Damping of injection perturbations at the European Synchrotron Radiation Facility

Top-up operation was recently introduced at the European Synchrotron Radiation Facility (ESRF) to provide constant beam current to the beam line users. This mode of operation involves frequent injections that can be the source of significant perturbations on the stored beam. Beam lines running experiments with a timescale longer than the injection period may be impacted by such perturbations. The ESRF storage ring injection systems and layout were not designed to allow for transparent injection, i.e., without visible perturbations on the stored beam. These perturbations are driven directly or indirectly by rapidly pulsing elements, the effect of which cannot be corrected by standard methods such as feedback loops. Major efforts were put into the development of mitigation measures at the ESRF. Depending on the source of perturbation different approaches were used. They all contribute to the achievement of transparent injections and unperturbed continuous data acquisition for the beam lines. After a review of the ESRF injection systems, these developments and the resulting reduction of the injection perturbations are described in this paper.