Numerical Study On The Discharge Characteristics In Atmospheric Radio-Frequency Microplasmas

Atmospheric pressure plasma has become indispensable components of numerous industrial applications owing to their high efficiencies and low costs. Under atmospheric pressure, however, the gas discharge parameter to the laboratory diagnosis is very difficult, some methods commonly used in low pressure is may not be applicable under atmospheric pressure. At the same time, the measurement of physical quantities more and more complex, especially the number of active particles (such as ROS and RNS) diagnosis, example for atomic oxygen, nitrogen, etc., is even more challenging work. In this paper, by means of numerical simulation study of atmospheric pressure rf discharge, as well as the evolution process of internal particles.First of all, a one-dimensional fluid model was used to study the electrical characteristics of the atmospheric pressure pure helium rf discharge. In atmospheric radio-frequency (rf) discharges, the plasma parameters, such as electron density, sheath thickness and sheath voltage, are hard to be probed experimentally, while the electrical characteristics, such as impedance, resistance and reactance, are relatively easy to be measured. In this paper we presented a simple theoretical model derived from the fluid description of generated plasmas without considering the circuit model to investigate the relationship between the plasma impedance and plasma parameters. By introducing the relaxation frequency the plasma impedance can be predicted, and the mean electron density and sheath thickness can also be obtained from the measured or simulated impedance and reactance, respectively.Secondly, incorporating17species and65reactions, we studied the evolution of the discharge spatial structure of the atmospheric pressure RF He/O2discharge when the spatial scale of the micro-gap discharge development. The numerical simulation results show that not the same as to the pure helium rf discharge, the atmospheric pressure RF He/02discharge will not transit from the traditional glow-plasma (GP) structure to a new sheath-dominated-plasma (SDP) structure, where the sheath region occupies a large portion of the electrode gap and almost no distinct bulk plasma region develops, when discharging gap decreases to200μm. This is mainly because that electrons are not the dominant negative particle any more, and the negative ions are mainly composed of O-and O2-.Finally, a one-dimensional fluid model was used to explore the influences of electrode gap on the electron density, electron temperature and the internal active particles (ROS) in atmospheric radio-frequency discharge under the constant power and power density condition. Gradually under the constant power as the spark gap to micro gap decreases, and the electron density and electron temperature are gradually increasing, the atomic oxygen density (O), excited atomic oxygen density (O (1d)) and excited oxygen molecules (SDO) is gradually increasing, only ozone (03) is gradually decreasing. And under the constant power density, with the decrease of the discharge gap, electron density, electron temperature, atom oxygen, excited atomic oxygen, excited oxygen molecules and ozone are monotone decreasing trends.