Magnetization effects in superconducting accelerator magnets

Measurements of the effect of the superconductor magnetization on the field shape of dipole magnets are presented. Such effects are most obvious at low fields where the current capability of the windings is very high and only a small fraction is used to support the transport current which produces the field. In most dipoles the fundamental field component is reduced slightly when the field is increasing and enhanced by an almost equal amount when the field is decreasing, The effect on the higher allowed harmonics such as the sextupole and decapole components is much greater, giving rise to considerable hysteretic behavior at the low field levels where the beam is injected into the accelerator. The measurements summarized in this paper indicate that it is possible to accurately specify the field from current measurements if a "standard" energizing cycle is used and the previous "history" of the magnet is known.