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LHC Beam Operations Past, Present and Future Maria Kuhn on behalf of the LHC team 03-14-2013 Moriond QCD 2013.

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Presentation on theme: "LHC Beam Operations Past, Present and Future Maria Kuhn on behalf of the LHC team 03-14-2013 Moriond QCD 2013."— Presentation transcript:

1 LHC Beam Operations Past, Present and Future Maria Kuhn on behalf of the LHC team Moriond QCD 2013

2 April 2010 Squeeze to 3.5 m LHC Timeline September 10, 2008 First beams around September 19, 2008 Disaster Accidental release of 600 MJ stored in one sector of LHC dipole magnets August 2008 First injection test August, x 10 33, 2.6 fb bunches October x bunches November 2010 Ions March 30, 2010 First collisions at 3.5 TeV 1380 June bunches November 29, 2009 Beam back June, fb -1 to ATLAS & CMS 6 June, x Moriond QCD July, 2012 Higgs like discovery

3 Integrated luminosity Moriond QCD 2013

4 2012: ~30 collisions/xing at beginning of fill with tails up to ~ : average 12 collisions/xing, with tails up to ~20 Record peak luminosity: 7.73 x cm -2 s -1 Peak luminosity

5 ALICE and LHCb (and TOTEM and ALFA) Peak luminosities achieved in ALICE around 5 x cm -2 s Moriond QCD 2013 LHCb 2012: 1.9 fb -1 delivered!

6 Luminosity NNumber of particles per bunch KbKb Number of bunches fRevolution frequency σ*σ*Beam size at interaction point FReduction factor due to crossing angle εEmittance εnεn Normalized emittance β*β*Beta function at IP 6 In 2012: ε n = 2.5  m  = 5.9 x  m  * = 18.8  m (p = 4 TeV,  * = 0.6m) Moriond QCD 2013

7 Performance from injectors 2012 Bunch spacing [ns] Protons per bunch [ppb] Norm. emittance H&V [  m] Exit SPS Design report x injected into LHC x tested251.2 x N.B. the importance of 50 ns in the performance so far. This at the expense of high pile-up Moriond QCD 2013

8 LHC Peak Performance in Moriond QCD 2013 Design Report 2012 Comments Energy [TeV] /7 design energy  * (IP1&IP5) [m] exploiting available aperture, tight collimator settings, stability Bunch spacing [ns] 2550 Number of bunches Half nominal number of bunches, given by 50 ns Bunch intensity [ppb] 1.15 x – 1.7 x % of nominal Normalized emittance [  m] 3.75 at collision ~2.5 at collision again remarkable injector performance (but emittance preservation challenges in LHC) Peak luminosity [cm -2 s -1 ] 1.0 x x % of design luminosity

9 WHAT WE HAVE LEARNT SO FAR… Moriond QCD 2013

10 Excellent single beam lifetime – vacuum Excellent magnetic field quality Beam-Beam – Head-on is not a limitation Collective effects! – Single and coupled bunch instabilities Better than expected aperture  * reach established and exploited – Not trivial: small beams at the IP means large beams at the triplets! In general – beam & optics Moriond QCD 2013

11 Operational robustness - LHC cycle Altogether good lifetime throughout the whole LHC cycle Machine remarkably reproducible – optics, orbit, collimator set-up, tune… Moriond QCD 2013 Pre-cycleInjection450 GeVRampSqueezeCollide

12 2012 Machine protection – the challenge met Beam 140 MJ Beam 140 MJ Not a single beam- induced quench at 4 TeV 11 magnet quenches at 450 GeV – injection kicker flash-over LHC status - Kruger 12 R. Assmann Can’t over stress the importance of this to the success of the LHC (so far). From commissioning to real confidence in under two years.

13 Availiability Moriond QCD 2013 Alick Macpherson

14 Machine performing well, huge amount of experience & understanding gained. Good system performance, excellent tools, reasonable availability following targeted consolidation. This is the legacy for post LS Moriond QCD 2013

15 LS Moriond QCD 2013

16 Moriond QCD 2013

17 LHC MB circuit splice consolidation proposal Phase I Installation of new shunts Phase II Application of clamp and bus bar insulation Phase III Insulation between bus bar and to ground, Lorentz force clamping Moriond QCD 2013

18 POSSIBLE LIMITATIONS FOR POST LS Moriond QCD 2013

19 25 ns & electron cloud Photoelectrons from synchrotron radiation accelerated by the proton beam Electrons bounce into chamber wall → secondary electrons are emitted Due to short bunch spacing, high bunch intensity and low emittance: electron cloud build-up! Moriond QCD

