Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 1/23 Acknowledgements: T. Kramer (AB/BT), E. Shaposhnikova (AB/RF) Wolfgang Hofle AB/RF Alexander Koschik AB/BT Abort gap cleaning with transverse damper update

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 2/23 Overview Principle of abort gap cleaning – reminder SPS as LHC test bed: planned experiments in the SPS for 2007 simulations for the SPS 2007 test bed case first simulation results for LHC

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 3/23 Principal of abort gap cleaning using the transverse damper 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] 1 st injected batch abort gap (119 missing bunches) amplitude can be modulated with any frequency between 1 kHz and 20 MHz; gate feedback action off during gap resonant excitation of transverse oscillations capture of beam by aperture limit (LHC: by collimators)

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 4/23 Results of cleaning experiment in SPS [9,10] (horizontal plane) After application of 6 cleaning pulses applied in center of batch (17 minutes later) LHC batch with 72 bunches in SPS bunch spacing 25 ns; start of coast

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 5/23 Earlier estimation for LHC abort gap cleaning Maximum capability of coherent excitation with LHC damper (assuming peak kick) of ~0.33  per turn [10] assume excitation off 7x10 -3 in tune (tune uncertainty, non-linearities) 450 GeV: collimators (7  ) reached after 55 turns (if collimators at 6  -> 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]

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 6/23 Current assumption: Longitudinal motion frozen SPS: injection: 2 MV, f s =182 Hz, Q s =0.004 (synch. period: 240 turns) LHC: injection: f s = 61.8 Hz (sync. period: 182 turns) collision: f s = 21.4 Hz (sync. period: 525 turns) Not a fundamental limitation, longitudinal motion can be switched on in MAD, However, limitations due to heavy computing load 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 Implementation of time (i.e. turn by turn) varying kicks in MAD (T. Kramer, A. Koschik) Tracking with MAD

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 7/23 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  H (  H = 3.1 mm,  H =89 m for  n = 3  m, 26 GeV/c) 2007: vertical plane: internal dump TIDV as aperture limit TIDV -> half gap 20.4 mm -> 6.9  V  V = 3 mm,  H =89 m for  n = 3  m, 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-q frac (for better efficiency due to hardware limitations)

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 8/23 Planned Experiment (MD) in the SPS in 2007 (2) Excitation conditions: Vertical dampers V1 (BDV ) and V2 (BDV ) phase advance 295 o Amplitude: maximum single turn kick: ~8  rad (total, i.e. each damper 4  rad) Beam conditions: LHC type beam with 25 ns bunch spacing, up to 4 x 72 bunches up to nominal intensity (SPS: 1.3x1011 protons / bunch) momentum: 26 GeV/c (injection plateau) longitudinal emittance: 0.35 eVs injected transverse emittances:  n = 3  m 4x4 hours parallel MD 1 dedicated MD at 26 GeV with beam stored (“coast”)

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 9/23 Simulations for the SPS experiment (A. Koschik) Tracking with MAD of 1100 macro-particles SPS: cleaning of captured beam simulated (limited possibilities to monitor un-captured beam this year in SPS) 11 slices with different  p/p, 100 macro-particles per slice, i.e. one slice at  p/p = 0 and 2x5 slices up to  p/p | max = +/- 1.5  current assumption (SPS MAD model)  p/p = +/ x central tunes:Q H = Q V = transverse emittances:  n = 3  m -> 26 GeV/c :  V = 2.96 TIDV (  =81 m) beam should be mainly lost at TIDV with half gap of 20.4 mm corresponding to 6.9 

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 10/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0 (!) Octupoles off k 3 =0 (!)

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 11/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0 Octupoles off k 3 =0 Influence on the vertical cleaning from H-chromaticity through coupling; still 100% cleaning 11 momentum slices, plus total losses

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 12/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0 Octupole(s) off k 3 =0 losses at TIDV remaining losses at selected MBBs 70% lost at TIDV 30% lost at various MBBs

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 13/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0.2 Octupoles off k 3 =0 ~25% cleaning but synchrotron motion will help here to clean other momentum slices on momentum slice total integrated

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 14/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0.0 Octupoles on k 3 = / 0.0 (OD/OF) ~89% cleaning

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 15/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0.2 Octupoles on k 3 = / (OD/OF) ~25% cleaning

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 16/23 Simulation results for the SPS experiment chromaticities  H =0.2  V =0.2 Octupoles on k 3 = / (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

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 17/23 Recapitulation: LHC: Time scales with RF on, at flat bottom energy (450 GeV) q =  E/  E bucket T 2  time to travel one RF period t gap time to cross abort gap (1200 periods ) qT2T2  gap mss Phase space trajectories at flat bottom (450 GeV, no energy loss) E. Shaposhnikova see [4,5] LHC case

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 18/23 Recapitulation: LHC: Time scales with RF on, at flat top energy (7 TeV) Time needed for an uncaptured particle to cross the abort gap as a function of the normalised initial maximum energy deviation [4,5] q t gap [s] At 7 TeV energy loss changes picture particles lost from the bucket with positive energy deviation pass through the hole between buckets and drift away from abort gap particles with negative energy deviation cross abort gap in maximum 25 s 1/6 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 E. Shaposhnikova LHC case

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 19/23 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

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 20/23 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 primary collimators betatron cleaning TCP.D6L7.B1 TCP.C6L7.B1 TCP.B6L7.B1 primary collimators momentum cleaning TCP.6L3.B1

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 21/23 Simulation results for the LHC Beam 1 (450 GeV/c) LHC Model nominal with multi-poles + correction ~100% cleaning seems feasible by tailored f(t) program Two different excitation programs

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 22/23  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) 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  Study simultaneous excitation in both planes

Wolfgang Hofle AB/RF LHC MAC - June 15, Abort gap cleaning with damper 23/23 1.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 and EPAC The LHC Design Report, CERN , vol. I, chapter 6, Geneva, The LHC Design Report, CERN , vol. I, Geneva, 2004; and P. Collier, “Baseline Proton Filling Schemes”, LHC Project Workshop –Chamonix XIII, CERN-AB , p. 30, Geneva, E. Shaposhnikova, “Abort Gap Cleaning and the RF System”, LHC Performance Workshop – Chamonix XII, 2003, CERN AB , p. 182, Geneva, E. Shaposhnikova, S. Fartoukh, B. Jeanneret, “LHC Abort Gap Filling by Proton Beam”, EPAC E. Shaposhnikova, “Longitudinal motion of uncaptured particles in the LHC at 7 TeV”, LHC Project Note 338, CERN, Geneva, B. Jeanneret, Private Communication. 8.W. Hofle, “Progress with the SPS Damper”, LHC Workshop Chamonix XI, 2001, CERN SL DI, , Geneva, T. Bohl, W. Hofle, T. Linnecar, E. Shaposhnikova, J. Tuckmantel, “Observation of Parasitic Beam and Cleaning with Transverse Damper”, AB-Note MD, CERN, Geneva, W. Hofle, “Experience gained in the SPS for the future LHC abort gap cleaning”, EPAC S. Fartoukh, O. Bruning, “Field Quality Specification for the LHC Main Dipole Magnets”, LHC Project Report 501, CERN, Geneva, References