Characteristics of Nonequilibrium Plasma Flow and Its Sterilization Efficacy in a Tube at Atmospheric Pressure

A nonequilibrium plasma flow produced uniformly in a tube was developed in this paper. The plasma was generated in polyvinyl chloride tube, 3 mm in inner diameter and 100 mm in length, between a wire electrode, 0.2 mm in diameter, and a grounded flat electrode located at the bottom of the tube. We investigated the spectrum, temperature, and ozone concentration of this plasma flow and its sterilization efficacy against Geobacillus stearothermophilus. The temperature in the tube showed uniformity along the wire electrode and increases as applied voltage was increased. With a wire electrode temperature of 337 K at a peak-to-peak applied voltage of 10 $\hbox{kV}_{\rm pp}$ in the sine wave and a frequency of 6 kHz, sterilization of $10^{5}$ cells was obtained. This result suggests the potential of the application of plasma flow rather than ethylene oxide for sterilization of the inner wall of tubes, such as catheters and artificial blood vessels.