| Paper |
Title |
Page |
| MOPCH011 |
Jitter Measurement by Spatial Electro-optical Sampling at the Flash Free Electron Laser
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71 |
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- A. Azima, S. Düsterer, J. Feldhaus, H. Schlarb
DESY, Hamburg
- A.L. Cavalieri
MPQ, Garching, Munich
- D. Fritz
Michigan University, Ann Arbor, Michigan
- K. Sengstock
Uni HH, Hamburg
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For pump-probe experiments carried out at the VUV-FEL at DESY, FEL laser pulses with 32 nm wavelength have to be synchronized with high precision to optical laser pulses generated by a TiSa oscillator. To measure the relative timing variations between the FEL and the optical laser, an electro-optical experiment to determine the electron beam arrival time at the undulator has been installed. Here, the electron beam profile is encoded spatially into the laser pulse and readout by an intensified camera. A similar experimental setup has been successfully used at the sub-picosecond pulsed source (SPPS) at higher charge and shorter rms bunch length. In this paper, we report about the achievements and difficulties of the Timing Electro-Optical (TEO) setup, that allows to post-order experimental user data with a precision of 100 fs rms and better.
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| MOPCH012 |
FEL Disturbance by Ambient Magnetic Field Changes
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74 |
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- H. Kapitza, P. Göttlicher, N. Heidbrook, H. Schlarb
DESY, Hamburg
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The VUV-FEL at DESY in Hamburg (Germany) is mostly located inside the circular accelerator PETRA which serves as an injector for the electron proton collider HERA. SASE was regularly lost in the VUV-FEL when protons were ramped to the injection energy in PETRA. This effect was mediated by magnetic field changes in the order of 1 microtesla, caused by time-dependent uncompensated magnet currents of more than 800 A which made PETRA act like a large current loop. The resulting beam displacements of several hundred micrometers in the undulators proved to be enough to make SASE fail. This serious disturbance of user runs was eliminated by introducing an improved compensation scheme which further limits residual currents in PETRA during proton injection. The consequences of this observation for the design of the XFEL are briefly discussed.
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| MOPCH013 |
Slice Emittance Measurements at FLASH
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77 |
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- M. Roehrs, C. Gerth, M. Huening, H. Schlarb
DESY, Hamburg
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The SASE process in Free Electron Lasers mainly depends on time-sliced parameters of charge density, energy spread and transverse emittance. At the VUV-FEL at DESY, electron bunches are compressed longitudinally in two magnetic chicanes in order to achieve high peak currents. The compression causes considerabe variations in slice emittance along the bunches. The vertically deflecting rf-structure LOLA, which is in operation at the VUV-FEL since early 2005, allows to resolve longitudinal variations in horizontal slice width for single bunches. The horizontal slice emittances can be determined by additionally varying the strengths of the quadrupoles upstream of LOLA. Results of slice emittance measurements using different bunch compression schemes are presented.
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| MOPCH014 |
Energy-time Correlation Measurements Using a Vertically Deflecting RF Structure
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80 |
| |
- M. Roehrs, C. Gerth, M. Huening, H. Schlarb
DESY, Hamburg
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To initiate the lasing process in SASE-based Free Electron Lasers, electron bunches with high peak currents are necessary. At the VUV-FEL at DESY, high peak currents are produced by bunch shortening in magnetic chicanes induced by a linear energy-time gradient. The residual uncorrelated time-sliced energy width after compression is a crucial parameter for the lasing process. The final energy-time correlation provides important information about the compression process. This paper presents a measurement of slice energy spread and energy-time correlation using a vertically deflecting rf-structure (LOLA). The structure allows to map the time delay of bunch slices to the vertical axis of a screen. After dispersing the bunches horizontally with a dipole, the energy-time correlation can be directly obtained in a single shot measurement. Results for different bunch compression schemes are presented. The measured bunch length in case of a non-compressed beam is compared to streak camera measurements.
