The ALBA booster is a synchrotron accelerating electrons delivered by the Linac from an energy of 100 MeV to 3 GeV. During the energy ramping, the magnetic fields are adapted to the corresponding energy of the electrons. At 3 GeV the electron beam is extracted to be sent to the storage ring and the magnetic fields are restored to their initial values. This cycle is repeated 3 times per second.

The booster is located in the same tunnel as the storage ring. Its large circumference of 249.6 m, the large number of dipole magnets (40) and the magnetic lattice based on dipoles with integrated gradient, provide an equilibrium emittance as low as 10 nm∙rad. Such a small emittance, and electron beam size, provide high efficiency injection for the so called top-up operation. In this mode electrons are injected every 5-10 minutes into the storage ring, without interrupting the experimental data acquisition and keeping the intensity of the circulating electron beam constant.

The following table summarizes the ALBA booster main parameters.

Injection energy  100 MeV
Extraction energy GeV
Circumference 249.6 m
Revolution period 832 ns
Number of superperiods 4
RF frequency 500 MHz
Harmonic number 416
Repetition rate 3.125 Hz
Betatron tunes νx / νy 12.26 / 7.38
Momentum compaction αc 3.6∙10-4
Beta function max bx / bz 12.5 / 11.5 m
Dispersion max   ηx 0.45 m
Natural chromaticity ξx / ξy -17 / -10
Emittance at 100 MeV ε 50 nm∙rad
Emittance at 3 GeV ε nm∙rad
Energy spread at 100 MeV σE/E 0.25∙10-3
Energy spread at 3 GeV σE/E 0.25∙10-3
Damping time at 3 GeV τs / τx / τy 4.5 / 8.0 / 6.3 ms
Maximum electron current mA


The ALBA booster ring is a modified FODO lattice based alternated focusing quadrupoles and gradient bending magnets. Both magnets of the unit cell have built-in sextupolar component in the iron pole profile to correct the natural chromaticity to positive values. The large circumference allows building wide arcs with relaxed optics: the maximum beta functions are 12.5 horizontal and 11.5 vertical and the maximum dispersion function is only 0.45 m.


Beta and dispersion functions of one quadrant of the booster ring.

The ring lattice has a four-fold symmetry, consisting of 4 arcs with 4 straight sections of 2.46 m. The basic structure of the arc is composed of 8 unit cells, each with a defocusing gradient bending magnet (BM10) and a focusing quadrupole (QH02). At each end of the arcs there is a matching cell consisting of a shorter combined function defocusing dipole (BM05) and three quadrupoles (QH01, QV01, QV02), which lead to zero dispersion in the straight sections where the RF-cavity and the injection elements are installed. The orbit correction is performed measuring the beam position at 44 beam position monitors and steering the orbit with 44 horizontal and 28 vertical corrector magnets.