CERN Hadron Linacs

Last updated
CERN accelerator complex
List of current particle
accelerators at CERN
Linac 3 Accelerates ions
AD Decelerates antiprotons
LHC Collides protons or heavy ions
LEIR Accelerates ions
PSB Accelerates protons or ions
PS Accelerates protons or ions
SPS Accelerates protons or ions
Internal view of the first CERN Linac Internal view Linac 1.jpg
Internal view of the first CERN Linac

The CERN hadron Linacs are linear accelerators that accelerate beams of hadrons from a standstill to be used by the larger circular accelerators at the facility.



The Linac [1] , some times referred to as the PS Linac [2] and much later Linac 1, [3] was CERN's first linear accelerator, built to inject 50 MeV protons into the Proton Synchrotron (PS). Conceived in the early 1950s, its principle design was based on a similar accelerator at AERE in England. [4] The first beams were accelerated in 1958, at currents of 5 mA and a pulse length of 20 μs, which was the world record at that time. [4] The accelerator was fully operational by September 1959, when the design energy of 50 MeV was first reached. [4] [5]

From then on, the Linac experienced a phase of rapid development and constant improvement of the output parameters. This culminated in 1978, when a maximal proton current of 70 mA at pulse lengths of 100 μs could be reached. [4] From 1972 on, the Linac didn't deliver the protons directly to the PS anymore, but to the Proton Synchrotron Booster (PSB). The PSB had been built to allow for higher energies of the protons beams already before they enter the PS.

After Linac 2 had taken over the task of accelerating protons in 1978, the Linac continued to be used as a reliable testbed for new developments. This included the testing and implementation of a radio-frequency quadrupole as the initial accelerator, which replaced the original Cockcroft-Walton generator in 1984. Furthermore, ways to create and accelerate deuterons, α-particles and H atoms were developed. The latter were used as test beams for LEAR. [4] From late 1986 on, the Linac was also used to accelerate oxygen and sulphur ions. [6] [7]

The Linac ceased to be used in experiments in summer of 1992. [8] It was then decommissioned and removed from its tunnel to make room for Linac 3; the construction of which started October 1992 after the Linac had been removed from the tunnel. Parts of the Linac remain as museum pieces in the Microcosm exhibit. [9]

Linac 2

Linac 2, in the beginning simply referred to as the new Linac [10] was announced in 1973. [11] It was decided to build a new linear accelerator, since the old Linac was unable to keep up with the technical advances of the other machines within CERN's accelerator complex. Linac 2 replaced the Linac as CERN's primary source of proton beams in 1978. It kept the same beam energy of 50 MeV, but allowed for more intense beams with beam currents of up to 150 mA and a longer pulse duration of 200 μs. [12]

Originally, it had been discussed to further upgrade the first Linac instead of building a completely new linear accelerator. However, it quickly became clear that the costs of such an update would almost be as expensive as the new Linac. Another fact in favor of this new construction was the possibility to ensure a smooth transition from one Linac to the other without any downtime in between. Also this two linac approach meant that the old Linac could provide a back-up for the new Linac for the first years of operation.

Construction of Linac 2 started in December 1973, with an estimated budget of 21.3 million CHF, and was completed in 1978. [13] Linac 2 was 36 meters long and was based at ground level at the main CERN site. It was located in a building parallel to the old Linac tunnel. [14]

Throughout its lifetime, Linac 2 went through several updates to keep up with the advances of CERN's accelerator system. The most important upgrade was the replacement of the old 750 kV Cockcroft-Walton generator with a Radio-frequency quadrupole in 1993. This raised the output current to 180 mA. [15]

In late 2000s, it was considered whether to upgrade Linac 2 or build a new linac for injecting particles into HL-LHC. The decision was in the end made to build a new accelerator, the Linac4 to succeed Linac 2 in 2020. Linac 2 was switched off 12 November 2018 at 15:00 by CERN's Director of Accelerators, and was subsequently decommissioned as part of the LHC Injector Upgrade project. In the decommissioning process, Linac 2 was disconnected from the other accelerators of CERN, so it can no longer used to inject particles into CERN accelerators or experiments. However, much of the Linac 2 accelerator hardware is left (as of October 2019) in place untouched, with the hope of making it into an exhibition about the history of CERN. [14]

