CHARACTERISATION OF THE SYSTEMATIC EFFECTS OF THE INSERTION DEVICES WITH PHOTON BEAM POSITION MONITORS

The X-ray photo-emission monitors at the Swiss Light Source (SLS) are used for beam-position diagnostics and beam stabilization down to the sub-micron level. The main systematic change of the photon beamposition is induced by varying insertion device (ID) settings, such as photon energy, harmonic-selection or light polarization. An ID beam-position correction scheme is based on digital beam-position monitors (DBPM) located inside the storage ring, combined with analogue Bergoz BPMs, located inside the ID straight section, and analogue photon monitors (XBPMs), in beam line front-ends. The use of XBPMs in this correction scheme will be demonstrated. Moreover, in order to achieve sub-micron photon-beam stability while changing the ID parameters with XBPMreadouts requires precise XBPM alignment and characterization for each ID-setting [1-2]. We present an account of the design and performance of the XBPMs as used for characterizing systematic effects of the U19, and the more challenging elliptical undulator UE44 [3], a newly designed fixed-gap APPLE II undulator recently installed at the advanced resonant spectroscopy beam line [4].