The present invention relates to a low energy ion gun (3; 103) for use in ion beam processing comprising: a plasma chamber (5) comprising an open ended, conductive, non-magnetic body, a first end of which is closed by a flat or minimally dished dielectric member and with electrodes (6) at a second end thereof opposite the first end; primary magnet means (16) arranged around the body for trapping electrons adjacent the wall of the plasma chamber in use of the ion gun and an r.f. induction device including a substantially flat coil (12) which lies adjacent to the dielectric member for inductively generating a plasma in the plasma chamber, characterised in that the electrodes include a first multi-aperture grid (29; 127) arranged for connection to a first positive potential source and positioned to contact the plasma in the plasma chamber; a second multi-aperture grid (29a; 128) arranged for connection to a second potential source of lower potential than the first source so as to produce a first acceleration field for accelerating ions towards and through the second grid; and a third multi-aperture grid (30; 129) arranged for connection to a third potential source of lower potential than the second potential source so as to produce a second acceleration field for accelerating ions towards and through the third grid, the apertures of the first, second and third grids being aligned so that particles emerging from an aperture of the first grid are accelerated through a corresponding aperture of the second grid and then through a corresponding aperture of the third grid in the form of a beamlet, a plurality of beamlets from the third grid forming a beam downstream of the third grid.