1. 6 months of beam operation in 2010
Status of the LHC
6 months of beam operation in 2010
LHC Status - SUSY Bonn
J. Wenninger
CERN
Drawing by
Sergio Cittolin

2. Outline Introduction LHC energy 2010/11
LHC performance targets and achievements
LHC beam operation
Outlook for 2010/11 and conclusions
LHC Status - SUSY Bonn

3. The Large Hadron Collider LHC
Installed in 26.7 km LEP tunnel
Depth of m
Lake of Geneva
LHC ring
LHC Status - SUSY Bonn
CMS, Totem
LHCb
Control Room
SPS ring
ATLAS, LHCf
ALICE

4. LHC layout and parameters
8 arcs (sectors), ~3 km each
8 long straight sections (700 m each)
beams cross in 4 points
2-in-1 magnet design with separate vacuum chambers → p-p collisions RF
- β* = 0.55 m (beam size =17 μm)
- Crossing angle = 285 μrad
- L = 1034 cm-2 s-1
Nominal LHC parameters
Beam energy (TeV)
7.0
No. of particles per bunch
1.15x1011
No. of bunches per beam
2808
Stored beam energy (MJ)
362
Transverse emittance (μm)
3.75
Bunch length (cm)
7.55

5. LHC accelerator complex
≥ 7 seconds from source to LHC
Beam 1
TI2
Beam 2
TI8
LHC proton path
The LHC needs most of the CERN accelerators...

6. LHC challenges
The LHC surpasses existing accelerators/colliders in 2 aspects :
The energy of the beam of 7 TeV that is achieved within the size constraints of the existing 26.7 km LEP tunnel.
LHC dipole field 8.3 T
HERA/Tevatron ~ 4 T
The luminosity of the collider that will reach unprecedented values for a hadron machine:
LHC pp ~ 1034 cm-2 s-1
Tevatron pp 3x1032 cm-2 s-1
SppS pp 6x1030 cm-2 s-1
Very high field magnets and very high beam intensities:
Operating the LHC is a great challenge.
There is a significant risk to the equipment and experiments.
A factor 2 in field
A factor 4 in size
LHC Status - SUSY Bonn
A factor 30
in luminosity

7. LHC dipole magnet 1232 dipole magnets.
B field 8.3 T ( K (super-fluid Helium)
2 magnets-in-one design : two beam tubes with an opening of 56 mm.
Operating challenges:
Dynamic field changes at injection.
Very low quench levels (~ mJ/cm3)
LHC Status - SUSY Bonn

8. Stored energy Increase with respect to existing accelerators :
A factor 2 in magnetic field
A factor 7 in beam energy
A factor 200 in stored beam energy
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Damage threshold

9. Collimation
To operate at nominal performance the LHC requires a large and complex collimation system
Previous colliders used collimators mostly for experimental background conditions.
beam
1.2 m
Ensure ‘cohabitation’ of:
360 MJ of stored beam energy,
super-conducting magnets with quench limits of few mJ/cm3
Almost 100 collimators and absorbers.
Alignment tolerances < 0.1 mm to ensure that over 99.99% of the protons are intercepted.
Primary and secondary collimators are made of Carbon to survive large beam loss.
LHC Status - SUSY Bonn

10. Outline Introduction LHC energy 2010/11
LHC performance targets and achievements
LHC beam operation
Outlook for 2010/11 and conclusions
LHC Status - SUSY Bonn

11. LHC target energy: the way down
When
Why
All main magnets commissioned for 7TeV operation before installation
Detraining found when hardware commissioning sectors in 2008
5 TeV poses no problem
Difficult to exceed 6 TeV
Machine wide investigations following S34 incident showed problem with joints
Commissioning of new
Quench Protection System
(nQPS)
7 TeV
Design
12 kA
5 TeV
Summer 2008
Detraining
9 kA
LHC Status - SUSY Bonn
Late 2008
3.5 TeV
Joints
Spring 2009
6 kA
1.18 TeV
Nov. 2009
nQPS
2 kA
450 GeV

