Author: Cassinari, L.
Paper Title Page
MOPS048 Microbunching Instability Studies at SOLEIL 709
 
  • C. Evain, J. Barros, J.B. Brubach, L. Cassinari, M.-E. Couprie, G. Creff, M. Labat, A. Loulergue, L. Manceron, R. Nagaoka, P. Roy, M.-A. Tordeux
    SOLEIL, Gif-sur-Yvette, France
 
  Microbunching instability arises in storage rings when the number of electrons in a bunch exceeds a threshold value. Its signature, i.e. a strong and irregular emission of Coherent Synchrotron Radiation (CSR) in the Terahertz (THz) domain, is studied at SOLEIL on the AILES infrared beamline, with the storage ring tuned in a low-alpha configuration (used to get shorter electron bunch). The comparison of this observed THz CSR with numerical simulations of the longitudinal electron bunch dynamics, permits to put in evidence that during the instability a modulation appears and drifts in the longitudinal profile of the electron bunch. The understanding of this instability is important as it limits some operation of the storage rings. Indeed the induced fluctuations prevent the use of THz on the far IR beamline at high current per bunch. And in normal alpha operation this instability may spoil the electron/laser interaction effects used to get femtosecond and/or coherent pulse in storage rings (with slicing, Coherent Harmonic Generation or EEHG schemes on storage ring).  
 
MOPS049 Study of Ion-induced Instabilities and Transverse Feedback Performance at SOLEIL 712
 
  • R. Nagaoka, L. Cassinari, M.D. Diop, J.-M. Filhol, M.-P. Level, A. Loulergue, P. Marchand, R. Sreedharan
    SOLEIL, Gif-sur-Yvette, France
 
  Experimental studies indicate that the SOLEIL storage ring at its maximum designed current of 500 mA is under a large influence of ions, potentially capable of inducing the so called fast beam-ion instability. To avoid it, the following three conditions have been empirically found effective: A reduced RF voltage, uniform filling and a large vertical chromaticity. While the choice of uniform filling appears contradictory to raising the ion instability threshold, it goes well with lowering of the RF voltage if outgassing due to beam-induced heating of the vacuum components is the primary source of ions. Additional difficulties associated are frequent occurrence of sudden beam blowups despite the presence of transverse feedback, which are large enough to trigger machine interlocks leading to complete beam losses. These blow ups may even take place horizontally inside in-vacuum insertion devices. The present paper reports on the results and findings obtained through experimental and simulation studies carried out on the collective beam dynamics and the transverse feedback performance, which are deeply interlinked, in order to clarify the mechanism of the encountered phenomena.  
 
TUPC068 SOLEIL Beam Orbit Stability Improvements 1156
 
  • N. Hubert, Y.-M. Abiven, F. Blache, F. Briquez, L. Cassinari, J.-C. Denard, J.-F. Lamarre, P. Lebasque, N. Leclercq, A. Lestrade, L.S. Nadolski
    SOLEIL, Gif-sur-Yvette, France
 
  The electron beam orbit stability has been significantly improved at synchrotron SOLEIL. Low frequency noise sources have been localized and identified: the fans installed on the storage ring to cool down the ceramic chambers of the kickers, shaker and FCT, were slightly wobbling the electron beam orbit at 46, 50, 54 and 108 Hz. The localization method and the solutions that will allow reducing the noise from 0.8 μm RMS down to 0.3 μm are presented. Besides, a new 160 m long beamline, NANOSCOPIUM, is being installed on a canted straight section. Its photon beam position stability requirements are very tight calling for the following improvements: addition of 2 more BPMs and fast correctors in the orbit feedback loops, new INVAR stands for BPM and XBPM integrating Hydrostatic Level System sensors. The paper is also discussing other projects that did or will contribute to improving the beam orbit stability: installation of 145 temperature sensors on the storage ring, a new analog feedforward correction system for insertion devices, and the use of the bending magnet X-BPM measurements in the slow and fast orbit feedback loops.  
 
THPC006 Experiments to Measure Electron Beam Energy using Spin Depolarization Method on SOLEIL Storage Ring 2915
 
  • J.F. Zhang, L. Cassinari, M. Labat, A. Nadji, L.S. Nadolski, D. Pédeau
    SOLEIL, Gif-sur-Yvette, France
 
  The electron beam energy on SOLEIL storage ring was successfully measured using spin depolarization method after several attempts over the past few years. The experimental results demonstrate that the effective polarization was 91.3%±3% and polarization time was 17±2.3 minutes as expected from the simulation using SLIM code. The beam was depolarized using an AC shaker and the depolarization was monitored using DCCT and beam loss monitors. The beam energy was measured with accuracy up to a few 10-5.