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LHC Luminosity Achievements & Limitations

LHC Luminosity Achievements & Limitations. O. Brüning. Commissioning – Strategy. Main goal for LHC run in 2010 & 2011: integrated luminosity of 1 fb -1  implies flat out operation with 100 pb -1 per month in 2011  implies routine operation with L > 10 32 cm -2 sec -1 in 2011!

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LHC Luminosity Achievements & Limitations

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  1. LHC Luminosity Achievements & Limitations O. Brüning

  2. Commissioning – Strategy • Main goal for LHC run in 2010 & 2011: integrated luminosity of 1 fb-1 •  implies flat out operation with 100 pb-1 per month in 2011 •  implies routine operation with L > 1032 cm-2 sec-1 in 2011! • Main goal for 2010: Commissioning of peak luminosity of 1032 cm-2 sec-1 •  not achievable with 2 1010 bunch intensity •  requires ca. 800 bunches with Nb > 8 1010 ppb and b* = 3.5m • or ca. 400 bunches with Nb > 8 1010 ppb and b* = 2m •  implies operation with stored beam energies above 30 MJ • compared to operation with ca. 2 MJ in Tevatron and • operations with 13 bunches of 2 1010  170 kJ LHC-CC10, December 2010 Oliver Brüning BE-ABP

  3. Four running periods: • Single bunches with low bunch intensities • Single bunches with nominal bunch intensities • Bunch trains (150ns) with nominal bunch intensities • Bunch trains with 50 ns bunch spacing Commissioning in 2010 LHC-CC10, December 2010 Oliver Brüning BE-ABP 3

  4. 2010 LHC Timeline 3/3 LHC status

  5. LHC: First collisions at 7 TeV on 30 March 2010 ALICE LHCb CMS LHC-CC10, December 2010 Oliver Brüning BE-ABP 5

  6. First Running Period (low bunch intensity) calculated Steve Myers ) > Seven Orders of magnitude below design At this point, just ahead of the ICHEP, Paris, (based on collisions at 450 GeV with 1.1e11 ppb) it was decided to change the mode of operation to high bunch intensities LHC-CC10, December 2010 Oliver Brüning BE-ABP 6

  7. Intensity ramp up for nominal bunch OP • Intensity ramp up: • Start with 3 x 3 •  L ≈ 5 1029 cm-2 sec-1 • Move on to 6 x 6, 8 x8, 12 x 12, 24 x 24 (1.5 MJ) over 4 weeks until end of July  L ≈ 4 1030 cm-2 sec-1 • Plan for a stable running period in August under constant conditions. • Constant b* and Xing angle. • Experience with machine reproducibility: •  orbit, collimation setup, etc. CM15, CA, November 2010

  8. 1) BPM Dependence on Intensity - Beam 1 • One nominal bunch of 1×1011 slowly scraped away using a primary collimator • 2 fills – one for low sensitivity and one for high sensitivity Low Sensitivity Dead zone where neither setting works well ×1010 0 2 4 6 8 10 12 High Sensitivity Rhodri Jones ×1010 0 2 4 6 8 10 12 Internal MPP Review – 17th June 2010 Rhodri Jones

  9. Second Running Period (High bunch Intensity calculated Steve Myers Maximum reached is 10.7x1030 cm-2s-1 9

  10. Week 31 Luminosity vs time 30 July to 9 August (25 bunches) Integrated Luminosity vs time

  11. Approaching 4pb-1(move to bunch trains) Bunch Trains Set Up LHC-CC10, December 2010 Oliver Brüning BE-ABP 11

  12. Measured 450 GeV Aperture • Predicted aperture bottlenecks in triplets (n1=7) do not exist. • “Measured” n1 = 10 – 12 (on-momentum) instead design n1 = 7 • Mechanical tolerances, closed orbit and beta-beat better than specified LHC-CC10, December 2010 Oliver Brüning BE-ABP 12

