RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
We present the design and performance of the beam diagnostic system of XFEL/SPring-8. The XFEL accelerator requires sub-um resolution beam position monitors (BPM), few-um resolution screen monitors, high-speed beam current monitors and a ten femtosecond resolution temporal structure measurement system. We designed an rf cavity BPM which has a resonant frequency of 4760 MHz and a position resolution of less than 1 um. For the screen monitor, thin stainless-steel foil (0.1 mm thick) is used to reduce beam divergence. In addition, a custom-made lens system having few-micron resolution was designed. For the beam measurement, we developed a differential current transformer (CT) with four ports, two are positive and the others are negative, to reduce common-mode noise. The rise time of the CT output pulse is 0.1 ns. To measure the temporal structure of a beam, we developed a C-band (5712 MHz) transverse deflecting cavity that has a disk-loaded backward traveling wave structure. The iris shape of the cavity is a race-track to separate x- and y-mode. This cavity can resolve a beam into femtosecond fragments. Thus, the beam diagnostic system satisfies the demands of the XFEL machine.
GSI, Darmstadt
TEMF, TU Darmstadt, Darmstadt
This contribution focuses on extensive simulations based on Finite Element Methods (FEM) which were successfully used for the design of several Beam Position Monitor (BPM) types. These simulations allow not only to reduce the time required for BPM prototyping but open up new possibilities for the determination of characteristic BPM features like signal strength, position sensitivity etc. Since a precise visualization of the signal propagation along the BPM structure is possible, effects like resonances, field inhomogeneties or complex cross talks between adjacent electrodes can be controlled. Moreover, modern simulation programs enable to define a charge distribution that is moving also at non relativistic velocities, which has an impact on the electromagnetic field propagation. It is shown that for slow ion beams the frequency spectrum of the BPM signal depends on the beam position. A variety of simulation methods are discussed in the context of different BPM realizations applied in hadron accelerators.
DESY, Hamburg
CERN, Geneva
RIKEN/SPring-8, Hyogo
PSI, Villigen
XFELs require high precision orbit control in the long undulator sections. Due to the pulsed operation of these systems the high precision has to be reached by single bunch measurements. So far cavity BPMs achieve the required performance and will be used at the European XFEL between each of the 116 undulators. Coupling between the orthogonal planes limits the precision of beam position measurements. A first prototype build at DESY shows a coupling between orthogonal planes of about -20 dB, but the requirement is lower than -40 dB (1%). The next generation Cavity BPM was build with tighter tolerances and mechanical changes, the orthogonal coupling is measured to be lower than -43 dB. This report discusses the various observations, measurements and improvements which were done.
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.
Brunel University, Middlesex
Muon ionization cooling provides the only practical solution to prepare high brilliance beams necessary for a neutrino factory or muon colliders. The muon ionization cooling experiment (MICE) is under development at the Rutherford Appleton Laboratory (UK). It comprises a dedicated beam line to generate a range of input emittance and momentum, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. A fist measurement of emittance is performed in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in liquid hydrogen and RF acceleration. A second spectrometer identical to the first one and a particle identification system provide a measurement of the outgoing emittance. By April 2009 it is expected that the beam and first set of detectors will have been commissioned, and a first measurement of input beam emittance may be reported. Along with the plan of measurements of emittance and cooling that will follow in the second half of 2009 and in 2010.
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.
Soreq NRC, Yavne
ACCEL, Bergisch Gladbach
RI Research Instruments GmbH, Bergisch Gladbach
The first phase of the SARAF high current proton/deuteron accelerator facility is currently under commissioning. Along with traditional beam diagnostics instruments, a beam halo measuring station was implemented into the SARAF diagnostic plate. The beam halo is planned to be characterized using a mini Faraday cap, on-line and off-line measurements of radiation from LiF target crystals and by monitoring energy spectra of Rutherford scattered particles from a thin gold foil. The first experience with 3 mA, pulsed proton beam included measuring energy spectra of the protons at energies up to 2.2 MeV scattered at 45 degrees from a 0.3 mg/cm2 thick gold foil. The beam was accelerated by SARAF RFQ and by several cryogenic resonators in the SARAF Prototype Superconductive Module. The energy spectra of the scattered particles were taken for different RFQ voltages and for different voltages and phases of the PSM resonators. The results were compared with time of flight measurements utilizing two phase probes installed at the D-plate. Comparison of the experimental spectra with results of the TRACK Monte-Carlo simulations was also performed.
