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Sreedharan, R.

Paper Title Page
MOPAN009 Transverse Feedback Development at SOLEIL 161
  • R. Nagaoka, L. Cassinari, J.-C. Denard, J.-M. Filhol, N. Hubert, M.-P. Level, P. Marchand, C. Mariette, F. Ribeiro, R. Sreedharan
    SOLEIL, Gif-sur-Yvette
  • K. Kobayashi, T. Nakamura
    JASRI/SPring-8, Hyogo-ken
  With reduced vertical chamber aperture adopted all around the machine, the transverse impedance for the SOLEIL ring is enhanced both in its resistive-wall and broadband content. The predicted instability threshold currents being significantly low as compared to the nominal current in multibunch and in several single bunch modes, a decision was taken to install a digital bunch by bunch feedback system, with an aim to make it operational since the beginning of the storage ring operation. The system implemented comprises components developed elsewhere, particularly the FPGA processor of SPring-8, chosen among different possible solutions. Using a BPM and a stripline in the diagonal mode, a single unit of the FPGA processor board has shown to successfully suppress resistive-wall and ion induced multibunch instabilities in either one or both transverse planes. On top of the system characteristics, the paper discusses details of the obtained performance, as well as future extensions to overcome the encountered limitations.  
WEOBC01 Beam Instability Observations and Analysis at SOLEIL 2019
  • R. Nagaoka, L. Cassinari, M.-E. Couprie, M. Labat, M.-P. Level, C. Mariette, R. Sreedharan
    SOLEIL, Gif-sur-Yvette
  Due to reduced vertical chamber aperture around the machine, the impedance was systematically evaluated and optimized 3D-wise at SOLEIL during the design stage, whose budget was then utilized to predict instability thresholds for multi and single bunches. These theoretical calculations are compared with observed instabilities. Transverse multibunch current thresholds are followed as a function of chromaticity, identifying the transition of different head-tail regimes that reflects the broadband impedance spectrum. Although low thresholds due to resistive-wall are basically confirmed, its combined effect with ion-induced instability is found to be significant, exhibiting a strong beam filling pattern dependence. To analyse the involved dynamics, a multibunch tracking code is developed in a structure that allows parallel computations with a cluster of processors. The obtained results are compared with empirical data. Analysis of single bunch instabilities is also made with an aim to identify the enhanced reactive impedance due to NEG coating.  
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WEPMN004 Operation of the SOLEIL RF Systems 2050
  • P. Marchand, H. D. Dias, M. D. Diop, M. E. El Ajjouri, J. L. Labelle, R. L. Lopes, M. Louvet, C. M. Monnot, F. Ribeiro, T. Ruan, R. Sreedharan, K. Tavakoli, C. G. Thomas-Madec
    SOLEIL, Gif-sur-Yvette
  • P. Bosland, P. Bredy
    CEA, Gif-sur-Yvette
  The 352 MHz RF accelerating systems for the SOLEIL Booster (BO) and Storage Ring (SR) have been commissioned. In the BO, a 5-cell copper cavity of the CERN-LEP type is powered with a 35 kW solid state amplifier. In the SR, the required RF accelerating voltage (up to 4.4 MV) and power (650 kW at full beam current of 500 mA) will be provided by two cryomodules, each containing a pair of superconducting cavities, specifically designed for SOLEIL. The parasitic impedances of the high order modes are strongly attenuated by means of four coaxial couplers, located on the tube connecting the two cavities. The first cryomodule is operational, while the second one, which is being constructed by ACCEL (Germany), will be implemented beginning of 2008. Both cryomodules will be cooled down with liquid helium from a single 350 W liquefier and each cavity is powered with a 190 kW solid state amplifier. With the first cryomodule and two amplifiers in operation, the first year objective of storing 300 mA was successfully achieved. The RF system commissioning and operation results are reported.