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| MOPCH016 |
Bunch Compression Monitor
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86 |
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- H. Delsim-Hashemi, J. Rossbach, P. Schmüser
Uni HH, Hamburg
- O. Grimm, H. Schlarb, B. Schmidt
DESY, Hamburg
- A.F.G. van der Meer
FOM Rijnhuizen, Nieuwegein
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An accelerated bunch of electrons radiates coherently at wavelengths longer than or comparable to the bunch length. The first generation Bunch Compression Monitor (BCM) that is installed at the VUV-FEL applies this principle by measuring the total radiation intensity. For a better control on the degree of the compression, the radiated intensity in different bandwidth can be used. Dependent on the changes in the structure of the bunch, its radiation spectrum changes correspondingly. A new generation BCM uses wavelength dependent diffracting devices and multi-channel sensors to measure the signal in different wavelength channels simultaneously. This paper describes the construction of the first prototypes and experimental results in different short wavelength bands measured at the linac of the VUV-FEL at DESY, Hamburg.
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| TUPCH022 |
Large Horizontal Aperture BPM for use in Dispersive Sections of Magnetic Chicanes
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1043 |
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- K.E. Hacker, H. Schlarb
DESY, Hamburg
- F. Loehl
Uni HH, Hamburg
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A beam position monitor with a large horizontal aperture for use in dispersive sections of FLASH magnetic chicanes will be installed in October 2006. It has a horizontal range of 13 cm and a resolution requirement of better than 10 microns. A stripline design mounted perpendicularly to the the electron beam direction is used to provide broadband electrical pulses traveling in opposite directions, the phases of which give a measure of the beam position. The phase measurement will be accomplished through an optical method developed for a beam arrival time monitor. Results from simulation and recent beam arrival-time measurements will be used to justify expectations for the BPM performance.
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| TUPCH024 |
Comparative Study of Bunch Length and Arrival Time Measurements at FLASH
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1049 |
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- H. Schlarb, A. Azima, S. Düsterer, M. Huening, E.-A. Knabbe, M. Roehrs, R. Rybnikov, B. Schmidt, B. Steffen
DESY, Hamburg
- M.C. Ross
SLAC, Menlo Park, California
- P. Schmüser, A. Winter
Uni HH, Hamburg
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Diagnostic devices to precisely measure the longitudinal electron beam profile and the bunch arrival time require elaborate new instrumentation techniques. At the VUV-FEL, two entirely different methods are used. The bunch profile can be determined with high precision by a transverse deflecting RF structure. The method is disruptive and does not allow to monitor multiple bunches in a macro-pulse train. Therefore, it is augmented by two non-disruptive electro-optical devices, called EO and TEO. The EO setup uses a dedicated diagnostic laser synchronized to the machine RF. The longitudinal electron beam profile is encoded in the intensity profile of a chirped laser pulse and analyzed by looking at the spectral composition of the pulse. The second setup, TEO, utilizes the TiSa-based laser system used for pump-probe experiments. Here, the temporal electron shape is encoded into a spatial dimension of laser pulse by an intersection angle between the laser and the electron beam at the EO-crystal. In this paper, we present a comparative study of bunch length and arrival time measurements performed simultaneously with all three experimental techniques.
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| TUPCH025 |
Precision RF Gun Phase Monitor System for the VUV-FEL
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1052 |
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- H. Schlarb, N. Heidbrook, H. Kapitza, F. Ludwig, N. Nagad
DESY, Hamburg
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For RF photo-injectors, the properties of the high brightness beam critically depend on the synchronization between the RF gun acceleration phase and the photo-cathode laser. At the VUV-FEL, the phase stability is determined by operating the RF gun close to zero-crossing RF phase. This allows the conversion of phase variations into charge variations which then is readout by a precision charge measurement system based on toroids. In this paper, we discuss the limitation of this method. Resolution reduction of the charge measurement system due to electro-magnetic-interference is discussed in detail.
