• C. Bruni, Y. Fedala, J. Haissinski, M. Lacroix, B. Mouton, R. Roux, A. Variola, Z.F. Zomer
  LAL, Orsay
• E. Bressi
  CNAO Foundation, Milan
• P. Brunelle, M.-E. Couprie, J.-C. Denard, N. Guillotin, P. Lebasque, A. Loulergue, P. Marchand, F. Marteau, R. Nagaoka
  SOLEIL, Gif-sur-Yvette
• P. Gladkikh
  NSC/KIPT, Kharkov

The goal of X-ray sources based on Compton back scattering processes is to develop a compact device, which could produce an intense flux of monochromatic X-rays. Compton back-scattering resuls from collisions between laser pulses and relativistic electron bunches. Due to the relative low value of the Compton cross section, a high charge electron beam, a low emittance and a high focusing at the interaction point are required for the electron beam. In addition, the X-ray flux is related to the characteristics of the electron beam, which are themselves dynamically affected by the Compton interaction. One possible configuration is to inject frequently into a storage ring with a low emittance linear accelerator without waiting for the synchrotron equilibrium. As a consequence, the optics should be designed taking into account the characteristics of the electron beam from the linear accelerator. The accelerator ring design for a 50 MeV electron beam, aiming at producing a flux higher than 10¹³ ph/s, will be presented.

• J.-M. Filhol, J.C. Besson, P. Brunelle, L. Cassinari, M.-E. Couprie, J.-C. Denard, C. Herbeaux, N. Hubert, J.-F. Lamarre, J.-P. Lavieville, P. Lebasque, M.-P. Level, A. Loulergue, P. Marchand, A. Nadji, L.S. Nadolski, R. Nagaoka, M.-A. Tordeux
  SOLEIL, Gif-sur-Yvette

After two years of operation, the SOLEIL 3rd generation synchrotron light source is delivering photons to 20 beamlines with a current of 250mA in multibunch or hybrid modes, and 60 mA in 8 bunch mode. The radiation control of the beamline hutches is performed at 300 mA, but recently a 455mA current was stored during machine tests following the installation of the second RF cryomodule. It is foreseen to reach the maximum current of 500mA in the early 2009 and to operate in top-up mode from then on. The new transverse feedback loop has enabled to improve the performance of the single bunch and multibunch beams. The beam position stability is in the range of few micrometers thanks to the efficiency of the fast orbit feedback. Fifteen insertion devices are now installed in the storage ring, ten others are under construction, and a cryogenic undulator is under development. A big effort is being taken in order to compensate the effects of these insertion devices on the machine performance. The good operation performance achieved in 2007 (first year) has been improved in 2008 during which ~4 000 hours will have been delivered to the users with a 95.5% availability and a 30 hours MTBF.

• F. Marteau, C. Benabderrahmane, P. Berteaud, F. Briquez, P. Brunelle, L. Chapuis, M.-E. Couprie, T.K. El Ajjouri, J.-M. Filhol, C.A. Kitegi, O. Marcouillé, M. Massal, A. Nadji, L.S. Nadolski, R. Nagaoka, K. Tavakoli, M. Valléau, J. Vétéran
  SOLEIL, Gif-sur-Yvette
• O.V. Chubar
  BNL, Upton, Long Island, New York

SOLEIL storage ring presents a very high fraction of the total circumference dedicated to accommodate insertion devices. Over the presently planned 25 insertion devices presenting a large variety of systems, 15 have been already installed and commissioned by the end of 2008. The UV-VUV region is covered with electromagnetic devices (one HU640 and 3 HU256), offering tuneable polarisations. An electromagnet/permanent magnet undulator using copper sheets as coils for fast switching of the helicity is under construction. 13 APPLE-II types undulators, with period ranging from 80 down to 36 mm, provide photons in the 0.1-10 keV region, some of them featuring tapering or quasi-periodicity. 5 U20 in-vacuum undulators cover the 3-30 keV range whereas an in-vacuum wiggler, with magnetic forces compensation via adequate springs is designed to cover the 10^-50 keV spectral domain. R&D on cryogenic in-vacuum undulator has also been launched. A magnetic chicane using permanent magnet dipoles has also been designed in order to accommodate two canted undulators on the same straight section. The processes for optimizing the insertion devices and their achieved performances will be described.

• R. Nagaoka, L. Cassinari, J.-M. Filhol, M. Labat, M.-P. Level, C. Mariette, R. Sreedharan
  SOLEIL, Gif-sur-Yvette

Ever since the first user operation, the digital transverse bunch by bunch feedback system developed at SOLEIL has successfully been operated, achieving a stable multibunch beam at the highest intensity in the two planes at zero chromaticity with a single chain working in a diagonal mode. Since then a vertical stripline, optimised to generate large deflections to combat the strong single bunch headtail instability, was installed to construct another chain. The combined use of the two chains allowed enhancing the feedback performance. In particular, by differentiating the feedback gain between high and low intensity bunches, the system is capable of working in hybrid filling modes. In parallel, online applications were integrated into the control system to allow measuring the tunes by selectively exciting a single bunch, damping and growth rates, and analysing the bunch by bunch data in frequency or time domain for post-mortem purposes. Future plans including installation of a horizontal stripline and a noise reduction by avoiding the baseband conversion of the beam signal are also discussed.

• R. Nagaoka
  SOLEIL, Gif-sur-Yvette
• R. Bartolini, J. Rowland
  Diamond, Oxfordshire

Good understanding of instabilities is of great importance in light source rings that provide high current beams. The inherently large machine impedance, which often evolves with continuous changes of insertion devices, enhances collective effects that need to be well controlled to assure the machine performance. The problem is usually not straightforward, as one must quantify short and long range wakes that excite single and multi bunch instabilities, the coupling between instabilities and different planes, as well as Landau effects in arbitrary filling modes. The paper presents the study made on DIAMOND and SOLEIL using the multiparticle tracking codes sbtrack and mbtrack. While sbtrack performs a 6-dimensional single bunch tracking, mbtrack does its direct extension to multibunches. The most recent code development includes a MATLAB version and a high precision Fourier analysis of collective modes. The study emphasises the use of realistic impedance models, either empirically or numerically constructed, and aims to elucidate the relative importance of different physical effects by closely comparing with experimental observations.