RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
In the XFEL project at SPring-8, the resolution of a beam position monitor (BPM) is required to be less than 1 um. Therefore, we developed an rf cavity BPM (RF-BPM) to achieve a precise position resolution. The RF-BPM has two cavities: one is a TM110 cavity for position detection and the other is a TM010 cavity for phase reference and charge normalization. The resonant frequency is 4760 MHz and the loaded Q factor is approximately 50 for both cavities. The designed performance of the RF-BPM cavity was confirmed by low-level rf measurement. The rf signal is detected by an IQ demodulator to obtain the intensity and the phase. Although the BPM signal is a mixture of a position signal and a slope signal, the IQ demodulator can easily distinguish them because the phases of these signals are 90 degrees different from each other. We developed a new circuit that has small errors: the intensity error is 1 % and the phase error is 0.5 degree. The RF-BPM system has been tested by using a 250 MeV electron beam at the SCSS test accelerator. We report results of confirmed RF-BPM performances; position resolution, xy coupling, linearity, dynamic range, beam arrival timing measurements etc.
DESY, Hamburg
The European XFEL is an X-ray free-electron-laser that is currently being built in Hamburg. It is organized as an international Project and will be a large scale user facility. Based on superconducting TESLA technology electron beams of high average power will be send to several undulator lines simultaneously to produce hard X-Rays with high average intensity and a peak brilliance by far superior to any 3rd generation light source. This paper will present the current status of the planning, the development and the prototyping process for this facility. It will cover as well as the BPM system, the other main diagnostic systems, like beam size measurements, charge, dark current and beam loss and protection systems.
SLAC, Menlo Park, California
CERN, Geneva
Synchrotron-light telescopes will monitor the profiles of the two LHC proton beams. At collision energy (7 TeV), each telescope will image visible light from a superconducting dipole used to increase beam separation for the RF-cavities. At injection (0.45 TeV), this source must be supplemented by a two-period superconducting undulator 80 cm from the dipole. We will present the mechanical and optical layouts of the telescope. The initial plan to use dipole edge radiation at high beam energy, for its increased visible emission, suffers from significant diffractive blurring. We will instead collect radiation from the first 2 to 3 m of the dipole’s interior. An optical "trombone" delay line will provide the large shift in focus. We will discuss calculations and measurements of blurring by diffraction and by this extended source, and present an alternative optical design using off-axis elliptical mirrors.
ESRF, Grenoble
An additional electron beam emittance measurement at the ESRF storage ring is now installed that uses X-ray radiation from an undulator. The method consists in detecting the monochromatic spatial profile of the fifth harmonic of the undulator spectrum. The photon energy is roughly 30 keV, selected with a single bounce (3,1,1) Si monochromator. The X-rays are converted to visible light using a scintillating screen which is then imaged to a CCD camera. The emittance value is deduced from the image size, source distance, and the beta-function at the source point, taking into account the precisely known photon beam divergence. The direct use of undulator radiation is advantageous in terms of the precise knowledge of the source position and lattice parameters in the straight section. For this reason this device will find its main application as a horizontal emittance monitor with improved absolute precision compared to that of the pinhole cameras which are making use of bending magnet radiation. This paper will present the details of the method, the setup and the obtained results.
Uni HH, Hamburg
PSI, Villigen
DESY, Hamburg
A seeded free-electron laser operating in the soft X-ray (XUV) spectral range will be added to the SASE FEL facility FLASH. The seed beam will be generated by higher harmonics of a near infrared laser system. A dedicated transport system will guide the radiation into the electron accelerator environment. Within the seed undulator section compact diagnostic units have to be designed to control the transverse overlap of the photon and the electron beam. These units contain a BPM a wire scanner and an OTR screen for the electron diagnostic. A Ce:YAG screen and a MCP readout for the wire scanner are foreseen to measure the photon beam position.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
An electron beam halo monitor has been developed in order to protect undulator permanent magnets against radiation damage for the X-ray free electron Laser facility at SPring-8 (XFEL/SPring-8). The halo monitor will be installed at the upstream of the undulator and detect the electron beam that might hit the undulator magnets. Diamond detector, which operates in photoconductive mode, is good candidate for electron beam sensor, because diamond has excellent physical properties, such as, high radiation hardness, high insulation resistance and sufficient heat resistance. Pulse-by-pulse measurement suppresses the background noise efficiently, especially in the facilities having extremely high intense beam but low repetition rate, such as XFELs. The linearity of output signal on injected beam has been demonstrated in the range of 103 to 107 electron/pulse. The feasibility check for this monitor was performed at the SPring-8 compact SASE source (SCSS) test accelerator for XFEL/SPring-8. We observed the unipolar pulse signal with the pulse length of 0.4 nsec FWHM. The beam profiles of the halo can be also measured by scanning the sensor of this monitor.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
Fiber-based beam loss monitors offer the possibility to detect beam losses over long distances, with good position accuracy and sensitivity at a reasonable cost. For the undulator section of the SPring-8 X-FEL, radiation safety considerations set the desirable detection limit at 1 pC (corresponding to a 0.1% beam loss) over more than a hundred meter. While a theoretical approach offers some hints, the selection of the optimum fiber is not straightforward. Glass fibers of different diameter (100 to 600 μm), index profile (graded/stepped) and from three different makers were therefore characterized (signal strength, dispersion, attenuation) at the SPring-8 Compact SASE Source (SCSS), a 1/16th model of the future X-FEL. Beam tests (Fujikura SC400) showed that, at 250 MeV, the detection limit corresponding to a 10 mV signal is below 1 pC over 60 m and 3 pC over 120 m. The position accuracy was found to be better than 30 cm. Finally, the fiber lifetime has been estimated to be over 13000 h from dose measurements at the SCCS.
