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Der LHC Beschleuniger am CERN: Kollisionen intensiver Teilchenstrahlen bei hoher Strahlenergie

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Title: Der LHC Beschleuniger am CERN: Kollisionen intensiver Teilchenstrahlen bei hoher Strahlenergie


1
Der LHC Beschleuniger am CERN Kollisionen
intensiver Teilchenstrahlen bei hoher
Strahlenergie
  • Rüdiger Schmidt - CERN
  • TU Darmstadt
  • Januar 2008

Der LHC Just another collider? Kollision
intensiver Teilchenstrahlen Injectorkomplex und
LHC Operation und Betriebssicherheit Status und
Ausblick
2
Vortrag GradKolleg 2004
3
Installation of cryogenic distribution line in
the LHC tunnel started during summer 2003
Status 2007
4
Energy and Luminosity
  • Particle physics requires an accelerator
    colliding beams with a centre-of-mass energy
    substantially exceeding 1TeV
  • In order to observe rare events, the luminosity
    should be in the order of 1034 cm-2s-1
    (challenge for the LHC accelerator)
  • Event rate
  • Assuming a total cross section of about 100 mbarn
    for pp collisions, the event rate for this
    luminosity is in the order of 109 events/second
    (challenge for the LHC experiments)
  • Nuclear and particle physics require heavy ion
    collisions in the LHC (quark-gluon plasma .... )

5
The CERN Beschleuniger Komplex
LEP ee- (1989-2000) 104 GeV/c LHC pp und
Ionen 7 TeV/c 26.8 km Umfang 8.3 Tesla
supraleitende Magnete
Schweiz Genfer See
LHC Beschleuniger (etwa 100m unter der Erde)
CERN-Prevessin
SPS Beschleuniger
CERN Hauptgelände
Frankreich
6
The LHC just another collider ?
Name Start Particles Max proton energy GeV Length m B Field Tesla Stored beam energy MJoule
TEVATRON Fermilab Illinois USA 1983 p-pbar 980 6300 4.5 1.6 for protons
HERA DESY Hamburg Germany 1992 p e p e- 920 6300 5.5 2.7 for protons
RHIC Brookhaven Long Island USA 2000 Ion-Ion p-p 250 3834 4.3 0.9 per proton beam
LHC CERN Geneva Switzerland 2008 Ion-Ion p-p 7000 26800 8.3 362 per proton beam
7
Challenges for LHC
  • High-field (8.3 Tesla) superconducting magnets
    operating at a temperature of 1.9 K with an
    energy stored in the magnets of 10 GJ
  • Beam-parameters pushed to the extreme
  • Energy stored in the beam two orders of magnitude
    above others
  • Transverse energy density three orders of
    magnitude compared to other accelerators
  • Consequences for several systems (machine
    protection, collimation, vacuum system,
    cryogenics, )
  • GJoule beams running through superconducting
    magnets that quench with mJoule
  • Complexity of the accelerator (most complex
    scientific instrument ever constructed) with
    10000 magnets powered in 1712 electrical circuits

8
New approaches and novel technologies
  • Two-In-One superconducing magnets inside helium
    1.9 K system
  • Compressors operating at cold to provide helium
    at 1.9 K
  • Beam screen inside vacuum chamber at higher
    temperature
  • High Temperature Superconductors at an industrial
    scale, for current leads
  • High current power convertors and control of the
    current with an unprecedented accuracy of 1 ppm
  • New devices and materials for absorbing the
    particles
  • Radiation studies for the accelerator at an
    unprecedented scale
  • Development of radiation tolerant electronics and
    highly radiation resistant optical fibres
  • Overall consideration for machine protection an
    accidental release of the energy can lead to
    massive damage
  • Approach for machine protection systems driven by
    studies on safety, reliability and availability
    using formal methods

