Design Updates of the X‐ray Beam Position Monitor for Beamline Front Ends

At the Advanced Photon Source (APS), each insertion device (ID) beamline front end has two x‐ray beam position monitors (XBPMs) to monitor the x‐ray beam position in both the vertical and horizontal directions. The XBPMs measure photoelectrons generated from the CVD‐diamond‐based sensory blades and deduce the beam position by comparison of the relative signals from the blades. Using the method proposed by G. Decker, which involves the introduction of a chicane into the accelerator lattice that directs unwanted x‐rays away from the photosensitive XBPM blades, the photon source stability has been improved by addition of XBPMs in the storage ring global orbit feedback. In recent years, design updates for the XBPM mechanical structure and geometric configuration have been made to improve its performance. We present these design updates in this paper. Test results of the XBPM design updates are also discussed here.