Hollow cathode cold atmospheric plasma source with monoatomic and molecular gases

Abstract

Performance of the radio frequency (r.f.) hollow cathode at atmospheric pressure was tested for neon, argon, nitrogen and air. A non-equilibrium (cold) atmospheric plasma was generated in the gas flowing through the cathode. The electrode system was installed in a chamber open to ambient atmosphere. Two r.f. frequencies 13.56 and 27.12 MHz were compared. Similarly to the low pressure hollow cathodes the higher frequency was found to be more suitable for all tested gases, due to a lower minimum r.f. voltage and related power for ignition and sustaining a stable plasma. The fused hollow cathode (FHC) source produces a stable and uniform plasma over large area in monoatomic gases, suitable for surface treatment of temperature sensitive materials, for cleaning and surface activation applications. However, a substantial difference was found in discharge performance when using a molecular gas. An optimization of the impedance matching network enabled generation of a stable cold plasma at r.f. powers below 50 W in both air and nitrogen. Possibilities of a stable uniform air (or nitrogen) plasma generation over large areas by the FHC sources are discussed, too.