Chromaticity
= Chromaticity
{title2=$\xi=dQ/d\delta$}
The <derivative> of transverse betatron tune $Q$ with respect to relative <momentum> error $\delta$. For a thin-lens <FODO cell> with fixed quadrupole fields, natural cell chromaticity is $-\tan(\mu/2)/\pi$ on the stable phase-advance branch. Zero corrected chromaticity requires additional momentum-dependent focusing.