STATUS OF CERN
K. Hübner, CERN, Geneva, Switzerland

An overview of the present CERN facilities is given
and their planned development is outlined as required by
the approved physics programme.
Although the main task of CERN in the next years willbe the construction of LHC, a small but significant
programme for accelerator R&D has been defined. It
comprises a multi-TeV linear collider, advanced neutrino
beams and the upgrading of LHC.

Given the importance of the contributions of the USA,
Japan, and Russia, these states have an observer status at
the CERN Council and participate in the Committee ofCouncil sessions that deal with LHC matters. Further
observer states are the European Union, Israel andTurkey.
A summary of the accelerator complex is given inpoint 2 and of the physics programme in point 3. The
present and planned accelerator R&D is outlined inpoint 4.

1 INTRODUCTION

2 THE ACCELERATORS

Abstract

The European Organisation for Nuclear Research
The first element of the proton accelerator chain is a
(CERN) in Geneva, Switzerland, operates one of the 50 MeV linac (L2), followed by the four-ring PS Boosterworld's largest laboratories in High Energy Physics. It(PSB) and the CERN Proton Synchrotron (CPS)
serves more than 5000 users, the majority of which
providing up to 24 GeV/c protons either directly to thecomes from Europe. It is financed by 20 European
experiments or 14 GeV/c protons to the 400 GeV Super
Members States but also receives major contributions Proton Synchroton (SPS).
from the USA, Japan and Russia for the construction of
The PSB synchrotron has recently been upgraded fromthe Large Hadron Collider (LHC) which will provide 1 to 1.4 GeV for LHC to overcome the space charge limit
proton - proton collisions with a centre-of-mass energy of at PS injection[1]. This has also had a beneficial effect for
14 TeV. In addition, substantial contributions to LHC are ISOLDE which is a facility where radio-active ions are
made by Canada and India. A large number of states investigated. These ions are produced in special targets
participate in the financing of the detectors used in the of the PSB beam. Fig. 1 shows a schematic view of thegeneral and LHC physics programmes, with CERN CERN accelerators.
providing only a fraction of this budget.
Fig. 1 - CERN's chain of accelerators in 2000

After the closure of the West Area Neutrino Facility(WANF) at the SPS, a new muon neutrino beamproviding CERN muon Neutrinos to Gran Sasso (CNGS)
is under construction. The facility consists of a 400 GeV
proton beam line, a carbon target, pulsed magnetic hornand reflector focusing pions at about 30 and 60 GeV
towards Gran Sasso, and a 2.45 m diameter, 1 km longevacuated tube in which pions and kaons can decay andwhich is terminated by a hadron stop. The muon
neutrinos continue for 730 km with an average energy of
18 GeV to the Gran Sasso National Laboratory of INFN
for a long baseline experiment. The layout is shown in
Fig. 2. The facility will be operational in 2005[2].

Fig. 2 - The CNGS layout
This accelerator chain is also used with ions. Initially,in 1992, Sulphur ions were accelerated. Since 1994, after
the construction of a special linac (L3), lead ions can be
accelerated up to 158 GeV/u. This linac including the ion
source and the RFQ was constructed by a collaboration
between GSI/Germany, LNF/INFN/Italy, GANIL/France,
and CERN with contributions from institutes in India
and Switzerland [3].
The CPS also provides a proton beam at 24 GeV/c to
produce antiprotons at 3.5 GeV/c which are stored in the

