Abstract: An ion source is described, including a source of neutral particles which arrive at an ionization support positioned inside a chamber which is closed by a cap and which includes lateral walls. The cap includes an outlet orifice opposite which a plate defines a main ionization active surface. An electric field is applied between said device and by an electrode place downstream from the orifice in the direction of ion emission and fitted with a corresponding opening. Overall, the ionization support defines, by virtue of its active surface, and by virtue of holes surrounding said central active surface, a baffle assembly which prevents neutral atoms from passing directly to the outlet orifice, and which contributes to a high degree of ionization.