  13. Optics Rogelio Tomas LHC-CC10, December 2010 Oliver Brüning BE-ABP

  14. Plan for getting to 1032 before ion run LMC 18th August. • Parameters and Conditions • Nominal bunch intensity 1.1 1011 • smaller than nominal emittances: 2.5mm  3mm (3.75mm) • Stick to β* = 3.5 m in all IPs with 175 mrad crossing angle • Commission bunch trains • New setup for injection process (crossing angle) • Complete re-do of the whole machine protection set-up • Go to 150 ns bunch spacing • Commission faster ramp (10 A/s) LHC-CC10, December 2010 Oliver Brüning BE-ABP 14

  15. Test ramp 10 A/s 1st attempt reached 1.7TeV 2nd attempt perfect ramp up to 3.5TeV Ramp duration reduced from 46 to 16 minutes LHC-CC10, December 2010 Oliver Brüning BE-ABP 15

  16. Bunch Train Schedule 48  368       312  424 LHC-CC10, December 2010 Oliver Brüning BE-ABP 16

  17. Third Running Period (bunch trains) • Steps of 50 nominal bunches (~ 3.2 MJ) • 3 fills per step (making it into stable beams) • 20 hours of stable beams LHC-CC10, December 2010 Oliver Brüning BE-ABP 17

  18. Typical emittances in collision 2.5 mm  ca. 50% higher than nominal beam-beam parameter!!! Emittances @ Collisions LHC-CC10, December 2010 Oliver Brüning BE-ABP 18

  19. LHC protons 2010: mission accomplished 250 bunches with ca. 2.6 1013 ppb L0 > 1032 cm-2 s-1  Emittance in collision < 3 mm Gianluigi Arduini LHC-CC10, December 2010 Oliver Brüning BE-ABP 19

  20. Approaching 50pb-1(move to ions) LHC-CC10, December 2010 Oliver Brüning BE-ABP 20

  21. Fill 1409: 12.10.2010 en = 1.6 mm; Nb = 1011; 256 bunches x / IP = 7.7 10-3  xtot = 0.023!! Beam-Beam: Bunch by bunch Fill lost during ‘adjust’! 21 LHC status

  22. 2010 - records Mike Lamont Courtesy Atlas M. Lamont @ Evian December 2010

  23. electron cloud effects  vacuum instabilities  cryogenic load  bunch spacing  beam scrubbing UFOs  fill abort and overall efficiency  beam scrubbing? faults and overall efficiency:  average turnaround time  statistics (Evian: ca. 25%) beam-beam effects:  working point  collision patterns Potential Performance Limitations in 2011 LHC-CC10, December 2010 Oliver Brüning BE-ABP 23

  24. First observations with bunch train operation (> 100) •  pressure rise in common vacuum region •  first indications of cleaning • instabilities & emittance growth at end of bunch trains (24 & 36) • can be stabilized by Q’ • heat load increase in cold regions with trains of 50ns (24 & 36) • first indications of cleaning Electron Cloud Effects and Scrubbing LHC-CC10, December 2010 Oliver Brüning BE-ABP 24

  25. 104 - 8 bunch injection ML @ LHC 8:30 01.10.10 Pressure at Pt 1 from fill 1373 Relatively low increase in rampGauges in question between DFBX & D1 around 58.8 m from IP 25 LHC status

  26. 152 and then 104… ML @ LHC 8:30 01.10.10 104 nothing 26 LHC status

  27. UFO dependencies: • rate proportional to total beam current (# bunches) • occurrence in all locations • most UFOS occur below BLM threshold • no UFOs observed at injection (even with 680 bunches) UFOs LHC-CC10, December 2010 Oliver Brüning BE-ABP 27

  28. UFOs: Unidentified Falling Objects Beam loss monitor post-mortem LHCb IR7 IR1 Arc Arc s Time evolution of loss 1 bin = 40 ms 0.5 ms Dump trigger Jan Uythoven