9
A total number of 1232 dipole magnets are
required to close the circle
10
LHC dipole magnet lowered into the tunnel
First cryodipole lowered on 7 March 2005 Descent
of the last magnet, 26 April 2007
11
Interconnecting two magnets out of 1700
12
Current leads with High Temperature
Superconductor
Feedboxes (DFB) transition from copper cable
to super-conductor
Water cooled Cu cables
12
13
DFB with 17 out of 1600 HTS current leads
14
RF cavities, four per beam with some 10 MVolt
15
LHC From first ideas to realisation
1982 First studies for the LHC project 1983
Z0 detected at SPS proton antiproton collider
1985 Nobel Price for S. van der Meer and C.
Rubbia 1989 Start of LEP operation
(Z-factory) 1994 Approval of the LHC by the
CERN Council 1996 Final decision to start the
LHC construction 1996 LEP operation at 100 GeV
(W-factory) 2000 End of LEP operation 2002
LEP equipment removed 2003 Start of the LHC
installation 2005 Start of hardware
commissioning 2008 Commissioning with beam
planned
16
Colliding very intense proton beams
17
High luminosity by colliding trains of bunches
  • Number of New Particles
  • per unit of time
  • The objective for the LHC as proton proton
    collider is a luminosity of about 1034 cm-1s-2
  • LEP (ee-) 3-4 1031
    cm-2s-1
  • Tevatron (p-pbar) some 1032
    cm-2s-1
  • B-Factories gt 1034 cm-2s-1

IP
40 m in straight section (not to scale)
18
Luminosity parameters
What happens with one particle experiencing the
force of the em-fields or 1011 protons in the
other beam during the collision ?
19
Limitation beam-beam interaction
20
Electromagnetic force on a particle in the
counterrotating beam
Optimising luminosity by increasing N
Bunch intensity limited due to this strong
non-linearity to about N 1011
21
Beam beam interaction determines parameters
Number of protons N per bunch limited to about
1011 f 11246 Hz Beam size at IP s 16 ?m for ?
0.5 m (beam size in arc s 0.2 mm
with one bunch Nb1
with Nb 2808 bunches (every 25 ns one bunch)
L 1034 cm-2s-1
gt 362 MJoule per beam
22
Livingston type plot Energy stored magnets and
beam
based on graph from R.Assmann
23
What does this mean?
10 GJoule the energy of an A380 at 700 km/hour
corresponds to the energy stored in the LHC
magnet system Sufficient to heat up and melt 12
tons of Copper!!
  • 90 kg of TNT

362 MJoule the energy stored in one LHC beam
corresponds approximately to
  • 8 litres of gasoline
  • 15 kg of chocolate

Its how ease the energy is released that matters
most !!
24
Very high beam current consequences
  • Dumping the beam in a safe way
  • Beam induced quenches (when 10-8-10-7 of beam
    hits magnet at 7 TeV)
  • Beam cleaning (Betatron and momentum cleaning)
  • Radiation, in particular in experimental areas
    from beam collisions (beam lifetime is dominated
    by this effect)
  • Beam instabilities due to impedance
  • Synchrotron radiation at 7 TeV - power to
    cryogenic system
  • Photo electrons - accelerated by the following
    bunches
  • Single particle dynamics dynamic aperture and
    magnet field quality, in particular in the
    presence of dynamic effects in superconducing
    magnets during the ramp

25
The LHC accelerator complexComplexity due to
the LHC main ring AND due to the injector chain
26
LHC Layout eight arcs (sectors) eight long
straight section (about 700 m long)
Beam dump blocks
IR5CMS
IR6 Beam dumping system
IR4 RF Beam instrumentation
IR3 Momentum Beam Cleaning (warm)
IR7 Betatron Beam Cleaning (warm)
IR8 LHC-B
IR2ALICE
IR1 ATLAS
Injection
Injection
27
The CERN accelerator complex injectors and
transfer
Beam 2
5
LHC
4
6
Beam 1
7
3
2
SPS
8
TI8
TI2
1
Booster
protons
LINACS
CPS
High intensity beam from the SPS into LHC at 450
GeV via TI2 and TI8 LHC accelerates from 450
GeV to 7 TeV
Ions
LEIR
Beam size of protons decreases with energy ?2
1 / E Beam size large at injection Beam fills
vacuum chamber at 450 GeV
28
LHC transfer lines and injections - overview
TI 8 beam tests 23/24.10.04 6/7.11.04
IR8
  • combined length 5.6 km
  • over 700 magnets
  • ca. 2/3 of SPS

