Production of atmospheric pressure non-equilibrium plasma with microwave and applications for plasma processing

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We have developed a new type of microwave plasma source which can produce a non-equilibrium cold plasma at atmospheric pressure. In this apparatus, plasma was produced in the quartz glass pipe surrounded by slit aluminum pipe which works as the microwave antenna. It was found that the discharges were stable and reproducible at wide gas pressure range from 10 Pa to atmospheric pressure. It was observed that the plasma uniformly spread over the discharge quartz pipe (diameter 20mm, length 300mm) even at atmospheric pressure. The gas temperatures of approximately 500℃ and the electron temperature of 1〜2eV have been obtained. This indicates that non-equilibrium cold plasma was produced in this apparatus.The characteristics of the atmospheric pressure non-equilibrium plasma produced by pulse-time-modulated microwave have been investigated. The gas temperature measured by a thermocouple in pulse modulated mode plasma was about 350℃ at the pulse period of 2msec and 0.8 duty ratio, whereas that obtained in the continuous wave (CW) mode plasma was about 500℃ with same time-averaged microwave power of 800W. On the other hand, the time-averaged ion saturation current in pulse modulated mode plasma was comparable to that of CW mode plasma.We have developed an atmospheric pressure ejected plasma (plasma torch) source for processing arbitrary shaped objects. The gas temperature of about 400℃ and the flame length of about 40mm have been obtained. This system has produced plasmas using a variety of gases and gas mixture, including argon, helium, oxygen and nitrogen at atmospheric pressure. This system has been applied to the sterilization of micro-organisms on the plastic plate. Small amounts of O_2 gas was added into argon plasma as reactive species for oxidizing. The killing of all micro-organisms can be accomplished in a few seconds by direct exposure to the active species of this system.