Numerical Simulation On The Characteristics Of Reactive Species In Atmospheric Rf Pulse-modulated Discharge

Since the 1990’s, low-temperature plasma has been widely used in insision, Welding, spraying, surface modification, thin film deposition, etching and so on. Most of them especially spraying, surface modification, thin film deposition which need uniform and gentle processing require large-volume, stable and reactive low-temperature plasma. Experts and researchers have discovered many methods such as dielectric barrier discharge, pulse discharge, microplasma, capacitively discharge with higher radio frequency to get such kind of plasma as is described above. All of them have improved the uniformity and stability of plasma which further promoted the industrial application.Compared with dielectric barrier discharge, atmospheric radio frequency discharge can generate more electron and higher electron energy. It’s dispensing with vacuum equipment also put it into a wider application. To optimize the atmospheric rf discharge for larger electron density, first we simulate the discharge under constant power with a one-dimensional fluid model. The evolution of electron density and electron energy versus electrode spacing is presented which shows that the profile of electron density resembles the shape of a bell. The gap corresponding to the top of the bell is called the optimal gap. In the following we further studied the optimal gaps under higher frequencies and found that they decreased with the frequency increasing. The path length of an electron becomes shorter under higher frequency so the gap an electron needs to be trapped between the electrode becomes shorter too.To get uniform, stable and large-volume plasma, researchers put forward a new discharge form called the pulse-modulated discharge in the recent years. By switching on and off the power supply periodically, the discharge operated in a discontinuous state to suppress the high temperature and save the power as well. We simulate the pulse-modulated discharge under a constant voltage in the following fourth chapter. The evolution of electron density, electron energy and various reactive species versus duty cycle, modulation frequency and oxygen admixture is presented which shows that the electron density is larger than that in the continuous mode under some certain duty cycle and the reason is presented.At last in the fifth chapter we studied the microplasma under smaller gap and higher frequency. The current waveform shows that in the first rf cycle when the power is switched on, the current is extremely strong, much larger than the following current, and the reason is presented from the numerical point of view. In the end we simulated the current density, electron density and various reactive species versus duty cycle as well. On the one hand, the simulation results can be used to explore the underlying discharge physics so as to predict the discharge phenomenon in a wider parameter range. On the other hand, the characteristics of the reactive species versus various discharge parameters may be a guidance in the controlling of the industrial application meaning a great application value.