An ion source is disclosed for ion implantation applications, having control apparatus for selectively adjusting a density profile associated with an elongated ion beam being extracted from a plasma confinement chamber. The control apparatus comprises a plurality of magnet pairs proximate an elongated extraction exit through which a ribbon beam is extracted from the ion source, with the magnet pairs individually comprising upper and lower electro-magnets disposed above and below the extraction exit opening to provide adjustable magnetic fields in a pre-extraction region so as to adjust the density profile of an extracted ribbon beam.