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| TUPCH028 |
Layout of the Optical Synchronization System for FLASH
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1061 |
| |
- A. Winter, P. Schmüser, A. Winter
Uni HH, Hamburg
- F. Loehl, F. Ludwig, H. Schlarb, B. Schmidt
DESY, Hamburg
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The present RF synchronization system of the VUV-FEL can typically stabilize the arrival time of the electron bunches at the undulator to about 200 fs on a timescale of minutes and to several picoseconds on a timescale of hours. To improve the machine stability and to ensure optimal performance for the VUV-FEL user facility, a new ultra-precise timing system is mandatory. The optical synchronization system under construction will satisfy three goals: Firstly, it provides a local oscillator frequency with the same stability as the existing low-level RF regulation, secondly, it can synchronize the experimental lasers of the FEL users with a precision in the order of 30 fs, thirdly, it provides an ultra-stable reference for beam arrival time measurements and enables a feedback on the electron beam to compensate residual drifts and timing jitter. The optical synchronization system is based on an optical pulse train from a mode-locked laser with a highly stabilized repetition rate. This paper describes the proposed layout of the optical synchronization system, the integration into the machine layout and the diagnostic experiments to monitor the performance of the system.
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| TUPCH029 |
High-precision Laser Master Oscillators for Optical Timing Distribution Systems in Future Light Sources
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1064 |
| |
- A. Winter, P. Schmüser, A. Winter
Uni HH, Hamburg
- J. Chen, F.X. Kaertner
MIT, Cambridge, Massachusetts
- F.O. Ilday
Bilkent University, Bilkent, Ankara
- F. Ludwig, H. Schlarb
DESY, Hamburg
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X-ray pulses with a pulse duration in the 10 fs regime or even less are needed for numerous experiments planned at next generation free electron lasers. A synchronization of probe laser pulses to the x-ray pulses with a stability on the order of the pulse width is highly desirable for these experiments. This requirement can be fulfilled by distributing an ultra-stable timing signal to various subsystems of the machine and to the experimental area to provide synchronization at the fs level over distances of several kilometers. Mode-locked fiber lasers serve as laser master oscillators (LMO), generating the frequencies required in the machine. The pulse train is distributed through length-stabilized fiber links. This paper focuses on the LMO, devoting special attention to the phase noise properties of the frequencies to be generated, its reliability to operate in an accelerator environment, and the residual timing jitter and drifts of the RF feedback for the fiber links. A prototype experimental system has been constructed and tested in an accelerator environment and its performance characteristics will be evaluated.
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| TUPCH081 |
Technical Aspects of the Integration of the Optical Replica Synthesizer for the Diagnostics of Ultra-short Bunches in FLASH at DESY
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1199 |
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- V.G. Ziemann
UU/ISV, Uppsala
- N.X. Javahiraly, P. van der Meulen
FYSIKUM, AlbaNova, Stockholm University, Stockholm
- M. Larsson
Stockholm University, Department of Physics, Stockholm
- E. Saldin, H. Schlarb, E. Schneidmiller, A. Winter, M.V. Yurkov
DESY, Hamburg
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In this paper we present an overview of current status of the Optical Replica synthesizer at DESY. The method is based on producing an "optical copy" of the electron bunch with its subsequent analysis with optical techniques*. To this end, a near-IR laser beam is superimposed on the electron beam in the first undulator of an optical klystron. In the following dispersive section the laser-induced energy modulation is transformed into a density modulation . The modulated electron bunch then produces a strong optical pulse in the second undulator. Analysis of this near-IR pulse (the optical copy) then provides information about the profile, the slice emittance and the slice energy spread of the electron bunch. We discuss the implementation of such a measurement set-up at the FLASH facility at DESY and investigate the influence of various parameters on the performance of the device. Topics we address include the dispersive chicane, as well as the requirements for the seed laser pulses and the detection and analysis of the near-IR pulse.
*E. Saldin, et al. "A simple method for the determination of the structure of ultrashort relativistic electron bunches," Nucl. Inst. and Methods A 539 (2005) 499.
