 Interleaving dipole magnets with an appropriate arrangement of quadrupole and sextupole magnets can give a suitable strong focusing system that can give a much smaller beam size.The FODO and Chasman-Green lattice structures are simple examples of strong focusing systems, but there are many others.Dipole and quadrupole magnets deflect different particle energies by differing amounts, a property called chromaticity by analogy with physical optics.