reported by wolfgang hofle cern be/rf/fb
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Transverse feedback to cure electron-cloud induced single bunch vertical instability and TMC-Instability in the SPS Progress 2008- 2009. reported by Wolfgang Hofle CERN BE/RF/FB. Team Wolfram Fisher, Riccardo De Maria (BNL) - PowerPoint PPT PresentationTRANSCRIPT
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 1/23
reported by
Wolfgang HofleCERN BE/RF/FB
Transverse feedback to cure electron-cloud induced single bunch vertical
instability and TMC-Instability in the SPS
Progress 2008- 2009
TeamWolfram Fisher, Riccardo De Maria (BNL)
John Byrd, M. Furman, Stefano De Santis, Jean-Luc Vay (LBL), Joel R. Thompson (Cornell)Gianluigi Arduini, Giovanni Rumolo, Urs Wehrle (CERN)
TMCI: Elias Métral, Benoit Salvant (CERN)John D. Fox, Georges Ndabashimiye, Mauro Pivi, Claudio Rivetta (SLAC)
Acknowledgement: T. Bohl, G. Kotzian, F. Caspers, T. Linnecar
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 2/23
Interest expressed in 2007 by J. Byrd (LBL, Berkeley) and J. Fox (SLAC) to collaborate on transverse feedbacks in the frame work of LARPnow receiving increased support from LARP
Joint MDs in 2008 and 2009
Preparation of instrumentation, pick-up response analysis (2008-2009)R. de Maria, U. Wehrle, W. Hofle (CERN)
Simulations by Joel R. Thompson with head tail (2008)
Simulations by Jean-Luc Vay et al. (LBL)
Web meetings to follow-up collaborations organized by J. Fox (SLAC)
Analysis of MD data of 2009: C. Rivetta (SLAC)
Single bunch MDs: B. Salvant, E. Métral et al.
Preparation of hardware for beam transfer function measurementW. Hofle, U. Wehrle, D. Valuch (CERN)
LARP Initiative for SPS e-cloud FB- single bunch TMCI
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 3/23
Observation of electron cloud instability in the past
From G. Arduini et al, Proceedings E-cloud 2004
Observation of oscillations with strip line coupler (head tail monitor) along batch:- horizontal plane: coupled bunch behavior, strong correlation between bunches, low frequency (~ 1 MHz), taken care of by the present transverse feedback system-vertical plane: some bunches oscillate with large amplitude, single bunch oscillations, weak correlation between adjacent bunches, controlled by current transverse feedback and high chromaticity, emittances at the limit for nominal LHC beam (blow-up at tail of batch)
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unstable bunch (-signal)
-signals always stable (yellow)
unstable bunch (-signal)
stable bunch (-signal)
10 ns/div
5x72 bunches injected; 25 ns bunch spacing; machine well scrubbed with four batchesshown are the last three bunches of the 5th batch, vertical pick-up, shortly after injectionevidence of single bunch multi-100 MHz transverse instability,
Instability at injection of 5th batch, analysis ongoing
Wolfgang Hofle BE/RF 4/23SPS Studies WG - November 17, 2009
MD with LHC nominal beam in June 2008
Considerable effort followed to understand signals and de-convolve coupler and cable response
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 5/23
Exponential coupler
Four such couplers installed in SPS (four electrodes at 45 degrees)can be used for MDs, hybrids and cables checked and their transfer functions measured in March 2008 (R. de Maria, Gerd Kotzian)
Developed for SPS by T. Linnecar, Reference: CERN-SPS-ARF-SPS/78/17 phase response not linear frequency !