TT40
TT40 beam tests 8.9.03
LSS4
TI 8
SPS 6911 m 450 GeV
LHC
IR2
LSS6
TI 2 beam test 28/29.10.07
TI 2
29
Transfer line TI8 (MIBT magnet)
30
LHC accelerator
LHC Main SystemsSuperconducting
magnetsCryogenicsVacuum systemPowering
(industrial use of High Temperature
Superconducting material)
31
Regular arc Magnets
32
Regular arc Cryogenics
33
Dipole magnets for the LHC
1232 Dipolemagnets Length about 15 m Magnetic
Field 8.3 T Two beam tubes with an opening of 56
mm
34
Operating temperature of superconductors
J kA/mm2
J kA/mm2
The superconducting state only occurs in a
limited domain of temperature, magnetic field and
transport current density Superconducting magnets
produce high field with high current
density Lowering the temperature enables better
usage of the superconductor, by broadening its
working range
T K
B T
35
Critical current density of technical
superconductors
Ph.Lebrun
36
Dipole magnet cross section
37
Specific heat of liquid helium and copper
Discovery of He II phase transition (1927) by
W.H. Keesom and M.Wolfke
38
Equivalent thermal conductivity of He II
G. Bon Mardion et al.
39
Principle of He II cooling of LHC magnets
40
Cold compressors of LHC 1.8 K units
Axial-centrifugal impeller
Air Liquide IHI-Linde
1st stage cartridge
4 stages
41
Operation and machine protection
42
LHC magnetic cycle and beam operation
beam dump
energy ramp
coast (2?360 MJ)
coast
7 TeV
start of the ramp
injection phase 12 batches from the SPS (every 20
sec) one batch 216 / 288 bunches
450 GeV
L.Bottura
43
Beam lifetime with nominal intensity at 7 TeV
Beam lifetime Beam power into equipment (1 beam) Comments
100 h 1 kW Healthy operation
10 h 10 kW Operation acceptable, collimation must absorb large fraction of beam energy (approximately beam losses cryogenic cooling power at 1.9 K)
0.2 h 500 kW Operation only possibly for short time, collimators must be very efficient
1 min 6 MW Equipment or operation failure - operation not possible - beam must be dumped
ltlt 1 min gt 6 MW Beam must be dumped VERY FAST
Failures will be a part of the regular operation
and MUST be anticipated
44
  • What happens in case the full LHC beam impact
    onto material?

Since 2003/4 collaboration with GSI and TU
Darmstadt, N.Tahir (GSI), D.H.H.Hoffmann and many
others
45
Beam losses into material
  • Proton losses into material lead to particle
    cascades
  • The energy deposition increases the temperature
  • For the maximum energy deposition as a function
    of material there is no straightforward
    expression
  • Programs such as FLUKA are being used for the
    calculation of the energy deposition
  • The material could be damaged..
  • losing their performance (mechanical strength)
  • melting and vaporisation
  • Magnets could quench..
  • beam lost - re-establish condition will take
    hours
  • Repair could take a long time

46
Damage of material for impact of a pencil beam
copper
graphite
47
Full LHC beam deflected into copper target
Copper target
2808 bunches
2 m
Energy density GeV/cm3 on target axis
Target length cm
48
SPS experiment Beam damage at 450 GeV
  • Controlled SPS experiment
  • 8?1012 protons clear damage
  • beam size sx/y 1.1mm/0.6mm
  • above damage limit
  • 2?1012 protons
  • below damage limit

25 cm
0.1 of the full LHC beam energy 10 times the
beam area
49
STEP1 Calculation of energy deposition of a 7
TeV proton beam in material with a beam of ?0.2
mm (FLUKA)
at 16 cm
copper, one bunch
copper, per proton
carbon, one bunch
carbon, one bunch
50
STEP2 Hydrodynamic simulations with BIG-2
including the response of the target with LHC
beam for copper
  • After an impact of some bunches, pressure and
    temperature in the beam heated region increase
    drastically.
  • A hydrodynamic simulation with a model including
    a multiphase semi-empirical equation-of-state
    describes the target behaviour during the
    diffferent phases of heating and expansion.
  • State changes and pressure waves are taken into
    account by the numerical simulation.

