Magnetic performance of the LEP bending magnets

The 3304 steel-concrete cores of the LEP (Large Electron Positron colliding beam accelerator) bending magnets have been individually measured to determine the excitation characteristics (field integral on central orbit versus current), and one out of ten has been submitted to a complete measurement of the field pattern in the aperture. The end and junction effects, as well as the field distortion due to the vacuum chamber both in static conditions (due to residual magnetism of the chamber materials) and during field ramping (influence of eddy currents), have been determined on some average cores. The authors briefly describe the measuring benches and give the average values and RMS (root-mean-square) dispersions of the dipole, quadrupole, sextupole, octupole, and decapole components seen by the beam at different field levels and during ramping. The effects on the machine parameters are analyzed for each component and compared with results obtained in the first injection tests