Bunch Pattern Control in Top-up Mode at the Swiss Light Source

One of the features of advanced third generation light sources is the bunch pattern control in the storage ring, where various filling patterns are of interest for different experiments. The most important step is to keep a uniform charge distribution over all (electron) bunches during the top-up operation. Such a bunch pattern control has been implemented at the Swiss Light Source (SLS). It provides a filling pattern with bunch-to-bunch fluctuation of only a few percent. Since a dependency of the medium term orbit stability on the actual filling pattern was observed in the past, the stability could significantly be improved. Three major ingredients have made the implementation possible: precise timing system, flexible control system and sophisticated diagnostics. The method is applied in the user operation recently and proved to be reliable. This paper describes the hardware and software involved in the filling pattern feedback.