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Title: Commissioning the LHC Accelerator and its Physics Programme


1
Commissioning the LHC Accelerator and its Physics
Programme
  • Emmanuel Tsesmelis (CERN)
  • Presentation at The University of Oxford
  • 6 March 2008

2
Introduction
3
LHC Accelerator Experiments
CMS/TOTEM
LHCb
ATLAS/LHCf
ALICE
4
LHC LAY-OUT
  • The LHC is a two-ring superconducting
    proton-proton collider made of eight 3.3 km long
    arcs separated by 528 m Long Straight Sections.
  • While the 8 eight arcs are nearly identical, the
    4 straight sections are very different.

5
LHC Nominal Beam Parameters
25 ns bunch spacing
6
Main magnets
7
LHC Main Bending Cryodipole
8.3 T nominal field 11850 A nominal field
8
Lowering of Last Dipole Magnet 26 April 2007
30000 km underground at 2 km/h!
  • 1700 cryo-magnets assemblies
  • 1232 Main Dipoles
  • 474 Short Straight Sections
  • 16 Separation Dipoles
  • 32 Low ß Triplets
  • 200 warm magnets

9
The LHC Arcs
10
Short Straight Sections of the Arcs
  • Cold masses of SSS contain main quadrupole
    magnets and various lattice corrector magnets.
  • Parameters of MQ at 7 TeV
  • Nominal Gradient 223 T/m
  • Nominal Current
  • 11870 A

11
Inner Triplet Quadrupoles
US Japan collaboration
Inner triplet warm assembly in test hall
Inner Triplet at IR2
Nominal Gradient 215 T/m Nominal Current 7000
A
12
cryogenics
13
Cryogenics Infrastructure 4.5 K Refrigerators
14
1.8 K Refrigerators
15
Cryogenic Distribution Infrastructure
16
QRL Installation
Internal Compensators
  • 3.3 km of QRL / sector
  • 2100 internal welds made with automatic orbital
    welding machines
  • 700 external manual welds

Special Connections
17
Electrical feedboxes
18
Electrical Feedbox Design
DFBA
19
DFBA Installation
DFBAO-HCM Leaving Assembly Hall 183
DFBAO-HCM Lowered at Point 2
20
DFB Interconnection
DFBAO in Sector 7-8
DFBMA in Sector 7-8
21
Magnet interconnections
22
Identification of Lines
23
Magnet Interconnections
  • Consist of several operations
  • TIG welding of cryogenic channels (50 000 welds)
  • Induction soldering of main superconducting
    cables ( 10 000 joints)
  • Ultrasonic welding of auxiliary superconducting
    cables ( 20 000 welds)
  • Mechanical assembly of various elements
  • Installation multi-layer insulation ( 200 000
    m2)

DIPOLE-DIPOLE INTERCONNECT BEFORE FINAL CLOSURE
All interconnections completed in November 2007
24
Collimation system
25
The Collimator Lay-out
  • LHC Ring
  • Interaction Region 1

TCTH
TCTV
ATLAS
26
Installation Planning
  • Collimation is a performance-driven system low
    energy and low intensity requires much less
    collimators.
  • Every installation plan adapted to LHC
    performance goals, LHC schedule and collimator
    production schedule.
  • Several scenarios have been defined
  • Full system ? 116 collimators
  • Minimal system 7 TeV (only required
    collimators) ? 70 collimators
  • Starting system for 7 TeV ? 92 collimators
  • Minimal system for 450 GeV ? 36 collimators

27
Hardware commissioning
28
Sector Hardware Commissioning
80K
1.9 K
Commissioning of technical systems without beam
Preparation for c-down
Pressure Test
Electrical Quality Assurance (ELQA)
  • There are 8 sectors
  • Utilities and machine technical systems are
    sectorised
  • Assembly and commissioning almost independent
  • Each system and utility tested and qualified
    independently prior the Sector Test
  • Leak and pressure test
  • Preparation for cool-down (flushing, filling,
    repairs)
  • ELQA at warm
  • Cool-down and ELQA at cold
  • Power test power converters connected to the
    magnets for the first time and tested up to the
    nominal current

29
A Systematic Approach
  • The systems to be commissioned in the cold parts
    of the machine include
  • Magnets, power converters, interlocks, quench
    detection and energy extraction systems.
  • The associated utility systems AC distribution,
    water cooling, ventilation, access control and
    safety systems.
  • The systems in the Long Straight Sections
    include
  • Injection, RF, beam dump, beam instrumentation,
    collimators, and interlocks.