Antiproton Decelerator (AD) ring and subsequently
decelerated to 5.6 MeV (100 MeV/c). In order to keep
the emittance within reasonable bounds, rf deceleration
alternates with stochastic and electron cooling. This new
ring is built mainly from components of the Antiproton
Collector (AC) ring which was decommissioned after the
first phase of CERN's antiproton programme in 1996.
The AD was commissioned in 1999 and has now been in
operation since the summer 2000 [4]The AD experiments normally decelerate antiprotons
further by degrader foils to accumulate them at very low
energy in magnetic traps. However, this process is notvery efficient. In order to improve the yield for the traps,
a decelerating RFQ (RFQD) has been constructed whichobtains antiprotons at an energy which can be set
between 20 and 100 KeV. This device has beencommissioned and transfer efficiencies of 30 % (44 %design) have been achieved in the first preliminary
measurements [5].
The Large Electron Positron (LEP) collider was
operating at a beam energy of 46 GeV (Z0 resonance)from 1989 to 1995. The beam energy has been increased
gradually since 1995 and has reached 104 GeV in 2000[6].
This has been achieved by building up a powerfulsuperconducting rf system which eventually provided 3.6
GV together with the remaining part of the Copper rf
system (0.12 GV). The superconducting rf system
consisted finally of 288 cavities (272 Nb-film on Cu, 16
Nb bulk). It operated surprisingly well at an average
gradient of 7.4 MV/m (Nb film system)[7] though it had
been designated for 6 MV/m.)[8].
In order to make space for the LHC which will be
installed in the LEP tunnel (27 km circumference), LEP
dismantling started in December 2000 and will take agood fraction of 2001. The LHC is under construction
and all major components are in production. The
running-in will start at the beginning of 2006 and a firstphysics run of seven months with protons is planned tostart in summer of that year. The latter run will befollowed by a run with lead ions lasting about six weeks
in 2007 [9].
The injector chain has to be upgraded for LHC
operation. The PS complex upgrade for protons is nearlycomplete and the specified beam parameters have beensuccessfully obtained[1]. In order to obtain lead ion
bunches of sufficient intensity for LHC, a Low-Energy
Ion Ring (LEIR) has to be constructed in the next years
which will act as a buffer between the fast-cycling linac(L3) and the slow-cycling PSB. It will use most of thecomponents of the Low-Energy Antiproton Ring (LEAR)
which was decommissioned in 1996 after the first phaseof CERN's antiproton programme.

3.

THE PHYSICS PROGRAMMEThe scope of the CERN physics programme is verybroad. It ranges from the preparation of experiments with
the LHC to experiments with anti-hydrogen virtually at
rest at AD[10].
At the moment, 26 experiments are approved notcounting the 56 approved experiments with radio-activeions at ISOLDE. The results from the four LEP
experiments (ALEPH, DELPHI, OPAL and L3) arebeing analysed and the detectors are being dismantled.

Four large LHC detectors (ALICE, ATLAS, CMS and
LHCb) are being constructed by truly global
collaborations and will start data taking in 2006.
The fixed-target programme has been much reduced tofree resources for LHC. At present, twelve experiments
are approved and are all located in the North Area of the
SPS. The slow-extracted (5 s spill) proton beam is usedby NA 48 to study CP-violation in the K-meson system,
and COMPASS to investigate hadron structure withpolarised muon beams, in particular, the gluon
polarisation in a longitudinally polarised nucleon. The
slow-extracted fully stripped lead ions are used at either
40, 80 or 158 GeV/u by a number of experiments
searching for quark-gluon plasma.
At the PS complex, three experiments are approved.
The East Hall houses DIRAC an experiment measuring
the lifetime of the π + π - atoms to test low-energy QCD
predictions, and HARP measuring precisely the yield of 2
to 15 GeV/c protons and pions with a variety of targets,
which is of great relevance for the design of targets foradvanced neutrino beams. The third experiment PS 213
starting in 2001 will use the new nTof facility at the PS
where a neutron beam is generated in a lead target bysingle bunches of 24 GeV/c protons. Using time-of-flightmethods and a 190 m long flight path neutron-induced
nuclear reactions can be studied with an extremely highenergy-resolution. The facility is housed in a transfer
tunnel originally built to transfer protons from the CPS
to the West Hall of the SPS.
Three experiments are approved at the AD which
provides antiprotons at 100 MeV/c. Their principal aim
is to produce anti-hydrogen by combining the cooled
antiprotons with positrons in traps and to compare its
spectroscopy with that of hydrogen. This should provide
a very sensitive test of the CPT theorem.
The ISOLDE facility produces radio-active ions using
1.4 GeV protons from the PSB for 56 approved
experiments which range from studies of weakinteractions and nuclear physics (46 %), solid statephysics (23 %), atomic physics (17 %), particle andastrophysics (11%), to biology and medicine (3 %).
A particular and unique feature of CERN is that itprovides free-of-charge, a large variety of high-energy
test beams to the global community in particular for testsof LHC detector components but also for many otherexperiments including space-based detectors. These test
beams are derived from targets in the 400 GeV slowextracted proton beam which can be shared between the
North and the West Hall of the SPS. Four beam lines
exist in the North Hall and two in the West Hall with twoto three positions for experiments along the beam lines.
The experiments have to alternate but with muons
simultaneous operations of two test set-ups is possible.
The PS East Hall offers five beam lines which are allused for LHC detector tests.