12. LHC target energy: the way up
When
What
Train magnets
6.5 TeV is in reach
7 TeV will take time
Repair joints
Complete pressure relief system
Commission nQPS system
7 TeV
2014 ?
Training
6 TeV
2013
Stabilizers
LHC Status - SUSY Bonn
2011
3.5 TeV
nQPS
2010
1.18 TeV
2009
450 GeV

13. Ramp rate
At the start of the run the ramp rate had to be limited to 2 A/s (1.2 GeV/s) for magnet protection reasons.
Ramp duration TeV: 46 minutes
Since mid-July the rate for down-ramps and magnet pre-cycles (magnetic history reset) were increased to nominal value of 10 A/s (6 GeV/s).
Ramp speed with beam will be increased to 10 A/s (6 GeV/s) in September.
Ramp duration TeV: 16 minutes
LHC Status - SUSY Bonn
3500 GeV
2 A/s
10 A/s
450 GeV

14. Outline Introduction LHC energy 2010/11
LHC performance targets and achievements
LHC beam operation
Outlook for 2011 and conclusions
LHC Status - SUSY Bonn

15. Collider luminosity Collision rate is proportional to luminosity
Parameters:
Number of particles per bunch 
Number of bunches per beam kb
Beam sizes at the collision point s
Betatron function (focusing) at IP b*
Normalized transverse emittance e
Revolution frequency f
Crossing angle factor F ~ 1
Intensity
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Interaction Region
Beam quality (emittance)
“Thus, to achieve high luminosity, all one has to do is make (lots of) high population bunches of low emittance to collide at high frequency at locations where the beam optics provides as low values of the amplitude functions as possible.”
PDG 2005, chapter 25

16. Collimation performance
Present stage collimation system sets limit to total intensity.
Assumptions:
Max. loss rate of 0.1%/s assumed (0.2h lifetime).
Ideal cleaning.
Performance degradation:
Deformed jaws.
Tilt & offset & gap errors.
Machine alignment.
Machine stability
Tight coll. settings are a challenge at early stage.
Intermediate coll. settings make use of aperture to relax tolerances.
Collimator settings
LHC Status - SUSY Bonn
Imax ~61013 protons per beam at 3.5TeV with intermediate collimator settings
(about 20% nominal intensity)
30 MJ stored beam energy

17. Goals for 2010-2011 Collect 1 fm-1 of data/exp at 3.5 TeV/beam.
2009
2010
2011
Repair of Sector 34
1.18
TeV
nQPS
6kA
3.5 TeV
Isafe < I < 0.2 Inom
β* ~ 3.5 m
Ions
~ 0.2 Inom
No Beam B
Beam
Goal for the run:
Collect 1 fm-1 of data/exp at 3.5 TeV/beam.
To achieve this goal the LHC must operate in 2011 with
L ~ 2×1032 cm-2s-1 ~ Tevatron Luminosity
which requires ~700 bunches of 1011 p each ~ 7x1013 p
(stored energy of ~30 MJ – 10% of nominal)
Implications:
Strict and clean machine setup.
Machine protection systems at near nominal performance.

18. Commissioning phases Phase 1: low intensity commissioning of the LHC.
Low intensity single bunches. No/very limited risk of damage.
Commissioning of the protection systems.
Phase 2: operation without crossing angle.
Bunches with large spacing (> ms).
Up to around kb=50 bunches.
Simplified operation in the interaction regions.
Machine protection system running in.
Phase 3: operation with crossing angle.
Bunches with close spacing (≤ 150 ns).
Aim for ~400 bunches in 2010.
LHC Status - SUSY Bonn
We are at end of phase 2

