1. The Status of the LHC machine
L. Ponce
CERN /Beams Department
Operation group

2. Outline Introduction LHC energy in 2010/2011 LHC performances
High intensity issues
Outlook
LHC status – Moriond 2011

3. 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)
7.6

4. 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 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 – Moriond 2011
A factor 30
in luminosity

5. Stored energy
The present beam intensity will slice open a vacuum chamber even at injection
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
80 kg TNT
LHC status – Moriond 2011

6. Outline Introduction LHC energy in 2010/2011 LHC performances
High intensity issues
Outlook
LHC status – Moriond 2011

7. 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 – Moriond 2011
Late 2008
3.5 TeV
Joints
Spring 2009
6 kA
1.18 TeV
Nov. 2009
nQPS
2 kA
450 GeV 7

8. 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
2015 ?
Training
6 TeV
2014
Stabilizers
LHC status – Moriond 2011
2011
3.5 TeV
nQPS
2010
1.18 TeV
2009
450 GeV 8

9. (Probability) Maximum Safe Energy
Probability per Year of burning an interconnect
Going to 4TeV, 50s implies a significant increase in the risk of burning an interconnect
LHC Status – Moriond 2011
Remaining choice
Presented in Chamonix 2011 by A. Verweij

10. Outline Introduction LHC energy in 2010/2011 LHC performances
High intensity issues
Outlook
LHC status – Moriond 2011

11. Luminosity : collider figure-of-merit
The event rate N for a physics process with cross-section s is proprotional to the collider Luminosity L:
“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
LHC status – Moriond 2011
High beam “brillance” N/e
(particles per phase space volume)
 Injector chain performance !
To maximize L:
Many bunches (k)
Many protons per bunch (N)
Small beam sizes s*x,y= (b *e)1/2
b * : beam envelope (optics)
e : beam emittance, the phase space volume occupied by the beam (constant along the ring)
Small envelope
 Strong focusing !
Optics property
Beam property 11

12. Peak luminosity performance
Peak luminosity > 21032 cm-2s-1
(368 bunches/beam, 348 colliding bunches)
LHC status – Moriond 2011
Integrated proton luminosity 2010 ~48 pb-1 12

13. Associated LHC parameters
2010
Nominal
Limited by
Energy
3.5 TeV
7 TeV
Hardware
N (p/bunch)
1.11011
1.151011
kb (no. bunches)
368
(348 coll/IP)
2808
Machine protection
e (mm rad)
2.5-5
3.75
b* (m)
3.5 (3.5)
0.55 (10)
Aperture, tolerances
Stored energy (MJ) 28
360
L (cm-2s-1)
21032
1034
LHC status – Moriond 2011
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. 13

14. Outline Introduction LHC energy in 2010/2011 LHC performances
High intensity issues
Outlook
LHC status – Moriond 2011

15. SEUs QPS crate SEU count (RADMON) during off momentum loss map
LHC status – Moriond 2011
Thijs Wijnands
Not a problem at the moment but being monitored carefully

16. Unidentified Flying Objects - UFOs
As the beam intensity was increased unexpected fast beam loss events were observed in the super-conducting regions of the ring:
Fast loss over ~0.5-2 ms, leading to a dump of the beam.
Most events occurred during ‘rock’ stable periods.
Losses in regions of very large aperture.
The hypothesis quickly emerged that it is not the beam that moves to the aperture, but rather the opposite !
‘Dust’ particles ‘falling’ into the beam, estimated size ~100 mm thick Carbon-equivalent object.
We do not understand the mechanism that triggers such events.
It is clearly induced by (presence of) beam – electromagnetic fields at the surface of the vacuum chamber. Sparking ???
Good news: signal amplitude seems to not depend on beam intensity
Strategy for 2011: increase the BLM thresholds
LHC status – Moriond 2011 16

17. Intensity and vacuum (150 ns)
Vacuum pressure increases were observed around the 4 experiments from the moment LHC switched to 150 ns train operation
Intensity
2·1013 p+
LHC status – Moriond 2011
3·10-7 mbar
Pressure
10-7 mbar 17

18. Vacuum effects
It was not possible to operate the LHC with bunch spacing of 50 ns for experiments data taking because the vacuum pressure increases were already too large at injection.
Pressures easily exceeded 4x10-7 mbar (normal is 10-9 or less) leading to closure of the vacuum valves.
Signs of cleaning by beam, with strong dependence on bunch intensity and bunch spacing.
Consistent with the signature of electron clouds.
e- cloud drive pressure rise, beam unstabilities and possibly overload the cryogenic system by the heat deposited on the chamber walls !
LHC status – Moriond 2011
 The cloud can ‘cure itself’: the impact of the electrons cleans the surface (Carbon migration), reduces the electron emission probability and eventually the cloud disappears – ‘beam scrubbing’
Inject as much beam as you can (run at the limit of the vacuum / beam stability), operate for some time and Iterate until conditions are acceptable / good ( several days) – experience from the SPS. 18

19. Outline Introduction LHC energy in 2010/2011 LHC performances
High intensity issues
Outlook
LHC status – Moriond 2011

20. Present LHC proton parameters
End 2010
Nominal
N (p/bunch)
1.21011
1.151011
kb (no. bunches)
368
2808
e (mm rad)
2.4-4
3.75
b* (m)
3.5
0.55
s* (mm)
45-60 16
L (cm-2s-1)
21032
1034
LHC status – Moriond 2011
Improvements for 2011:
Reduction of b* to 1.5 m (measured aperture larger than design).
Increase of N to 1.41011 or higher if possible.
Increasing number of bunches using 50 ns or 75 ns spacing.
Must overcome e-clouds effects. 20

21. Days for Luminosity operation
Item
Days
Total proton operation
264
5 MDs (4 days)
- 20
6 TS (4+1 days)
- 30
Special requests
- 10
Commissioning
- 20 to -30
Intensity ramp up
- 30 to -40
Scrubbing run
Total High intensity
124 to 144 (135 days for integrated L)
LHC status – Moriond 2011
Assume 135 days at peak luminosity
Stable period shrinks quickly if there are many exotic requests !

22. Estimated peak and integrated luminosity
Baseline for 2011 is 2e32 Peak and 1fb-1 (integrated)
But following 2010, we are confident we will do better
value for b* = 1.5m in IP1/ 5
days
HubnerFactor
Fills
with kb Nb
e11 e mm L
Hz/cm2
Stored energy MJ
L Int
fb-1
160
0.3
150 ns
368
1.2
2.5
~5.2e32
~30
~1.9
135
0.2
75 ns
936 2
1.8
~1.3e33
~1.6e33
~1.8e33
~75
~2.7
~3.3
~3.7
125
0.15
50 ns
1404
~2e33
~110
~2.8
LHC status – Moriond 2011
Possible integrated Luminosity of 2-3 fb-1

23. Conclusions Beam energy will stay at 3.5 TeV for 2011 run
For 2012 run, can be revisited based on 2011 run experience
Estimated no. of days at high luminosity ~135 days (for a total time of 260 days !) – 50% !!
In order not to waste time we must have a good plan and not let ourselves be diverted from the target of stable high intensity running.
Luminosity of 1033 cm-2s-1 could be reached with 75 ns beams.
Integrated L ~1-3 fb-1.
Optimum parameters to be selected carefully taken into account all parameters – for example injection efficiency may favor low e over high bunch charge.
Efficiency, efficiency, efficiency.
Not given yet… (UFOs, e-cloud, SEU)…but on the good way
LHC status – Moriond 2011

24. LHC status – Moriond 2011