A processing system is disclosed, having a power transmission element with an interior cavity that propagates electromagnetic energy proximate to a continuous slit in the interior cavity. The continuous slit forms an opening between the interior cavity and a substrate processing chamber. The electromagnetic energy may generate an alternating charge in the continuous slit that enables the generation of an electric field that may propagate into the processing chamber. The electric field may interact with process gas in the processing chamber to generate plasma for treating the substrate. The interior cavity may be isolated from the process chamber by a dielectric component that covers the continuous slit. The power transmission element may be used to control plasma density within the process chamber, either by itself or in combination with other plasma sources.