  29. UFOs • UFO dump count now 18. • UFOs have reappeared despite threshold increase. • 2 UFO dumps triggered by exp. BCMs (LHCb, ALICE) and not by machine BLMs. • UFO rate at ~ 1 event/hour with 360 bunches at 3.5 TeV. • Rate essentially proportional to intensity. JW @ LMC 1.12.10 380 hours of stable beams (full set) E. Nebot LMC, J. Wenninger

  30. UFO distribution • Structure significant ? • c JW @ LMC 1.12.10 E. Nebot LMC, J. Wenninger

  31. The summers corny crown Walter Venturini @ Evian December 2010 66% availability 31

  32. September trains Walter Venturini @ Evian December 2010 72% availability 32

  33. Luminosity – performance: • 1) maximize bunch current (beam-beam limit) • 2) minimize beam size (constant beam power) • 3) maximize number of bunches operation at beam-beam limit  use R for performance optimization - leveling Performance optimization for the LHC LHC-CC10, December 2010 Oliver Brüning BE-ABP 33

  34. Operation at the Beam-Beam Limit • Options for maximizing luminosity at the beam-beam limit: • 1) keep b* and N/e constant • increase current at constant brightness • en > 3.75 10-6 mm requires controlled e blow up at top energy • 2) keep en constant and increase N with 1/R (LPA) •  1) and 2) imply larger than ultimate • beam currents; 2) requires larger than • ultimate brightness! • 3) keep N constant and vary e as R • (referred to as small emittance scheme) •  requires smaller than nominal emittance •  leveling via Crab Cavities • 4) compensate R at IP and minimize b* •  is compatible with ultimate beam parameters; requires Crab Cavities (for alternating crossing) LHC-CC10, December 2010 Oliver Brüning BE-ABP 34

  35. head-on beam-beam limit: • independent of beam energy and b* • limit reached at N = 0.8 (1.6) 1011ppb with 4 exp and nom. en • limit reached at N = 1.2 (2.4) 1011ppb with 3 exp and nom. en • limit reached at N = 0.4 (0.8) 1011ppb with 4 exp and ½ nom. en • limit reached at N = 0.6 (1.2) 1011ppb with 3 exp and ½ nom. en • existing injector complex: • LHC injector chain can produce nominal beam with • 50ns spacing and en = 1mm to 1,5 mm (2008 MDs; E. Metral) • LHC injector chain could produce single ultimate bunch with • en = 2mm in single batch PS injection • limited by TMCI around 1.8 1011 ppb (PAC’07; CERN-AB-2007-037) •  50ns bunch spacing could be possible with ultim. intensity (MD) LHC Performance Optimization LHC-CC10, December 2010 Oliver Brüning BE-ABP 35

  36. Option based on smaller than nominal emittance: • -50ns bunch spacing • nominal luminosity possible with ultimate bunches • reduced electron cloud (LHC & SPS) • increased triplet aperture in terms of beam sigma • possibility for increased beam separation • reduced long range beam-beam • self consistent orbit & collimation tolerances • possibility for luminosity leveling • reduced total beam current (MPP & R2E) • requires control over emittance growth (‘hump’; noise)! • implies larger than nominal beam-beam parameter • implies higher power density for failure modes LHC Performance Optimization LHC-CC10, December 2010 Oliver Brüning BE-ABP 36

  37. example for small emittance scheme: LHC Performance Optimization Frank Zimmermann Nominal* LHC-CC10, December 2010 Oliver Brüning BE-ABP 37

  38. Spare Transparencies

  39. LHC Challenges: Beam-Beam Interaction DA from simulations: Werner Herr & Dobrin Kaltchev 1/10 1/13 1/16 1/3 with b-b and xtot = 0.01 nominal tune LMC, April 2010 O. Brüning – BE-ABP 39

  40. cooling & e- heat for 25 ns spacing L. Tavian, 2005 H. Maury Cuna, 2009 “ultimate” nominal spare cooling capacity at zero luminosity (=total-SR -impedance) e-cloud heat load for SEY=1.3 spare cooling capacity for 0.55 m b* going above Nb=1.7x1011 & ultimate luminosity requires dedicated IR cryo plants; limit then becomes Nb~2.3x1011

