Filamentation in argon microwave plasma at atmospheric pressure

Filamentation in an argon plasma is studied using a microwave cavity at atmospheric pressure. We show that the size and gas temperature of the filaments increase with the power absorbed by the plasma. The appearance of an additional filament occurs at specific values of the absorbed power. Each new filament appears with a smaller diameter than that of its parent filament but the sum of the diameters of all filaments evolves linearly with the absorbed power. A secondary filament emerges from a set of microfilaments created by a perturbation of the electric field (a slight increase in the incident power above a threshold value). This perturbation occurs over a larger radius than that of the parent filament. By resorting to modeling, we found that the filamentation process involves either a decrease in the effective frequency for momentum-transfer collisions, i.e., a lower electron temperature, or an increase in the electron density. We could show that a small change in the relative positions occupied by two filaments in the microwave cavity requires a strong variation in the electron temperature. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3125525]