THE LARGE HADRON COLLIDER - PRESENT STATUS AND PROSPECTS
L.R. Evans, CERN, Geneva, Switzerland
Abstract
The Large Hadron Collider (LHC), due to becommissioned in 2005, will provide particle physics withthe first laborator y tool to access the energy frontier above
1 TeV. In order to achieve this, protons must be
accelerated and stored at 7 TeV, colliding with an34-2-1
unprecedented luminosity of 10 cm s . The 8.3 Tesla
guide field is obtained using conventional NbTi
technology cooled to below the lambda point of helium.
Considerabl e modification of the infrastructure aro und theexisting Large Electron Positron collider (LEP) tunnel isneeded to house the LHC machine and detectors. A briefstatus report is given and future pr ospects are di scussed.

1 INTRODUCTION
The LHC project is now mid-way to completion. TheLEP machine is now being removed and the tunnel
infrastructure prepar ed for LHC installatio n. Most of themajor contracts for the manufacture of machinecomponents have been placed an d har dware is beginning
to arri ve at CERN. A brief status report on some of themajor systems is given below. The revised schedule formachine completion is discussed.

2 INJECTORSThe existing injector chain will be used for pr oducing
the LHC beams. In order to achieve the require dperformance in terms of bunch intensity and emittancewith the nominal bunch spacing of 25 ns, a number ofmodifications are re quired, part icularly in the PScomplex. The classical technique of generat ing the 25 ns
bunch spacing (h= 84 in the PS) from the beam injectedfrom the PS Booster (h= 7) is by debunching andrebunching on the higher harm onic. This techniquesuffers from two major disadvantages. The 25 ns spacing
is too small for the risetime of the extraction kickers,
resulting in a number of bunches lost or with large
betatr on oscillations. In addition, the beam tends tobecome unstable during the debunching process when theenergy sprea d becomes too low for adequate Landau
damping. To overcome these problems, a novel technique
has been developed [1] which consists of stepwise bunch
splitting using intermediate harmonic cavities. By leavingout one Booster bunch, a large enough gap can be left for
the kickers and the beam never gets unstable since theenergy sprea d is too large. Using this technique, beams
satisfying the LHC specifications on emittance, intensityand bunch length have alread y been obtained (Fig. 1) [2] .
This beam is now available for commissioning thenext link in the injector chain, the SPS. Machine studies
have alread y started an d have clearly demonstrated theonset of the electron cloud instability (see below) aspredicted.

3.5

BAD

3
2.5
2
1.5

H54
H64
V75
V85

GOOD

10.5
00500

1000

1500

2000

2500

Time (ms)1st bunch injection

PSB output

2nd batchinjection

1.4-25GeV
acceleration PS output(SEM-wiresin TT2)

(SEM-grids inmeas. line)

Figure 1: Transverse emittance in the PS from injection toextraction for the nominal LHC beam.

3 MAGNETS
The LHC will require more than 8000 superconducting
magnets of different types. The most challenging are the1232 superconducting two-in-one dipoles, which must
operat e reliably at the nominal field of 8.3 Teslacorres ponding to a centre-of-mass energy of 14 TeV, withthe possibility of being pushed to an ultimate field of9 Tesla.
Extensive R&D with short models culminated in theproduction of six prototypes where the coils were
manufacture d at three different firms and cold massassembly at CERN. After satisfactory performance of
these prototypes, series production has start ed. The firstseries dipole has been tested at CERN (Fig. 2 ), witha good performance (Fig. 3 ). Pro duction will now slowly
ramp up to the required rat e of six dipoles per week. The
prototype magnets ar e being assembled into a full cell ofthe LHC (six dipoles and two quadrupoles) in its final
configurat ion, including an external cryoline, in order torefine installation procedures and to cold test the string as
an integrate d system (Fig. 4).
The 400 main quadr upoles are integrat ed into Short
Straight Sections (SSS) also containing sextupole anddipole for chr omaticity and orbit correction respectively.
The quadrupoles have been designed at Saclay in theframework of a collaborat ion with CEA. Three prototypes
have been built; all meet the design performance. The
integration of the SSS into their cryostats has been madein collaborat ion with CNRS. Orders have now beenplaced for series manufacture and for cryostat integration.
The first series units will arrive by the end of the year.

