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LHC Status
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SUSY 2010
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Drawing by
Sergio
Cittolin
Status of the LHC
6 months of beam operation in 2010
J.
Wenninger
CERN
Outline
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Introduction
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The Large Hadron Collider LHC
3
CMS, Totem
ATLAS,
LHCf
LHCb
ALICE
Lake of Geneva
Installed in 26.7 km LEP tunnel
Depth of 70
-
140 m
Control Room
LHC layout and parameters
4
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
-
β
*
= 0.55 m (beam size =17 μm)
-
Crossing angle = 285 μrad
-
L = 10
34
cm
-
2
s
-
1
RF
Nominal LHC parameters
Beam energy (TeV)
7.0
No. of particles per bunch
1.15x10
11
No. of bunches per beam
2808
Stored beam energy (MJ)
362
Transverse emittance (μm)
3.75
Bunch length (cm)
7.55
LHC accelerator complex
5
Beam 1
TI2
Beam 2
TI8
LHC proton path
The LHC needs most of the CERN accelerators...
≥ 7 seconds from
source to LHC
LHC challenges
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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
~ 10
34
cm
-
2
s
-
1
Tevatron
pp
3x10
32
cm
-
2
s
-
1
SppS
pp
6x10
30
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
A factor
30
in luminosity
LHC dipole magnet
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1232
dipole
magnets
.
B
field
8.3 T (11.8 kA) @ 1.9 K
(super
-
fluid
Helium
)
2 magnets
-
in
-
one design : two beam
tubes with an opening of 56 mm.
Operating challenges:
o
Dynamic
field
changes
at
injection.
o
Very
low
quench
levels
(~
mJ
/cm
3
)
Stored energy
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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
Damage threshold
Collimation
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beam
1.2 m
To operate at nominal performance the LHC requires a large and
complex collimation system
o
Previous colliders used collimators mostly for experimental
background conditions.
Ensure ‘cohabitation’ of:
o
360 MJ
of stored beam energy,
o
super
-
conducting magnets with quench
limits of
few mJ/cm
3
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.
Outline
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LHC energy 2010/11
LHC target energy: the way down
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2002
-
2007
7
TeV
Summer 2008
5
TeV
Spring 2009
3.5
TeV
Nov. 2009
450
GeV
Detraining
nQPS
2 kA
6 kA
9 kA
When
Why
12 kA
Late 2008
Joints
1.18
TeV
Design
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
)
LHC target energy: the way up
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Train magnets
–
6.5
TeV
is in reach
–
7
TeV
will take time
Repair joints
Complete pressure relief system
Commission
nQPS
system
2014 ?
2010
Training
Stabilizers
nQPS
When
What
7
TeV
3.5
TeV
1.18
TeV
450
GeV
2011
2013
2009
6
TeV
Ramp rate
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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
2 A/s
10 A/s
450
GeV
3500
GeV
Outline
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LHC performance targets and achievements
Collider luminosity
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“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
Parameters:
–
Number of particles per bunch
–
Number of bunches per beam
k
b
–
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
Collision rate is
proportional to luminosity
Interaction Region
Beam quality (emittance)
Intensity
F
f
k
N
F
f
k
N
L
b
y
x
b
e
b
s
s
*
2
2
4
4
Collimation performance
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I
max
~6
13
protons per beam at 3.5TeV with
intermediate collimator settings
(about 20% nominal intensity)
30 MJ stored beam energy
Present stage collimation system
sets limit to total intensity.
Assumptions:
o
Max. loss rate of 0.1%/s
assumed (0.2h lifetime).
o
Ideal cleaning.
Performance degradation:
o
Deformed jaws.
o
Tilt & offset & gap errors.
o
Machine alignment.
Machine stability
o
Tight coll. settings are a
challenge at early stage.
o
Intermediate coll. settings
make use of aperture to relax
tolerances.
Collimator settings
Goals for 2010
-
2011
17
Repair of Sector 34
1.18
TeV
nQPS
6kA
3.5
TeV
I
safe
< I < 0.2
I
nom
β* ~ 3.5 m
Ions
3.5
TeV
~ 0.2
I
nom
β* ~ 3.5 m
Ions
2009
2010
2011
No Beam
B
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
10
32
cm
-
2
s
-
1
~ Tevatron Luminosity
which requires ~700 bunches of 10
11
p each ~ 7x10
13
p
(
stored energy of ~30 MJ
–
10% of nominal
)
Implications:
Strict and clean machine setup.
Machine protection systems at near nominal performance.
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
m
s).
o
Up to around k
b
=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
Commissioning steps in 2010
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Restart with beam.
Commissioning to 3.5
TeV
.
o
Low intensity beams.
First collisions at 3.5
TeV
.
Squeeze (
b
* reduction) commissioning.
o
b
* = 2 m for collisions (injection 10 /11 m).
Increase number of bunches to 13 per beam.
o
Bunch population N = 3
10
10
p ~ 30% of nominal.
Switch to nominal bunch intensity.
o
Luminosity ~N
2
Gain ~ 10
o
Back off in
b
* to 3.5 m.
Loss ~ 0.6
Increase number of bunches up to 49 per beam.
o
Bunch population N = 9
-
10
10
10
p.
o
Stability run in August with 25 bunches/beam.
