Confined Geometry Interactions of Downstream RF-Excited Atmospheric Plasma Wires

We report on the generation and propagation of plasma by-products via the electrical excitation of argon gas flowing in an insulating millimeter-sized tube at excitation frequencies of 13.56-25 MHz. An electrode on the outer surface of the tube acted to capacitively couple excitation RF energy (<1 W to tens of watts) into the plasma, resulting in a plume that extends into open air for millimeter distances that are far beyond the main plasma excitation volume (ldquoplasma wiresrdquo). By using identical tubes with flowing argon but with the external electrode grounded, we demonstrate the plasma plume propagation between multiple tubes. Contrary to prior work, the open-air plasma wires propagate opposite the gas flow direction.