Author: Schlarb, H.
Paper Title Page
MOOAA03 Fast Feedback Strategies for Longitudinal Beam Stabilization 26
  • S. Pfeiffer, M.K. Bock, H. Schlarb, Ch. Schmidt
    DESY, Hamburg, Germany
  • W. Jałmużna
    TUL-DMCS, Łódź, Poland
  • G. Lichtenberg, H. Werner
    TUHH, Hamburg, Germany
  The key for pump-probe and seeding experiments at Free Electron Lasers such as FLASH is a femtosecond precise regulation of the bunch arrival time and compression. To maintain this beam based requirements, both for a single bunch and within a bunch train, it is necessary to combine field and beam based feedback loops. We present in this paper an advancement of the currently implemented beam based feedback system at FLASH. The principle of beam based modulation of the RF set point can be superimposed by a direct feedback loop with a beam optimized controller. Recent measurements of the achieved bunch arrival time jitter reduction to 20 fs have shown the performance gain by this direct feedback method *. The combination of both approaches will be presented and possible advantages are discussed.
* C. Schmidt et al., “Feedback Strategies for Bunch Arrival Time Stabilization at FLASH Towards 10 fs,” FEL’2011, Shanghai, August 2011, THPA26, http://www.
slides icon Slides MOOAA03 [0.544 MB]  
MOOAC01 The European XFEL LLRF System 55
  • J. Branlard, G. Ayvazyan, V. Ayvazyan, M.K. Grecki, M. Hoffmann, T. Jeżyński, I.M. Kudla, T. Lamb, F. Ludwig, U. Mavrič, S. Pfeiffer, H. Schlarb, Ch. Schmidt, H.C. Weddig, B.Y. Yang
    DESY, Hamburg, Germany
  • P. Barmuta, S. Bou Habib, L. Butkowski, K. Czuba, M. Grzegrzółka, E. Janas, J. Piekarski, I. Rutkowski, D. Sikora, L. Zembala, M. Żukociński
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
  • W. Cichalewski, K. Gnidzińska, W. Jałmużna, D.R. Makowski, A. Mielczarek, A. Napieralski, P. Perek, A. Piotrowski, T. Pożniak, K.P. Przygoda
    TUL-DMCS, Łódź, Poland
  • S. Korolczuk, J. Szewiński
    The Andrzej Soltan Institute for Nuclear Studies, Centre Świerk, Świerk/Otwock, Poland
  • K. Oliwa, W. Wierba
    IFJ-PAN, Kraków, Poland
  The European X-ray free electron laser accelerator consists of 800 superconducting cavities grouped in 25 RF stations. The challenges associated with the size and complexity of this accelerator required a high-precision, modular and scalable low level RF (LLRF) system. TheμTCA technology (uTCA) was chosen to support this system and adapted for RF standards. State-of-the-art hardware development in close collaboration with the industry allowed for the system continuity and maintainability. The complete LLRF system design is now in its final phase and the designed hardware was installed and commissioned at FLASH. The uTCA hardware system, measurement results and system performance validation will be shown. Operational strategy and plans for future automation algorithms for performance optimization will also be presented in this paper.  
slides icon Slides MOOAC01 [12.188 MB]  
MOPPR016 Femtosecond Level Electron Bunch Diagnostic at Quasi – CW SRF Accelerators: Test Facility ELBE 810
  • M. Gensch, C. Kaya, U. Lehnert, P. Michel, Ch. Schneider, W. Seidel
    HZDR, Dresden, Germany
  • G. Geloni
    European XFEL GmbH, Hamburg, Germany
  • M. Helm
    FZD, Dresden, Germany
  • H. Schlarb, A. Shemmary, N. Stojanovic
    DESY, Hamburg, Germany
  Funding: BMBF through the PIDID proposal and HGF through the ARD initiative
At the srf based prototype cw accelerator ELBE a new electron beamline, providing for femtosecond electron bunches with nC bunch charges and repetition rates in the 1 – 200 KHz regime and with pC bunch charge and repetition rates of 13 MHz is currently constructed. The 40 MeV electrons will be used in photon-electron interaction experiments with TW and PW class laser and the generation of broad band and narrow bandwidth coherent THz pulses. In this paper we outline ideas for novel online diagnostics of the electron bunch properties (e.g. arrival time and bunch form) based on the time and frequency domain analysis of the emitted coherent THz radiation but also based on direct measurements by e.g. electro-optic sampling. The suitability of ELBE as a testbed for diagnostic of future cw X-ray photon sources (e.g. energy recovery linacs) will be discussed.
MOPPR017 Preliminary Measurement Results of the Upgraded Energy BPM at FLASH 813
  • U. Mavrič, M. Felber, C. Gerth, H. Schlarb
    DESY, Hamburg, Germany
  • W. Jałmużna, A. Piotrowski
    TUL-DMCS, Łódź, Poland
  The energy beam position monitor in the dispersive section of the two bunch compressors is a valuable instrument for regular operation of FLASH. Recently, an upgrade of the existing instrument to a uTCA form factor has been started. The basic principle of the time-of-flight measurement will remain the same, however the detection of the phases and amplitudes of two pulses has been moved to the programmable gate array. Other changes include different RF frequencies of detection, optimization of the front-end section and integration into the control system. A preliminary version of the system has been tested at FLASH and the results are presented in the paper.  
