A device comprising an RF cavity enclosure including a tubular section having a plurality of interior structures radially or axially arranged which forms an unobstructed inner hollow center within the tubular section. Each interior structure of the plurality of interior structures includes side walls between which is formed an internal hollow sub-cavity. Resonating cavities exist between adjacent interior structures to produce a resonating frequency response. Vents are formed in at least one side wall for permeation of a gas into the internal hollow sub-cavity. A high-power microwave system and method of manufacture are provided.