A pair of plasma beam sources are connected across an AC power supply to alternatively produce an ion beam for depositing material on a substrate transported past the ion beams. Each plasma beam source includes a discharge cavity having a first width and a nozzle extending outwardly therefrom to emit the ion beam. The aperture or outlet of the nozzle has a second width, which second width is less than the first width. An ionizable gas is introduced to the discharge cavity. At least one electrode connected to the AC power supply, alternatively serving as an anode or a cathode, is capable of supporting at least one magnetron discharge region within the discharge cavity when serving as a cathode electrode. A plurality of magnets generally facing one another, are disposed adjacent each discharge cavity to create a magnetic field null region within the discharge cavity.