30
Electrical Quality Assurance
31
Power Converter Commissioning
32
Power Converter Commissioning
Commissioning campaign in short circuit started
in mid-2006 100 commissioned
1720/1720 installed
33
ELQA and Cool-down
Sector 7-8
2007
34
Radiofrequency Cavities
35
Summary LHC Cryogenics
4 March 2008
36
LHC Cool-down Status
Sector 56
Sector 45
Sector 78
Sector 81
37
Sector 4-5
Sector 56
Sector 45
38
Sector 4-5 Evolution of Temperature
Quench of dipoles
25Jan08 Stop of 1.8K Ref. unit due to vacuum
interlock
13Feb08 Stop of 1.8K Ref. unit due to water stop
US45
21Jan08 Stop of 18kW due to oil system
Quench of Quads
39
Sector 4-5 Power Converter Currents
19 February 2008 at 1500Hardware Commissioning
Team
Ramp of 138 power converters to a current
equivalent to 5.3 TeV 9 kA (including all high
current magnets with nominal LHC optics)
40
Sector 4-5 Inner Triplet Squeeze Test
41
LHC Transfer Lines and Injections
23.10.2004, 1339 ? first beam at end of TI 8
IR8
  • combined length 5.6 km
  • over 700 magnets
  • ca. 2/3 of SPS

TI 8 beam tests 23./24.10.04 6./7.11.04
28.10.2007, 1203 ? first beam at end of TI 2
TT40 beam tests 8.9.03
TI 8
SPS
LHC
IR2
TI 2
TI 2 beam test 28./29.10.07
TI 2 upstream part installed and HW commissioned
by 2005.
PMI2
42
Beam commissioning
43
Schedule for 2008
  • LHC Machine will be cold in mid-June 2008.
  • Although the LHC Machine will not be fully
    commissioned to 7 TeV by mid-June 2008, the plan
    is to inject first beam at 450 GeV soon
    thereafter.
  • 450 GeV operation is part of normal setting up
    procedure for beam commissioning to high-energy.
  • Work to commission the LHC Machine to 7 TeV will
    continue in parallel and be interleaved with the
    450 GeV injection.
  • No provision in schedule for any major mishap,
    e.g. additional warm-up/cool-down of sector
    (3-month turn-around).

44
Proton Commissioning Strategy
  • Pilot physics run
  • First collisions
  • 43 bunches, no crossing angle, no squeeze,
    moderate intensities
  • Push performance
  • Performance limit 1032 cm-2 s-1 (event pileup)
  • 75ns operation
  • Establish multi-bunch operation, moderate
    intensities
  • Relaxed machine parameters (squeeze and crossing
    angle)
  • Push squeeze and crossing angle
  • Performance limit 1033 cm-2 s-1 (event pileup)
  • 25ns operation I
  • Nominal crossing angle
  • Push squeeze
  • Increase intensity to 50 nominal
  • Performance limit 2 1033 cm-2 s-1
  • 25ns operation II
  • Push towards nominal performance

45
Beam Commissioning to 7 TeV Collisions
46
Beyond Initial Run
Stage A
B
C
2008
No beam
Beam
D
2009

No beam
Beam
47
Commissioning the physics programme
48
ATLAS and CMS
  • Of central importance for ATLAS CMS and for the
    Collider is to elucidate the nature of
    electroweak symmetry breaking for which the Higgs
    mechanism (and accompanying Higgs boson(s)) are
    presumed to be responsible.
  • The ATLAS CMS general-purpose detectors are now
    well into their commissioning stage.
  • ATLAS and CMS are expected to have experiment
    set-ups ready for the start of LHC operation in
    2008.

49
The ATLAS Experiment
50
The CMS Experiment
51
Search for Higgs at LHC Start-up
  • Sizeable integrated luminosity is needed before
    significant inroads can be made in SM Higgs
    search.
  • However, even with moderate luminosity per
    experiment, Higgs boson discovery is possible in
    particular mass regions.

Example Reach ATLAS CMS
52
Search for SUSY at LHC Start-up
  • Due to their high production cross-sections,
    squarks and gluinos can be produced in large
    numbers even at modest luminosities.
  • Potential for discovery of SUSY is sizeable even
    at LHC start-up.

