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Acknowledgements: T. Kramer (AB/BT), E. Shaposhnikova (AB/RF)

Abort gap cleaning with transverse damper update. Wolfgang Hofle AB/RF Alexander Koschik AB/BT. Acknowledgements: T. Kramer (AB/BT), E. Shaposhnikova (AB/RF). Overview.

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Acknowledgements: T. Kramer (AB/BT), E. Shaposhnikova (AB/RF)

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  1. Abort gap cleaning with transverse damper update Wolfgang Hofle AB/RFAlexander Koschik AB/BT Acknowledgements: T. Kramer (AB/BT), E. Shaposhnikova (AB/RF) LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  2. Overview Principle of abort gap cleaning – reminderSPS as LHC test bed: planned experiments in the SPS for 2007simulations for the SPS 2007 test bed casefirst simulation results for LHC LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  3. Principal of abort gap cleaning using the transverse damper resonant excitation of transverse oscillations capture of beam by aperture limit (LHC: by collimators) amplitude can be modulated with any frequency between 1 kHz and 20 MHz; gate feedback action off during gap 1st injected batch abort gap (119 missing bunches) cleaning pulse (gate) centered in abort gap modulation of pulse with betatron frequency full amplitude up to ~ 1 MHz possible LHC nominal bunch pattern 2808 bunches [3] LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  4. Results of cleaning experiment in SPS [9,10] (horizontal plane) LHC batch with 72 bunches in SPSbunch spacing 25 ns; start of coast After application of 6 cleaning pulses applied in center of batch (17 minutes later) LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  5. Earlier estimation for LHC abort gap cleaning Maximum capability of coherent excitation with LHC damper (assuming peak kick) of ~0.33 s per turn [10]assume excitation off 7x10-3 in tune (tune uncertainty, non-linearities)450 GeV: collimators (7s) reached after 55 turns (if collimators at 6 s -> even faster)estimate for 7 TeV: ~220 turns to reach collimators [10] more accurate description needs tracking studies to take into account cleaning efficiency and all non-linearities from [11] LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  6. Tracking with MAD Implementation of time (i.e. turn by turn) varying kicks in MAD (T. Kramer, A. Koschik) Current assumption: Longitudinal motion frozen Not a fundamental limitation, longitudinal motion can be switched on in MAD, However, limitations due to heavy computing load SPS: injection: 2 MV, fs=182 Hz, Qs=0.004 (synch. period: 240 turns) LHC: injection: fs= 61.8 Hz (sync. period: 182 turns) collision: fs = 21.4 Hz (sync. period: 525 turns) With expected cleaning times of the same order of magnitude as the synchrotron period, we should see the effect of chromaticity, hence assumption not justified in all cases LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  7. Planned Experiment (MD) in the SPS in 2007 (1) following initial experiments in 2002 in the SPS (reported at the LHCMAC in July 2004)new experiments are planned for week 32 in the SPS (August 2007) objective: benchmark simulations and optimize excitation pulse fixed frequency or sweep; cleaning speed and efficiency in presence of non-linearities and coupling 2002: horizontal plane both dampers H1 and H2 could be used straightforward applying the same signal to both of them as they are installed next to each other -> no phase advance in between them Problem: large horizontal aperture, TIDH -> half gap ~55 mm -> 17.8 sH (sH= 3.1 mm, bH=89 m for en= 3 mm, 26 GeV/c) 2007: vertical plane: internal dump TIDV as aperture limit TIDV -> half gap 20.4 mm -> 6.9 sV(sV= 3 mm, bH=89 m for en= 3 mm, 26 GeV/c) Problem: dampers V1 and V2 at 295 degrees phase advance, need to take this into account for the excitation; excitation at 1-qfrac (for better efficiency due to hardware limitations) LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  8. Planned Experiment (MD) in the SPS in 2007 (2) Beam conditions:LHC type beam with 25 ns bunch spacing, up to 4 x 72 bunchesup to nominal intensity (SPS: 1.3x1011 protons / bunch)momentum: 26 GeV/c (injection plateau) longitudinal emittance: 0.35 eVs injected transverse emittances: en = 3 mm 4x4 hours parallel MD 1 dedicated MD at 26 GeV with beam stored (“coast”) Excitation conditions: Vertical dampers V1 (BDV 214.55) and V2 (BDV 221.76) phase advance 295o Amplitude: maximum single turn kick: ~8 mrad (total, i.e. each damper 4 mrad) LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  9. Simulations for the SPS experiment(A. Koschik) Tracking with MAD of 1100 macro-particlesSPS: cleaning of captured beam simulated (limited possibilities to monitor un-captured beam this year in SPS) 11 slices with different Dp/p, 100 macro-particles per slice, i.e. one slice at Dp/p = 0 and 2x5 slices up to Dp/p |max= +/- 1.5 scurrent assumption (SPS MAD model) Dp/p = +/- 2.37 x 10-3central tunes: QH = 26.13 QV = 26.18transverse emittances: en = 3 mm -> 26 GeV/c : sV = 2.96 mm @ TIDV.11892 (b=81 m)beam should be mainly lost at TIDV with half gap of 20.4 mm corresponding to 6.9 s LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  10. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0 (!) Octupoles off k3=0 (!) LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  11. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0 Octupoles off k3=0 11 momentum slices, plus total losses Influence on the vertical cleaning from H-chromaticity through coupling; still 100% cleaning  LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  12. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0 Octupole(s) off k3=0 losses at TIDV remaining losses at selected MBBs 70% lost at TIDV  30% lost at various MBBs LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  13. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0.2 Octupoles off k3=0 on momentum slice ~25% cleaning but synchrotron motion will help here to clean other momentum slices total integrated LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  14. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0.0 Octupoles on k3= -0.875 / 0.0 (OD/OF) ~89% cleaning LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  15. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0.2 Octupoles on k3= -0.875 / -0.875 (OD/OF) ~25% cleaning LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  16. Simulation results for the SPS experiment chromaticities xH=0.2 xV=0.2 Octupoles on k3= -0.875 / -0.875 (OD/OF) Modulated excitation leads to “continuous” losses need for more simulations and optimised excitation (frequency program) could switch between different frequency programs; excitation in both planes simultaneously LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  17. LHC case Recapitulation: LHC: Time scales with RF on, at flat bottom energy (450 GeV) q = DE/DEbucket T2p time to travel one RF period tgap time to cross abort gap (1200 periods) E. Shaposhnikova Phase space trajectories at flat bottom (450 GeV, no energy loss) see [4,5] LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  18. LHC case Recapitulation: LHC: Time scales with RF on, at flat top energy (7 TeV) At 7 TeV energy loss changes pictureparticles lost from the bucket with positive energy deviation pass through the hole between buckets and drift away from abort gapparticles with negative energy deviation cross abort gap in maximum 25 s1/6 of ring contributes to abort gap filling, particles lost from other 5/6 of ring are intercepted by the momentum collimation before reaching the abort gap tgap [s] E. Shaposhnikova q Time needed for an uncaptured particle to cross the abort gap as a function of the normalised initial maximum energy deviation [4,5] LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  19. Simulation results for the LHC Beam 1 (450 GeV/c) LHC Model nominal with multi-poles + correction ~76% cleaning very fast cleaning of central momentum slices as expected LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  20. Simulation results for the LHC Beam 1 (450 GeV/c) LHC Model nominal with multi-poles + correction primary collimators betatron cleaning TCP.D6L7.B1 TCP.C6L7.B1 TCP.B6L7.B1 primary collimators momentum cleaning TCP.6L3.B1 ~76% cleaning very fast cleaning of central momentum slices - as expected LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  21. Simulation results for the LHC Beam 1 (450 GeV/c) LHC Model nominal with multi-poles + correction Two different excitation programs ~100% cleaning seems feasible by tailored f(t) program LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  22. Conclusions • First results of studies confirm feasibility of abort gap cleaning • The necessity to design optimized frequency sweeps/modulation to achieve full cleaning has been shown in simulations • Further studies to prepare for week 32 MD in SPS: prepare tailored excitation pulses with varying f(t); analysis: compare measurements and simulations to gain confidence in simulations for the LHC case • Continue studies for LHC abort gap cleaning -> switch on RF (full 6D simulation) • Study simultaneous excitation in both planes LHC MAC - June 15, 2007 - Abort gap cleaning with damper

