Magnetic performance of insertion devices at the Advanced Photon Source

The insertion devices (IDs) at the Advanced Photon Source have been magnetically tuned to minimize the integrals of the field through the devices and to minimize the variation of those integrals with gap, with a goal of not perturbing the stored particle beam. Measurements of the particle beam motion as the ID gap was changed found that the closed-orbit distortion was better than the requirement and agreed well with predictions based on magnetic measurement results. Another goal of the magnetic tuning is to ensure high brilliance in the low-order harmonics by keeping the rms phase error small