Local orbit feedback systems coupled by transfer function errors

A stable and well positioned beam in a third generation synchrotron light source is of paramount importance to the proper functioning of the beamlines. The positioning of the beam at each insertion device straight section is performed by a local orbit beam bump excited by a feedback system. The presence of unavoidable errors in the correction procedure leads to mutual coupling of different feedback systems. The stability of the correction procedure, when applied to an arbitrarily perturbed orbit oscillation, is examined in terms of the feedback parameters. Two distinct instabilities are discussed, the first depends wholly on the magnitude of the correction errors whilst the second is related to the correction and perturbation frequencies. (orig.)