Particle Accelerators

Taking a closer look at LHC

Accelerators works with charged particles that are accelerated to speeds close to the speed of light. By letting very fast and energetic particles collide in the accelerators, the scientists can extract information about matters smallest components. In such collisions are new particles created, which will provide information about the secrets of particle physics. In some sense the big accelerators can be said to be today's "super microscopes".

An ordinary CRT television set is a simple form of particle accelerator (electrons).

There are two basic types: linear accelerators and circular accelerators.

Normally, linear accelerators are related with collisions on fixed target and the circulars with collisions head-on, but both can be used to provide the two types of collisions. To see a brief discussion about the differences, in terms of energy, between these types of collisions see...

About linear versus collider a short discussion can be found here...


A linear particle accelerator (also called a linac) is an linear electrical device for the acceleration of subatomic particles. The design of a linac depends on the type of particle that is being accelerated: electron, proton or ion. They range in size from a cathode ray tube to the 3,4 km long Stanford Linear Accelerator Center (SLAC) in California

Maybe, an linear accelerator (CLIC  or ILC) will be the new machine in certain particle physics research for the post-LHC era.

The first particle accelerator in CERN's accelerator chain is a linear accelerator: LINAC4.


In the circular accelerator, particles move in a circle until they reach sufficient energy. The particle track is typically bent into a circle using electromagnets. The advantage of circular accelerators over linear accelerators is that the ring topology allows continuous acceleration, as the particle can transit indefinitely. Another advantage is that a circular accelerator is relatively smaller than a linear accelerator of comparable power.

Depending on the energy and the particle being accelerated, circular accelerators used in Particles Physics suffer a disadvantage in that the particles emit synchrotron radiation.

It is importante to note that a circular accelerator is not completely circular. It consists of straight parts inserted into arcs, in which the interaction points are installed (with detectors which register the events), particle injection zones (at high velocities, reached through previous accelerators), and extraction zones in which particle bunches -bunches- are retrieved when they do not present the necessary conditions for the required number of collisions that should occur at the interaction zones.

On the other hand, in these straight parts the charged particle beams do not generate synchrotron radiation (which is produced in the curved parts), thus avoiding damage to detectors, collimators, injection and extraction devices, radio-frequency cavities etc.

The LHC, PSB, PS and SPS that form the CERN accelerator chain are all circular accelerators. So is the large accelerator of the future FCC.

Summing up

The advantage of a circular accelerator over a linear accelerator is that the particles in a circular accelerator receive successive pulses at each turn, so they can deliver very high-energy particles without having to have an enormous length. In addition, the fact that the particles go round and round means that there is a high chance of collision at the points where the particle beams cross.

In contrast, linear accelerators are much easier to build than circular accelerators, as they do not require the large magnets needed to put the particles into the circular path. In addition, the charged particles in the circular accelerator radiate energy constantly (synchrotron radiation), and the lower the mass, the greater the radiated energy.

For this reason, linear accelerators are considered for electrons/positrons (CLIC or ILC projects) and circular accelerators for protons/antiprotons (such as Fermilab's Tevatron, the LHC or the FCC).


Xabier Cid Vidal, PhD in experimental Particle Physics for Santiago University (USC). Research Fellow in experimental Particle Physics at CERN from January 2013 to Decembre 2015. Currently, he is in USC Particle Physics Department ("Ramon y Cajal", Spanish Postdoctoral Senior Grants).

Ramon Cid Manzano, secondary school Physics Teacher at IES de SAR (Santiago - Spain), and part-time Lecturer (Profesor Asociado) in Faculty of Education at the University of Santiago (Spain), until his retirement in 2020. He has a Degree in Physics and in Chemistry, and is PhD for Santiago University (USC).



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 For the bibliography used when writing this Section please go to the References Section

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