Introduction to the Accelerators


img-21To produce Synchrotron Light in a controlled manner, it is necessary to use particle accelerators, capable of controlling the movement of high-energy charged particles at speeds close to the speed of light. A Synchrotron Light Source consists of two main sets of particle accelerators: an Injection System and a Storage Ring.

The Injection System includes a Linear Accelerator (or Linac) and a Injector Synchrotron (or Booster) that are responsible for producing the electron beam and its acceleration to the operating energy of the Storage Ring. The Storage Ring is the main accelerator responsible for the storage of electron for long periods of time.

At Sirius, the Storage Ring and Booster are concentric and located in the same circular tunnel. With 518.4 meters of circumference, the Storage Ring will be installed in the larger perimeter of the tunnel, while the 496.8 meter Booster will be installed in the smaller perimeter. The Linac will be located in its own 32 meter long tunnel, connected to the inside of the tunnel.

The particle accelerators that form the Synchrotron Light Source are composed of many sets of magnets that deflect and focus the electron beam; a ultra-high vacuum chamber delimiting where electrons travel and allowing them to remain stored in a free environment; RF cavities, used both for accelerating the electron beam and to replenish the energy lost in the form of synchrotron radiation; and a set of auxiliary systems that allows the accelerator to work as a whole.

Electron Storage

This structure is required for an ultrarrelativistic electron beam be stored for several hours emitting light which is used to analyze the structure of different materials, both organic and inorganic.

The Injection System is responsible for the production of the electron beam and its acceleration to the operating energy of the Storage Ring, which is 3 GeV. The Injection System includes a Linear Accelerator (Linac), a Booster Synchrotron and two transport lines, which are used to transfer the electron beams from an accelerator to another.

The Linac operates in a pulsed manner. Twice per second, a current pulse is produced by the Linac and injected into the Booster. Then it will be accelerated in the Booster to the final energy and ejected for the second transmission line, finally being injected into the Storage Ring.

The Storage Ring is the main accelerator, optimized to maintain the electron beam stored for long periods while producing synchrotron light. The storage ring of the Synchrotron Light Source Sirius is designed to operate in the energy of 3 GeV.

Throughout this process, many devices must work synchronously to perform optimally the electron beam transfer from one machine to another.

Finally, the experimental stations, called Beamlines, are installed around the storage ring. They are like complex microscopes that receive and focus the synchrotron radiation so that it illuminates the samples of the materials under study and allow the observation of their microscopic properties.

Brightness and Emittance

The research that can be carried out in the Beamlines is closely linked to the quality of light produced by the Source. The quality of a Synchrotron Light Source is characterized by its brightness, defined as the number of photons emitted by the source in a determined spectral range of energy, per unit time, per unit size and angular divergence of the source. The higher the brightness, the better the quality of the light source.

Some scientific applications and experimental methods can only be carried out in light sources with high brightness and coherence. Thus, there is a constant search for building synchrotrons increasingly bright, from which Sirius stands out for being designed to have the highest brightness in the world among the sources with its energy range.

One of the most effective ways to increase the brightness of light sources is the reduction of a quantity called emittance. The emittance of a synchrotron light source is a measure of the size and angular divergence of the electron beam. The better collimated is the electrons beam, that is, the lower the emittance, the higher the brightness of the source.

In turn, emittance, which is a constant feature of the machine and depends only on the configuration of the magnetic lattice of the Storage Ring, which is one of the main parameters of a Synchrotron Light Source.

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 specification of the Magnetic Lattice is the most important stage of the project of a Synchrotron Light Source. The evolution of light sources in the direction of lower emittance and higher brightness is possible through the innovation in the projects of the Magnetic Lattice and the technological developments that these projects generate. It is extremely important that there is a great conformity between designed and executed Lattice, which imposes tight tolerances in regards to construction errors, positioning and excitation of the components of the Lattice.

With the chosen Lattice, the natural emittance of Sirius will reach a value about 360 times smaller than the emittance of UVX, the Synchrotron Light Source currently in operation at the LNLS. This emittance value will make Sirius one of brightest Synchrotron Light Sources in the world.