Figure 2: The first series dipole being transported to themeasurements bench.
Training quenches at 1.8K
Magnetic Field at Quench B [Tesla]

10.00
9.75

No quench

9.50
9.25
9.00
8.75
8.50
8.25
8.00
7.75
7.50
7.25
7.00
01

2

3

45Quench Number
HCMBB-A0001-01000001.T1

Ultimate Field = 9T

Nominal Field = 8.34 Tesla

Figure 5: A full-length insertion quadrupole being
lowered into a vertical cryostat at KEK.

Figure 3: Training curve of the first series dipole.

Figure 6: The first full-length prototype at FNAL.

Figure 4: Assembly of a full LHC cell (the "string").
The dispersion suppressors, long straight sections andinsertion regions contain many special magnets, the mostchallenging of which are the high gradient (220 T/m)large aperture (70 mm) quadrupoles for the inner tripletsof the low-beta insertions. Two different versions of thesequadrupoles have been designed at FNAL and KEK, andhave been validated through short models. The first fulllength prototypes have now been built and are being
prepared for testing (Figs. 5 and 6).
Each insertion triplet will contain a mixture of US andJapanese magnets. The final integration into the cryostats
will be made at FNAL in collaboration with LBL.

Many other superconducting magnets are needed fortrimming the optics and for correcting latticeimperfections. A full list is given in Table 1.
Contracts for all elements have been placed in industry
and series production has started. Half of the MCS andMCDO magnets are being manufactured in India in theframework of a collaboration agreement.
A large number of conventional magnets are also
required. In the two transfer lines from the SPS to LHC
there are 360 six metre long dipoles and 180 quadrupoles,
all manufactured at BINP Novosibirsk in the frameworkof the CERN/Russia agreement. The delivery of thesemagnets is now nearly complete. Also from Russia are thewarm separation dipoles (BINP) and the septum magnets
for the beam abort channels (IHEP, Protvino, see Fig. 7).

Table 1

4 CRYOGENICS

Name

Quantity

PurposeMSCB

376

MCS2464

MCDO

1232

MO336

MQT256

MCB
MQM

266
100

MQY

20

Combined chromaticity/closed orbit correctors
Dipole spool sextupole for
persistent currents at
injection
Dipole spool
octupole/decapole for
persistent currents
Landau octupole for
instability control
Trim quad for latticecorrection
Orbit correction dipoles
Dispersion suppressor
quadrupoles
Enlarged aperture
quadrupoles

The most important elements of the cryogenic system
are the eight large (18 kW) cryoplants together with theirassociated cold compressors for the production ofsuperfluid helium, and the distributed cryogenic line
feeding the magnet system. Four of the 18 kW plants will
be recuperated from the LEP cryogenic system withsuitable upgrades. The first of the new plants has now
arrived at CERN and is being prepared for testing (Fig. 9).
It will be housed in the cryogenic building at Point 1,
which is close to the magnet test hall. It can therefore beused to provide helium for the test benches as well as forcooling the machine. The first cold compressor, built by
a German/Japanese consortium, will be delivered toCERN in the spring of 2001.

Figure 9: The lower cold box of the first 18 kW cryoplant.
The magnet system is cooled through an external
composite cryogenic line which connects to the magnet
cryostats through a jumper connection at the end of each
106 m lattice period. Three prototype sections of thecryoline, from three different manufacturers, have beensuccessfully tested and a call for tender for the fullproduction has been launched. One of the prototypes isbeing used to cool the string.
Figure 7: Extraction septum magnet from IHEP.
Two of the long straight sections of the LHC are usedfor beam collimation. In view of the high radiation levels
these straight sections are equipped with special twin
aperture warm quadrupoles (52 units) built in Canada in
the framework of the CERN/TRIUMF agreement (Fig. 8).

Figure 8: Warm quadrupole for cleaning insertion.

