SLAC, Menlo Park, California
A new stripline beam position monitoring (BPM) readout and processing system was installed and successfully tested over a two-week period at the Accelerator Test Facility 2 (ATF2), in KEK, Japan during February 2010. The core analog processing board used in the system is a duplicate of that developed for, and in use at, the Linac Coherent Light Source (LCLS) at SLAC. The digitization, processing and control front-end were custom designed for ATF2 using a 14-bit 100-MHz VME digitizer and an EPICS Input/Output Controller (IOC) running on the VME controller. Control of the analog boards is via EPICS, which controls a serial-over-TCP/IP port server. Hardware for the readout of up to 14 BPMs with 3 spare analog boards was delivered. The goal of this installation was to provide ~<10 micron resolution, non-charge-dependent readout of the ATF2 electron beam with long-term gain stability compensation. These criteria were tested and successfully met. This design was found to be highly effective and to have many advantages, especially that it required minimal installation effort at ATF2.
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.
