Transcript Document

LHC Status - SUSY 2010 - Bonn
24.08.2010
Status of the LHC
6 months of beam operation in 2010
J. Wenninger
CERN
Drawing by
Sergio Cittolin
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Outline
Introduction
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The Large Hadron Collider LHC
Installed in 26.7 km LEP tunnel
Depth of 70-140 m
Lake of Geneva
LHC Status - SUSY 2010 - Bonn
CMS, Totem
Control Room
LHCb
ATLAS, LHCf
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ALICE
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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
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
- β* = 0.55 m (beam size =17 μm)
- Crossing angle = 285 μrad
- L = 1034 cm-2 s-1
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LHC accelerator complex
≥ 7 seconds from
source to LHC
Beam 1
Beam 2
TI8
TI2
LHC proton path
The LHC needs most of the CERN accelerators...
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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
LHC Status - SUSY 2010 - Bonn
constraints of the existing 26.7 km LEP tunnel.
LHC dipole field 8.3 T
A factor 2 in field
HERA/Tevatron
A factor 4 in size
~4T
 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
A factor 30
in luminosity
Very high field magnets and very high beam intensities:
 Operating the LHC is a great challenge.
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 There is a significant risk to the equipment and experiments.
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LHC dipole magnet

1232 dipole magnets.

B field 8.3 T (11.8 kA) @ 1.9 K
(super-fluid Helium)
Operating challenges:
o
Dynamic field changes at injection.
o
Very low quench levels (~ mJ/cm3)
2 magnets-in-one design : two beam
tubes with an opening of 56 mm.
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

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Stored energy
Increase with respect to existing accelerators :
• A factor 2 in magnetic field
• A factor 7 in beam energy
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• A factor 200 in stored beam energy
Damage threshold
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Collimation
 To
operate at nominal performance the LHC requires a large and
complex collimation system
o
Previous colliders used collimators mostly for experimental
background conditions.

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1.2 m
beam
Ensure ‘cohabitation’ of:
o
360 MJ of stored beam energy,
o
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.
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Outline
LHC energy 2010/11
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LHC target energy: the way down
When

All main magnets commissioned for
7TeV operation before installation
7 TeV
Why
2002-2007 Design
12 kA
LHC Status - SUSY 2010 - Bonn

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)
5 TeV Summer 2008 Detraining
9 kA
3.5 TeV
6 kA
1.18 TeV
Late 2008
Spring 2009
Nov. 2009
Joints
nQPS
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2 kA
450 GeV
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LHC target energy: the way up
When

Train magnets
– 6.5 TeV is in reach
– 7 TeV will take time

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Repair joints
 Complete pressure relief system

What
Commission nQPS system
7 TeV
6 TeV
3.5 TeV
2014 ? Training
2013
Stabilizers
2011
nQPS
2010
1.18 TeV
2009
450 GeV
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LHC Status - SUSY 2010 - Bonn
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.
o Ramp duration 0.45-3.5 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.
o Ramp duration 0.45-3.5 TeV: 16 minutes
3500 GeV
2 A/s
10 A/s
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450 GeV
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Outline
LHC performance targets and achievements
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Collider luminosity
N 2kb f
N 2kb f 
L
F
F
*
4s xs y
4b e
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
Parameters:
– Number of particles per bunch
– Number of bunches per beam

– Beam sizes at the collision point
– Betatron function (focusing) at IP
– Normalized transverse emittance
s
b*
e
– Revolution frequency
– Crossing angle factor
f
Collision rate is
proportional to luminosity
kb
Intensity
Interaction Region
Beam quality (emittance)
F~1
“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
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Collimation performance
Present stage collimation system
sets limit to total intensity.

