Status of the LHC

24.08.2010

LHC Status
-

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

24.08.2010

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Introduction

24.08.2010

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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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7


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.