Der LHC Proton-Proton Collider und Der LHC Proton-Proton Collider und seine supraleitende Magneteseine supraleitende Magnete

Rüdiger Schmidt - CERN

Universität Wien

Februar 2002

2

Mit dem LHC will man am CERN möglichst intensive Teilchenstrahlen bei einer Energie von 7 TeV auf kleinstem Raum zur Kollision bringen, um möglichstviele neue Teilchen zu erzeugen

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LEP Event

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108 events / sekunde

LHC Event

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29 Oktober 2002

Rüdiger Schmidt

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Was ist der LHC ?Was ist der LHC ?

Der nächste Beschleuniger, der in einen neuen Energiebereich vorstossen wird - 7 TeV/c => Neue Physik (Higgs Teilchen)

Proton-Proton Collider mit sehr hoher Luminosität und Energie Ablenkmagnetfeld in Bogen :

Schwerionen - Collider mit sehr hoher Energie

LHC und die CERN Infrastruktur

im LEP Tunnel, Länge etwa 27 km, 8 Sektionen mit 4 Experimenten Optimale Ausnutzung der existierenden CERN Beschleuniger für den LHC

(SPS, PS, Booster, LEAR, Linacs, Ionenquellen)

1982 : Erste Studien zum LHC Projekt

1994 : Genehmigung durch den CERN Council

1996 : Entscheidung zum Bau des Beschleunigers

2006/2007: Inbetriebnahme mit Strahl

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Das CERN ist das führende europäische Forschungsinstitut für Teilchenforschung

Es liegt bei Genf im schweizerischen -französischen Grenzgebiet

Österreich ist eines der CERN Mitgliedsländer, und somit wesentlich am Bau des LHC beteiligt

LHCproton-protonCollider7 TeV/c imLEP Tunnel

LEP: e+e- 104 GeV/c (1989-2000)

Umfang26.8 km

Injectionfrom SPS at450 GeV/c

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8 arcs with a length of about 2.8 km

8 straight sections with a length of about 600 m

Straight sections are used for physics experiments, and for accelerator systems

Beam cleaning, beam dump, RF-acceleration, and beam instrumentation

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ÜbersichtÜbersicht

LHC Parameter

Energie und Luminosität

LHC Layout

Supraleitende Magnete für den LHC

Machine Protection

•Elektromagnetismus und Relativitätstheorie•Thermodynamik•Mechanik•Quantenmechanik•Physik nichtlinearer Systeme•Festkörperphysik und Oberflächenphysik•Teilchenphysik und Strahlungsphysik

+ Ingenieurwissenschaften

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Energie Energie

LEP Ablenkfeld B = 0.123 tesla

Maximaler Impuls 103 GeV/c

Radius 2805 m

Elektromagnete teilweise aus Beton

LHC Ablenkfeld B = 8.33 tesla

Maximaler Impuls 7000 GeV/c

Radius 2805 m Magnetfeld mit Eisenmagneten maximal 2 tesla, daher werden

supraleitende Magnete benötigt

B = p / e0 • R

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Energy in the magnet system: 11 GJ

In case of failure, extract energy with a time constant of up to about 100 s

Drop 35 tons from 28 km

Energy stored in MagnetsEnergy stored in Magnets

The energy in the magnetscorresponds to an energy that melts 7500 kg of copper

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LuminositätLuminosität

L = N2 f n b / 4xy

mit N ......... Teilchen im Paket

f ......... Umlauffrequenz

nb......... Anzahl der Paket

xy ... Strahldimensionen am Wechselwirkungspunkt

Anzahl der „Neuen Teilchen“:

Das Ziel ist eine Luminosität von etwa 1034 [cm-1s-2] LEP (e+e-) : 3-4 1031 [cm-1s-2] Tevatron (p-pbar) : 3 1031 [cm-1s-2] B-Factories: > 1033 [cm-1s-2]

Wie lässt sich so eine hohe Luminosität erreichen ?

