LHC Beam Operations
Past, Present and Future
Maria Kuhn on behalf of the LHC team
03-14-2013
Moriond QCD 2013
August 2008
First injection test
August, 2011
November 29, 2009
2.3 x 1033, 2.6 fb-1
1380 bunches
Beam back
4 July, 2012
September 10, 2008
Higgs like discovery
June 28 2011
First beams around
October 14
2010
April 2010
1 x 1032
248 bunches
1380 bunches
1380
6 June, 2012
6.8 x 1033
Squeeze to 3.5 m
2008
2009
2010
03-14-2013
Disaster
Accidental release
of 600 MJ stored
in one sector of
LHC dipole
magnets
2012
November 2010
Ions
March 30, 2010
September 19,
2008
2011
First collisions at
3.5 TeV
18 June, 2012
6.6 fb-1
to ATLAS & CMS
Moriond QCD 2013
LHC Timeline
2
Integrated luminosity 2010-2012
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Peak luminosity 2010-2012
2011: average
12 collisions/xing,
with tails up to ~20
Record peak luminosity:
7.73 x 1033cm-2s-1
2012: ~30 collisions/xing
at beginning of fill
with tails up to ~ 40.
ALICE and LHCb
(and TOTEM and ALFA)
LHCb 2012:
1.9 fb-1
delivered!
Peak luminosities achieved in ALICE around 5 x 10 30cm-2s-1
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Luminosity
N kb f
N kb f g
L=
F
=
F
* *
*
4ps xs y
4pen b
2
2
N
Number of particles per bunch
Kb
Number of bunches
f
Revolution frequency
s = be
*
σ*
Beam size at interaction point
F
Reduction factor due to crossing angle
ε
Emittance
εn
Normalized emittance
β*
Beta function at IP
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*
In 2012:
εn = 2.5 mm
e = 5.9 x 10-4 mm
s* = 18.8 mm
(p = 4 TeV, b* = 0.6m)
6
Performance from injectors 2012
Design
report
injected
into LHC
tested
Bunch
spacing
[ns]
Protons per
bunch [ppb]
Norm.
emittance H&V
[mm]
Exit SPS
25
1.15 x 1011
3.5
50
1.7 x 1011
1.8
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
Design
Report
2012
Energy [TeV]
7.0
4.0
4/7 design energy
b* (IP1&IP5) [m]
0.55
0.6
exploiting available aperture,
tight collimator settings, stability
25
50
2808
1374
Bunch spacing
[ns]
Number of
bunches
Comments
Half nominal number of bunches,
given by 50 ns
Bunch intensity
[ppb]
1.15 x 1011
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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1.6 – 1.7 x 1011 150 % of nominal
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WHAT WE HAVE LEARNT SO
FAR…
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In general – beam & optics
• 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!
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Operational robustness - LHC cycle
Pre-cycle Injection 450 GeV Ramp
Squeeze Collide
• Altogether good lifetime throughout the whole
LHC cycle
• Machine remarkably reproducible
– optics, orbit, collimator set-up, tune…
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2012 Machine protection – the challenge met
Beam
140 MJ
11 magnet quenches at 450 GeV –
injection kicker flash-over
Not a single beaminduced quench at 4 TeV
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.
3-12-2012
LHC status - Kruger
R. Assmann
12
Availiability
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Alick Macpherson
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13
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
Phase
III
PhaseIII
Insulation between
Application
bus
of
bar
clamp
and of
to
and
ground,
busshunts
barLorentz
insulation
force clamping
Installation
new
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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,…
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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Total intensity [p]
2.5
2
1.5
25 ns & electron cloud
1
0.5
The SEY
evolution significantly slows down during the last scrubbing
0
10
20
30
40
50
60
70
80
Time [h]
fills (more than expected from simulations and lab. experiments)
1.6
Reconstructed comparing heat load meas. and PyECLOUD sims.
SEY max
1.55
1.5
1.45
1.4
1.35
End of 2012 tests
Giovanni Iadarola and team - Evian 12
10
20
30
40
50
60
70
80
Time [h]
• 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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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
Tobias Baer
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OPERATIONAL SCENARIOS
AFTER LS1
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Beam from injectors LS1 to LS2
Number of
bunches
Bunch intensity
[1011 ppb]
Emittance at
injection
[mm]
Emittance in
collisions
[mm]
25 ns ~nominal
2760
1.15
2.8
3.75
25 ns BCMS
50 ns
50 ns BCMS
2520
1380
1260
1.15
1.65
1.6
1.4
1.7
1.2
1.9
2.3
1.6
BCMS = Batch Compression and (bunch) Merging and (bunch) Splittings
Rende 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,…
Batch compression &
triple splitting in PS
24
50 ns versus 25 ns
GOOD
50 ns
25 ns
• Lower total beam current
• Higher bunch intensity
• Lower pile-up
• Smaller emittance
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
Expect to move to 25 ns because of pile up…
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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 performance
Number
of
bunches
Bunch
intensity
[1011 ppb]
b*/
crossing
angle
Emittance
LHC [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
~24
25 ns
BCMS
2520
1.15
45/149
1.9
1.7 x 1034
52
~45
2.5
1.6 x 1034
level to
0.8 x 1034
87
level to
44
~40*
1.6
2.3 x 1034
level to
0.8 x 1034
138
level to
44
~40*
50 ns
50 ns
BCMS
•
•
•
•
•
1380
1260
1.6
1.6
42/136
38/115
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 approximate27
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 mandatory
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2015 STRATEGY
– FOR DISCUSSION
10-12-12
LHC Operation
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30
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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BACKUP
10-12-12
LHC Operation
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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
Ezio Todesco – Chamonix 12
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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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