The Duo-Plasmaline is a direct microwave plasma source without using a magnetic field. In a simplified description, it works like an inverse luminescent tube excited by microwaves. The Duo-Plasmaline consists of a copper rod as inner conductor centred in a quartz tube. The inside of the tube is at atmospheric pressure whereas the outside is at low pressure of about 1000 Pa down to 10 Pa.
The microwave with a frequency of 2.45 GHz generated by two magnetrons is fed into the copper rods at both ends. When the electric field strength exceeds the breakdown field strength a discharge ignites in the outer low pressure regime concentrated at the ends of the tube. The plasma represents a conductive medium and replaces the missing outer conductor of the coaxial waveguide. With increasing microwave power the plasma grows from both ends along the tube, and an axially homogeneous plasma is formed. To demonstrate the potential of such a plasma source, a three meter long Duo-Plasmaline was built at the IGVP.
A combination of such Duo-Plasmalines can be used to obtain a two dimensional plasma array. Single sources as well as 2, 4 and 8 parallel arranged Plasmalines are available for plasma assisted surface treatment like surface activating, etching and deposition.