][][ 212 cmscmLtN

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Rüdiger Schmidt

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Large number of bunchesLarge number of bunches

2835 bunches - spacing of about 25 ns

Minimum beam size at IP of 0.5 m

Bunch structure with 25 ns spacing Experiments: more than 1 event / collision Vacuum system: photo electrons

Crossing angle to avoid long range beam beam interaction Interaction Region quadrupoles with gradient of 250 T/m

and 70 mm aperture

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Rüdiger Schmidt

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Beam current and energy stored in the beamBeam current and energy stored in the beam

Many bunches - Current in one beam about 0.5 A

Energy in one beam about 330 MJ

Dumping the beam in a safe way Beam induced quenches (when 10-7 of beam hits magnet at 7

TeV) Beam stability and Magnet Field quality Beam cleaning (Betatron and momentum cleaning) Synchrotron radiation - power to cryogenic system Radiation, in particular in experimental areas from beam

collisions (beam lifetime is dominated by this effect)

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Challenges:Challenges: Energy stored in the beam Energy stored in the beam

R.Assmann

One beam, nominal intensity(corresponds to an energy that melts 500 kg of copper)

Momentum [GeV/c]

Ene

rgy

stor

ed in

the

bea

m [

MJ]

x 200

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Energy in two LHC Beams: 700 MJ

Dump the beams in case of failure within 89 s after dump kicker fires

The beam dump is the onle element in the LHC that can stand the beam impact

Energy in Beams Energy in Beams

Drop it from 2 km

One beam, nominal intensitycorresponds to an energy that melts 500 kg of copper

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SummaryLHC Parameter

Momentum at collision 7 TeV/cMomentum at injection 450 GeV/cDipole field at 7 TeV 8.33 TeslaCircumference 26658 m

Luminosity 1034 cm-2s-1 Number of bunches 2808 Particles per bunch 1.1 1011 DC beam current 0.56 AStored energy per beam 350 MJ

Normalised emittance 3.75 µmBeam size at IP / 7 TeV 15.9 µmBeam size in arcs (rms) 300 µm

Arcs: Counter-rotating proton beams in two-in-one magnetsMagnet coil inner diameter 56 mmDistance between beams 194 mm

High beam energy in LEP tunnelsuperconducting NbTi magnets at 1.9 K

High luminosity at 7 TeV very high energy stored in the beam

beam power concentrated in small area

Limited investment small aperture for beams

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LHC Layout

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Layout of the LHC ringLayout of the LHC ring: 8 arcs, and 8 long : 8 arcs, and 8 long straight sections straight sections

Momentum Cleaning

Betatron Cleaning

Beam dump system

RF + Beam instrumentation

One sector

= 1/8

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Periodischer Aufbau: FODO ZellePeriodischer Aufbau: FODO Zelle

Dipol- und Quadrupol Magnete– Teilchenbahn stabil für Teilchen mit Sollimpuls

Sextupol Magnete– zur Korrektur von Teilchenbahnen für Teilchen mit Impulsabweichung

– Teilchenbahn stabil für kleine Amplituden (etwa 10 mm)

Multipol-Korrekturmagnete– Sextupol - und Dekapolkorrekturmagnete am Ende der Dipolmagnete

– Teilchenbahnen können instabil werden (selbst nach vielen Umläufen kann eine Teilchenbahn plötzlich instabil werden , z.B. 106)

QF QD QFdipolemagnets

small sextupolecorrector magnets

decapolemagnets

LHC Cell - Length about 110 m (schematic layout)

sextupolemagnets

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Bahnstabilität durch Supraleitende Magnete - Bahnstabilität durch Supraleitende Magnete - Quadrupol- und MultipolfelderQuadrupol- und Multipolfelder

LHC

Teilchenschwingungim Quadrupolfeld(kleine Amplitude)

Harmonische Schwingung(Koordinatentransformation)

Kreisbewegung im Phasenraum

z

y

y

y'

LHC

Teilchenschwingungbei nichlinearen Feldernund grosser Amplitude

Amplitude wächst bis zumTeilchenverlust

Keine Kreisbewegung im Phasenraum

z

y

y

y'

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distance about 100 m

Interaction point

QD QD QF QD QF QD

Experiment

Crossing angle for multibunch operation

Focusing quadrupole for beam 1, defocusing for beam 2 High gradient quadrupole magnets with large aperture (US-JAPAN) Total crossing angle of 300 mrad Beam size at IP 16 m, in arcs about 1 mm

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Layout of insertion for ATLAS and Layout of insertion for ATLAS and CMS CMS

200 m

inner quadrupoletriplet

separationdipole (warm)

recombinationdipole

quadrupoleQ4

quadrupoleQ5

ATLAS or CMS

inner quadrupoletriplet

separationdipole

recombinationdipole

quadrupoleQ4

quadrupoleQ5

collision point

beam I

Example for an LHC insertion with ATLAS or CMS

24 m

beamdistance194 mm

beam II

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1232 main dipoles +

3700 multipole corrector magnets

392 main quadrupoles +

2500 corrector magnets

Regular arc:

Magnets

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Regular arc:

Cryogenics

Supply and recovery of helium with 26 km long cryogenic distribution line

Static bath of superfluid helium at 1.9 K in cooling loops of 110 m length

Connection via service module and jumper

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Insulation vacuum for the cryogenic distribution line

Regular arc:

Vacuum

Insulation vacuum for the magnet cryostats

Beam vacuum for

Beam 1 + Beam 2

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Vacuum Vacuum chamberchamber

Beam vacuum systemBeam vacuum system

Beam screen is required for most of the machine

Beam screen Beam screen with cooling with cooling channels and channels and pumping slotspumping slots

Ensures vacuum stability

Captures synchrotron radiation at 5-20 K

Beam stability => Low impedance: thin copper layer

Electron cloud effects:- Minimise reflectivity- Beam scrubbing (as in SPS)

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One of 1800 interconnection between One of 1800 interconnection between two superconducting magnets: LHCtwo superconducting magnets: LHC

6 superconducting bus bars 13 kA for B, QD, QF quadrupole

20 superconducting bus bars 600 A for corrector magnets (minimise dipole field harmonics)

42 sc bus bars 600 A for corrector magnets (chromaticity, tune, etc….) + 12 sc bus bars for 6 kA (special quadrupoles)

13 kA Protection diodeTo be connected:

• Beam tubes• Pipes for helium• Cryostat• Thermal shields• Vacuum vessel• Superconducting cables

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Dipolmagnete für den LHC

1232 DipolmagneteLänge 15 mMagnetfeld 8.3 T2 Strahlrohre mit 56 mm Öffnung

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Spulenanordnung für DipolmagneteSpulenanordnung für Dipolmagnete

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Rüdiger Schmidt

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Ansicht des Dipolmagnet im KryostatAnsicht des Dipolmagnet im Kryostat

Vakuumröhre für Strahlen

Supraleitende Spule

Nichtmagnetische Stahlklammern

Ferromagnetisches Eisen

Stahlzylinder für Helium

Isoliervakuum

Stützfüsse

Vakuumtank

Two - in One MagnetTwo - in One Magnet

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Die Entdeckung der Die Entdeckung der SupraleitungSupraleitung

1908 -- Kamerlingh Onnes verflüssigt Helium.

1911 -- R-T Messung für Quecksilber

?"…. Mercury has passed into a new state, which on account

of its extraordinary electrical properties may be called the superconductive state …."

Copyright A.Verweij

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Magnetfeld - Stromdichte - TemperaturMagnetfeld - Stromdichte - Temperatur

Materialeigenschaften:

Tc kritische Temperatur

Bc kritisches Feld

Produktionsprozess:

Jc kritische Stromdichte

Temperature [K]A

pplie

d fie

ld [

T]

Superconductingstate

Normal state

Bc

TcNiedrigere Temperatur

grössere Stromdichte

Typisch: für NbTi:

2000 A/mm2

@ 4.2K, 6T

Für 10 T, Operation unterhalb 1.9 K erforderlichCopyright A.Verweij

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Typische SupraleiterTypische Supraleiter

Das hohe kritische Feld der Supraleiter Typ II lässt den Bau von Magneten mit hoher Feldstärke zu

1962 -- Entwicklung von kommerziellen

Niobium-Titan (NbTi) supraleitenden Drähten.

Charakterisierung von Supaleitern durch:TemperaturMagnetfeldStromdichte

Copyright A.Verweij

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Helium:Helium:PhasendiagrammPhasendiagramm

T>T: HeI

T<T: HeII(superflüssiges Helium)

T=2.17 K

LHC: T=1.9 K

P1.2 bar

Copyright A.Verweij

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Helium ParameterHelium Parameter

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7Temperature (K)

Cp

(J

/g/K

)

T

Spezifische Wärme von Helium als Funktion von T

Phasenübergangbei 2.18 Kelvin

Superflüssiges Helium (He II)

Copyright A.Verweij

He II, 1.9K He I, 4.2K Water, 300K SC @ 8T,1.9K

SC @ 8T,4.2K

thermal cond. ~100,000 0.02 1 ~400 ~400

viscosity 0.01 – 0.1 3 1000

Cp 4 5 0.0001 0.0004

Temperature [K]

Fie

ld [

T]

SC

n

T

z.B durch Teilchenverluste Erwärmung If T > Tcritical Quench

T=temperaturemargin (1.4 K for LHC)

Tc

Bc

Quench = Übergang Supraleitung Quench = Übergang Supraleitung NormalleitungNormalleitung

T 5.425 103 K sec-1Temperaturanstieg pro Sekunde:

TPsc

Asc Lsc cvcuErwärmung von Kupfer:

cvcu 3.244joule

K cm3Specifische Temperatur von Kupfer bei 300 C :

Psc 1.76 105 wattPsc cu Isc2

Lsc

Asc

cu 1.76 10 6 ohm cmWiderstand von Kupfer bei 300 K:

Lsc 1 mLänge des Leiters :

Isc 10000 ampStrom :

Asc 10 mm2Querschnittsfläche :

Leistung im Falle eines Quenches im Supraleiters:

Spezifische Wärme

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QuenchQuench

Bewegung des Supraleiters um einige m kann einen Quench auslösen

Strahlverluste von etwa 10-6 können die Dipolmagnete bei 7 TeV zum Quenchen bringen

Der Supraleiter wird mit Kupfer stabilisiert - der Widerstand von Kupfer unterhalb einer Temperatur von 30 K ist etwa 1/100 im Vergleich zum Widerstand bei 300 K

Der Magnetstrom muss im Quenchfall schnell abgeschaltet werden (etwa 100 ms)

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Ein supraleitender DrahtEin supraleitender Draht

1 mm6 m

Typischer Wert für maximalen Strom bei 8 T, 1.9 K: 800 A

Copyright A.Verweij

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LHC: Superconducting MagnetsLHC: Superconducting Magnets

Dipole assembly in industry

Arc 15-m dipoles and quadrupoles

Insertion dipoles and quadrupoles

Corrector magnets

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Cryostating and measurements (main Cryostating and measurements (main dipoles and other magnets)dipoles and other magnets)

SMA18 cryostating hallat CERN for installing dipole magnets into cryostats

SM18: 12 measurement stations are prepared for cold tests of possibly all superconducting magnets

A.Rijllard

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Sextupoles and decapoles to be installed at the extremities of the main dipoles

Delivery must precede dipole magnet fabrication (contribution from India and fabrication in industry)

Corrector magnet fabricationCorrector magnet fabrication - - construction for 11 types of magnets construction for 11 types of magnets startedstarted

L. Garcia-Tabares

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Machine protection: Machine protection: Beam energyBeam energy

Beam Cleaning:Beam Cleaning: Capture particles in the warm sections of the LHC with an efficiency of better than 99.9% to avoid losses that could quench superconducting magnets

In case of equipment failure, beam instabilities etc:

• Capture initial beam losses that could damage LHC equipment

• Beam Loss Monitors close to collimators and other aperture restrictions produce a fast and reliable signal to dump the beam if beam losses become unacceptable

For 7 TeV: fast beam loss between 106 and 107 protons could quench a dipole magnet

The beam dump block The beam dump block isis the only system that can the only system that can stand the full 7 TeV beam - 3stand the full 7 TeV beam - 3··101014 14 protons

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Beam Cleaning SystemBeam Cleaning System

Collimators close to the beam are required during all phases of operation

• Sophisticated beam cleaning system with many collimators has been designed limit aperture to about 6-10

• Together with the Beam Loss Monitors produce a fast and reliable signal to dump the beam if beam losses become unacceptable

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+- 3 1.3 mm

Beam +/- 3 sigma

56.0 mm

Beam in vacuum chamber at 7 TeVBeam in vacuum chamber at 7 TeV

Example for Example for failure failure at 450 GeVat 450 GeV

Assume that the current inone orbit correctormagnet is off by 10% of maximum current (Imax = 60 A)

12.0 mm

16.0 mm

Beam +/- 3 sigma

Beam +/- 3 sigmaand orbit corrector10 % / 100 % of Imax

56.0 mm

Ralphs EURO

Beam +/- 3 sigma

56.0 mm

1 mm

+/- 8 sigma = 4.0 mm

Example: Setting of collimators at 7 TeV - with luminosity opticsExample: Setting of collimators at 7 TeV - with luminosity optics Beam must always touch collimators first !Beam must always touch collimators first !Collimators might remain at injection position during the energy Collimators might remain at injection position during the energy rampramp

Ralphs EURO

Collimators at Collimators at 7 TeV, squeezed7 TeV, squeezed

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Particles that touch collimator after failure of normal conducting D1 magnets

After about 13 turns 3·109 protons touch collimator, about 6 turns later 1011 protons touch collimator

V.Kain

“Dump beam” level

1011 protons at collimator

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Beam Loss MonitorsBeam Loss Monitors

Primary strategy for protection: Beam loss monitors at collimators continuously measure beam losses

