A plasma reactor includes a chamber body having an interior space that provides a plasma chamber and having a ceiling, a gas distributor to deliver a processing gas to the plasma chamber, a pump coupled to the plasma chamber to evacuate the chamber, a workpiece support to hold a workpiece, and an intra-chamber electrode assembly. The intra-chamber electrode assembly includes an insulating frame, a first plurality of coplanar filaments that extend laterally through the plasma chamber between the ceiling and the workpiece support along a first direction, and a second plurality of coplanar filaments that extend in parallel through the plasma chamber along a second direction perpendicular to the first direction. Each filament of the first and second plurality of filaments includes a conductor at least partially surrounded by an insulating shell. A first RF power source supplies a first RF power to the conductor of the intra-chamber electrode assembly.