ANL, Argonne
Recent developments at the Advanced Photon Source (APS) in high-resolution beam position monitoring for both the electron and the x-ray beams has provided an opportunity to study beam motion well below the measurement threshold of the standard suite of instrumentation used for orbit control. The APS diagnostics undulator beamline 35-ID has been configured to use a large variety of high-resolution beam position monitor (BPM) technologies. The source-point electron rf BPMs use commercially available Libera Brilliance electronics from Instrumentation Technologies, together with in-house-developed field-programmable gate array-based data acquisition digitizing broadband (10 MHz) amplitude-to-phase monopulse receivers. Photo-emission-based photon BPMs are deployed in the 35-ID front end at distances of 16 and 20 meters from the source, and a prototype x-ray fluorescence-based photon BPM is located at the end of the beamline, approximately 42 meters from the source. Detailed results describing AC noise and long-term drift performance studies will be provided.
ANL, Argonne
Accurate and stable x-ray beam position monitors (XBPMs) are key elements in a feedback system for obtaining desired x-ray beam stability. For the low-emittance mode of operation of the APS, the cross sections of the undulator x-ray beams are not upright ellipses, and the effective beam sizes in the horizontal and vertical planes depend on the undulator gaps. These beam characteristics introduce strong gap dependence in blade-type XBPMs designed for upright elliptical beams. A center-of-mass detector XBPM will significantly reduce the gap dependence of the BPM readings. We report the development status of a high-power center-of-mass XBPM at the APS. We note that users often discard more than 50% of the undulator beam power outside of the monochromatic beam. These photons can be intercepted by the limiting aperture of the beamline, and then the x-ray fluorescence footprint can be imaged onto a detector. The position of the x-ray beam can be read out using position-sensitive silicon photodiodes. Thermal analyses show that the XBPM can be used for the measurement of beam with a total power up to 20 kW for the 7-GeV / 200-mA operation of a 5-m undulator in the APS.
ANL, Argonne
The Advanced Photon Source (APS) storage ring rf beam position monitors (BPMs) are impacted by the presence of beam-excited transverse electric (TE) modes. These modes are excited in large-aperture vacuum chambers and become trapped between the bellow end flanges. The TE modes are vertically oriented and are superimposed on the TEM beam position signals, corrupting the BPM measurements. Erroneous step changes in beam position measurements and systematic intensity dependence in the vertical plane have been traced to these modes, placing a fundamental limitation on vertical beam position stabilization. Experiments were conducted suppressing these modes on a test vacuum chamber. These experiments were simulated with MAFIA and Microwave Studio, confirming experimental results. We will describe the measurements, simulations, and prototype test results.
ANL, Argonne
As the Advanced Photon Source (APS) prepares for a large-scale upgrade, many of the fundamental limitations on beam stability have to be identified. Studies have been conducted to measure thermal mechanical effects of both the water and air handling systems impacting insertion device vacuum chambers (IDVES). Mechanical stability of beam position monitor pickup electrodes mounted on these small-gap IDVES places a fundamental limitation on long-term x-ray beam stability for insertion device beamlines. Experiments have been conducted on an ID vacuum chamber indicating that the BPM blocks are moving with water temperature cycles at the level of 10 microns/degree C. Measurements and potential engineering solutions will be described.