Monday, October 20, 2014


Since I heard about particle accelerators for the first time, like the Large Hadron Collider (LHC) in CERN, I have been interested in learning more about these high technology machines.

With the construction of the Alba Synchrotron near the city where I live, I even could eventually visit one kind of them: A synchrotron.

Barcelona Synchrotron Park

Alba Synchrotron is a part of the Barcelona Synchrotron Park, a complex of electron accelerators to produce synchrotron light, which includes wavelengths from infrared to X-rays. Synchrotron light is a kind of light emitted by electrons or other charged particles of high energy and rotating within a containtment ring.  As the X-rays have a similar wavelength to the distance between atoms, synchrotron light allows the visualization of the atomic structure of matter as well as the study of its properties.

Barcelona Synchrotron Park
Barcelona Synchrotron Park

Alba Synchrotron

The ALBA Synchrotron is a 3rd generation Synchrotron Light facility, being the newest source in the Mediterranean area,  located in Cerdanyola del Vallès, 15 km from Barcelona city centre. Its characteristics as a third generation source make it comparable to the new facilities found in Germany, Switzerland, France and the United Kingdom.

Alba Synchrotron in Barcelona
Alba Synchrotron located near Barcelona

The ALBA Synchrotron light source is the most important singular scientific facility in the south of Europe. The facility consists in a linear accelerator and a synchrotron which accelerates electrons at near-light speed, at an energy of 3 GeV. 

Alba Synchrotron in Barcelona
Inside the Alba Synchrotron facility

Generating Synchrotron Light

The procedure for generating synchrotron light is:

1- A source generates an electron beam as thin as a hair, and the beam is accelerated through a linear accelerator (also known as LINAC by its acronym in English). The electrons almost reach the speed of light and a first energy level, 100MeV.

2- The electron beam is directed to a second circular accelerator, called booster, that increases its energy to the level operation of the synchrotron, 3 GeV. The low-emittance, full-energy Booster is placed in the same tunnel as the Storage Ring.

The RadioFrequency (RF) systems of ALBA are responsible of the electrons acceleration in the Booster and the Storage Ring. In the Booster, the energy of the electrons is increased from 100MeV to 3GeV. In the Storage Ring, the RF systems just restore the energy that the electrons lose due to synchrotron radiation (1.3MeV/turn maximum).

Radiofrequency system of Alba Synchrotron
The acceleration is accomplished creating high electric fields in the path of the electrons. The electric fields are created in resonant cavities which are fed by RF Amplifiers.

3- Electrons are injected into a storage ring of 270 meters where revolve for several hours and emit synchrotron radiation, which is used at the beamlines. This storage ring is optimised to produce a continuum of wavelengths of electromagnetic radiation, from infrareds to X rays. They are stored and maintained within the ring using magnetic fields.

Alba Synchrotron in Barcelona
The booster and the storage ring are located inside this structure

Booster and storage ring of Alba Synchrotron
Booster and storage ring of Alba Synchrotron

4- When the electrons moving around in the ring take a curve, they emit extremely intense light with wavelengths ranging from the visible to X-rays. This light is highly focalized, polarized and then emitted in the form of pulses like a camera flash. So using electromagnetic devices the trajectory of the electrons are deflected or forced to oscillate. Electrons lose energy as light, thus generating synchrotron light.

5- The energy lost by electrons in the form of synchrotron radiation (those beams of light) is compensated by RF cavities giving them energy to keep spinning and the process is repeated.

6- The synchrotron light is focused and selected (selection of the wavelength) by optical devices (lenses and mirrors) that guide it towards the experimental stations.

7- Each beamline is a real laboratory to prepare and analyze samples, analyzing the information obtained and thus study the most varied problems: from masterpieces of Renaissance art to chronic degenerative diseases.

Basic Physical Principle of Operation

The ALBA accelerators rely on electromagnets to guide and focus the electrons along the trajectory under the influence of magnetic fields, electrons follow the Lorentz force:

At ALBA four different types of magnets are in use:

  • Dipole magnets: these are typical construction electromagnets with an iron yoke, in a C-form or H-from and two coils wound around the yoke. Dipole magnets are used to deflect the electrons in the transfer lines and also to provide orbit correction.

Dipole of Alba Synchrotron in Barcelona
The red magnet is a dipole

  • Quadrupole magnets: as the name indicates, these have four magnetic poles and therefore 4 coils. The magnetic field created by a quadrupole increases linearly with the distance from the center. Quadrupoles are used to focus the electrons and enable the transport of an electron beam over long distances, like for example, an electron beam circulating inside the ALBA storage ring.

Quadrupole of Alba Synchrotron in Barcelona
On the left a sextupole magnet and, on the right, a quadrupole magnet

  • Combined function magnets: are a combination of a dipole magnet and a quadrupole magnet. They are used both in the booster and in the storage ring and fulfil two functions at the same time: on one side, they are responsible for the electrons completing the 360º of circumference around both circular accelerators, and on the other side, they provide additional focusing. By the use of combined magnets, space has been saved inside the accelerators. This space has been used to increase the length available to insertion devices.

Magnets of Alba Synchrotron in Barcelona
A dipole magnet (red), a sextupole magnet (yellow) and a quadrupole magnet

  • Sextupole magnets: have six poles as its name indicates and are used to provide additional focusing. The magnetic field increases quadratically with the distance from the center.

Sextupole magnet of Alba Synchrotron in Barcelona
Sextupole magnet of Alba Synchrotron


ALBA's 270 meter perimeter has 17 straight sections all of which are available for the installation of insertion devices.

ALBA currently has seven operational state-of-the-art phase-I beamlines, comprising soft and hard X-rays, which are devoted mainly to biosciences, condensed matter (magnetic and electronic properties, nanoscience) and materials science. Additionally, two phase-II beamlines are in construction (infrared microspectroscopy and low-energy ultra-high-resolution angular photoemission for complex materials).

During operation of the beamlines, the accelerators run 24 hours a day, 7 seven days a week. About 75% of the time that the accelerators are powered up is dedicated to providing beam to the beamlines. The rest is dedicated to improving the quality of the beam as well as the further development of the accelerators.

Beamline of Alba Synchrotron in Barcelona
One of the operational beamline of Alba Synchrotron

Beamline of Alba Synchrotron in Barcelona
High technology equipment in a beamline of Alba Synchrotron

Applications of Alba Synchrotron

  • BIOLOGY AND BIOMEDICINE to improve the diagnosis and treatment of certain diseases and develop drugs.
  • NANOTECHNOLOGY to study and build electronic and magnetic devices to the nanometer scale.
  • MATERIALS SCIENCE to create more durable materials, corrosion-resistant, lightweight, elastic.
  • ENVIRONMENT to analyze toxic materials of, soil, rocks.
  • PHYSICS to determine the atomic structure of liquids and solids.
  • CHEMISTRY: to analyze and improve the efficiency of chemical reactions.
  • HISTORICAL AND ARTISTIC HERITAGE To study art or archaeological objects noninvasively.

Alba Synchrotron in Catalonia
One last picture before leaving the Alba Synchrotron after a really interesting visit

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