Magnetic Performance of the Main Superconducting Magnets for the LHC

The field strength and homogeneity of all the LHC superconducting magnets were measured as a part of the production control and qualification process that has taken place during the past four years. In addition to field measurements at room temperature performed on the integral of the production, a significant part of the magnets has been subjected to extensive magnetic measurements at cold. The measurements at cryogenic temperatures, generally performed up to excitation currents of 12 kA corresponding to the ultimate LHC energy of 7.6 TeV, were mainly based on static and dynamic field integral and harmonic measurements. This allowed us to study in detail the DC effects from persistent current magnetization and long-term decay during constant current excitation. These effects are all expected to be of relevance for the field setting and error compensation in the LHC. This paper reports the main results obtained during these tests executed at operating conditions. The integrated field quality is discussed in terms of distribution (average and spread) of the field strength and low-order harmonics as obtained for all the main ring magnet families (dipoles, main and matching quadrupoles). The dependence of field quality on coil geometry, magnet and cable manufacturer is analyzed. A projection of the field quality expected for the critical components in the machine is presented.