Bunch purity evolution during APS storage ring top-up operations

During top-up operations of the Advanced Photon Source (APS) storage ring, a growth of the charge in the buckets on the trailing time side of the target RF buckets was observed in the bunch purity monitor data. This system is based on a photon counting technique that provides subns time resolution with a dynamic range of greater than 10⁶. The satellite bucket growth was related to the number of linac bunches being injected into the particle accumulator ring (PAR) and the adjustment of the 12^th harmonic RF cavity phase. Besides measuring this growth in the +3,+1 buckets relative to the 22 singlets targeted during top-up, we also report a special configuration and extended counting period that detected charge at the 10^-9 level of the target bucket.