Warm-Cold Magnetic Field Correlation in the LHC Main Dipoles

We present the result of the analysis of warm-cold correlation on measured integrated dipole field strength, magnetic length and harmonics for the first 31 cryodipoles measured. This activity is of high importance to qualify sampling strategies and reduce the number of cold tests. The correlations have simple linear form, and are characterized by the r.m.s. of the warm-cold offset. We report the r.m.s. distance computed for beginning and end of injection conditions, and nominal field. The quality of the correlation, indicated by the r.m.s. of the distance between cold and warm conditions, is best for nominal conditions, degrading by at most a factor 2 at end of injection. In addition we examine the correlation of the geometric harmonics, which is as good as for nominal conditions, and discuss the features of the distribution of the warm-cold differences using the example of the normal sextupole. The present sample of data is still compatible with a single normal distribution, i.e. it is not possible to distinguish multimodal behaviour.