4.

ACCELERATOR R&D

This is only a brief summary, as it is covered by othercontributions at this conference.

4.1

LHC

In the past, the main thrust for LHC has been focusedon the development of the 9T (8.35T nominal)
superconducting magnets and the 2K cryogenic system.
This programme is concluded and the major components
are in production [9].
However, in order to exploit fully the investment andthe potential of LHC, studies have started with a view toincreasing the luminosity of LHC from the nominal 1034
cm-2 s-1 per experiment to 1035cm-2 s-1. Four measures
can be envisaged [11] :i)increase the beam currents until the beam-beamlimit is reached, which is expected to happen
around 2.5 x 1034 cm-2 s-1 ;ii)increase the focusing at the interaction points bylowering β* from 0.5 m to 0.25 m which should
increase the luminosity by a factor 2 leading
potentially to 5 x 1034 cm-2 s-1. This requires
insertion quadrupoles of larger aperture and, inturn, new superconducting cable instead of the
NbTi cable foreseen for the first-generation
quadrupoles, so that a higher magnetic field canbe sustained in the coils. To this end, R&D on
Nb3Sn cable has been undertaken incollaboration with the University of Twente in
the Netherlands and research on Nb3Al cablehas been commissioned in Japan through KEK.
iii)
An additional step could be doubling thenumber of bunches which could lead to a further
factor 2 and a luminosity close to 1035cm-2 s-1
provided the adverse effects [12] of more andenhanced parasitic crossings of the bunches canbe controlled. It has the advantage that it does
not decrease the luminosity lifetime and thenumber of events per bunch crossing stays
constant. However, the time resolution of thedetectors will need improvement as the bunches
will be spaced 12.5 ns instead of 25 ns.
iv)
the luminosity can also be increased by raising
the beam currents provided the dynamic
aperture is sufficient to accommodate larger
beam emittances. The latter must be blown up to
respect the beam-beam limit. Obviously, thismeasure can only be envisaged after a numberof years of operation when the behaviour of thestorage ring has been sufficiently studied andunderstood.

4.2

Superconducting rf cavities

This is a research line at CERN which has been
pursued since the 1960's. It has been the basis for theindustrial construction of the superconducting LEP rf

system which eventually enabled LEP to reach 104 GeV
per beam.
This R&D has continued all the time at a modest scale
mainly to explore the potential of the Nb-film techniquedeveloped at CERN. Since the cavities are made fromcopper, this technique makes them more mechanicallystable than Nb-bulk cavities and the high thermal
conductance of copper makes them virtually quench-free.
However, accelerating gradients until now haveremained below the gradients achievable with Nb-bulk[13].
The Nb-bulk cavities, however, have reached evenhigher gradients with surface treatment called electropolishing and developed at KEK. Single cells preparedwith this technique in a collaborative effort between
DESY, CEA/Saclay and CERN have reached gradientsin excess of 35 MV/m, reproducing the results of KEK
where even 40 MV/m has been achieved [14].

4.3

CLIC

CERN has studied in parallel to the LHC a Compact
Linear Collider (CLIC) operating at 30 GHz. Recent
studies concentrate on a collider with a centre-of-massenergy of 3 TeV with a luminosity of 1035cm-2 s-1 to reachbeyond the LHC physics. In order to make it very
compact a high acceleration gradient of 150 MV/m has
been chosen which makes the facility relatively short,and rf power is provided by a second, low-energy (1.2
GeV) electron beam running in parallel with the electron
and positron main beam so that a small diameter tunnel
is sufficient. This second beam, the drive beam, isdecelerated in special 30 GHz structures converting the
kinetic energy of the drive beam into about 400MW/m rf
power. Once the energy of the second beam is as low as
0.12 GeV it must be dumped and replaced, whichhappens every 600 m [15,16].
A number of test facilities [17] have been constructed
and a new CLIC Test Facility (CTF3) is under designand construction will start in 2001. This new test facility
will be built on the premises of the LEP pre-injector
consisting of the linac LIL and the accumulator EPA (seeFig. 1) which will be decommissioned in 2001. Many of
the components from these accelerators will be reused.
The drive beam generation scheme will be tested in
CTF3 and the drive beam will be used to demonstrateacceleration with 150 MV/m. In parallel, thedevelopment of critical components will continue. Since
rf conditioning and testing of components is
indispensable for this R&D, the availability of a 30 GHz
rf source before operation of CTF3 would be very
desirable. The most promising source at present appears
to be a gyroklystron.