19. Commissioning steps in 2010
Restart with beam.
Commissioning to 3.5 TeV.
Low intensity beams.
First collisions at 3.5 TeV.
Squeeze (b* reduction) commissioning.
b* = 2 m for collisions (injection 10 /11 m).
Increase number of bunches to 13 per beam.
Bunch population N = 31010 p ~ 30% of nominal.
Switch to nominal bunch intensity.
Luminosity ~N2 Gain ~ 10
Back off in b* to 3.5 m. Loss ~ 0.6
Increase number of bunches up to 49 per beam.
Bunch population N = 9-101010 p.
Stability run in August with 25 bunches/beam.
Feb. 28th
March
March 30th
Mid April
Mid-April – mid-May
June
July - August
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20. Peak luminosity performance
Peak luminosity = 9.51030 cm-2s-1
(48 bunches/beam, 36 colliding bunches)
LHC Status - SUSY Bonn
36 colliding
pairs
8 colliding
pairs/IR

21. Integrated luminosity
Integrated luminosity ~ 2.2 pb-1 ( )
Figures : status 16th Aug 2010
LHC Status - SUSY Bonn

22. Availability About 30% of time in physics data-taking.
A lot commissioning still on-going !
Min. turn-around time collisions to collisions ~4 hours.
3.5 TeV
Energy
LHC Status - SUSY Bonn
6.51030
cm-2s-1
01 – 21 August 2010
Lumi

23. Outline Introduction LHC energy 2010/11
LHC performance targets and achievements
LHC beam operation
Outlook for 2010/11 and conslusions
LHC Status - SUSY Bonn

24. Machine Protection
Extensive testing of the machine protection system was performed, mostly in March/April 2010.
 20’000 signal enter the beam abort system.
Only about 10% of the beams above injection energy are dumped by the operators !
LHC Status - SUSY Bonn
Beam dumps > 450 GeV

25. Extraction septum magnets
Beam dump
Extraction kickers
Dilution kickers
Extraction septum magnets
Dump block
Complex beam dumping system commissioned.
Beam swept over dump surface (power load)
LHC Status - SUSY Bonn

26. Aperture and collimation
With collisions the aperture limit of the LHC is in the strong focusing quadrupoles (triplets) that are installed just next to the experiments.
Hierarchy of collimators must be preserved in all phases to avoid quenching super-conducting magnets and for damage protection.
b* is presently limited to 3.5 m by aperture and tolerances.
Collimation hierarchy
Exp.
LHC Status - SUSY Bonn
Primary
6 σ
Secondary
8.8 σ
Dump Protection
10.5 σ
Tertiary
15 σ
Triplet
18 σ

27. Collimation
Collimator alignment is made with beam and then monitored from the loss distribution around ring.
Beam cleaning efficiencies ≥ 99.98% ~ as designed
TCT = tertiary coll.
LHC Status - SUSY Bonn

28. Magnet quenches
A local loss of some ~107 protons/s may lead to a quench at 3.5 TeV.
Compared to 51012 stored protons.
So far no quench was observed at 3.5 TeV thanks to the excellent performance of the collimation system for absorbing lost protons and to the fast reaction of the loss monitors.
In only 5 occasions did some beam escape and was lost locally around super-conducting elements.
Beam loss detection system dumped the beams in time before a magnet could quench.
Events are under investigation... Possible cause are dust particles!
LHC Status - SUSY Bonn
The absence of problems with beam loss and quenches is good news for increasing the beam intensity !

29. Relative beam size error
Beam Optics
Beam optics is within specifications and reproducible over 3 months.
A stable machine is essential to reach high intensity and minimize frequent setup overhead, in particular for collimation.
Relative beam size error
 (Db/b)   10%
LHC Status - SUSY Bonn
Specification:  0.2

30. Beam Emittance
Beam emittances below nominal can be produced and injected into the LHC (e = 2 mm rad as compared to 3.5 mm rad design).
This provides margin for emittance blow-up due to various noise sources – great value for a machine in early phase of operation.
Momentum and magnetic fields at the LHC are sufficiently strong for the protons to emit visible light that can be used to image the beams in real-time.
The energy loss per turn is 7 keV at 7 TeV, 0.4 keV at 3.5 TeV.
LHC Status - SUSY Bonn
Beam emittances in collisions are now mostly at design or below – the only exception being beam 2 in the vertical plane.