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Pick-up 319.01 re-cabled with resistive combiners
Wolfgang Hofle BE/RF 8/23January 2009
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2.5 ns/divInjection, 26 GeV/c (longer bunch)
Single bunch signals after modification of pick-up connection (resistive combiners)(stable short bunch with ~5 x109 protons per bunch)
Wolfgang Hofle BE/RF 9/23January 2009
5 ns/div450 GeV/c(shorter bunch)
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 10/23
Reconstructing signal from pick-up
see DIPAC 2009 paper mopd17 (R. de Maria et al. )
response measurement with short bunch
Reconstructed signal during debunching
longitudinal transverse
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Single bunch signals after modification of pick-up connection(stable bunch with ~5 x109 protons per bunch)
Wolfgang Hofle BE/RF 11/23January 2009
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Single bunch signals after modification of pick-up connection(stable bunch with ~5 x109 protons per bunch)
Wolfgang Hofle BE/RF 12/23January 2009
averages of 20 measurementsA and B time-aligned (A+17 ps)
pick-up strips not exactly equal !
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Measurements on all four exponential couplers in the SPS(data from November 4th, 2008)
Wolfgang Hofle BE/RF 13/23January 2009
FC, resistive combiners1st bunch of a trainPU backwards installed
FC, resistive combiners1st bunch of a trainPU forwards installed
CCR, H-183 combinerssingle bunch (semi-short)PU forwards installed
vertical BPWA,small diameter
(now) vertical BPWA,small diameter
horizontal BPW,large diameter
vertical BPWA,small diameter
CCR, H-183 combiners1st bunch of a train PU forwards installed
1st bunch of bunch train oscillates -> jitter in measurement; single bunch -> no jitter
slow rise-time fast rise-time
fast rise-timefast rise-time
saturation or cable?
319.01
317.98
321.01
319.31
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 14/23
Single bunch – spectral domain
see DIPAC 2009 paper mopd17 (R. de Maria et al. )
Beam pipe diameter = 107 mm
de-bunching, RF off
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 15/23
Single Bunch and 25 ns bunch trainsTransverse instability with captured
beam
see DIPAC 2009 paper mopd17 (R. de Maria et al. )
single bunch instability (TMCI)low chromaticity
E-cloud instability
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 16/23
Single bunch results
See PAC 2009 paper TH5RFP047 (B. Salvant et al. )
Forrest of signals > 1.5 GHzfrom beam but enhanced by pick-up
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 17/23
Simulation with headtail(e-cloud)
no feedback, spectrum extends to ~ 1GHz
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 18/23
Simulations with head-tail
See PAC 2009 paper TH5RFP076 (J. R. Thompson et al. )and AB report CERN-AB-2008-070
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 19/23
Courtesy J.D. Fox, simulations by team at LBNL (J.-L. Vay et al.)
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 20/23
Courtesy J.D. Fox, analysis of 2009 MD data by C. Rivetta (SLAC)
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Wolfgang Hofle BE/RF 21/23January 2009
Pick-up 319.01 re-cabled with hybrids for excitation (up to ~200 W)Pick-up 321.01 used for observation
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Wolfgang Hofle BE/RF 22/23January 2009
Observed (transverse) spectrum with single bunch at 4xRF frequency (26 GeV/c)
Same spectrum observed with and without excitation; signal disappears when beam is switched off need to repeat spectrum measurement versus time with ramp down of chromaticity to catch onset of TMCI + excitation, NWA versus spectrum analyser
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Wolfgang Hofle BE/RF SPS Studies WG - November 17, 2009 23/23
Conclusions and outlook
Instrumentation in the SPS improved and method developed to reconstruct time evolution of internal bunch motion, results for e-cloud and single bunch instability, should we build a new pick-up (precision-long coupler ?)
Head-tail simulations with e-cloud and feedback showed that a minimum bandwidth of 300 MHz is necessary to damp the instability but unrealistic high gain is required; with larger bandwidth the necessary gain can be reduced, in practice with realistic gains up to 1 GHz bandwidth required
Qualitatively the measured internal bunch motions agrees with simulation - strong head-tail tune shift observed as in simulation
Single bunch measurements started as well (TMCI)
Set-up prepared for beam transfer function measurements, not yet successful, need more time, possibly more RF power or a better sensitivity and a good technique for chromaticity control, first measurements concentrate on single bunch
J. D. Fox at SLAC is now looking into the technology available for ADCs, DACs, signal processing to cope with the required bandwidth