N.Tahir (GSI), D.H.H.Hoffmann et al.
51
Density change at 16 cm in target after impact of
100 bunches
copper solid state
radial
100 bunches target density reduced to 10
Target radial coordinate cm
  • After an impact of about 100 bunches, the beam
    heated region has expanded drastically and the
    density in the inner region decreases by about a
    factor of 10.
  • The bulk of the following beam will not be
    absorbed and continues to tunnel further and
    further into the target, between 20 and 40 m.
  • Such effects have been observed for heavy ion
    beams.
  • The LHC might be an interesting tool to study
    HighEnergyDensityMatter.

N.Tahir (GSI), D.H.H.Hoffmann et al.
52
The only component that can stand a loss of the
full beam is the beam dump block all other
components would be damaged
beam absorber (graphite)
about 8 m
about 35 cm
concrete shielding
53
Schematic layout of beam dump system in IR6
Septum magnet deflecting the extracted beam
Beam 1
H-V kicker for painting the beam
Q5L
Beam Dump Block
Q4L
about 700 m
Fast kicker magnet
Q4R
about 500 m
Q5R
Beam 2
54
Temperature of beam dump block at 80 cm inside
up to 800 0C
L.Bruno Thermo-Mechanical Analysis with ANSYS
55
Operational margin of a superconducting magnet
Applied Magnetic Field T
Applied magnetic field T
This is about 1000 times more critical than for
TEVATRON, HERA, RHIC
Bc critical field

Tc critical temperature
9 K
Temperature K
56
Beam Cleaning System
  • Multi-stage beam halo cleaning (collimation)
    system to protect sensitive LHC magnets from beam
    induced quenches and damage
  • Halo particles are first scattered by the primary
    collimator (closest to beam)
  • Scattered particles (forming the secondary halo)
    are absorbed by the secondary collimators, or
    scattered to form the tertiary halo.
  • More than 100 collimators jaws needed for the
    nominal LHC beam.
  • Primary and secondary collimators made of Carbon
    to survive severe beam impact !
  • Collimators must be precisely aligned (lt 0.1 mm)
    to guarantee a high efficiency above 99.9 at
    nominal intensities.

Primary collimator
Secondary collimators
Protection devices
Tertiary collimators
Triplet magnets
Experiment
Absorbers
Tertiary halo
hadronic showers
Primary halo particle
Its not easy to stop 7 TeV protons !!
Secondary halo
hadronic showers
Beam
57
Accidental kick by the beam dump kicker at 7 TeV
part of beam touches collimators (about 20
bunches from 2808)
Beryllium
P.Sievers / A.Ferrari / V. Vlachoudis
58
(No Transcript)
59
First collimator in the tunnel
Vacuum tank with two jaws installed Designed for
maximum robustness Advanced Carbon Composite
material for the jaws with water cooling!
R.Assmann et al
60
  • Interception of beam-induced heat loads at 5-20
    K (supercritical helium)
  • Shielding of the 1.9 K cryopumping surface from
    synchrotron radiation
  • High-conductivity copper lining for low beam
    impedance
  • Low-reflectivity sawtooth surface at equator to
    reduce photoemission and electron cloud

56.0 mm
- 3? 1.3 mm
Beam in vacuum chamber with beam screen at 7 TeV
61
About 3600 beam loss monitors to detect particle
losses and to trigger a beam dump
  • Ionization chambers to detect beam losses
  • Montitors in the arc
  • Monitors close to all collimators
  • Simulation and experiments to determine threshold
    for beam losses
  • Student from TU Darmstadt involved for his
    Masters project

62
Status summary
  • Installation and magnet interconnections finished
  • Cryogenics
  • Nearly finished and operational (e.g. cryoplants)
  • Two sectors been at 1.9 K, third sector being
    cooled down
  • Cooldown for other sectors to start soon
  • Powering system commissioning on the way
  • Power converters commissioning on short circuits
    in tunnel finished
  • Magnet powering tests started in two sectors,
    main dipoles at 8.5 kA corresponding to 5 TeV
  • Other systems (RF, Beam injection and extraction,
    Beam instrumentation, Collimation, Interlocks,
    Controls)
  • Essentially on schedule for first beam in 2008
  • Injector complex and transfer lines ready

63
  • From 300K to 80K precooling with LN2. 1200 tons
    of LN2 (64 trucks of 20 tons). Three weeks for
    first sector.
  • From 80K to 4.5K. Cooldown with refrigerator.
    Three weeks for the first sector. 4700 tons of
    material to be cooled.
  • From 4.5K to 1.9K. Cold compressors at 15 mbar.
    Four days for the first sector.

