Abstract: An ion source has a peripheral wall, a back face and a front face which together define a plasma chamber extending along an axis. In one embodiment, a central aperture emits ions from plasma formed in a generally annular containment band about the aperture, and a plurality of magnets define magnetic field lines extending into the band, so that electrons traveling from the cathode are trapped in the band and highly effective ionization is achieved, producing high beam currents. An anode at the back of the source expels ions from the central region. In another or further embodiment, the plasma chamber has an anode plate which extends across the back of the source, and provides a broad expulsion field for expelling and preferably shaping a high current in ion output beam. A fluid inlet introduces an ionizable fluid in the peripheral region to interact with the trapped electrons, generating plasma with high efficiency.