Bunch fill pattern at BESSY monitored by time-correlated single photon counting

Time-resolved experiments employing the timing distribution of synchrotron radiation in contemporary electron storage rings demand a precise control of the bunch fill pattern. At BESSY an X-ray detector based on an Avalanche Photodiode Diode (APD) in combination with time-correlated single photon counting (TSPC) has been developed and used since 1999. After improving the detector and using a novel state-of-the-art TCSPC electronics we demonstrate by several examples that this composition allows for a reliable control of the bunch timing on a ps scale and a dynamics of up to 10 7 for bunch purity measurements within complicated fill patterns in a variety of operation modes of the BESSY II storage ring.