Non-linearities in light sources

Correction of a light source's large chromaticity, while maintaining suf cient dynamic aperture and momentum acceptance, requires careful optimization of the sextupole con guration in rst and second order of sextupole strength. In this paper we try to explain chromaticity and its correction in a most intuitive way. Accompanied by the stepwise improvement of a test lattice, the scheme is then expanded from plain correction with two sextupole families to installation of `harmonic' sextupole for rst and second order optimization. The approach is very visual and pragmatic at the expense of the mathematical formalism which may be found in the references.