• N. Pupeter, B. Aminov, F. Aminova, A. Borisov, M. Getta, W. Jalmuzna, T. Jezynski, S. Kolesov, H. Piel, D. Wehler
  CRE, Wuppertal
• F. Ludwig, S. Simrock
  DESY, Hamburg

For future applications in Light Sources and Large Scale Linear Accelerators we have developed a fully digital LLRF system which overcomes the intrinsic problems of analogue and semi digital LLRF systems by realizing all functions in the high speed cores of FPGAs. Due to its modular design using either the ATCA or the VME form factor the LLRF system can be configured conveniently according to the specific requirements of the accelerator to control the rf field in individual resonators or in a combination of cavities. The LLRF input stage can be custom designed for rf frequencies of up to 3.9 GHz. The hardware and software architectures of the Cryoelectra digital LLRF control system are presented.

• M. Felber, V.R. Arsov, M.K. Bock, P. Gessler, K.E. Hacker, F. Löhl, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt, A. Winter
  DESY, Hamburg
• S. Schulz, L.-G. Wißmann, J. Zemella
  Uni HH, Hamburg

Next generation FEL light sources like the European XFEL require timing stability between different subsystems of 10^-20 fs. In optical synchronization systems, the timing information is distributed across the facilities via sub-ps laser pulses travelling on length stabilized optical fibers. Different methods are available for RF extraction from the pulse train. In this paper, we characterize the long-term phase stability of a 1.3 GHz signal gained from the direct conversion of a higher harmonic of the pulse repetition frequency, and from a voltage controlled oscillator locked with a PLL that uses a Sagnac-Loop as balanced optical-microwave phase detector.

• S. Schulz, L.-G. Wißmann, J. Zemella
  Uni HH, Hamburg
• V.R. Arsov
  PSI, Villigen
• M.K. Bock, M. Felber, P. Gessler, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt
  DESY, Hamburg
• F. Löhl
  CLASSE, Ithaca, New York
• A. Winter
  ITER, St Paul lez Durance

The free-electron laser FLASH and the planned European XFEL generate X-ray light pulses on the femtosecond time-scale. The feasibility of time-resolved pump-probe experiments, special diagnostic measurements and future operation modes by means of laser seeding crucially depend on the long-term stability of the synchronization of various laser systems across the facility. For this purpose an optical synchronization system is being installed and tested at FLASH. In this paper, we report on the development and the performance of a background-free optical cross-correlation scheme to synchronize two individual mode-locked lasers of different center wavelengths and repetition rates with an accuracy of better than 10 fs. The scheme can be tested by linking a Ti:sapphire oscillator, used for electro-optical diagnostics at FLASH, to both a locally installed erbium-doped fiber laser and the end-point of an actively length-stabilized fiber link distributing the pulses from a master laser oscillator. After the commissioning of this fiber link, the diagnostics laser can be synchronized to the electron beam and first accelerator based measurements on the performance of the system will be carried out.