X-ray imaging of the APS storage ring beam stability effects: from the Alaskan earthquake to undulator field changes

The Advanced Photon Source (APS) 7-GeV storage ring serves as a national X-ray synchrotron radiation user facility. The stability and beam quality of the electron beam, and hence the photon beams, are monitored continuously by an array of diagnostics. In particular, X-ray imaging techniques are employed in the diagnostics sector of the ring to characterize beam position, size, and emittance. The X-ray synchrotron radiation (XSR) emitted by the electrons as they pass through the field of a dipole magnet is imaged by a pinhole camera. The images are processed by a Datacube MV200 video digitizer, and the results are provided through the EPICS platform. We have detected the effects on the beam ranging from the arrival of shock waves from the Alaskan earthquake of November 3, 2002 to the variation of the undulator fields by the users during their scans. In the latter case, the beam size effects were observed at the submicron level. Examples of beam centroid and size effects will be presented including some due to longitudinal instabilities at elevated stored beam currents.