Nonthermal Atmospheric RF Plasma in 1-D Spherical Coordinates: A Parametric Study

We present 1-D simulations of atmospheric-pressure RF-excited plasma with two concentric spherical electrodes and the inner electrode powered. The gap distance between the inner and outer electrodes is 1 mm. The gas used is helium with a small amount of nitrogen as an impurity. The coupled continuity equations and electron energy equation are solved with Poisson´s equation using the finite element method. In this paper, we particularly focus on the influence of a blocking capacitor, nitrogen concentration, and secondary electrons. In the presence of a blocking capacitor, the self-bias voltage alters sign from negative to positive as the power increases. Reduction of relative nitrogen concentration from 10^-3 to 10^-6 leads to significant changes in the gas-phase chemistry as well as species flux impacting the outer electrode. Secondary electrons turned out to play a minor role in the transition from the corona to glow modes. We also show that the directed ion kinetic energy distribution to the outer electrode largely depends on the discharge mode.