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

Wolfgang Hofle AB/RF

LHC MAC - June 15, 2007 - Abort gap cleaning with damper 1/23

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

Wolfgang Hofle AB/RFAlexander Koschik AB/BT

Abort gap cleaning with transverse damper update



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



Principal of abort gap cleaning using the transverse damper

cleaning pulse (gate) centered in abort gapmodulation of pulse with betatron frequencyfull amplitude up to ~ 1 MHz possible

LHC nominal bunch pattern 2808 bunches [3]

1st 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 oscillationscapture of beam by aperture limit(LHC: by collimators)



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 SPSbunch spacing 25 ns; start of coast



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]



Current assumption: Longitudinal motion frozen

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)

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



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 themas they are installed next to each other -> no phase advance in between themProblem: 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 limitTIDV -> 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 intoaccount for the excitation; excitation at 1-qfrac (for better efficiency due to hardware limitations)



Planned Experiment (MD) in the SPS in 2007 (2)

Excitation conditions:Vertical dampers V1 (BDV 214.55) and V2 (BDV 221.76) 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 bunchesup 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”)



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 = +/- 2.37 x 10-3

central tunes: QH = 26.13

QV = 26.18

transverse emittances: n = 3 m -> 26 GeV/c :

V = 2.96 mm @ TIDV.11892 (=81 m)

beam should be mainly lost at TIDV with half gap of 20.4 mm corresponding to 6.9



Simulation results for the SPS experiment

chromaticities H=0.2V=0 (!)

Octupoles offk3=0 (!)

-50 0 50 100 150 200 250 3000

2

4

6

8

10

12

Turn number

N

Lost

[%

]

Loss Rate vs. Turn number



0 50 100 150 200 250 3000

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Turn number

NLo

st [

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Integrated Losses vs. Turn number


chromaticities H=0.2V=0

Octupoles offk3=0

Influence on the vertical cleaningfrom H-chromaticity through coupling;still 100% cleaning

11 momentum slices,plus total losses



0 1000 2000 3000 4000 5000 6000 70000

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Position s [m]

NLo

st [

%]

Loss Pattern


chromaticities H=0.2V=0

Octupole(s) offk3=0

losses at TIDV

remaining losses at selected MBBs

70% lost at TIDV 30% lost at various MBBs



0 100 200 300 400 500 600 700 800 900 10000

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Turn number

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chromaticities H=0.2V=0.2

Octupoles offk3=0

~25% cleaningbut synchrotron motion will help here to clean other momentum slices

on momentum slice

total integrated



0 100 200 300 400 500 6000

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Turn number

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Octupoles onk3= -0.875 / 0.0(OD/OF)

~89% cleaning



0 100 200 300 400 500 600 700 800 900 10000

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Octupoles onk3= -0.875 / -0.875(OD/OF)

~25% cleaning





Octupoles onk3= -0.875 / -0.875(OD/OF)

0 200 400 600 800 1000 1200 1400 1600 1800 20000

5

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Turn number

NLo

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Modulated excitation leads to “continuous” lossesneed for more simulations and optimised excitation (frequency program)could switch between different frequency programs; excitation in both planes simultaneously



Recapitulation: LHC: Time scales with RF on, at flat bottom energy (450 GeV)

q = E/Ebucket

T2 time to travel one RF periodtgap time to cross abort gap (1200 periods)

q T2 gap

ms s

1.01 16 19.2

1.1 10.1 11.3

Phase space trajectories at flat bottom (450 GeV, no energy loss)

E. Shaposhnikova

see [4,5]

LHC case



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

tgap [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



0 100 200 300 400 500 600 700 800 900 10000

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Simulation results for the LHC Beam 1 (450 GeV/c)

LHC Modelnominalwith multi-poles+ correction

~76% cleaningvery fast cleaning of central momentum slices as expected



0 0.5 1 1.5 2 2.5

x 104

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Position s [m]

NLo

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Loss Pattern


LHC Modelnominalwith multi-poles+ correction

~76% cleaningvery fast cleaning of central momentum slices - as expected

primary collimatorsbetatron cleaningTCP.D6L7.B1TCP.C6L7.B1TCP.B6L7.B1

primary collimatorsmomentum cleaningTCP.6L3.B1




LHC Model nominal with multi-poles + correction

~100% cleaning seems feasible by tailored f(t) program

0 100 200 300 400 500 600 700 800 900 10000

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Two different excitation programs



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



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. 1873 and EPAC 2004.

2. The LHC Design Report, CERN-2004-003, vol. I, chapter 6, Geneva, 2004 3. 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.

4. E. Shaposhnikova, “Abort Gap Cleaning and the RF System”, LHC Performance Workshop – Chamonix XII, 2003, CERN AB-2003-008, p. 182, Geneva, 2003.

5. E. Shaposhnikova, S. Fartoukh, B. Jeanneret, “LHC Abort Gap Filling by Proton Beam”, EPAC 2004.

6. E. Shaposhnikova, “Longitudinal motion of uncaptured particles in the LHC at 7 TeV”, LHC Project Note 338, CERN, Geneva, 2004.

7. B. Jeanneret, Private Communication.8. W. Hofle, “Progress with the SPS Damper”, LHC Workshop Chamonix XI, 2001, CERN SL-

2001-003 DI, 117-124, Geneva, 2001.9. 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, 2003.10. W. Hofle, “Experience gained in the SPS for the future LHC abort gap cleaning”, EPAC 2004.11. S. Fartoukh, O. Bruning, “Field Quality Specification for the LHC Main Dipole Magnets”, LHC

Project Report 501, CERN, Geneva, 2001.

References

Documents

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