  High quality electron beams, with high spatial and tempo- ral resolution,
have an important use in electron diffraction experiments to probe and study
the constituents of matter. A cold electron source is being developed based on
elec- tron ionisation from an atom cloud trapped by using AC magneto-optical
methods in the University of Manchester. The technique will produce bunches of
electrons well suited for high precision and single shot electron diffraction.
In this paper issues of modelling at low energies for this state of art
electron source with very low energy spread are presented, with a focus on
newly developed tools to model the scat- tering in the meshes used to support
the extraction electric fields. The dependence on emittance growth on mesh wire
thickness is studied.
