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Schlarb, H.

Paper Title Page
MOOBAB01 Time-Resolved Phase Space Tomography at Flash Using a Transverse Deflecting RF-Structure 104
  • M. Roehrs, C. Gerth, H. Schlarb
    DESY, Hamburg
  To initiate Self-Amplification of Spontaneous Emission (SASE) in single-pass Free Electron Lasers (FEL), electron bunches with high peak current and small slice emittance and energy spread are necessary. At FLASH at DESY, this is accomplished by longitudinal bunch compression in two magnetic chicanes. The compression process may be accompanied by distortions from coherent synchrotron radiation and space charge forces. Their effect on the bunch properties can be studied with a vertically deflecting rf-structure (LOLA), which allows to measure the longitudinal phase space distribution and horizontal slice emittance of single bunches. In combination with tomographic methods the horizontal phase space distribution of time slices can be reconstructed. In this paper measurement results for SASE operation are presented and compared to simulations and bunch properties infered from the radiation signal.  
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MOPAN017 Noise and drift characterization of direct laser to RF conversion scheme for the laser based synchronization system for FLASH at DESY 182
  • F. Ludwig, B. Lorbeer, H. Schlarb, A. Winter
    DESY, Hamburg
  Funding: This contribution is funded by the EUROFEL project.

The next generation of FEL's (Free Electron Lasers) require a long and short term stable synchronisation of RF reference signals with an accuracy of 10 fs. For that an optical synchronisation system is developed for FLASH at DESY, that is based on optical pulse train which carry the timing information encoded in its precise repetition rate. The optical pulse train has to be converted into an RF signal to provide a local reference for calibration and operation of RF based devices. The drift and jitter performance of the optical to RF converter influences directly the phase stability of the accelerator. Three different methods for optical to RF converters, namely the direct photodiode detection, injection locking and a sagnac loop interferometer are currently under investigation. In this paper we concentrate on the jitter and drift performance of the direct photodiode conversion and show its limitations from measurement results.

MOPAN020 Status of the Laser Master Oscillator System at FLASH 191
  • A. Winter, F. Loehl, H. Schlarb, P. Schmuser
    DESY, Hamburg
  • W. J. Jalmuzna
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw
  An optical synchronization system based on the timing-stabilized distribution of ultra-short optical pulses has been proposed for next generation light sources, e.g. the European XFEL. The concept will be implemented and tested at FLASH at DESY. This paper describes the status of the optical master oscillator, which consists of two mode-locked Erbium-doped fiber lasers running in parallel.  
TUPMN023 Status of the Optical Replica Synthesizer at FLASH 965
  • S. Khan, J. Boedewadt, A. Winter
    Uni HH, Hamburg
  • G. Angelova, V. G. Ziemann
    UU/ISV, Uppsala
  • M. Hamberg, N. X. Javahiraly, M. Larsson, P. Salen, P. van der Meulen
    FYSIKUM, AlbaNova, Stockholm University, Stockholm
  • A. Meseck
    BESSY GmbH, Berlin
  • E. Saldin, H. Schlarb, B. Schmidt, E. Schneidmiller, M. V. Yurkov
    DESY, Hamburg
  A novel laser-based method to measure the longitudinal profile of ultrashort electron bunches, known as Optical Replica Synthesizer*, will be implemented at the free-electron laser FLASH at DESY. The paper describes its technical layout and the status of the project.

* E. Saldin, E. Schneidmiller, M. Yurkov, NIM A 539 (2005), 499

WEPMN011 Multichannel Downconverter for the Next Generation RF Field Control for VUV- and X-Ray Free Electron Lasers 2071
  • M. Hoffmann, F. Ludwig, H. Schlarb, S. Simrock
    DESY, Hamburg
  Funding: We acknowledge financial support by DESY Hamburg and the EUROFEL project.

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 critically influences the phase and amplitude stability. For the RF field control, a multichannel RF downconverter is used to detect the field vectors and control the vectorsum of 32 cavities. In this paper a new design of an 8 channel downconverter is presented. The downconverter frontend consists of a passive rf double balanced mixer input stage, intermediate filters and an integrated 16bit analog-to-digital converter (ADC). The design includes a digital motherboard for data preprocessing and communication with the controller. In addition we characterize the downconverter performance in amplitude and phase jitter, temperature drifts and channel crosstalk in laboratory environment as well as for accelerator operation.

WEPMN012 Beam Loading Compensation Using Real Time Bunch Charge Information from a Toroid Monitor at FLASH 2074
  • E. Vogel, C. Gerth, W. Koprek, F. Loehl, D. Noelle, H. Schlarb, T. Traber
    DESY, Hamburg
  Funding: Deutsches Elektronen-Synchrotron - DESY

At pulsed linear accelerators, fast proportional rf control compensates beam loading sufficiently for single or a few bunches. In the case of long bunch trains, additional measures have to be taken commonly by adding a compensation signal to the rf drive signals calculated from the predicted beam intensity. In contrast to predictive methods, techniques based on real time beam measurements are sensitive to fast changes of the beam intensity and bunch patterns. At FLASH we apply a beam loading compensation scheme based on toroid monitor signals. This paper presents the compensation scheme, the calibration procedure and the effect on the beam.

FROAC04 Sub-10 Femtosecond Stabilization of a Fiber Link Using a Balanced Optical Cross Correlator 3804
  • F. Loehl, H. Schlarb
    DESY, Hamburg
  • J. Chen, F. X. Kaertner, J. Kim, F. Wong
    MIT, Cambridge, Massachusetts
  • J. M. Mueller
    TUHH, Hamburg
  Synchronization of various components with fs stability is needed for the operation of free-electron-lasers such as FLASH or the European XFEL. One possibility to realize a high precision synchronization is to use a mode-locked Er-doped fiber laser as a master clock and to distribute ultra short laser pulses inside the machine using actively stabilized fiber links. In this paper we demonstrate the stabilization of a 300 m long fiber link with a self-aligned balanced cross-correlator using a single type II phase-matched PPKTP crystal. This approach allowed us to reduce the timing jitter added by the link to below 10 fs.  
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