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| TUPCH188 |
Phase Stability of the Next Generation RF Field Control for VUV- and X-ray Free Electron Laser
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1453 |
| |
- F. Ludwig, M. Hoffmann, H. Schlarb, S. Simrock
DESY, Hamburg
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For pump and probe experiments at VUV- and X-ray free electron lasers the stability of the electron beam and timing reference must be guaranteed in phase for the injector and bunch compression section within a resolution of 0.01 degree (rms) and in amplitude within 1 10-4 (rms). The performance of the field detection and regulation of the acceleration RF directly influences the phase and amplitude stability. In this paper we present the phase noise budget for a RF-regulation system including the noise characterization of all subcomponents, in detail down-converter, ADC sampling, vector-modulator, master oscillator and klystron. We study the amplitude to phase noise conversion for a detuned cavity. In addition we investigate the beam jitter induced by these noise sources within the regulation and determine the optimal controller gain. We acknowledge financial support by DESY Hamburg and the EUROFEL project.
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| THXPA03 |
Laser Systems and Accelerators
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2728 |
| |
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The presentation will cover the use of laser systems in accelerators. Topics covered will be the use of lasers for the production of electron beam from photocathodes, timing and diagnostics, laser heater systems to control space charge effects, as seed systems. Challenges in terms of stability, pulse shaping, power and pulse lengths, wavelength range and tuning will be covered for the various aspects.
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Transparencies
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| THOPA03 |
An Integrated Femtosecond Timing Distribution System for XFELs
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2744 |
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- J. Kim, J. Burnham, dc. Cheever, J. Chen, F.X. Kaertner
MIT, Cambridge, Massachusetts
- M. Ferianis
ELETTRA, Basovizza, Trieste
- F.O. Ilday
Bilkent University, Bilkent, Ankara
- F. Ludwig, H. Schlarb, A. Winter
DESY, Hamburg
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Tightly synchronized lasers and rf-systems with timing jitter in the few femtoseconds range are an important component of future x-ray free electron laser facilities. In this paper, we present an optical-rf phase detector that is capable of extracting an rf-signal from an optical pulse stream without amplitude-to-phase conversion. Extraction of a microwave signal with less than 10 fs timing jitter (from 1 Hz to 10 MHz) from an optical pulse stream is demonstrated. Scaling of this component to sub-femtosecond resolution is discussed. Together with low noise mode-locked lasers, timing-stabilized optical fiber links and compact optical cross-correlators, a flexible femtosecond timing distribution system with potentially sub-10 fs precision over distances of a few kilometres can be constructed. Experimental results on both synchronized rf and laser sources will be presented.
*A. Winter et al. "Synchronization of Femtosecond Pulses", Proceedings of FEL 2005.**J. Kim et al. "Large-Scale Timing Distribution and RF-Synchronization for FEL Facilities", Proc. of FEL 2004.
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Transparencies
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| THPPA01 |
High-precision Laser Master Oscillators for Optical Timing Distribution Systems in Future Light Sources
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2747 |
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- A. Winter, P. Schmüser, A. Winter
Uni HH, Hamburg
- J. Chen, F.X. Kaertner
MIT, Cambridge, Massachusetts
- F.O. Ilday
Bilkent University, Bilkent, Ankara
- F. Ludwig, H. Schlarb
DESY, Hamburg
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Abstract to be supplied
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Transparencies
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| THOBFI01 |
A Sub 100 fs Electron Bunch Arrival-time Monitor System for FLASH
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2781 |
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- F. Loehl, K.E. Hacker, F. Ludwig, H. Schlarb, B. Schmidt
DESY, Hamburg
- A. Winter
Uni HH, Hamburg
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The stability of free-electron lasers and experiments carried out in pump-probe configurations depends sensitively on precise synchronization between the photo-injector laser, low-level RF-systems, probe lasers, and other components in the FEL. A measurement of the jitter in the arrival-time of the electron bunch with respect to the clock signal of a master oscillator is, therefore, of special importance. For this task, we propose an arrival-time monitor based on a beam pick-up with more than 10GHz bandwidth which permits measurements in the sub 100 fs regime. The RF-signal from the beam pick-up is sampled by an ultra-short laser pulse using a broad-band electro-optical modulator. The modulator converts the electron bunch arrival-time jitter into an amplitude modulation of the laser pulse. This modulation is detected by a photo detector and sampled by a fast ADC. By directly using the laser pulses from the master laser oscillator of the machine, any additional timing jitter is avoided. In this paper we present the layout of the system and first experimental results.
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Transparencies
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