Linac 3

Linac 3, also referred to as the Lead Linac [16] was constructed inside the former tunnel of Linac 1 and got commissioned in the summer of 1994 (construction started October 1992). It had been specially constructed to accelerate heavy ions, after tests with Linac 1 and an increasing demand from the scientific community suggested to build a new Linac dedicated specifically to this task. [6] The accelerated particles are mainly lead ions, which are provided to the Proton Synchrotron Booster (PSB), LHC and fixed target experiments at the SPS and LEIR. For LEIR's commissioning, also oxygen ions were accelerated. [17]

After preparations from 2013 on, Linac 3 was adapted to accelerate argon ions in 2015. These were used by the NA61/SHINE experiment. [18] [19]

Similarly, Linac 3 accelerated xenon ions in 2017 for NA61's fixed-target physics programme. On October 12, 2017, these were delivered to the Large Hadron Collider (LHC) for a unique run of data taking: For the first time, xenon ions were accelerated and collided in the LHC. For six hours, LHC's four experiments could take data of the colliding xenon ions. [20]

Linac 3 is expected to stay in use at least until 2022. [21]


Linac4, some times imprecisely referred to as Linac 4, is a current linear accelerator replacing the retired Linac 2. Unlike its predecessors, Linac4 accelerates negative hydrogen ions to an energy of 160 MeV. [22] The ions are then injected to the Proton Synchrotron Booster (PSB) where both electrons are then stripped from each of the hydrogen ions and thus only the nucleus containing one proton remains. By using hydrogen ions instead of protons, the beam loss at the injection is reduced and simplified and this also allows more particles to accumulate in the synchrotron. [23]

CERN approved the construction of Linac4 on June 2007. Project started in 2008. [9]

Linac4 has been built in its own tunnel, parallel to Linac 2, in the main CERN site. The reason for building the accelerator in its own new tunnel is that its building could take place simultaneously with the operation of Linac 2. [14]

Linac4 has increased the energy by a factor of three over its predecessor, Linac 2, and achieve an energy of 160 MeV. This energy increase, when combined with the increased accumulation of particles, will enable the beam intensity to double when later delivered to LHC. This is part of the planned luminosity increase of the LHC which is scheduled for 2021. [24]

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The European Organization for Nuclear Research, known as CERN, is a European research organization that operates the largest particle physics laboratory in the world. Established in 1954, the organization is based in a northwest suburb of Geneva on the Franco–Swiss border and has 23 member states. Israel is the only non-European country granted full membership. CERN is an official United Nations Observer.

Fermilab High-energy particle physics laboratory in Illinois, USA

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operated by the Fermi Research Alliance, a joint venture of the University of Chicago, and the Universities Research Association (URA). Fermilab is a part of the Illinois Technology and Research Corridor.

Tevatron Particle accelerator

The Tevatron was a circular particle accelerator in the United States, at the Fermi National Accelerator Laboratory, east of Batavia, Illinois, and is the second highest energy particle collider ever built, after the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. The Tevatron was a synchrotron that accelerated protons and antiprotons in a 6.28 km (3.90 mi) ring to energies of up to 1 TeV, hence its name. The Tevatron was completed in 1983 at a cost of $120 million and significant upgrade investments were made during its active years of 1983–2011.

Large Hadron Collider Particle collider

The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider and the largest machine in the world. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.

Large Electron–Positron Collider

The Large Electron–Positron Collider (LEP) was one of the largest particle accelerators ever constructed.

Synchrotron Type of cyclic particle accelerator

A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed path increases with time during the accelerating process, being synchronized to the increasing kinetic energy of the particles. The synchrotron is one of the first accelerator concepts to enable the construction of large-scale facilities, since bending, beam focusing and acceleration can be separated into different components. The most powerful modern particle accelerators use versions of the synchrotron design. The largest synchrotron-type accelerator, also the largest particle accelerator in the world, is the 27-kilometre-circumference (17 mi) Large Hadron Collider (LHC) near Geneva, Switzerland, built in 2008 by the European Organization for Nuclear Research (CERN). It can accelerate beams of protons to an energy of 6.5 teraelectronvolts (TeV).

International Linear Collider Proposed linear accelerator for subatomic particles

The International Linear Collider (ILC) is a proposed linear particle accelerator. It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV. Although early proposed locations for the ILC were Japan, Europe (CERN) and the USA (Fermilab), the Kitakami highland in the Iwate prefecture of northern Japan has been the focus of ILC design efforts since 2013. The Japanese government is willing to contribute half of the costs, according to the coordinator of study for detectors at the ILC.


