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MAGNETIC LATTICE

BACK

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.

The Magnetic Lattice is a carefully designed combination of dipoles, quadrupoles and sextupoles which has a direct impact on the characteristics of the electron beam and on the light that is produced.

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


Various configurations for the Magnetic Lattice of the Sirius Storage Ring were analyzed over the last years. The selected Lattice consists of 20 magnetic cells of five deflections each, known as a 5BA (Five Bend Acromat) Lattice. With this Lattice, the natural emittance of Sirius reaches the value of 0.24 nm.rad for an electron energy of 3 GeV. For comparison purposes, this value is approximately 360 times smaller than the emittance of the UVX, the 1.37 GeV Synchrotrn Light Source currently in operation in the LNLS. This emittance value will make Sirius one of the brightest Synchrotron Light Sources in the world.

Among the studied magnetic lattice, the 5BA was the one with the best compromise between low emittance and large number of straight sections for insertion devices considering the maximum circumference of the ring. The Storage Ring will be 518,4m long in circumference with 20 dispersion-free straight segments, alternating between 7.5m and 6.5m in length, for insertion devices and machine utilities.

HIGH FIELD DIPOLE

An innovation in the Sirius lattice is the introduction of high field permanent magnets of 3.3 Tesla in the middle of the central 0.58 T dipole of the 5BA cell. Besides contributing to the reduction of emittance, these high field dipoles will also produce hard X-rays with critical photon energy of about 20 keV, which means that the dipoles produce usable photon flux up to about 120 keV.

This configuration minimizes the total power of the dipole radiation emitted by the electron beam. The combination of dipoles with low magnetic fields and high field inserts only in the positions of the light output to generate hard X-rays is an innovative aspect of the project, which not only reduces the total radio frequency (RF) power required, but also reduces the need for cooling of the vacuum chamber.

The main elements of the magnetic lattice of the Sirius Storage Ring are 120 low-field dipoles (0.58 Tesla), 20 high field thin dipoles (3.3 Teslas), 260 quadrupole, 280 sextupoles, 160 slow horizontal orbit corrector magnets, 80 quick horizontal orbit corrector magnets, slow vertical 120 orbit corrector magnets and 80 quick vertical orbit corrector magnets.

Booster Acelerator


The Sirius injection system consists of a 150 MeV linear accelerator (LINAC), an Injector Accelerator ring (Booster) that accelerates the electron beams to the operation of energy of Storage Ring and two transport lines, one from LINAC to Booster (LTB) and one from Booster to Storage Ring (BTS). The injection system works in top-up mode, that is, the electron beams are continuously injected into the Storage Ring.

The Magnetic Lattice of the Booster consists of 50 modified FODO cells with magnets suitable to produce low emittance beams.

The main difference between this design and other Boosters is that it contains only of arc sections, with no long dispersion-free straight sections. The full circumference of 496.8 meters has plenty of component-free straight segments of about 4 meters. Thus, both injection and extraction, as well as the RF cavity are located in those segments. This concept allows the construction of a highly symmetrical magnetic system with the need for only a few families of magnets.

The Booster and Storage Ring are concentric and share the same tunnel, thus the high symmetry of the Lattice also allows the maximization of the radial distance between the Storage Ring and the Booster, minimizing the variation in size of the corridor between the two concentric rings.

The natural emittance obtained in the Booster at the extraction energy of 3 GeV is very low – 3.47 nm.rad – which is essential to provide a good injection into the Storage Ring with the injection process by the Multipolar Pulsed Magnet.