20 Electron cloud: possible consequences single-bunch instability multi-bunch instability emittance growth gas desorption from chamber walls heat load particle losses, interference with diagnostics,… Moriond QCD 2013 Electron bombardment of a surface has been proven to reduce drastically the secondary electron yield (SEY) of a material. This technique, known as scrubbing, provides a mean to suppress electron cloud build-up and its undesired effects

21 25 ns & electron cloud Downside: scrubbing takes time (several weeks!) Electron cloud free environment after scrubbing at 450 GeV seem not be reachable in acceptable time. Post LS1 operation with high heat load and electron cloud density seems to be unavoidable Moriond QCD 2013 Reconstructed comparing heat load meas. and PyECLOUD sims. The SEY evolution significantly slows down during the last scrubbing fills (more than expected from simulations and lab. experiments) End of 2012 tests Giovanni Iadarola and team - Evian 12

22 UFOs UFOs: showstopper for 25 ns and 6.5 TeV? – 10x increase and harder UFOs – (but no increase in low intensity fills) UFO “scrubbing”: does it work? Deconditioning expected after LS1 Post LS1 operation: start with lower energy and/or 50 ns Moriond QCD 2013 Tobias Baer

23 OPERATIONAL SCENARIOS AFTER LS Moriond QCD 2013

24 Beam from injectors LS1 to LS2 Number of bunches Bunch intensity [10 11 ppb] Emittance at injection [  m] Emittance in collisions [  m] 25 ns ~nominal ns BCMS ns ns BCMS BCMS = Batch Compression and (bunch) Merging and (bunch) Splittings Batch compression & triple splitting in PS 24

25 50 ns versus 25 ns 50 ns25 ns GOOD Lower total beam current Higher bunch intensity Smaller emittance Lower pile-up BAD High pile-up Need to level Pile-up stays high High bunch intensity – instabilities… Larger crossing angle; higher  * Larger emittance Electron cloud: need for scrubbing; emittance blow-up; Higher UFO rate Higher injected bunch train intensity Higher total beam current Expect to move to 25 ns because of pile up… Moriond QCD 2013

26  * & crossing angle  * reach depends on: – available aperture – collimator settings – required crossing angle which in turn depends on emittance bunch spacing Moriond QCD 2013

27 Potential performance Number of bunches Bunch intensity [10 11 ppb]  */ crossing angle Emittance LHC [  m] Peak Luminosity [cm- 2 s -1 ] ~Pile-up Int. Lumi per year [fb -1 ] 25 ns / x ~24 25 ns BCMS / x ~45 50 ns / x level to 0.8 x level to 44 ~40* 50 ns BCMS / x level to 0.8 x level to 44 ~40* All values at 6.5 TeV collision energy 1.1 ns bunch length 150 days proton physics 85 mb cross-section * different operational model – caveat - unproven All numbers approximate 27

28 Potential performance – in words Nominal 25 ns – gives more-or-less nominal luminosity (1.0 x cm- 2 s -1 ) BCMS 25 ns – gives a healthy 1.7 x cm- 2 s -1 – peak around 50 – 83% nominal intensity Nominal 50 ns – gives a virtual luminosity of 1.6 x cm- 2 s -1 with a pile-up of 87 – levelling mandatory BCMS 50 ns – gives a virtual luminosity of 2.3 x cm- 2 s -1 with a pile-up of 138 – levelling even more mandatory Moriond QCD 2013

29 2015 STRATEGY – FOR DISCUSSION LHC Operation 29

30 30

31 Conclusions Availability better than might have been expected. Machine now magnetically, optically, operationally well understood System performance – generally good to excellent – issues identified and being addressed Limitations well studied, well understood and quantified – still some potential implications for post LS1 operation Restart post LS1 with 50 ns – before moving to 25 ns – non electron cloud free environment to be accepted at least initially Moriond QCD 2013

32 BACKUP LHC Operation 32

33 Post LS1 energy Our best estimates to train the LHC (with large errors) –  30 quenches to reach 6.25 TeV –  100 quenches to reach 6.5 TeV Two quenches/day  2 to 5 days of training per sector The plan – Try to reach 6.5 TeV in four sectors in March 2014 – Based on that experience, we decide if to go at 6.5 TeV or step back to 6.25 TeV in March 2014 Ezio Todesco – Chamonix Moriond QCD 2013

34 2015 strategy – more detailed Low intensity commissioning of full cycle – 2 months First stable beams – low luminosity Intensity ramp-up – 1 to 2 months 50 ns operation (at pile-up limit) – Characterize vacuum, heat load, electron cloud, losses, instabilities, UFOs, impedance Options thereafter: – 1 week scrubbing for 25 ns, say 1 week to get 25 ns operational (if  * and crossing angles are changed), intensity ramp up with 25 ns with further scrubbing required – Commission levelling of 50 ns and push bunch intensity up, emittance down… not at all favored by experiments! Moriond QCD 2013


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