DESY, Hamburg
In this contribution we describe how Coherent Optical Transition Radiation can be used as a diagnostic tool for characterizing electron bunches in X-ray Free-electron lasers. The proposed method opens up new possibilities in the determination of ultra-short, ultra-relativistic electron bunch distributions.
DESY, Hamburg
High-brightness electron bunches with low energy spread, small emittance and high peak currents are the basis for the operation of high-gain Free Electron Lasers (FELs). As only part of the longitudinally compressed bunches contributes to the lasing process, time-resolved measurements of the bunch parameters are essential for the optimisation and operation of the FEL. Transverse deflecting structures (TDS) have been proven to be powerful tools for time-resolved measurements. Operated in combination with a magnetic energy spectrometer, the measurement of the longitudinal phase space can be accomplished. Especially in case of ultra-short electron bunches with high peak currents for which a time resolution on the order of 10 fs would be desirable, both the TDS and magnetic energy spectrometer have intrinsic limitations on the attainable resolution. In this paper, we discuss the fundamental limitations on both the time and energy resolution, and how these quantities are connected.
DESY, Hamburg
Future accelerators like the International Linear Collider and Free-Electron Lasers require beam position measurements with resolutions between few nanometres and 1 μm. Cavity Beam Position Monitors (BPM) are able to achieve the resolution. This paper shows the basic principles of this type of monitor, followed by a brief history of the developments. Since different institutes are designing Cavity BPM system for different projects, an overview is given on their recent developments including results and limitations compared with their requirements.
SLAC, Menlo Park, California
ANL, Argonne, Illinois
We present the performance of the cavity beam position monitor (BPM) system for the Linac Coherent Light Source (LCLS) undulator at SLAC. The construction and installation phase of 36 BPMs have been completed. Commissioning is underway. The X-band cavity BPM employs a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at nominal center frequency of 11.384 GHz. The signal processing electronics features a low-noise single-stage three-channel heterodyne receiver that has selectable gain and phase locking local oscillator. The approximately 40MHz intermediate frequency is digitized to 16 bits at a 119 MHz sampling rate then reduced to baseband digitally. Phase and charge are normalized with respect to the reference cavities. System requirements include sub-micron position resolution for a single-bunch beam charge of 200 pC. Early commissioning results indicate single-bunch resolutions better than 500 nm rms and stabilities better than 1 micron drift over 24 hours.
DESY, Hamburg
PETRA III, a new high-brilliance synchrotron radiation source, is under commissioning at DESY. Its beam position measurement system is based on the Libera Brilliance electronics. BPM system is used for machine starting up and development. The system will also be used for the beam observation and orbit feedback. This paper presents the infrastructure, features of the BPM system and experience with the commissioning of the BPM electronics.
Diamond, Oxfordshire
A relatively new development for synchrotron light sources is the concept of producing two independent X-ray beams in a single straight using two canted undulators. Two beams, separated by an angular divergence in the order of 1 mrad, proceed down the same front end before being separated into two experimental hutches. This creates a challenge for the position measurement of the two adjacent X-ray beams in the front end. Traditional four blade tungsten vane XBPMs are an established solution for accurate and reliable monitoring of the position of a single beam, so this approach has been developed to create an eight blade XBPM that is capable of resolving two beams independently. This paper presents first results from Diamond’s I04 and J04 IDs and illustrates the techniques used for position calibration and background subtraction.
DESY, Hamburg
The basic design for the machine protection system (MPS) for the light-source PETRA III is discussed. High synchrotron radiation can damage absorbers and vacuum chambers. Therefore the MPS identifies alarm conditions from different systems, including the BPM, temperature and vacuum systems and creates a dump command within 100us. For diagnostic purposes a post-mortem trigger is implemented and a first alarm detection is planned. The initial commissioning of the MPS with its alarm-delivering systems is described.
SLAC, Menlo Park, California
By scanning the electron beam energy in LCLS, the sharp K-edge absorption energies in nickel and yttrium were exploited to measure spectral features of x rays from a single undulator section. We show measurements obtained using a Ni foil, with beam energy tuned to scan the first harmonic across the K-edge, and similar measurements obtained using the yttrium component of a YAG screen, with the beam tuned to match the third harmonic. These spectral features allow the precise determination of the position of central ray, and provide some measure of the undulator K parameter. A refinement of this method should allow precise matching of the K parameters of multiple undulator sections after their installation in March 2009.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
DESY, Hamburg
Local beam losses and beam profiles at particle accelerators are determined by measuring the ionizing radiation outside the vacuum chamber. Four different fiber optic radiation sensor systems will be presented. Two are based on the increase of radiation-induced attenuation of (Ge+P)-doped multimode graded index fibers, whereas with the third system detects the Cerenkov light generated by relativistic electrons in radiation hard fibers. The used fiber is an undoped multimode step-index fiber with 300 um core diameter. Dosimetry at high dose levels uses the radiation induced Bragg wavelength shift of Fiber Bragg Gratings. The selection of a suitable fiber for the individual application is an important requirement and depends on the type, doping, used wavelength and annealing behavior. In addition, the dose range, dose rate and temperature must be considered. At six accelerators all systems are used for in-situ beam optimization and dose measurement. This paper summarizes the basic of this measurement technology and the experience at linear accelerators and at storage rings.
Uppsala University, Uppsala
Uni HH, Hamburg
DELTA, Dortmund
FYSIKUM, AlbaNova, Stockholm University, Stockholm
DESY, Hamburg
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
We present very promising recent results from the optical replica synthesizer experiment in FLASH where we manipulate ultrashort electron bunches in FLASH with a laser in order to stimulate them to emit a coherent light pulse with the temporal structure of the electron bunches and subsequently analyze the light pulses with laser diagnostic (FROG) methods.