Author: Turgut, O.
Paper Title Page
MOEPPB015 Excitation of Intra-bunch Vertical Motion in the SPS - Implications for Feedback Control of Ecloud and TMCI Instabilities 112
 
  • J.D. Fox, J.M. Cesaratto, M.T.F. Pivi, C.H. Rivetta, O. Turgut, S. Uemura
    SLAC, Menlo Park, California, USA
  • W. Höfle, U. Wehrle
    CERN, Geneva, Switzerland
 
  Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP).
Electron cloud and transverse mode coupled-bunch instabilities (TMCI) limit the bunch intensity in the CERN SPS. Intra-bunch fast feedback systems are a possible method to control these effects. This paper presents experimental measurements of single-bunch motion in the SPS driven by a GHz bandwidth vertical excitation system*. The primary goal is to quantify the change in internal bunch dynamics as instability thresholds are approached, and quantify the frequencies of internal modes as Ecloud effects become significant. The beam response is sampled at 20 GS/sec. in response to arbitrary excitation patterns, with data in 2011 taken at 3 bunch intensities. We show the excitation of barycentric, head-tail and higher vertical modes. The beam motion is analyzed in the time domain, via animated presentations of the sampled vertical signals, and in the frequency domain, via spectrograms showing the modal frequencies vs. time. The demonstration of the excitation of selected internal modes is a significant step in development of the feedback control techniques.
* "A 4 GS/Sec. Synchronized Vertical Excitation System for SPS Studies - Steps Towards Wideband Feedback," these proceedings.
 
 
WEPPR090 A 4.2 GS/s Synchronized Vertical Excitation System for SPS Studies - Steps Toward Wideband Feedback 3144
 
  • J.D. Fox, J.J. Olsen, C.H. Rivetta, I.I. Rivetta, O. Turgut, S. Uemura
    SLAC, Menlo Park, California, USA
  • W. Höfle, U. Wehrle
    CERN, Geneva, Switzerland
 
  Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP).
A 4.2 GS/s beam excitation system with accelerator synchronization and power stages is described. The system is capable of playing unique samples (32 samples/bunch) for 15,000 turns on selected bunch(es) in the SPS in synchronism with the injection and acceleration cycle. The purpose of the system is to excite internal modes of single-bunch vertical motion, and study the bunch dynamics in the presence of developing Electron cloud or TMCI effects. The system includes a synchronized master oscillator, SPS timing functions, an FPGA based arbitrary waveform generator, 4.2 GS/sec. D/A system and four 80W 20 -1000 MHz amplifiers driving a tapered stripline pickup/kicker. A software GUI allows specification of various modulation signals and selection of bunches and turns to excite, while a remote control interface allows simple control/monitoring of the RF power stages located in the tunnel. Excitation signals developed to excite head-tail and other modes of vertical motion are illustrated. The successful use of this system for SPS MD measurements in August and November 2011 is a vital proof-of-principle for wideband feedback using similar functions to correct the beam motion.