Author: Pfeiffer, S.
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]  
THPPC077 Resonance Control of Superconducting Cavities at Heavy Beam Loading Conditions 3467
  • M.K. Grecki, S. Pfeiffer
    DESY, Hamburg, Germany
  Funding: The research leading to these results has received funding from the European Commission under the EuCARD FP7 Research Infrastructures grant agreement no. 227579
The SC cavities operated at high Q level need to be precisely tuned to the RF frequency*. Well tuned cavities assure the good field stability and require minimum level of RF power to reach the operating gradient level. The TESLA cavities at FLASH are tuned with the help of slow (step motors) and fast (piezo) tuners driven by the control system**. The goal of this control system is to keep the detuning of the cavity as close to zero as possible in the presence of disturbing effects (Lorentz force detuning and microphonics). The detuning of the cavity can be determined using a few measurement methods. The most common is to measure detuning from the phase derivative at the end of the RF pulse. In order to calculate the detuning during the whole RF pulse the cavity equation must be solved taking into account all the driving forces (RF power delivered to the cavity and beam contribution). This in not the trivial task, particularly in the heavy beam conditions, since all signals must be precisely calibrated. This work presents the methods and algorithms to evaluate and control the detuning of the superconducting cavities in the heavy beam loading conditions adequate for ILC operation.
* Grecki M., Piezo operation experience at FLASH, LLRF-2011, DESY, 09.2011
** Grecki M. et al. Piezo Control for Lorentz Force Detuned SC Cavities of DESY FLASH, IPAC'10, Kyoto, Japan, pp.1452-1454