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Schmidt, B.

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MOPD090 Upgrade and Evaluation of the Bunch Compression Monitor at the Free-electron Laser in Hamburg (FLASH) 912
 
  • C. Behrens, B. Schmidt, S. Wesch
    DESY, Hamburg
  • D. Nicoletti
    Università di Roma I La Sapienza, Roma
 
 

The control and stabilization of RF systems for accelerators has a considerable importance. In case of high-gain free-electron lasers (FEL) with magnetic bunch compressors, the RF phases determine the attainable bunch peak current, which is a relevant parameter for driving the FEL process. In order to measure the bunch peak current in a simple and fast but indirect way, both bunch compressors at FLASH are equipped with compression monitors (BCM) based on pyroelectrical detectors and diffraction radiators (CDR). They provide substantial information to tune the bunch compression and are used for beam-based feedback to stabilize RF phases. This monitor system becomes more important and more challenging after the installation of a third-harmonic RF system for longitudinal phase space linearization in front of the first bunch compressor. In this paper, we describe the hardware upgrade of the bunch compression monitor and show the expected performance by simulations of the CDR source and the radiation transport optics. Particle tracking simulations are used for generation of the simulated BCM-signal for various compression schemes. Comparison with experimental data will be presented.

 
WEOCMH02 Recent Developments of the Beam Arrival Time Monitor with Femtosecond Resolution at FLASH 2405
 
  • M.K. Bock, M. Felber, P. Gessler, K.E. Hacker, F. Ludwig, H. Schlarb, B. Schmidt, J. Zemella
    DESY, Hamburg
  • F. Löhl
    CLASSE, Ithaca, New York
  • S. Schulz, L.-G. Wißmann
    Uni HH, Hamburg
 
 

At FLASH an optical synchronisation system with femtosecond stability is now being installed and commissioned. The system is based on pulses from a passively modelocked fibre laser which are distributed in length-stabilised fibres to various end-stations. Several modifications and improvements with respect to the original layout, especially concerning permanent operation and reliability, are already incorporated at this stage. The electron bunch arrival-time monitors (BAM), based on electro-optical modulation, are an integral part of the system. Built on the experiences with first prototypes, the most recent version of the BAM, installed prior to the first bunch compressor, includes essential changes affecting the optical layout, the mechanical and thermal stability as well as the electronics for read-out and controls. The revised BAM showed improved performance and will be complemented by a second congenerous BAM after the first bunch compressor during the present FLASH upgrade. The experiences with installation as well as the scope of improvements as to simplification and long-term stability will be presented.

 

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WEPEB076 Precision Synchronization of the FLASH Photoinjector Laser 2875
 
  • S. Schulz, L.-G. Wißmann
    Uni HH, Hamburg
  • V. R. Arsov
    PSI, Villigen
  • M.K. Bock, M. Felber, P. Gessler, K.E. Hacker, F. Ludwig, H. Schlarb, B. Schmidt, J. Zemella
    DESY, Hamburg
 
 

After its upgrade, the free-electron laser in Hamburg (FLASH) will start operating with an exchanged RF-gun driven by an improved photoinjector laser. Since the SASE FEL process is very sensitive to the RF gun phase it is highly desirable to implement phase stabilization feedback, which, in turn, requires an arrival-time stabilization of the photoinjector laser pulses. In this paper we report on the synchronization of the photoinjector laser system to the optical timing reference using an optical cross-correlation scheme. This enables not only the measurement of the timing jitter, but also the stabilization using adaptive feed-forward algorithms acting on an EOM incorporated in the laser's pulse train oscillator. First results from the commissioning and future plans for a feedback system are discussed.