Revision of the Closed Orbit Corrector System of the LHC

The closed orbit corrector system of the LHC has been revisited in accordance with the project progress. The magnet measurement procedures are now well defined. This makes the error on the magnet strength and positioning better known than at the time the orbit correctors were specified. The LHC is in a favourable context in the sense that we have a precise knowledge of the vertical movement of the LEP tunnel and that an efficient code to detect field errors is available. Under these conditions the strength of the closed orbit correctors in the arc and in the dispersion suppressors is sufficient. The demand on closed orbit correctors in the insertions can be somewhat relaxed. The tolerances on the longitudinal positions of the dipoles and quadrupoles are easy to satisfy and do not impose further constraints on the closed orbit corrector system.