Control of field quality for the production of the main LHC dipoles

We review the warm magnetic measurements of the first four main dipole prototypes (8 apertures) and their agreement with nominal design. We then estimate the order of magnitude of the corrections that may be needed to re-center the low-order normal harmonics around the nominal values for the forthcoming series production. Correction strategies that provide the minumum impact on production schedule and costs are analysed. For the case of b3 and b5 two possibilities are considered: a variation of the shims to optimize the azimuthal length of the two coil layers, and a variation of the copper wedges of the inner layer, leaving unchanged the azimuthal coil size. For optimizing b2 and b4, we consider modifications of the shape of the ferromagnetic insert, that is placed between the collars and the yoke. Comparison between measurements and simulations of the implemented insert modifications are given and a final design is proposed. Intrinsic limits to the control of field quality during the production are discussed.