TUPPP053 Investigations on the Optimum Accelerator Parameters for the Ultra-Short Bunch Operation of the Free-Electron Laser in Hamburg (FLASH) 1718
  • M. Rehders, J. Rönsch-Schulenburg, J. Roßbach
    Uni HH, Hamburg, Germany
  • T. Limberg, H. Schlarb, S. Schreiber
    DESY, Hamburg, Germany
  Funding: The project is supported by the Federal Ministry of Education and Research of Germany (BMBF) under contract No. 05K10GU2 and FSP301.
In order to produce the shortest possible radiation pulses using Free Electron Lasers like FLASH, various possibilities have been proposed during the last decade. Probably the most robust method is the generation of electron bunches that in the most extreme case are as short as a single longitudinal optical mode of the SASE (Self-Amplified Spontaneous Emission) radiation. For FLASH this means that the bunch length has to be a few fs only. As a consequence, very low bunch charges (in the order of 20 pC) have to be used. To achieve these extremely short bunch lengths, a new photo-injector laser has been installed, which allows for the generation of shorter electron bunches right at the cathode. Simulations of the electron bunches and their six-dimensional phase-space distribution have been performed to investigate the optimum accelerator parameters during injection and to determine how to realize them. First results are discussed in this contribution.
WEPPD048 Laser Synchronization at REGAE using Phase Detection at an Intermediate Frequency 2624
  • M. Felber, M. Hoffmann, U. Mavrič, H. Schlarb, S. Schulz
    DESY, Hamburg, Germany
  • W. Jałmużna
    TUL-DMCS, Łódź, Poland
  A new linear accelerator is being set up for electron diffraction experiments at DESY. This machine, called REGAE (Relativistic Electron Gun for Atomic Exploration) is composed of a photo-cathode gun and a buncher cavity. It uses a single laser system for both, the generation of the electron bunches and for pump-probe experiments. The required timing jitter between the electron bunches and the laser pulses at the experiment is in the order of 10 fs rms. The conventional method for laser synchronization using RF technique to measure phase-jitter in the baseband is susceptible to distortions caused by ground-loops and electro-magnetic interference. At REGAE a new scheme for an RF-based laser synchronization is deployed. It uses a down-converter which mixes a higher harmonic of the laser repetition rate down to an intermediate frequency (IF). The IF is digitized and its phase calculated. This information is used for the feedback controller keeping the laser and the RF synchronized.  
WEPPD049 Characterization of the Engineered Photodiode-based Fiber Link Stabilization Scheme for Optical Synchronization Systems 2627
  • T. Lamb, M.K. Bock, M. Felber, F. Ludwig, H. Schlarb, S. Schulz
    DESY, Hamburg, Germany
  • S. Jabłoński
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
  Pulsed optical synchronization systems are used in modern FELs like FLASH and will be used in the upcoming European XFEL. Their purpose is to distribute synchronization signals with femtosecond stability throughout the machine. Optical fibers are used to transport the pulses carrying the timing information to their end-stations. These fibers have to be continuously delay stabilized in order to achieve the desired precision. In this paper, a photodiode-based detector to measure the drifts of the fiber delay and allows their active correction is presented. Promising results from a first prototype setup of a photodiode-stabilized optical fiber link were the starting point for an engineering of this concept. An enclosure with free-space optics, fiber optics and integrated electronics for the detector, operating at 9.75 GHz, was designed. This unit includes all required parts to stabilize four fiber links. It allows to investigate the temperature sensitivity of the detector. Furthermore, results from drift measurements carried out with a two channel engineered detector are presented in this paper.  
THEPPB014 LLRF Testing of Superconducting Cryomodules for the European XFEL 3263
  • J. Branlard, V. Ayvazyan, T. Jeżyński, H. Schlarb
    DESY, Hamburg, Germany
  • W. Cichalewski, W. Jałmużna, A. Piotrowski
    TUL-DMCS, Łódź, Poland
  During the installation phase of the European XFEL (2014), an average of one superconducting cryomodule per week will be tested and validated before being installed into the XFEL tunnel. Extensive tests will be carried in order to assess the RF performance of each cryomodule. A series of low level RF (LLRF) tests are planned as part of this validation phase, and will assess the cryomodule effective operating gradient, tuning range, compensation of Lorentz force detuning and microphonic behavior. These tests will be carried at DESY, in the Cryomodule Test Bench (CMTB) during the early stage of cryomodule production, and later at the Accelerating Module Test Facility (AMTF). Due to the pace and quantity of the modules to be tested, these tests have to be fully automated. This contribution presents the LLRF tests for the XFEL cryomodule validation, the challenges associated with automation, along with the first experimental results obtained on pre-series cryomodules tested at CMTB.