold Correlations on Magnetic Field in the LHC Main Quadrupoles

In this report we analyse the correlations between magnetic measurements at room temperature and at 1.9 K for the main LHC quadrupoles. Most of the work is devoted to the correction of room temperature data to remove the effect of high collar permeability, which has been shown to disappear in operational conditions. The proposed algorithm allows reconstructing solid correlations and extrapolating room temperature data to operational conditions in a reliable way. The analysis is completed by an overview of correlations for all field harmonics.