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.
SLAC, Menlo Park, California
ANL, Argonne
CERN, Geneva
The Linac Coherent Light Source (LCLS) is a free-electron laser (FEL) at SLAC producing coherent 1.5 angstrom x-rays. This requires precise and stable alignment of the electron and photon beams in the undulator. We describe construction and operational experience of the beam position monitor (BPM) system which allows the required alignment to be established and maintained. Each X-band cavity BPM employs a TM010 monopole reference cavity and a single TM110 dipole cavity detecting both horizontal and vertical beam position. The processing electronics feature low-noise single-stage three-channel heterodyne receivers with selectable gain and a phase-locked local oscillator. Sub-micron position resolution is required for a single-bunch beam of 200 pC. We discuss the specifications, commissioning and performance of 36 installed BPMs. Single shot resolutions have been measured to be about 200 nm rms at a beam charge of 200 pC.
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.