  41. cooling & e- heat for 50 ns spacing L. Tavian, 2005 H. Maury Cuna, 2009 “LPA” spare cooling capacity at zero luminosity (=total-SR -impedance) (longer flat bunches) spare cooling capacity for 0.25 m b* e-cloud heat load for SEY=1.5! going above Nb=2.3x1011 & ultimate luminosity requires dedicated IR cryo plants; limit then becomes Nb~5.0x1011

  42. Performance Tables Limitations are highlighted in yellow; values to be demonstrated are in italic. M. Vretenar @ Chamonix 2010

  43. SPS: present achievements E. Chaposhnicova @ Chamonix 2010 → SPS upgrade is necessary for intensity above nominal LHC Chamonix 2010

  44. Collimation Trade-off: Gap Size/Impedance versus Beta*/Tolerances R. Assmann, C. Bracco - Larger beta* - Lower peak lumi + Larger tolerances Larger gaps – Lower impedance Minimal allowed triplet aperture n1 Smaller gaps – Highest impedance + Lower beta* + Higher peak lumi - Lower tolerances At 3.5 TeV: n1 ≥ 10.5 for intermediate collimation settings R. Assmann

  45. Phase 1 Intensity Limit vs Loss Rate at 7 TeV Loss map simulations and LHC design values Nominal LHC design intensity worse Tightest gaps • This is a limitation from cleaning efficiency. In addition: • Predicted 50% intensity limit from collimator-induced impedance (assumes octupoles at full current for Landau damping) • Collimator material lifetime with radiation damage. • Warm magnet lifetime with radiation damage (5 years). • SC link cable in IR3. Intermediate gaps “Iberian Peninsula challenge” Adjust LHC design assump-tion? Assume LHC loss rates 100 times lower than Tevatron, 10 times lower than spec? Maybe not a good idea! LHC beams will be very high intensity, running at the beam-beam limit. better R. Assmann, CERN 45

  46. Impedance with SLAC Design and Cryo-Collimators Baseline: Stabilize with transverse feedback! See talk E. Metral. Phase II Phase I Nominal Gap Gap x 1.2 Gap x 1.5 Gap x 2 Stable working area Metallic Cu secondary collimators (phase II) require less gap opening for stability  illustrates lower impedance compared to phase I! R. Assmann, CERN

  47. LHC Challenges: Long Range Beam-Beam Frank Zimmermann diffusion strength “dynamic aperture” • tail population and halo generation? • beam losses and background? • cleaning efficiency? • can partially be compensated for by wires • can be ‘cured’ by larger b* and crossing angle amplitude with independent of b* and energy J. Irwin, SSC-223 (1989) Y. Papaphilippou & F.Z., PRST-AB 2, 104001 (1999) Y. Papaphilippou & F.Z., PRST-AB 5, 074001 (2002) for nominal LHC: xsep~9.5s, xda~6s

  48. Summary of LHC Intensity Limits (7 TeV) R. Assman @ Chamonix 2010 R. Assmann Ideal scenario: no imperfections included! Note: Some assumptions and conditions apply… LMC: R. Assmann

  49. 1) BPM Dependence on Intensity - Beam 2 • One nominal bunch of 1×1011 slowly scraped away using a primary collimator • Sensitivity constantly changed from high to low • Outliers due to acquisition overlapping two sensitivity ranges • Sensitivity ranges seen to overlap as expected at around 5×1010 Internal MPP Review – 17th June 2010 Rhodri Jones

  50. 2008 LHC Timeline 1/3 CM15, CA, November 2010 • 2008 • Accelerator complete • Ring cold and under vacuum • September 10th 2008 • First beams around • September 19th 2008 • The incident • 2008 – 2009 • 14 months of major repairs and consolidation • New Quench Protection System for online monitoring and protection of all joints. • However: uncertainties about the splice quality • Risk of thermal runaway scenarios  decision to limit beam energy to 3.5 TeV for first operation LHC status

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