Beam loss monitors indicate increased losses => MUST BE FAST

After a failure: Beam loss monitors break Beam Permit Loop Beam dump sees “No Beam Permit” => dump beams

In case of equipment failure, enough time is available to dump the beam before damage of equipment - including all magnets and power converters - but issues such a General Power Cut etc. are still being addressed

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Prototype LHC cell:Prototype LHC cell: the 110 m long String 2 the 110 m long String 2

Full size model of one LHC cell (six dipoles and two quadrupoles)

2001: 3 dipoles and 2 quadrupoles

Cooled down to 1.9 K and onedipole and two quadrupole circuits were powered to nominal current

Cell has been completed (now six dipoles) and is today being cooled down

Experiment were performed in 2001 and will continue soon

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String 2:String 2: First Powering of dipole magnets First Powering of dipole magnets

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760.00

760.40

760.80

761.20

761.60

0 2 4 6 8 10 12 14 16 18 20Seconds

Amps

Imeas

Iref

String 2:String 2: Start of the LHC dipole circuit Start of the LHC dipole circuit ramp (0-20s) simulates ramp after ramp (0-20s) simulates ramp after injection of beam at 450 GeVinjection of beam at 450 GeV

50 ppm of full current = 350 MeV

Q.King et al. ICALEPS 2001

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String 2:String 2: LHC dipole circuit ramp (0- LHC dipole circuit ramp (0-4s)4s)

759.98

760.00

760.02

760.04

760.06

0 1 2 3 4Seconds

Amps

Imeas

Iref

2 ppm = 14 MeV

Results were achieved with a new method of digital regulation together withan ultra high precision current measurement system

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Integration and InstallationIntegration and Installation

Space in tunnel and underground areas is limited Equipment for many systems need to be installed 3-D computer model for tunnel and underground areas

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ConclusionsConclusions

The LHC is installed and commissioned in eight (rather)independent sectors - that allows for

activities to be performed in parallel

Installation of LHC started with “general services” March 2002

Civil engineering is nearly completed

Most contracts with industry for equipment supply have

been awarded

Fabrication of equipment under the responsibility of other labs goes well

Planning can now be based on deliveries and contractual documents

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ConclusionsConclusions

Fabrication of equipment

Installation of completed components

Very thorough commissioning of the hardware systems starting in 2005, sector by sector, as key for successful fast start up with beam

From

now

to

2006

String 2 gave us a lot of confidence as we observed a smooth commissioning of the hardware systems

In 2006 - one beam injected and transported across two sectors (25% of the ring)

Start-up with two beams in spring 2007

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LHC injector complex - pre-accelerators existLHC injector complex - pre-accelerators exist

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Transfer Lines SPS - LHCTransfer Lines SPS - LHC

Two new transfer line tunnels from SPS to LHC are being built. The beam lines use normal conducting magnets

Length of each line:about 2.8 km

Magnets are all available, made by BINP / Novosibirsk

Commissioning of thefirst line for 2004

Dipole magnets waiting for installation

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Accelerator physics and operationAccelerator physics and operation Dynamic aperture of 11 sigma: for all magnets the maximum

tolerated multipoles were specified

Preparations based on very well controlled slow ramp with PELP function (parabolic, exponential, linear and parabolic)

Accurate modelling of beam dynamics through the cycle Magnetic multipoles Dynamic effects in superconducting magnets Beam beam effects - head on / parasitic crossings

Preparation of slow feedback for tune and orbit, and possibly chromaticity - prototyping at the SPS

Online magnetic measurements (multipole factory) for feed-forward to corrector circuits

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Powering and Quench ProtectionPowering and Quench Protection

Almost 1800 circuits from 60 A to 24 kA distributed around the 27 km LHC accelerator => 1800 Power Converter

The eight sectors of the LHC are largely independent - accurate tracking of current is required

Very high performance is needed for the 24 main circuits with main dipole and quadrupole magnets at I = 12 kA

For the main circuits the current needs to be controlled at the ppm level (12 mA at 12 kA)

Protection of 8000 magnets, 1800 High Temperature Superconductor current leads, and a large number of superconducting bus bars

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Machine protection: Machine protection: Magnet energy

Energy in dipole magnets: 10 GJoule

… per sector reduced to 1.3 GJoule

Uncontrolled release of energy is prevented:

Fire quench heaters

Current by-passes magnet via power diode

Extract energy by switching a resistor into the circuit - the resistor with a mass of eight tons is heated to 300 °C

All components of the system have been validated, and production started (part in collaboration with Russia and India)

13 kA switches from Protvino Russia