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Sreedharan, R.

Paper Title Page
TUPD028 Fast Beam-ion Instability Studies at SOLEIL 1985
 
  • R. Nagaoka, L. Cassinari, M.D. Diop, M.-P. Level, C. Mariette, R. Sreedharan
    SOLEIL, Gif-sur-Yvette
 
 

Ever since the commissioning times, transverse instabilities, which now have been identified as the so called Fast Beam-Ion Instability (FBII), have existed in the SOLEIL storage ring. Though along with the improvement of the vacuum level with increasing beam dose its relative importance has decreased to a large extent as compared to the classical instabilities due to the coupling impedance, the FBII still exists persistently at high current, making it difficult to attain a stable beam at the final goal of 500 mA. In particular, sudden beam losses are frequently encountered after keeping the beam stable over a certain time with transverse feedback at the final current, which raised a question as to whether the observed phenomena are compatible with the saturating effect of the FBII. Experimental analysis using the bunch by bunch feedback diagnostics as well as theoretical and numerical analysis using multibunch tracking have been carried out to understand the instability quantitatively and to elucidate the mechanism of the beam losses.

 
WEPEB029 Operational Status of the Transverse Bunch by Bunch Feedback System at SOLEIL 2746
 
  • R. Nagaoka, L. Cassinari, M.D. Diop, M.-P. Level, C. Mariette, R. Sreedharan
    SOLEIL, Gif-sur-Yvette
  • T. Nakamura
    JASRI/SPring-8, Hyogo-ken
 
 

In this paper we introduce and discuss the recent developments made in our digital transverse bunch by bunch feedback system at SOLEIL, which is routinely in service since the first user operation in both the high average current and high bunch current modes. The above includes installation of a third chain with a dedicated 4-electrode stripline intended to operate in the horizontal plane, an attempt to sample the BPM signal directly at the RF frequency without down-converting to the baseband following the success at SPring-8, a refined tuning procedure by measuring the feedback damping times as a function of the band frequency, as well as exploration of different digital filters ensuring a larger working range in terms of betatron tunes or a faster response against single bunch instabilities. The achieved performance and results are described. The observed evolution of the machine impedance and instabilities shall also be presented.