LHC Beam Operations Past, Present and Future

Maria Kuhn on behalf of the LHC team

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April 2010Squeeze to 3.5 m

2008 2009 2010 2011

LHC Timeline

September 10, 2008First beams around

September 19, 2008Disaster Accidental release of 600 MJ stored in one sector of LHC dipole magnets

August 2008First injection test

August, 20112.3 x 1033, 2.6 fb-1

1380 bunches

October 14 20101 x 1032

248 bunches

November 2010IonsMarch 30, 2010

First collisions at 3.5 TeV

1380

June 28 20111380 bunches

November 29, 2009Beam back

2012

18 June, 20126.6 fb-1

to ATLAS & CMS

6 June, 20126.8 x 1033

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4 July, 2012Higgs like discovery

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Integrated luminosity 2010-2012

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2012: ~30 collisions/xing at beginning of fill

with tails up to ~ 40.

2011: average 12 collisions/xing, with tails up to ~20

Record peak luminosity: 7.73 x 1033cm-2s-1

Peak luminosity 2010-2012

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ALICE and LHCb (and TOTEM and ALFA)

Peak luminosities achieved in ALICE around 5 x 10 30cm-2s-1

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LHCb 2012: 1.9 fb-1 delivered!

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Luminosity

N Number of particles per bunchKb Number of bunchesf Revolution frequency

σ* Beam size at interaction pointF Reduction factor due to crossing angleε Emittance εn Normalized emittanceβ* Beta function at IP

In 2012:εn = 2.5 mme = 5.9 x 10-4 mms* = 18.8 mm(p = 4 TeV, b* = 0.6m)

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Performance from injectors 2012Bunch

spacing[ns]

Protons per bunch [ppb]

Norm. emittance H&V

[mm]Exit SPS

Design report

25 1.15 x 1011 3.5

injected into LHC

50 1.7 x 1011 1.8

tested 25 1.2 x 1011 2.7

N.B. the importance of 50 ns in the performance so far.This at the expense of high pile-up.

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LHC Peak Performance in 2012

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Design Report 2012 Comments

Energy [TeV] 7.0 4.0 4/7 design energy

b* (IP1&IP5) [m] 0.55 0.6 exploiting available aperture,

tight collimator settings, stabilityBunch spacing [ns] 25 50

Number of bunches 2808 1374 Half nominal number of bunches,

given by 50 nsBunch intensity [ppb] 1.15 x 1011 1.6 – 1.7 x 1011 150 % of nominal

Normalized emittance [mm]

3.75 at collision

~2.5 at collision

again remarkable injector performance (but emittance preservation challenges in LHC)

Peak luminosity [cm-2s-1] 1.0 x 1034 7.73 x 1033 77 % of design luminosity

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WHAT WE HAVE LEARNT SO FAR…

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• 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• b* reach established and exploited

– Not trivial: small beams at the IP means large beams at the triplets!

In general – beam & optics

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Operational robustness - LHC cycle

• Altogether good lifetime throughout the whole LHC cycle

• Machine remarkably reproducible– optics, orbit, collimator set-up, tune…

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Pre-cycle Injection 450 GeV Ramp Squeeze Collide

LHC status - Kruger 12

2012 Machine protection – the challenge met

3-12-2012

Beam140 MJ

Not a single beam-induced quench at 4 TeV

11 magnet quenches at 450 GeV – injection kicker flash-over

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.

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Availiability

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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 LS1

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LS1

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LHC MB circuit splice consolidation proposal

Phase IInstallation of new shunts

Phase IIApplication of clamp and bus bar insulation

Phase IIIInsulation between bus bar and to ground, Lorentz force clamping

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POSSIBLE LIMITATIONS FOR POST LS1

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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!

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Electron cloud: possible consequences• single-bunch instability• multi-bunch instability• emittance growth• gas desorption from chamber walls• heat load • particle losses, interference with diagnostics,…

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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

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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.

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10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5x 1014

Time [h]

Tota

l int

ensi

ty [p

]

10 20 30 40 50 60 70 801.35

1.4

1.45

1.5

1.55

1.6

Time [h]

SEY

max

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 testsGiovanni Iadarola and team - Evian 12

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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

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Tobias Baer

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OPERATIONAL SCENARIOS AFTER LS1

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Beam from injectors LS1 to LS2 Number of

bunchesBunch intensity

[1011 ppb]Emittance at

injection [mm]

Emittance in collisions

[mm]

25 ns ~nominal 2760 1.15 2.8 3.7525 ns BCMS 2520 1.15 1.4 1.950 ns 1380 1.65 1.7 2.350 ns BCMS 1260 1.6 1.2 1.6

BCMS = Batch Compression and (bunch) Merging and (bunch) Splittings

Batch compression & triple splitting in PSRende Steerenberg, Gianluigi Arduini,

Theodoros Argyropoulos, Hannes Bartosik, Thomas Bohl, Karel Cornelis, Heiko Damerau, Alan Findlay, Roland Garoby, Brennan Goddard, Simone Gilardoni, Steve Hancock, Klaus Hanke, Wolfgang Höfle, Giovanni Iadarola, Elias Metral, Bettina Mikulec, Yannis Papaphilippou, Giovanni Rumolo, Elena Shaposhnikova,…

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50 ns versus 25 ns50 ns 25 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 b*• Larger emittance• Electron cloud: need for scrubbing;

emittance blow-up; • Higher UFO rate• Higher injected bunch train intensity• Higher total beam current

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b* & crossing angle• b* reach depends on:

– available aperture– collimator settings – required crossing angle which in turn depends on

• emittance• bunch spacing

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Potential performanceNumber

of bunches

Bunch intensity

[1011 ppb]

b*/crossing

angleEmittanceLHC [mm]

Peak Luminosity

[cm-2s-1]~Pile-up

Int. Lumi per year

[fb-1]

25 ns 2760 1.15 55/189 3.75 0.93 x 1034 25 ~2425 nsBCMS 2520 1.15 45/149 1.9 1.7 x 1034 52 ~45

50 ns 1380 1.6 42/136 2.51.6 x 1034

level to0.8 x 1034

87 level to

44 ~40*

50 nsBCMS 1260 1.6 38/115 1.6

2.3 x 1034

level to0.8 x 1034

138 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

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Potential performance – in words• Nominal 25 ns

– gives more-or-less nominal luminosity (1.0 x 1034 cm-2s-1)

• BCMS 25 ns – gives a healthy 1.7 x 1034 cm-2s-1

– peak <m> around 50– 83% nominal intensity

• Nominal 50 ns– gives a virtual luminosity of 1.6 x 1034 cm-2s-1 with a pile-up of 87– levelling mandatory

• BCMS 50 ns– gives a virtual luminosity of 2.3 x 1034 cm-2s-1 with a pile-up of 138– levelling even more mandatory03-14-2013 Moriond QCD 2013

LHC Operation 29

2015 STRATEGY – FOR DISCUSSION

10-12-12

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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

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LHC Operation 32

BACKUP

10-12-12

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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

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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 b* 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!

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