A shared current loop, multiple field apparatus and process for magnetron gas discharge processing is disclosed. The apparatus includes an evacuable chamber for containing a reactant gas. A multi-part cathode associated with a current loop generates multiple, independent electrical fields. The cathode comprises a first cathode portion for generating a first electric field that forms a gas discharge including ions. The second cathode portion generates a second, independent electric field. The second electric field extracts ions from the gas discharge, and may also control the energy with which the extracted ions strike an item to be processed. Each cathode portion is electrically insulated from the other and may be connected to a separate power source.