Feb. 28th
March
March 30
th
Mid April
Mid
-
April
–
mid
-
May
June
July
-
August
Peak luminosity performance
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8 colliding
pairs/IR
36 colliding
pairs
Peak luminosity = 9.5
10
30
cm
-
2
s
-
1
(48 bunches/beam, 36 colliding bunches)
Integrated luminosity
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Integrated luminosity ~ 2.2 pb
-
1
(23.08.2010)
Figures : status 16
th
Aug 2010
Availability
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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
6.5
30
cm
-
2
s
-
1
Energy
Lumi
01
–
21 August 2010
Outline
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LHC beam operation
Machine Protection
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Beam dumped from hardware
Machine Protection tests
Beam dump by operator
Beam interlocks
Extensive testing of the machine protection system was
performed, mostly in March/April 2010.
o
20’000 signal enter the beam abort system.
Only about
10%
of the beams above injection energy are dumped
by the operators !
Beam dumps > 450
GeV
Beam dump
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Extraction
kickers
Dilution kickers
Extraction
septum magnets
Dump block
Complex beam dumping
system commissioned.
Beam swept over dump
surface (power load)
Aperture and collimation
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Primary
6
σ
Secondary
8.8
σ
Dump Protection
10.5
σ
Tertiary
15
σ
Triplet
18
σ
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.
Collimation hierarchy
Exp.
Collimation
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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.
Magnet quenches
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A local loss of some ~10
7
protons/s may lead to a quench at 3.5
TeV
.
o
Compared to 5
10
12
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.
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 !
Beam Optics
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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.
Relative beam size error
(
Db/b)
10%
Specification:
0.2
Beam Emittance
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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
below nominal can be produced and injected
into the LHC (
e
= 2
m
m
rad
as compared to
3.5
m
m
rad
design
).
This provides margin for emittance blow
-
up due to various noise
sources
–
great value for a machine in early phase of operation.
Beam
emittances
in collisions are now mostly at design or below
–
the only exception being beam 2 in the vertical plane.
Noise on the beam
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The beams are periodically excited by an unknown noise source (‘hump’) of
varying frequency
–
affects mostly beam2 in vertical plane.
o
Amplitude ~
m
m.
When the frequency coincides with the beam
eigen
-
modes (‘tunes’) it leads to
emittance blow
-
up.
Beam 1
Beam 1
Beam 2
Beam 2
Horizontal plane
Vertical plane
Frequency/Rev. frequency
Time
ㄠ桯畲
乯楳攠桵浰
乯楳攠桵浰
T畮e
Beam
-
beam interaction
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-
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).
Effects 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.
20
30
40
50
60
70
0
2
4
6
8
10
time [min]
losses [%]
fill 1264 - beam 1
20
30
40
50
60
70
0
2
4
6
8
10
time [min]
losses [%]
fill 1264 - beam 2
Beams in collision
Beams in collision
Beam1
Beam2
Intensity
loss (%)
Lifetimes
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Beam intensity lifetimes with colliding beams:
o
Dip to 2
-
5 hours in first minutes.
o
Progressive increase to ~100 hours.
Luminosity lifetimes:
o
Around 20
-
30 hours due to emittance growth.
Beams in collision
Lifetime (h)
100
200
300
Present LHC parameters
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F
f
k
N
F
f
k
N
L
b
y
x
b
e
b
s
s
*
2
2
4
4
Parameter
Present
Nominal
Limited
by
N (p/bunch)
1
10
11
1.15
10
11
k
b
(no. bunches)
48
2808
Machine protection
e
(
m
m
rad
)
2.5
-
5
3.75
b
⨠⡭*
㌮3
〮05
䅰敲瑵牥Ⱐ潬敲e湣ns
L
捭
-
2
s
-
1
)
6.5
10
30
10
34
Squeezing at the IP (
b
*) is limited by aperture and tolerances.
o
Beams are larger at 3.5
TeV
~ 1/
.
o
s
x
=
s
y
= ~45
-
60
m
m
-
nominal value is 15
m
m 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
m
s), no crossing angle at the IR.
Outline
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Outlook for 2010/11 and conclusions
Fall 2010
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336
192 240 288
6 12 12 24 24 24 24 48 48 96 144
Switch to
bunch trains
To reach the target of 10
32
cm
-
2
s
-
1
an
intensity increase of factor 10
is required until end of October (start of
Pb
ion run).
o
But the most important is the slope of the increase!
Fall 2010
-
2011
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To reach the target of 10
32
cm
-
2
s
-
1
,
o
the intensity must be increased very rapidly,
o
bunch train operation must be commissioned (1
-
2 weeks).
>> 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.
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.
o
But the most important is the slope of the increase!
Summary and outlook 2011
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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 9.5x10
30
cm
-
2
s
-
1
Machine protection and collimation systems perform well, and one
can anticipate a luminosity increase towards few 10
31
to
10
32
cm
-
2
s
-
1
in 2010.
Final value for 2010 will depend on machine availability and length of
commissioning bunch train operation.
A long run at 10
32
cm
-
2
s
-
1
or above is in sight for 2011.
1 fm
-
1
of integrated data is in reach.
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