Production of large-volume atmospheric-pressure dielectric barrier discharge using high-rate helium flow

It is desirable to increase the volume of atmospheric-pressure plasma to expand the range of applications. In this work, we attempted to generate a large-volume dielectric barrier discharge at atmospheric pressure. The discharge tube had a diameter of 2.7 cm and a length of 12 cm. An end of the discharge tube was closed, whereas the other end was open to air and it was used as the inlet and the outlet of helium. The tube was not evacuated. Two ring electrodes were attached on the outside of the discharge tube, and they were connected to a high-voltage power supply at a frequency of 1-5 kHz and the electrical ground. The generation of the discharge was possible if we used a helium flow at a rate of 500-4000 sccm. We observed both the filament and glow discharge modes [S. Okazaki, et al., J. Phys. D: Appl. Phys. 26, 889 (1993)]. The glow discharge mode was obtained at a higher flow rate. The phase-resolved optical emission pattern observed using a gated ICCD camera showed the propagation of the discharge from the instantaneous cathode to the anode. We currently examine the generation of the discharge in the presence of liquid water inside the discharge tube.