Collimator settings
Assumptions:
Max. loss rate of 0.1%/s
assumed (0.2h lifetime).
o Ideal cleaning.
LHC Status - SUSY 2010 - Bonn
o

Performance degradation:
Deformed jaws.
o Tilt & offset & gap errors.
o Machine alignment.
o

Machine stability
Tight coll. settings are a
challenge at early stage.
o Intermediate coll. settings
make use of aperture to relax
tolerances.
o
 Imax
~61013 protons per beam at 3.5TeV with
intermediate collimator settings
(about 20% nominal intensity)
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30 MJ stored beam energy
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Goals for 2010-2011
2009
Repair of Sector 34
No Beam
2010
1.18 nQPS
TeV 6kA
B
3.5 TeV
Isafe < I < 0.2 Inom
β* ~ 3.5 m
2011
Ions
3.5 TeV
~ 0.2 Inom
Ions
β* ~ 3.5 m
Beam
Beam
Goal for the 2010-11 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.
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Commissioning phases

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

Phase 1: low intensity commissioning of the LHC.
o
Low intensity single bunches. No/very limited risk of damage.
o
Commissioning of the protection systems.
Phase 2: operation without crossing angle.
o
Bunches with large spacing (> 1 - 2.5 ms).
o
Up to around kb=50 bunches.
o
Simplified operation in the interaction regions.
o
Machine protection system running in.
Phase 3: operation with crossing angle.
o
Bunches with close spacing (≤ 150 ns).
o
Aim for ~400 bunches in 2010.
We are at end
of phase 2
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Commissioning steps in 2010

Restart with beam.
Feb. 28th

Commissioning to 3.5 TeV.
March
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Low intensity beams.

First collisions at 3.5 TeV.
March 30th

Squeeze (b* reduction) commissioning.
Mid April
o

Increase number of bunches to 13 per beam.
o

b* = 2 m for collisions (injection 10 /11 m).
Bunch population N = 31010 p ~ 30% of nominal.
Switch to nominal bunch intensity.
Luminosity ~N2
o Back off in b* to 3.5 m.
o

Mid-April – mid-May
June
Gain ~ 10
Loss ~ 0.6
Increase number of bunches up to 49 per beam.
July - August
Bunch population N = 9-101010 p.
o Stability run in August with 25 bunches/beam.
o
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Peak luminosity performance
Peak luminosity = 9.51030 cm-2s-1
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(48 bunches/beam, 36 colliding bunches)
36 colliding
pairs
8 colliding
pairs/IR
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Integrated luminosity
Integrated luminosity ~ 2.2 pb-1
(23.08.2010)
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Figures : status 16th Aug 2010
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Availability
 About
30% of time in physics data-taking.
o
A lot commissioning still on-going !
o
Min. turn-around time collisions to collisions ~4 hours.
3.5 TeV
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Energy
Lumi
01 – 21 August 2010
6.51030
cm-2s-1
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Outline
LHC beam operation
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Machine Protection
 Extensive
testing of the machine protection system was
performed, mostly in March/April 2010.
o
 20’000 signal enter the beam abort system.
about 10% of the beams above injection energy are dumped
by the operators !
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 Only
Beam dumped from hardware
Machine Protection tests
Beam dump by operator
Beam interlocks
Beam dumps > 450 GeV
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Beam dump

Dump block
Complex beam dumping
system commissioned.
Beam swept over dump
surface (power load)
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Dilution kickers
Extraction
septum magnets
Extraction
kickers
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Aperture and collimation
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
With collisions the aperture limit of the LHC is in the strong focusing
quadrupoles (triplets) that are installed just next to the experiments.
o
Hierarchy of collimators must be preserved in all phases to avoid
quenching super-conducting magnets and for damage protection.
o
b* is presently limited to 3.5 m by aperture and tolerances.
Exp.
Collimation hierarchy
Primary
6σ
Secondary
8.8 σ
Triplet
Tertiary
18 σ
Dump Protection
15
σ
10.5 σ
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Collimation
 Collimator
alignment is made with beam and then monitored
from the loss distribution around ring.
 Beam
cleaning efficiencies ≥ 99.98% ~ as designed
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TCT = tertiary coll.
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Magnet quenches
 A local
o
loss of some ~107 protons/s may lead to a quench at 3.5 TeV.
Compared to 51012 stored protons.
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.
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 So
 In
only 5 occasions did some beam escape and was lost locally
around super-conducting elements.
o
Beam loss detection system dumped the beams in time before a magnet
could quench.
o
Events are under investigation... Possible cause are dust particles!
The absence of problems with beam loss and quenches
is good news for increasing the beam intensity !
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Beam Optics

