THE USE OF PHOTON MONITORS AT THE SWISS LIGHT SOURCE

The photon beam position monitors (PBPM) in a synchrotron facility are important tools for beam-line and machine diagnostics. In the last two years a number of PBPMs have been installed and commissioned at the Swiss Light Source (SLS). Their readouts have been systematically studied and the results have been correlated with data from the digital beam position monitor (DBPM) system. It turns out that the PBPMs help understanding the influence of insertion device gap changes on photon beam position and thus on photon flux and/or energy resolution near the beam-line experimental stations. In addition to the global fast orbit feedback (FOFB), a local slow feedback based on PBPM data has been implemented to remove remaining systematic effects of the DBPM system and to stabilize the photon beam to a micron level at the experimental station.