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History of the Synchrotron Light Sources

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Synchrotron Light, or Radiation, is a type of high-flux, high-brightness electromagnetic radiation that extends over a broad range of the electromagnetic spectrum from infrared light through ultraviolet radiation to x-rays. It is produced when charged particles, accelerated at speeds close to the speed of light, have their trajectory deflected by magnetic fields.

Discovery


The emission of this radiation was predicted theoretically for the first time by the Ukrainian Dmitri Iwanenko and the Russian Isaak Pomeranchuk in 1944 (Physical Review vol.65, p. 343, On the maximal energy attainable in betatron). In 1947 the first observation occurred in General Electric’s research laboratories. It was performed on a particle accelerator of the synchrotron type, with electrons accelerated up to 99.997% of the speed of light.

In a synchrotron accelerator, the charged particle beam is guided in circular orbits by a set of electromagnets. The magnetic field produced by the electromagnets can be varied in time and acts in a synchronized way on the particles, which at each turn have higher velocities and, therefore, higher energies. From this synchronous action comes the name synchrotron accelerator. It is due to this type of accelerator in which it was first observed that the synchrotron radiation received its name.

 

Later, in 1956, in a synchrotron accelerator of the University of Cornell, USA, the first spectroscopy experiments were carried out in the ultraviolet region with the use of the radiation produced in the accelerator. Thus was started the use of the synchrotron light as a tool for the study of the composition and structure of materials.

First Generation


In the 1950s and 1960s, particle accelerators originally developed for Nuclear Physics research were modified to allow continuous access to researchers wishing to work with synchrotron radiation. This was the case, for example, of the DESY (Deutsches Elektronen Synchrotron or German Electron Synchrotron) in Germany.

From the late 1960s and early 1970s, particle accelerators based on storage rings began to emerge, a type of synchrotron accelerator capable of keeping the particle beams circulating for long periods of time, replenishing the energy lost by the particles due to the emission of radiation.

For nuclear and particle physics, a storage ring increases control over where and how the accelerated particles will collide with each other or with a target. For scientists interested in using synchrotron radiation, the storage ring makes the production of this radiation continuous, guaranteeing long periods of exposure of the samples they wish to analyze.

These were, however, equipment for research in nuclear or particle physics and were not designed or used exclusively for the production of synchrotron light. The use of synchrotron radiation under such circumstances was called parasitic operation, and these accelerators are considered the first generation of synchrotron light sources.

Second Generation


With the success of the use of synchrotron radiation in experiments by different research areas, equipment designed optimally for its production and dedicated exclusively to its use began to emerge. This became known as the Second Generation of Synchrotron Light Sources.

In these second generation sources, as in other synchrotron accelerators, synchrotron light is produced when the electron beam path is curved by magnetic fields produced in dipoles magnets. However, the whole set of magnet machine, called the magnetic lattice, is designed to produce the greatest quantity and best quality of synchrotron radiation possible.

As the quality of synchrotron light sources increased, so did the number of users in various areas of knowledge and the number of experimental techniques available. Thus, it became clear the importance of developing increasingly brighter sources, that is, that would be producing more and more light in an increasingly focused way.

This is achieved by reducing the emittance of the machine, a measure of the size and angular divergence of the electron beam. The better collimated the electron beam, that is, the lower the emitance, the brighter the synchrotron light source.

Third Generation


The third generation of synchrotron light sources was characterized not only by the advancement in accelerator designs, designed to have lower emitters but also to be optimized for the use of so-called insertion devices. The sources of this generation began to emerge in the 1990s and many others were built over the next decade.

UVX, the current synchrotron light source of the LNLS was designed as a second-generation synchrotron and inaugurated in 1997. However, a number of improvements have been made, and currently three of its beamlines use synchrotron radiation produced by insertion devices.

Fourth Generation


Recent technological developments have allowed the definition of a fourth generation of synchrotron light sources, based on storage rings, with machines able to achieve “ultra low” emitance through innovative designs of the magnetic lattice, the set of magnets that controls the trajectory of the electron beam.

In this new generation, one source is already in operation – MAX-IV in Sweden – and one is under construction – Sirius in Brazil – with start-up planned for 2019. Still other sources around the world are already planning improvements such as : ESRF-II, in Grenoble, France; APS-U, in Argonne, USA; SPring8-II in Koutu, Japan.