GSI, Darmstadt
TUD, Darmstadt
Most timing systems used for particle accelerators send their time or reference signals via optical single mode fibres embedded in cables. An important question for the design of such systems is how fast the delay changes in the fibre optic cable take place, subject to the variation of the ambient air temperature. If this information is known, an appropriate method for delay compensation can be chosen, to enable a phase stabilised transmission of the timing signals. This is of interest particularly with regard to RF synchronisation applications. To characterise the velocity of the delay change, the delay behaviour after a sudden temperature change will be described. When trying to determine the step response, two problems occur. On the one hand, the material parameter of the coating, necessary for the calculation, is typically unknown. On the other hand, the measurement of the step response under realistic conditions is very laborious. Thus in this presentation it will be shown how the step response and, accordingly, the velocity of the delay change in a fibre optic cable can be calculated by means of theoretical considerations, utilizing the typical geometry of fibre optic cables.
PSI, Villigen
This contribution gives an overview of transverse sub-micron beam position measurement systems and techniques for 3rd and 4th generation light sources and collider projects. Topics discussed include mechanical, electrical and digital design aspects, environmental influences, machine operation and design considerations, as well as system- and beam-based measurement and calibration techniques.
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.
DPNC, Genève
INFN-Napoli, Napoli
Muon ionization cooling provides the only practical solution to prepare high brilliance beams necessary for a neutrino factory or muon colliders. The muon ionization cooling experiment (MICE) is under development at the Rutherford Appleton Laboratory (UK). It comprises a dedicated beam line to generate a range of input emittance and momentum. The measurement of emittance is the subject of another contribution. This talk focuses on the particle identification devices, with three time-of-flight stations, Cherenkov detectors, a preshower device and a full absorption calorimeter. These devices ensure the purity of the muon sample separating off pions in the incoming beam upstream of the cooling cell and muon decay electrons downstream of the cooling cell. By April 2009 it is expected that the beam and first set of detectors will have been commissioned, and operation performance will be reported.
DESY, Hamburg
To exploit the short radiation pulses in pump-probe experiments at single-pass free-electron lasers (FELs), stabilization of the longitudinal profile and arrival time of the electron bunches is an essential prerequisite. Beam energy fluctuations, induced by the cavity field regulation in the accelerating modules, transform into an arrival time jitter in subsequent magnetic chicanes used for bunch compression due to the longitudinal dispersion. The development of beam based monitors is of particular importance for the validation and optimization of the cavity field regulation. In this paper we present bunch-resolved energy jitter measurements that have been recorded with a synchrotron radiation monitor at the Free-electron LASer in Hamburg (FLASH). The cavity field detectors of the accelerating module have been identified as the main source of the stochastical noise which corresponds to a beam energy jitter of 0.012%. The reduction of deterministic cavity field imperfections by applying an adaptive feedforward learning algorithm for the cavity field regulation is demonstrated.
INFN/LNF, Frascati (Roma)
The SPARC FEL facility is under commissioning at the Frascati National Laboratories of INFN. The synchronization system is working as expected and various devices are used to monitor its performances. In particular this paper is focused on a comparison between the results obtained using different methods and instruments to perform laser, RF and beam synchronization measurements. Both electro-optical and full electrical techniques are used to obtain information about the phase noise of the RF fields inside the accelerating structures, the phase noise of the IR laser oscillator, the time of arrival of the laser UV pulse on the cathode and the time of arrival of the accelerated electron bunch at a selected reference position along the linac.
ANL, Argonne, Illinois
This paper will give a general overview of active and passive stabilization systems, which are mainly required for future X-FEL and high energy linear colliders. Key physics requirements for beam stability for X-FELs and linear colliders will be introduced and resulting technical implications discussed. New and innovative approaches to the design and development of state-of-the-art linear accelerator components and stabilization systems will be reviewed, and recent results shown from selected prototypes and new machine installations.