53
ATLAS and CMS Beam Conditions
Pile-up in CMS Inner Tracker ECAL H -gt ZZ -gt
2e 2?
  • Machine operation at nominal conditions
  • Maximize integrated luminosity in a low
    machine-induced background environment.
  • 25 ns bunch spacing
  • For a given L, 25 ns spacing preferable to 75 ns.
  • Ebeam 7 TeV
  • L ? 1033 cm-2 s-1

54
The ALICE Experiment
  • General-purpose heavy-ion experiment designed to
    study physics of strongly interacting matter
    quark-gluon plasma in nucleus-nucleus collisions.
  • LHC heavy-ion programme based on two components
  • Collide largest available nuclei at highest
    possible energy.
  • Systematic study of various collision systems
    (pp, pA, AA) with various beam energies.
  • As number of possible combinations of collision
    systems and energies is large, continuous
    updating of priorities will be required as data
    becomes available.
  • The ALICE experiment set-up is expected to be
    ready for first LHC operation in 2008.

55
ALICE Beam Conditions
  • Proton-proton runs at ?s 14 TeV
  • Commissioning starting-up experiment, reference
    calibration data, pp minimum bias event
    properties
  • L 1029 cm-2 s-1 ltngt1 event per TPC drift time
    (88 ?s).
  • Preferably by tuning ? (if possible) rather than
    displacing beams.
  • For L gt 1031 cm-2 s-1 would need to switch off
    sub-detectors and risk of radiation damage to
    sub-detectors increases.
  • Initial Pb Runs with Early Ion Scheme
  • Request short run with ions (days) as early as
    feasible and a 4-week ion run before the end of
    first full LHC physics run.
  • In addition to ALICE, ATLAS CMS have the
    potential to study ion-ion collisions.

56
The LHCb Experiment
Calorimeters
Magnet
Muon detector
RICH-2
OT
RICH-1
VELO
57
LHCb Beam Conditions
  • Due to high production cross-sections, study of
    B-mesons possible from the start of LHC
    operations.
  • Also applicable to ATLAS and CMS
  • Experiment designed for L 2 1032 cm-2 s-1 and
    25 ns bunch spacing
  • Vary 2m. lt ? lt 50m. to reach nominal L even at
    expected low bunch intensities in early LHC run
  • Physics maximised for single pp interaction
    events.

58
TOTEM Roman Pots at IR5
The TOTEM experiment will measure the total pp
cross section and study elastic scattering and
diffractive dissociation at the LHC.
59
TOTEM Beam Conditions
60
The LHCf Experiment
  • The LHCf Collaboration will measure photons and
    neutral pions in the very forward region of the
    LHC
  • To provide information for the elaboration of the
    cosmic-ray spectrum in the high energy region.
  • For the determination of the primary composition
    of cosmic-rays.
  • The measurements may also be used to calibrate
    Monte Carlo event generators, especially in the
    forward region.
  • Experiment ready for first LHC run in 2008.

61
LHCf Beam Conditions
  • Operate with bunch spacing ? 2 ?sec in order to
    reduce pile-up.
  • Data-taking is compatible with 43 bunch pattern
    expected at LHC start-up.
  • L lt 1030 cm-2 s-1 to avoid contamination of data
    with multiple events per bunch crossing.
  • Running LHCf down to L 1028 cm-2 s-1 would
    provide adequate data rates.

62
Lower Energy Runs
  • Lowering Ebeam makes matters worse for Higgs and
    SUSY searches for ATLAS and CMS.
  • No significant effect on B cross-section.
  • TOTEM requests low energy runs
  • ?s 1.8 TeV for comparison with TEVATRON
  • ?s 8 TeV to probe smaller values of
    four-momentum transfer.
  • Study of interference between nuclear and Coulomb
    interactions

63
Summary and Conclusions
  • It is expected that first injection into the LHC
    will take place in summer 2008.
  • Considerable experience has been gained on the
    first sectors to be commissioned and it is
    expected that future activities will thus be
    greatly accelerated.
  • The experiments are expected to be ready with
    their initial set-ups for the start of LHC
    operation in 2008.
  • With the LHC, the world particle physics
    community has the opportunity to address
    fundamental questions such as What is the origin
    of the mass of particles? and What is the nature
    of dark matter?
  • The LHC will be the most powerful instrument ever
    built to investigate properties of particles and
    the physics results from the LHC will determine
    the future course of high energy physics.
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