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

我们研制了一种新型的微波等离子体源，它可以在大气压下产生非平衡的冷等离子体。在该装置中，等离子体是在石英玻璃管中产生的，周围环绕着狭缝铝管，作为微波天线。结果表明，在10~大气压的较宽气压范围内，放电稳定，重复性好。观察到，即使在大气压下，等离子体也均匀地分布在放电石英管(直径20 mm，长度300 mm)上。获得了约500℃的气体温度和1~2 eV的电子温度。研究了脉冲时间调制微波产生的大气压非平衡等离子体的特性。在脉冲周期为2毫秒、占空比为0.8时，用热电偶测得脉冲调制模式等离子体中的气体温度约为350℃，而在时间平均功率为800W的连续波(CW)模式等离子体中测得的气体温度约为500℃。另一方面，脉冲调制模式等离子体中的时间平均离子饱和电流与连续模式等离子体中的离子饱和电流相当。我们研制了一种用于处理任意形状物体的大气压喷射等离子体(等离子体炬)源。获得了约400℃的气体温度和约40 mm的火焰长度。该系统在大气压下使用各种气体和混合气体产生等离子体，包括氩、氦、氧和氮。该系统已应用于塑料平板上微生物的杀菌。在Ar等离子体中加入少量O2气体作为反应物种进行氧化。通过直接接触这个系统的活性物种，可以在几秒钟内完成对所有微生物的杀灭。

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.