Horizontal emittance

The 'horizontal emittance of an x-ray synchrotron is given by:

$\epsilon _{x}\propto E^{2}\theta ^{3}\Gamma$

Where $\scriptstyle E$ is the ring energy, $\scriptstyle \theta$ is the angle per BM along the ring, and $\scriptstyle \Gamma$ is a quantity that depends on the ring lattice. An XFEL can be thought of as a limiting-case where $\scriptstyle \theta \to 0$.