31. Noise on the beam
The beams are periodically excited by an unknown noise source (‘hump’) of varying frequency – affects mostly beam2 in vertical plane.
Amplitude ~ mm.
When the frequency coincides with the beam eigen-modes (‘tunes’) it leads to emittance blow-up.
Time
Horizontal plane
Beam 1
Beam 2
LHC Status - SUSY Bonn
Tune
1 hour
Noise hump
Vertical plane
Beam 1
Beam 2
Noise hump
Frequency/Rev. frequency

32. Beam-beam interaction
Effects of the beam-beam force are visible on the lifetime of the various bunches.
Also sensitive to tune working point.
This will become even more complicated with trains of bunches.
- black witness bunches (zero collisions); - red bunches colliding in IP 1 5 and 2 (3 collisions); - blue bunches colliding in IP 1 5 and 8 (3 collisions); - green bunches colliding in IP 2 and 8 (2 collisions).
LHC Status - SUSY Bonn
Beams in collision
Beam1
Beam2
Intensity
loss (%)

33. Lifetimes Beam intensity lifetimes with colliding beams:
Dip to 2-5 hours in first minutes.
Progressive increase to ~100 hours.
Luminosity lifetimes:
Around hours due to emittance growth.
LHC Status - SUSY Bonn
Lifetime (h)
Beams in collision
300
200
100

34. Present LHC parameters
Nominal
Limited by
N (p/bunch)
11011
1.151011
kb (no. bunches) 48
2808
Machine protection
e (mm rad)
2.5-5
3.75
b* (m)
3.5
0.55
Aperture, tolerances
L (cm-2s-1)
9.51030
1034
LHC Status - SUSY Bonn
Squeezing at the IP (b*) is limited by aperture and tolerances.
Beams are larger at 3.5 TeV ~ 1/g.
sx = sy = ~45-60 mm - nominal value is 15 mm at 7 TeV.
The number of bunches is limited by machine protection and by the fact that LHC is not yet operated with bunch trains.
Bunch separation is large (>1 ms), no crossing angle at the IR.

35. Outline Introduction LHC energy 2010/11
LHC performance targets and achievements
LHC beam operation
Outlook for 2010/11 and conclusions
LHC Status - SUSY Bonn

36. Fall 2010
To reach the target of 1032 cm-2s-1 an intensity increase of factor 10 is required until end of October (start of Pb ion run).
But the most important is the slope of the increase!
LHC Status - SUSY Bonn
Switch to
bunch trains
336

37. Fall 2010-2011 To reach the target of 1032 cm-2s-1,
the intensity must be increased very rapidly,
bunch train operation must be commissioned (1-2 weeks).
>> Achievable integrated L is ~ pb-1 in 2010.
The goal is quite ambitious given the time left before the Pb ion run, but the main point is not the exact final luminosity, but rather that no problems or show-stoppers are encountered on the way.
So far there are no limitations.
The prospects for a very good run in 2011, 1 fm-1 of data, will be very high with a problem-free intensity (luminosity) increase in 2010.
But the most important is the slope of the increase!
LHC Status - SUSY Bonn

38. Summary and outlook 2011
Main beam commissioning phase of the LHC ended in June when operation with ~ nominal bunch intensities was established.
The LHC is now operating for physics data taking, with some interleaved commissioning activities in view of higher intensity.
Efficiency for physics data taking ~30% with peak luminosities of 9.5x1030 cm-2s-1
Machine protection and collimation systems perform well, and one can anticipate a luminosity increase towards few 1031 to 1032 cm-2s-1 in 2010.
Final value for 2010 will depend on machine availability and length of commissioning bunch train operation.
A long run at 1032 cm-2s-1 or above is in sight for 2011.
1 fm-1 of integrated data is in reach.
LHC Status - SUSY Bonn