SLAC, Menlo Park, California
The Linac Coherent Light Source (LCLS) X-ray FEL utilizing the last km of the SLAC linac has been operational since April 2009 and finished its first successful user run last December. The various diagnostics for electron beam properties including beam position monitors, wire scanners, beam profile monitors, and bunch length diagnostics are presented as well as diagnostics for the X-ray beam. The low emittance and ultra-short electron beam required for X-ray FEL operation has implications on the transverse and longitudinal diagnostics. The coherence effects of the beam profile monitors and the challenges of measuring fs-long bunches are discussed.
BNL, Upton, Long Island, New York
A residual gas x-ray beam position monitor (RGXBPM) was developed for PETRA-III storage ring. This type of x-ray beam position monitors (XBMP) tend to overcome some deficiencies of the blade type XBPMs, which are currently employed at the third generation synchrotron facilities as "white" undulator beam XBPMs. While blade XBPMs provide micron-accuracy resolution, the signal depends on the undulator gap and is also affected by stray radiation from bending magnets and focusing optics. The residual gas XBPM detects position of the centre of gravity of the undulator radiation; it has no elements that are hit by the x-ray beam, and complies with the windowless concept of the PETRA-III beamlines. Residual gas beam profile monitors were first developed to provide beam profile measurements at charged particles accelerators. The spatial resolution of RGXBPM was substantially improved in order to comply with the requirements at the PETRA III storage ring. Due to limited space, a thorough electrostatic optimization of RGXBPM was needed to achieve required electrical field quality. Test results obtained at the ESRF and commissioning of the RGXBPMs at PETRA-III will be reported.
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.
DESY, Hamburg
PETRA III is a high brilliant synchrotron light-source operating at 6GeV. The commissioning of the machine began in April 2009 *. In the first months of operation the Machine Protection System (MPS) ran on basic requirements to protect absorbers and vacuum chambers in the damping wiggler section and the undulator section against synchrotron light. Therefore several alarms distributed along the machine are identified and within 100us a dump command is created. The beam is dumped within 300us by switching of the rf system **. Prior the first user runs different improvements increasing the reliability and availability are planned and partly implemented in the MPS. This paper presents first commissioning results of the system and gives an overview of these new implementations as well as a more detailed discussion of some alarm conditions and the dump procedure. Additionally some key aspects of the Temperature Interlock as one major alarm-deliverer are described.
ANL, Argonne
For reliable radiation dosimetry of undulator magnets, a beam loss monitor (BLM) covering a large solid angle from the point of beam losses is highly desirable. A BLM that uses a Cherenkov radiator plate wrapping around the beam pipe is utilized in the Linac Coherent Light Source (LCLS) undulator systems, and a similar BLM geometry is currently being tested for the Advanced Photon Source (APS) undulators. We report on measurements made with large solid-angle BLMs recently installed in the APS storage ring (SR) and the booster-to-SR transfer line (BTS) to assess the following design and performance characteristics: (1) relative sensitivity of the Cherenkov detector as a function of the transverse position of electron entry into the quartz radiator; (2) signal intensity as a function of the detector distance from the nominal beam loss location at the undulator vacuum chamber entrance; and (3) the effect of incorporating different tungsten/lead enhancers upstream of the radiator. The measured data will be compared with numerical simulation of the beam loss processes.
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.
SLAC, Menlo Park, California
The Linac Coherent Light Source requires precision timing trigger signals for various accelerator diagnostics and controls at SLAC-NAL. A new timing system has been developed that meets these requirements. This system is based on COTS hardware with a mixture of custom-designed units. An added challenge has been the requirement that the LCLS Timing System must co-exist and “know” about the existing SLC Timing System. This paper describes the architecture, construction and performance of the LCLS timing event system.
SLAC, Menlo Park, California
The LCLS Undulator Beam Loss Monitor System is required to detect any loss radiation seen by the FEL undulators. The undulator segments consist of permanent magnets which are very sensitive to radiation damage. The operational goal is to keep demagnetization below 0.01% over the life of the LCLS. The BLM system is designed to help achieve this goal by detecting any loss radiation and indicating a fault condition if the radiation level exceeds a certain threshold. Upon reception of this fault signal, the LCLS Machine Protection System takes appropriate action by either halting or rate limiting the beam. The BLM detector consists of a PMT coupled to a Cherenkov radiator located near the upstream end of each undulator segment. There are 33 BLMs in the system, one per segment. The detectors are read out by a dedicated system that is integrated directly into the LCLS MPS. The BLM readout system provides monitoring of radiation levels, computation of integrated doses, detection of radiation excursions beyond set thresholds, fault reporting and control of BLM system functions. This paper describes the design, construction and operational performance of the BLM readout system.
ANL, Argonne
SLAC, Menlo Park, California
A large-solid-angle Cherenkov detector beam loss monitor has been built and tested as part of the Linac Coherent Light Source machine protection system (MPS). The MPS is used to protect the undulator magnets from high-energy electron beam loss that can lead to demagnetization. Lost primaries create a shower of secondary electrons that transit through the radiator medium. The radiator consists of an Al-coated plate of high-purity, fused silica, formed into a tuning fork geometry that envelopes the beam pipe preceding each undulator. The radiator transports Cherenkov photons via internal reflection through a tapered neck into a compact photomultiplier tube (PMT). A simple model based on line sources summed across image planes is used to calculate the radiator optical coupling efficiency etac as a function of the electron's transverse position. The results are compared for the case of normally incident electrons with a more detailed Monte Carlo random-walk simulation called RIBO. Both analytical and numerical models show etac to be relatively uniform over the full range of transverse positions in the radiator and to be a strong function of surface reflectivity.
DESY, Hamburg
DESY Zeuthen, Zeuthen
Additional beam diagnostics has been installed in the dump line at FLASH in 2009. Its purpose is to prevent damage by long high current electron beam pulses, as happened in autumn 2008, when a vacuum leak occurred near the dump vacuum window. Beam position monitors (BPM), scintillator-based loss monitors and temperature sensors have been installed thus far in the dump area. Additional BPMs and loss monitors have meanwhile been installed. These include a magnetic BPM placed after the vacuum window. Magnetic loops are used in order to prevent the influence of the ions on the pick-up signals. Four ionization chambers, consisting of air-filled tubes, and 4 glass fibers have been installed parallel to the vacuum pipe, along the last 2 m of beam pipe. Beam halo monitors were installed next to the magnetic BPM. These consist of 4 diamond and 4 sapphire sensors operating as solid state ionization chambers. The halo monitors are sensitive to very small losses. These additional diagnostic monitors were commissioned in autumn 2009, and have contributed to the successful run of long pulses with 3-9 mA current and up to 800 microsecond length. Their performance will be summarized in this paper.
DESY, Hamburg
The European XFEL is a 4th generation synchrotron radiation source, currently under construction in Hamburg. Based on different Free-Electron-Laser and spontaneous sources, driven by a 17.5 GeV superconducting accelerator, it will be able to provide several user stations with photons simultaneously. Due to the superconducting technology high average as well as peak brilliance can be produced. Flexible bunch pattern will allow for optimum tuning to the experiments demands. This paper will present the current planning of the electron beam diagnostics. An overview of the entire system will be given, as well as detailed insight into the main diagnostic systems, like BPM, charge and transmission diagnostics, beam size and beam loss monitor systems.