Aspects of the present disclosure provide systems and apparatuses for a substrate processing assembly with a laminar flow cavity gas injection for high and low pressure. A dual gas reservoir assembly is provided in a substrate processing chamber, positioned within a lower shield assembly. A first gas reservoir is in fluid communication with a processing volume of the substrate processing assembly via a plurality of gas inlet, positioned circumferentially about the processing volume. A second gas reservoir is positioned circumferentially about the first gas reservoir, coupled therewith via one or more reservoir ports. The second gas reservoir is in fluid communication with a first gas source. A recursive path gas assembly is positioned in an upper shield body adjacent to an electrode to provide one or more gases to a dark space gap.