Hollow cathode atmospheric pressure plasma sources for surface treatment

Generation of the cold atmospheric plasma in single cylindrical hollow cathodes and in structures forming Fused Hollow Cathode (FHC) is described and discussed in more detail. In all these systems the gas flows through the hollow cathode structure. A very important advantage is the possibility to operate the hollow cathode systems with the radio frequency (r.f.) plasma partly substituting the counter electrode. The frequency affects both the generation stage and the operation performance of the atmospheric plasma. The Fused Hollow Cathode noble gas cold atmospheric plasma was applied to low-temperature surface treatments of plastics, metals and semiconductors. The surface activation of plastics by the Fused Hollow Cathode plasma represents a very efficient method that is suitable for large area substrates. An optimization of the FHC system enabled generation of a stable cold plasma in molecular gases, nitrogen and air at low r.f. powers even over larger areas. Because of a short mean free path of particles at the atmospheric pressure and an influence of ambient air in the open systems, the plasma has typically a short-range impact of a few millimeters. The systems for surface treatments are therefore operating with helium at considerably high flows, of the order of 10 slm. A new Hybrid Hollow Electrode Activated Discharge (H-HEAD) cold atmospheric plasma source with argon flow of less than 0.5 slm was designed and developed. The source combines a microwave antenna launcher with a hollow cathode. The plasmas are coupled together in a flame of a controllable length up to approximately 20 cm. The plasma temperature can be controlled by the hollow cathode power. The Fused Hollow Cathode (FHC) and Hybrid Hollow Electrode Activated Discharge (H-HEAD) sources represent new types of atmospheric plasma systems with the possibility to become new processing tools on the market.