RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
Stable SASE FEL has been routinely used for user experiments since May 2008 at the SCSS test accelerator, which was constructed to perform a proof-of-principle experiment towards realization of a compact and high performance XFEL facility. In FY2008, a beam time of 840 hr (95 days) was provided to 11 research groups with a downtime rate of ~4%, a pulse energy of ~30μJ and an intensity fluctuation of ~10% in STD. A feature of our stable operation is power-saturated SASE FEL kept over a full operation period
- in spite of a day-by-day operation,
- without a complicated beam feedback control, and
- without hard maintenance.
ASCo, Clayton, Victoria
Argonne National Laboratory, Office of Naval Research Project, Argonne
Monash University, Faculty of Science, Monash University
SLAC, Menlo Park, California
This paper describes the implementation of a neural network hybrid controller for energy and bunch length stabilization. The structure of the controller consists of a neural network (NNET) feed forward control, augmented by a conventional Proportional-Integral (PI) feedback controller to ensure stability of the system. The system is provided with past states of the machine in order to predict its future state, and therefore apply appropriate feed forward control. Experiments performed at the Australian Synchrotron showed the ability of the NNET to cancel multiple frequency energy jitter and the successful augmentation of the system by a PI algorithm. The LCLS experiments showed that the system can be expended to predict and correct coupled energy-bunch length deviations, and showed the improved jitter attenuation by the NNET system in comparison to the PI algorithm alone. Focus is also made on the machine response that needs to be accurately known to best operate the correction. When machine settings are modified, the response is re-calculated with the help of a model, and slight adjustments are made to optimize the energy jitter reduction as the control is operating.
University of Ljubljana, Faculty of Electrical Engineering, Ljubljana
I-Tech, Solkan
ELETTRA, Basovizza
This paper presents a good solution for timing distribution and RF synchronization of multiple events at multiple remote locations in the accelerator facility with femtosecond precision. The proposed electro-optical synchronization system makes use of commercial telecom single-mode optical fibre operating at 1550 nm. Such fibre is subject to change in phase and group velocity correlated to temperature variations and is sensitive to acoustic perturbations. The synchronization system described makes use of stabilization of the fibre link which transports low-jitter microwave signal over a distance of 300 m. It consists of a transmitter, located at the place of low-jitter master oscillator, and receiver, located at the remote location. Both units are connected by a pair of optical single-mode fibres. Using a fibre pair instead of a single fibre allows for compensation of fibre-length changes. The added timing jitter of 20 fs at 100 Hz - 20 MHz is measured on the first experimental synchronization system. Even lower jitter is expected by some planned improvements in the transfer system and the industrialization of it.
STFC/RAL, Chilton, Didcot, Oxon
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
University of Dundee, Nethergate, Dundee, Scotland
The NLS project team is designing a UK-based ultrashort light pulse facility covering the whole spectrum from the terahertz to the soft X-ray. It will be based on a suite of sources including seeded FELs, conventional lasers and undulators. Experiments will frequently be multi-beam and will often depend on precise management of the pulse timings. With pulse durations of ~20fs or less the aim will be to reduce timing jitter to the 10-20fs level. In addition to the needs of the NLS’s users, stable operation of the machine itself will also require adequate timing control. In particular reproducible FEL operation will depend on good temporal overlap between the seed photons and the electron bunches. This paper covers both the underlying issues, (e.g. choice of pulse rates, passive and active timing management, requirements specification) and also the approaches taken in specific NLS areas (e.g. choice of clock and distribution system, management of electron bunch timing, management of fluctuations in beam transport paths). An overall jitter budget is presented.
DESY, Hamburg
Uni HH, Hamburg
At the Free-Electron Laser in Hamburg (FLASH), an optical synchronization system is being installed with a projected point-to-point stability of 10 fs. The system is based on the distribution of reference laser pulses over actively stabilized fiber links using optical cross-correlators. As an alternative to the complex cross-correlation scheme, which can achieve sub fs long-term stability and works well over several 100 m long fiber links, an RF-based technique which is much less complex and expensive could be used. It is based on the power detection of high harmonic frequencies in a balanced arrangement to reduce amplitude noise. For a 20 m long fiber link, it was demonstrated that a sub-5 fs rms long-term stability over 30 hours can be achieved. The system and the most recent measurements are presented here.