The Sirius project

The lattice design and beam dynamics optimization for Sirius, a new low-emittance synchrotron light source presently under construction at the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas, Brazil, is presented. The electron storage ring is based on a five-bend achromat (5BA) design achieving a bare lattice emittance of 0.28 nm rad for a 3 GeV beam. The circumference of 518 m contains 20 achromatic straight sections of alternating 7 m and 6 m in length. An innovative approach is adopted to enhance the performance of the storage ring dipoles by combining low-field (0.58 T) magnets for the main beam deflection with a very short 2 T permanent-magnet superbend sandwiched in the center dipole. This superbend creates 12 keV critical photon energy dipole sources with modest total energy loss from dipoles. In addition it also creates a longitudinal dipole field gradient that reduces the emittance by about 10%. The optimized dynamic aperture allows for top-up operation with off-axis injection and the optimized energy acceptance allows for a total beam lifetime of around 11 h at nominal current with a third-harmonic cavity.