Fig. 2: Electrical characteristics of the plasma source.

a Typical waveforms of applied voltage (gray solid line), discharge current (dark blue solid line), displacement current (light blue solid line), and integrated light emission (light red solid line) with the gas flowrate fixed at 0.5 l min⁻¹. The displacement component is enlarged by ten times. b Same as a, but with the gas flowrate fixed at 1.1 l min⁻¹. c Typical waveforms of applied voltage (gray solid line), discharge current (dark blue solid line), displacement current (light blue solid line), and integrated light emission (red solid line) with the gas flowrate fixed at 2.2 l min⁻¹. d Same as c, but with the gas flowrate fixed at 7.8 l min⁻¹ and the light emission indicated by the light red solid line. e The enlarged view of the applied voltage (gray solid line) and light emission (red solid line) marked in the gray shadow in the positive alternation at 2.2 l min⁻¹ in c. f The enlarged view of the applied voltage (gray solid line) and light emission (red solid line) marked in the orange shadow in the negative alternation at 2.2 l min⁻¹ in c. The shaded regions are introduced in order to focus the attention on the difference of light emission in the negative alternation from that in the positive alternation.