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What is a synchrotron light source?

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A Synchrotron Light Source is a large machine, designed to produce the synchrotron light, with the function of unveiling the molecular structure and electronic structure of the different materials to understand their fundamental properties. Today, they are the best tool ever created by science for this purpose, and are in constant improvement, so they can provide more and more information on the materials, with increasing resolution and detail.

The creation of such a complex machine is the product of a whole history of development of tools that have enabled man to observe matter with increasing detail, and which are decisive for the scientific advancement.

The versatility of synchrotron light sources allows the study of matter in its most varied forms and applications in practically all areas of scientific and technological knowledge, such as physics, chemistry, materials engineering, nanotechnology, biotechnology, pharmacology, medicine, geology and geophysics, agriculture, oceanography, oil and gas, paleontology and many others.

To produce synchrotron radiation it is necessary to keep electrons traveling at speeds close to that of light. By having their trajectory deflected by magnetic fields, these particles emit synchrotron light. Synchrotron light sources are composed of three of particle accelerators: a linear accelerator – or Linac, an injector accelerator – or Booster – and a Storage Ring.

Linear Accelerator


Initially, an electron beam is emitted from a cathode and is accelerated by electrostatic fields in the so-called electron gun.

Next, the electrons are injected in the linear accelerator, where they continue to be accelerated and, with speeds close to the light, the electrons are taken to the injector accelerator, through a transport line composed of electromagnets.

Injector Accelerator


The Injector Accelerator, or Booster, is a circular accelerator that has the role of increasing the energy of the electrons from the energy level of the Linac to the energy of operation of the Storage Ring.

Upon entering the Booster, the electrons are accelerated by radiofrequency cavities and, when they reach their final energy level, they are injected into the Storage Ring through another transport line.

Both Booster and Storage Ring are circular accelerators. In both, the electrons are held in stable orbits by a set of magnets that make up the so-called Magnetic Lattice. Magnetic Lattices have magnets with particular characteristics for the function of each accelerator.

Magnetic Lattice


The Magnetic Lattice is the set of magnets responsible for deflecting and focusing the electron beam, defining the path through which they propagate. The Magnetic Lattice is a carefully designed combination of dipoles magnets, responsible for bending the trajectory of the electrons, and quadrupole and sextupole magnets, which function to focus and correct the trajectory of the electron beam. The choice of the Magnetic Lattice has a direct impact on the characteristics of the electron beam and of the light produced.

The Magnetic Lattice of the Storage Ring is composed basically of three types of magnets: dipoles, quadrupoles and sextupoles. The magnets of the magnetic network form the basic cells that make up the superperiods. A storage ring is formed by several superperiods, composed by arc sections, connected to each other by long straight stretches.

The Dipole is the element responsible for the deflection of the trajectory of the electrons by setting the reference orbit around which the electrons remain stored. The quadrupoles are responsible for the focusing of the beam and the sextupole is used to correct the chromatic aberration resulting from the action of the quadrupole on a beam with a finite energy spread.

Storage Ring


When high-energy, high-speed electrons have their path deflected by magnetic fields, they produce a kind of high-brightness magnetic spectrum spectrum known as synchrotron light. Thus, synchrotron radiation is emitted in the passage of electrons by the dipoles, which makes them natural places for the output of lines of light. Synchrotrons that primarily use dipolar light lines are called second-generation synchrotrons.

Insertion Devices: The straight sections are specially designed to accommodate the insertion devices, which cause oscillations in the beam path. These oscillations are produced by magnetic fields generated by a succession of alternating magnetic poles. There is emission of synchrotron light at each oscillation of the trajectory. In the third and fourth generation synchrotrons radiation is emitted preferentially through these devices, as will be the case in the new fourth-generation Brazilian synchrotron light source called Sirius.

There are two basic types of insertion devices: the wigglers and the inverters. The main difference between them is basically given by the amplitude of the orbital oscillations of the electrons and the angular aperture of the emitted radiation.

In Wigglers, the angular deviation of the orbital oscillations is much greater than the radiation aperture, which means that there is no interference between the radiation emitted by each pole. However, if there are N poles, there is a gain of intensity by an N factor when compared to the emission of a dipole.

In the Undulators, the deviation of the orbit is of the same order as the angular aperture of the emitted radiation. With this, interference occurs between the waves emitted from each pole and the emitted spectrum consists of lines in the frequencies in which there is constructive interference. The intensity of the radiation of these lines, when compared to that of a dipole, has an increase proportional to N x N.

Beamlines


After its production in the accelerators, the synchrotron light is guided to the experimental stations, called Beamlines, installed around the Storage Ring. It is in the beamlines that the radiation passes through the samples to be analyzed.

Synchrotron Light Sources can accommodate several beamlines, and experiments are carried out using different techniques, such as Spectroscopy (from Infrared to X-rays), X-ray scattering, crystallography, tomography and others.

The technical requirements of a beamline depend on the characteristics of the light beam that will be needed to illuminate the samples in the analysis to be performed (such as energy resolution, size and divergence), as well as their interaction with the detection system.