LHC Sector 78 First cooldown
64
Magnet temperature in one sector
65
Current tracking between the three main circuits
of Sector 78
Courtesy F.Bordry
66
Ramping the dipole magnets to a current for 5 TeV
8000 A
Dipole magnet current
4000 A
12 hours
67
Temperature after an induced quench
10 minutes
68
Conclusions
69
Always smooth progress? No .. this is unrealistic
  • The LHC is a machine with unprecedented
    complexity
  • The technology is pushed to its limits
  • The LHC is a ONE-OFF machine
  • The LHC was constructed during a period when CERN
    had to substantially reduce the personel
  • Problems came up and were solved / are being
    solved, such as dipole magnets, cryogenics
    distribution line, collimators, inner triplet, RF
    fingers (PiMS), He level gauges, .
  • In my view what makes such project a success not
    absence of problems, but because problems are
    detected and adressed with competent and
    dedicated staff and collaborators that master all
    different technologies

70
  • Typical (recent) examples

71
Repair of the inner triplett
72
RF bellows in the 1700 interconnections
73
Arc plug-in module at warm temperature
74
Arc plug-in module at working temperature
75
Solution is on the way
  • Problem fingers bend into beampipe obstructing
    the aperture
  • Due to wrong angle of RF fingers PLUS size of the
    gap between the magnet apertures larger than
    nominal (still inside specification)
  • Laboratory tests and finite element analysis
    confirm the two factors
  • Only part of the interconnects is affected
  • Complete survey of sector 78 using X-ray
    techniques
  • Repair is not so difficultonce bad PiM identified
  • A technique was developed for quickly checking at
    warm the LHC beam aperture
  • Using air flow blowing a light ball equipped with
    a 40MHz transmitter through the beam vacuum pipe,
    use BPMs to detect it as it passes

76
Recalling LHC challenges and outlook
  • Enormous amount of equipment
  • Complexity of the LHC accelerator
  • New challenges in accelerator physics with LHC
    beam parameters pushed to the extreme


Fabrication of equipment
Installation
LHC hardware commissioning
LHC Beam commissioning
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
1 2 3 4 5 6 7 8 9 10 11 12
2005
2006
2007
2008
77
Conclusions
  • The LHC is a global project with the world-wide
    high-energy physics community devoted to its
    progress and results
  • As a project, it is much more complex and
    diversified than the SPS or LEP or any other
    large accelerator project constructed to date

Machine Advisory Committee, chaired by Prof. M.
Tigner, March 2002
  • We recognize that the planned schedule is very
    aggressive, given the complexity and potential
    for damage involved in the initial phases of
    operation.
  • It will be important to understand the
    performance of the machine protection system, the
    collimation system and the orbit feedback system
    as well as cycle repeatability and adequate
    beta-beat control before proceeding to run with
    significant stored beam energy. Pressure to take
    shortcuts must be resisted.

Machine Advisory Committee, chaired by Prof. M.
Tigner, June 2005
78
Acknowledgement
  • The LHC accelerator is being realised by CERN in
    collaboration with institutes from many countries
    over a period of more than 20 years
  • Main contribution come from the USA, Russia,
    India, Canada, special contributions from France
    and Switzerland
  • Industry plays a major role in the construction
    of the LHC
  • TU Darmstadt and GSI among the contributors
  • Thanks for the material from
  • R.Assmann, R.Bailey, F.Bordry, L.Bottura,
    L.Bruno, L.Evans, B.Goddard, M.Gyr, Ph.Lebrun

79
  • Vielen Dank für die Einladung
  • Möglichkeiten für zukünftige Zusammenarbeit im
    Bereich von Strahlverlust, Betriebssicherheit,
    HighEnergyDensity States of Matter,..
  • Beteiligung bei einem SPS Experiment, in dem der
    hochintensive 450 GeV Strahl auf Targets gelenkt
    wird?
  • Viele andere Bereiche..
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