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The random part of the integral field harmonics in a series of superconducting magnets has been used in the past to identify the reproducibility of the coil positioning. Using a magnetic model and a Monte-Carlo approach, coil blocks are randomly moved and the amplitude that best fits the magnetic measurements is interpreted as the reproducibility of the coil position. Previous values for r.m.s. coil displacements for Nb-Ti magnets range from 0.05 to 0.01 mm. In this paper, we use this approach to estimate the reproducibility in the coil position for Nb3Sn short models that have been built in the framework of the FNAL core program (HFDA dipoles) and of the LARP program (TQ quadrupoles). Our analysis shows that the Nb3Sn models manufactured in the past years correspond to r.m.s. coil displacements of at least 5 times what is found for the series production of a mature Nb-Ti technology. On the other hand, the variability of the field harmonics along the magnet axis shows that Nb3Sn magnets have already reached values similar to this obtained for Nb-Ti ones.
Date of Publication: June 2009