Beam optics is within specifications and reproducible over 3 months.
o
A stable machine is essential to reach high intensity and minimize
frequent setup overhead, in particular for collimation.
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Relative beam size error
 (Db/b)   10%
Specification:  0.2
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Beam Emittance

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LHC Status - SUSY 2010 - Bonn

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.

Beam emittances in collisions are now mostly at design or below
– the only exception being beam 2 in the vertical plane.
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Noise on the beam

The beams are periodically excited by an unknown noise source (‘hump’) of
varying frequency – affects mostly beam2 in vertical plane.
o

Amplitude ~ mm.
When the frequency coincides with the beam eigen-modes (‘tunes’) it leads to
emittance blow-up.
Time
Horizontal plane
LHC Status - SUSY 2010 - Bonn
Beam 1
1 hour
Beam 2
Tune
Noise hump
Beam 1
Beam 2
Vertical plane
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Noise hump
Frequency/Rev. frequency
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Beam-beam interaction
of the beam-beam force are visible on the lifetime of the
various bunches.
o
Also sensitive to tune working point.
o
This will become even more complicated with trains of bunches.
- black
- red
- blue
- green
witness bunches (zero collisions);
bunches colliding in IP 1 5 and 2 (3 collisions);
bunches colliding in IP 1 5 and 8 (3 collisions);
bunches colliding in IP 2 and 8 (2 collisions).
fill 1264 - beam 1
Intensity 10
loss (%)
fill 1264 - beam 2
10
Beams in collision
Beam1
losses [%]
6
4
0
20
Beam2
8
2
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Beams in collision
8
losses [%]
LHC Status - SUSY 2010 - Bonn
 Effects
6
4
2
30
40
50
time [min]
60
70
0
20
30
40
50
time [min]
60
70
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Lifetimes
 Beam
intensity lifetimes with colliding beams:
o
Dip to 2-5 hours in first minutes.
o
Progressive increase to ~100 hours.
 Luminosity
LHC Status - SUSY 2010 - Bonn
o
lifetimes:
Around 20-30 hours due to emittance growth.
Lifetime (h)
Beams in collision
300
200
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100
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Present LHC parameters
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N 2kb f
N 2kb f
L
F
F
*
4s xs y
4b e
Parameter
Present
Nominal
N (p/bunch)
11011
1.151011
48
2808
2.5-5
3.75
3.5
0.55
6.51030
1034
kb (no. bunches)
e (mm rad)
b* (m)
L (cm-2s-1)


Limited by
Machine protection
Aperture, tolerances
Squeezing at the IP (b*) is limited by aperture and tolerances.
o
Beams are larger at 3.5 TeV ~ 1/.
o
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.
o
Bunch separation is large (>1 ms), no crossing angle at the IR.
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Outline
Outlook for 2010/11 and conclusions
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Fall 2010
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).
 To
LHC Status - SUSY 2010 - Bonn
o
But the most important is the slope of the increase!
6
12
12
24
24
24
48
48
96 144
Switch to
bunch trains
192 240 288
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24
336
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Fall 2010-2011
 To
reach the target of 1032 cm-2s-1,
o
the intensity must be increased very rapidly,
o
bunch train operation must be commissioned (1-2 weeks).
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LHC Status - SUSY 2010 - Bonn
>> Achievable integrated L is ~ 25-50 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.
o
So far there are no limitations.
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.
 The
o
But the most important is the slope of the increase!
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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.
LHC Status - SUSY 2010 - Bonn
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.
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1 fm-1 of integrated data is in reach.
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