Interelectrode microwave glow discharge in atmospheric-pressure argon flow


 The spatio-temporal structure and plasma parameters of a new type of glow discharge – atmospheric-pressure interelectrode microwave discharge in gas flow – were studied experimentally and numerically. A multi-electrode coaxial-type cold plasma torch developed for large-area surface treatment was used as a gas discharge device. The torch was supplied with microwave power (2.45 GHz, ∼100 W) via a coaxial cable by a typical wave-guide plasmatron. Self-sustained glow discharges were excited between the round ends of the rod-like electrodes and inner wall of the cylindrical discharge chamber near the outlet. The filamentation of the discharge channel in the near-electrode regions was detected by high-speed video filming. The dendritic self-similar (fractal) character of the filaments’ structure was revealed and analyzed. The branching factor and fractal dimension of this structure were estimated as 3 and 1.1–1.3, respectively. Using discharge gas temperature T_g = 1200±100 K, as determined from the emission spectroscopy measurements, the following discharge plasma parameters were obtained from numerical calculations: electron temperature T_e = 1.14 eV and concentration n_e∼10^21-10^22 m^(-3), conductivity σ ∼ 400 Ω^(-1)m^(-1) , current density j ∼ 10^6 A/m^2, and electric field strength E ∼ 10^4 V/m.