5 VACUUM
One of the most critical factors affecting the vacuum
system is the electron cloud instability, now clearlyobserved in the B-Factories at KEK and SLAC as well as
in the SPS [3] for “LHC type” beams. Depending on thebunch spacing and intensity and the size of the vacuum
chamber, a resonant build-up of secondary electrons,seeded by synchrotron radiation or by ionisation ofresidual gas can occur. This electron cloud produces
heating of the chamber wall and can even cause beam
instability. A great deal of effort has been expended inunderstanding this effect, both through theory andnumerical simulation as well as experiments on a numberof machines. In the SPS, for the nominal 25 ns bunch
spacing, the threshold for the build-up of the cloud isconsistent with numerical simulations. The effect can becured with gaps in the bunch train and by a reduction of
the secondary emission coefficient of the surface, which
will naturally occur by the cleaning effect of thesynchrotron radiation and by the electron bombardment
itself.

6 ACCELERATING SYSTEMThe RF operates at 400.8 MHz, the second harmonic of
the SPS frequency. Each beam has a separate system
necessitating an increase of the beam separation from 194
to 410 mm. Eight single-cell cavities per beam operating
at an average gradient of 5 MV/m provides a total voltageof 16 MV. The cavities are made from copper sputteredwith a thin film of niobium. All cavities have beenmanufactured and are being assembled into four-cavity
modules. The first module has been tested at full powerwith all ancillaries.
In order to ease injection tolerances and to provide
damping of injection oscillations, an additional RF system
operating at the SPS frequency of 200.4 MHz is required.
The cavities are not superconducting in order to provide
the large bandwidth needed. There are four cavities per
beam with 750 kV per cavity. These cavities are now
under construction.

Figure 10: The vault for the Atlas experimental cavern.

7 CIVIL CONSTRUCTION
The civil engineering work consists of three main
packages concerning the LHC machine and theexperimental areas for ATLAS and CMS respectively(Figs. 10 and 11). For the machine, the work is distributed
geographically, both for surface buildings housing thelarge cryogenic plants and in the underground areas. The
most important underground work is the construction of
two 2.5 km long tunnels housing the transfer lines fromthe SPS to the LHC. These tunnels have now reached theLHC ring and the junction caverns are under construction.
The two experimental caverns are well advanced albeit
with about six months delay.

8 SCHEDULE
The original schedule, made in 1996, foresaw ringclosure in summer 2005 and a short pilot run before
a three month shutdown to finish the installation of thedetectors. Since then, a number of factors, in particular
the delay in LEP dismantling and the late delivery of theexperimental caverns, has necessitated a revision of theschedule in collaboration with the experiment spokespersons. According to the revised schedule, the first
sector, from Point 8 to Point 7, will be commissioned
between March and September 2004, culminating in thetransport of a proton beam through the sector. Successive
sectors will be cooled down as they become available withthe whole ring closed and cold by the end of 2005. Beamcommissioning will start in March 2006 with theobjective of a short pilot run to the end of April. This will
be followed by a three month shutdown to finish detector
installation followed by a physics run of seven months
duration. At the end of the proton run, it is foreseen tohave a six week run with Pb ion collisions.

Figure 11: Assembly of the barrel yoke in the CMS
surface building.

9 CONCLUSIONSThe construction of the Large Hadron Collider is now
well underway. Contracts for most of the major systems
have been placed and hardware has started to arrive.
A detailed installation schedule is being developed withthe objective of completing the machine by the end of2005 and a first physics run in 2006. Collaboration withlaboratories in France, Canada, India, Japan, Russia andthe United States has been highly appreciated and is vitalfor the timely commissioning of the machine.

10 REFERENCES[1] R. Garoby et al., “Demonstration of bunch triplethsplitting in the CERN PS", 7 EPAC, Vienna 2000.
[2] K. Schindl, “Performance of the LHC Pre-Injectors”
these proceedings.
[3] G. Arduini et al., “Electron Cloud: Observations withth
LHC - Type Beams in the SPS", 7 EPAC, Vienna
2000.