  23. References • A. Drees, L. Ahrens, R. Fliller III, D. Gassner, G.T. McIntyre, R. Michnoff, D. Trobojevic, “Abort Gap Cleaning in RHIC”, EPAC’02, Paris, p. 1873 and EPAC 2004. • The LHC Design Report, CERN-2004-003, vol. I, chapter 6, Geneva, 2004 • The LHC Design Report, CERN-2004-003, vol. I, Geneva, 2004; and P. Collier, “Baseline Proton Filling Schemes”, LHC Project Workshop –Chamonix XIII, CERN-AB-2004-014, p. 30, Geneva, 2004. • E. Shaposhnikova, “Abort Gap Cleaning and the RF System”, LHC Performance Workshop – Chamonix XII, 2003, CERN AB-2003-008, p. 182, Geneva, 2003. • E. Shaposhnikova, S. Fartoukh, B. Jeanneret, “LHC Abort Gap Filling by Proton Beam”, EPAC 2004. • E. Shaposhnikova, “Longitudinal motion of uncaptured particles in the LHC at 7 TeV”, LHC Project Note 338, CERN, Geneva, 2004. • B. Jeanneret, Private Communication. • W. Hofle, “Progress with the SPS Damper”, LHC Workshop Chamonix XI, 2001, CERN SL-2001-003 DI, 117-124, Geneva, 2001. • T. Bohl, W. Hofle, T. Linnecar, E. Shaposhnikova, J. Tuckmantel, “Observation of Parasitic Beam and Cleaning with Transverse Damper”, AB-Note-2003-021 MD, CERN, Geneva, 2003. • W. Hofle, “Experience gained in the SPS for the future LHC abort gap cleaning”, EPAC 2004. • S. Fartoukh, O. Bruning, “Field Quality Specification for the LHC Main Dipole Magnets”, LHC Project Report 501, CERN, Geneva, 2001. LHC MAC - June 15, 2007 - Abort gap cleaning with damper

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