Plasma processing apparatus (10) includes a cathode/target assembly (16) connected to a first terminal of an external power supply (54) and an anode/ion source (12) connected to a second terminal of the external power supply (54). The anode/ion source (12) includes an electrode member (38) having a central aperture (40) therein that defines an active surface (42) on the electrode member (38). A magnet member (48) positioned adjacent the electrode member (38) produces an electron-confining magnetic tunnel (B) adjacent the active surface (42) of the electrode member (38). The electron-confining magnetic tunnel (B) traps electrons adjacent the active surface (42), some of which ionize process gas (21). A shield member (44) having a central aperture (46) therein surrounds the electrode member (38) so that the central aperture (46) of the shield member (44) is generally aligned with the central aperture (40) in the electrode member (38).