4.4

Advanced neutrino beams

Already during the design phase of the CERN neutrino
beam to Gran Sasso, the possible upgrade of theperformance of CNGS has been considered. This
upgrading will require an improved performance of the
proton accelerator chain and of the target.
A more powerful injector of the PS than the present
one consisting of the linac L2 and the PSB booster
synchrotron would certainly improve the proton
accelerator chain. For this reason, a new more powerfullinac using the superconducting LEP cavities wasconsidered some time ago [18]. In the framework of therecent study of a neutrino factory [19], a new conceptual
design for this 2.2 GeV Superconducting Proton Linac(SPL) providing 4 MW beam power has been made [20].
The next step will be a quantitative study of its impact
on PS and SPS performance. SPL is also of interest for
an upgrade of ISOLDE. Note, however, that it cannot
improve the performance of LHC as the latter is limitedby the beam-beam effect.
The HARP experiment at the PS will precisely
measure the pion yield of 2.2 GeV protons in order toverify whether this proton energy is sufficient for thepion production required for the neutrino factory. The
answer should be available by the end of 2001.
Before proceeding to a fully-fledged neutrino factory,
it is interesting to consider the neutrino beam generated
by these low-energy protons provided that the 4 MW on
target can be achieved. It has been shown that this muon
neutrino beam would have a very low contamination withelectron neutrinos and, therefore, would be suited for the
search for oscillation between muon neutrinos andelectron neutrinos [21].
The CERN study of a neutrino factory [19] is based on
SPL feeding an accumulation ring with multi-turninjection (660 turns) so that the linac pulse (2.2 ms) iscompressed into a train (3.2 µs) of 140 bunches. In orderto obtain short bunches the beam is transferred to thecompressor ring where the bunches are shortened from
3.5 to 1 ns r.m.s. length by bunch rotation with a suitablerf system. This takes less than 10 turns. It is assumed
that these two rings could be housed together in the
CERN ISR tunnel which has a circumference of about
1 km.
The bunch train is then fast-extracted and hits a targetof two interaction lengths. Muons resulting from thedecaying pions are collected at an average energy of 300
MeV/c and enter rf cavities for phase rotation 30 m
downstream of the target followed by a transverse
cooling section which consists of a sequence of absorberand rf cavities (44 and 88 MHz). A final set of 88 MHz
cavities plus a set of 176 MHz cavities accelerates themuons to 2 GeV which is the injection energy of the firstrecirculator.
After acceleration to 10 GeV, the beam is transferred
to a second recirculator which raises the beam energy to
50 GeV. The muon storage ring has a bow-tie shape inorder to have two long straight sections and, therefore,
two neutrino beams generated by the decaying muons.

The neutrino beams would be directed towards detectors
at about 1000 and 3000 km.
The CERN scheme which uses a pulsed horn for thepion collection and rf for phase rotations compares wellin first approximation with the schemes developed inJapan and in the US[22]. However, much more simulationand development work is required before this comparison
can be put on a solid basis. The most critical items are
the target and the muon cooling. Both require a
considerable R&D effort which probably can only betackled by international collaboration given the scale ofeffort required.

5.

CONCLUSIONSCERN concluded the LEP Programme in 2000 and
LEP is being dismantled in 2001. All effort isconcentrated on the construction of the LHC accelerator
and the associated detectors which will start data taking
in 2006. Significant contributions are being made to theaccelerator by a number of Non-Member States.
The fixed-target programme has been reduced andrefocused. The construction of a new neutrino beam for along-baseline experiment together with the Gran Sasso
National Laboratory in Italy has been approved.
A small but significant R&D programme covers thestudy of LHC luminosity upgrading, a multi-TeV linear
electron-positron collider and a possible future neutrino
programme offering more powerful neutrino beams.
Given the complexity and challenges of the linear
collider and the neutrino factory, a great variety of R&D
issues have to be tackled. Since substantial resources are
required to make real progress, CERN seeks to join
forces with other laboratories engaged in this type of
R&D in order to advance the field and to prepare a
global approach.

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