Studies On Electric Breakdown Characteristics In RF Pulse-modulated Atmosphere Glow Discharge

In recent years, the research of the atmospheric radio frequency glow discharge (RF-APGD) is regarded by many researchers and engineers due to their advantages such as breakdown easily, easy to realize a large area uniform glow discharge, more suitable for industrial production, etc. and have a wide range of potential applications in different fields, including plasma etching、the surface modification of materials, thin film deposition, and so on. However, RF-APGD is easily transferred from glow to arc discharge due to thermal instability, which limits the applications of radio frequency atmospheric pressure. Scientific researchers found a new method namely pulse-modulated radio-frequency atmospheric pressure discharge, in order to reduce the gas temperature and suppress the thermal instability. The experimental studies mainly concentrated on the mode transition and the discharge stability, and made no effort to understand the mechanism and characteristics of the gas breakdown. Thus, it will be a significant work to study the mechanism and characteristics of the gas breakdown in RF-APGD.The aim of this paper is to investigate the contributions of positive ions and metastable states remaining from the previous pulse discharge, as well as the contributions of external ionization, such as cosmic rays, to the electrical breakdown in argon, and there are mainly two research contents in this paper:In the first part, we propose a new method, the time-varying RF plasma absorbed power, to determine the breakdown voltage in RF-APGD, and found that there are three types of breakdown:first, breakdown initiated in the flat of the pulse discharge waveforms; second, breakdown initiated in the maximum of the pulse rising edge; third, breakdown initiated in the pulse rising edge. Meanwhile, we study the influences of pulse modulation on the electrical breakdown voltage. It is shown that, from short pulse off-time to long pulse off-time, the breakdown voltage increases sharply at first and then it changes smoothly. If the pulse off-time is sufficient longer than more electrons survive, all electrons and metastable atoms generated during one pulse discharge will be lost before the onset of the next pulse discharge, only being related to the initial electron generated by cosmic ray, the influence of which on discharge is less; while when pulse off-time is short, a large number of initial electrons generated during one pulse discharge event will appear in the gas gap region, leading to the reduction of the breakdown voltage. By further decreasing pulse off-time, the more electrons generated during one pulse discharge event remains in the gas gap and dominate over discharge breakdown, resulting to the lower breakdown voltage.In the second part, a study is conducted on influence of different discharge parameters upon time delay of electrical breakdown, mainly discusses the effects of pulse off-time. It is shown that, from short pulse off-time to long pulse off-time, the breakdown voltage increases sharply at first and then it changes smoothly. Meanwhile, we obtain the three characteristic distributions of the breakdown time delay, the distribution function is Gaussian distribution, with the pulse off-time changes longer, it changes an exponential distribution, then to Gauss-exponential distribution. After that, we obtain the breakdown time delay trends at different experimental parameters (duty cycle, operating voltage, gas mixture etc) and analyze the reason. It is shown that the change of the breakdown time delay is due to the influence of residual ionization.