A new non-intercepting beam size diagnostics using diffraction radiation from a slit

A new non-intercepting beam size diagnostics for high-charge electron beams is presented. This diagnostics is based on the analysis of the angular distribution of the ''diffracted'' transition radiation emitted by the beam when crossing a slit cut in a metallic foil. It allows a resolution better than the radiation transverse formation zone. Numerical results based on the parameters of the TTF FEL beam are given as examples.