The High Energy Accelerator Research Organization, known as KEK, is a Japanese organization whose purpose is to operate the largest particle physics laboratory in Japan, situated in Tsukuba, Ibaraki prefecture. It was established in 1997. The term "KEK" is also used to refer to the laboratory itself, which employs approximately 695 employees. KEK's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics, material science, structural biology, radiation science, computing science, nuclear transmutation and so on. Numerous experiments have been constructed at KEK by the internal and international collaborations that have made use of them. Makoto Kobayashi, emeritus professor at KEK, is known globally for his work on CP-violation, and was awarded the 2008 Nobel Prize in Physics.

Super Proton Synchrotron Particle accelerator at CERN

The Super Proton Synchrotron (SPS) is a particle accelerator of the synchrotron type at CERN. It is housed in a circular tunnel, 6.9 kilometres (4.3 mi) in circumference, straddling the border of France and Switzerland near Geneva, Switzerland.

HERA (particle accelerator)

HERA was a particle accelerator at DESY in Hamburg. It began operating in 1992. At HERA, electrons or positrons were collided with protons at a center of mass energy of 318 GeV. It was the only lepton-proton collider in the world while operating. Also, it was on the energy frontier in certain regions of the kinematic range. HERA was closed down on 30 June 2007.

Proton Synchrotron CERNs first synchrotron accelerator

The Proton Synchrotron (PS) is a particle accelerator at CERN. It is CERN's first synchrotron, beginning its operation in 1959. For a brief period the PS was the world's highest energy particle accelerator. It has since served as a pre-accelerator for the Intersecting Storage Rings (ISR) and the Super Proton Synchrotron (SPS), and is currently part of the Large Hadron Collider (LHC) accelerator complex. In addition to protons, PS has accelerated alpha particles, oxygen and sulphur nuclei, electrons, positrons and antiprotons.

The High Luminosity Large Hadron Collider (HL-LHC; formerly SLHC, Super Large Hadron Collider) is an upgrade to the Large Hadron Collider started in June 2018 that will boost the accelerator's potential for new discoveries in physics, starting in 2027. The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to 1035 cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.

Alternating Gradient Synchrotron Particle accelerator at Brookhaven National Laboratory

The Alternating Gradient Synchrotron (AGS) is a particle accelerator located at the Brookhaven National Laboratory in Long Island, New York, United States.

Proton Synchrotron Booster CERN infrastructure

The Proton Synchrotron Booster (PSB) is the first and smallest circular proton accelerator in the accelerator chain at the CERN injection complex, which also provides beams to the Large Hadron Collider. It contains four superimposed rings with a radius of 25 meters, which receive protons with an energy of 50 MeV from the linear accelerator Linac 2 and accelerate them up to 1.4 GeV, ready to be injected into the Proton Synchrotron (PS). Before the PSB was built in 1972, Linac 1 injected directly into the Proton Synchrotron, but the increased injection energy provided by the booster allowed for more protons to be injected into the PS and a higher luminosity at the end of the accelerator chain.

A hadron collider is a very large particle accelerator built to test the predictions of various theories in particle physics, high-energy physics or nuclear physics by colliding hadrons. A hadron collider uses tunnels to accelerate, store, and collide two particle beams.

Particle accelerator Device to propel charged particles to high speeds

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.

Low Energy Ion Ring

The Low Energy Ion Ring (LEIR) is a particle accelerator at CERN used to accelerate ions from the LINAC 3 to the Proton Synchrotron (PS) to provide ions for collisions within the Large Hadron Collider (LHC).

An energy recovery linac (ERL) provides a beam of electrons used to produce x-rays by synchrotron radiation. First proposed in 1965 the idea gained interest since the early 2000s.


The Large Hadron Electron Collider (LHeC) is an accelerator study for a possible upgrade of the existing LHC storage ring - the currently highest energy proton accelerator operating at CERN in Geneva. By adding to the proton accelerator ring a new electron accelerator, the LHeC would enable the investigation of electron-proton and electron-ion collisions at unprecedented high energies and rate, much higher than had been possible at the electron-proton collider HERA at DESY at Hamburg, which terminated its operation in 2007. The LHeC has therefore a unique program of research, as on the substructure of the proton and nuclei or the physics of the newly discovered Higgs boson. It is an electron–ion collider, similar to the plans in the US and elsewhere, although the present design would not include polarized protons.

LEP Pre-Injector

The LEP Pre-Injector (LPI) was the initial source that provided electrons and positrons to CERN's accelerator complex for the Large Electron–Positron Collider (LEP) from 1989 until 2000.


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