Numerical Study Of Atmospheric Pressure Pulse-Modulated Radio-Frequency Dielectric Barrier Discharge

Atmospheric pressure radio-frequency glow discharge (RF-APGD) is one of the most effective methods used to create plasmas at the present. Comparing with the low pressure radio-frequency glow discharge, it has many advantages in cost, efficiency and so on. Presently, the research of atmospheric pressure radio-frequency glow discharge is regarded by many engineers and researchers. And it is widely used in many fields, such as large scale integration, modification of materials, material synthesis, and disinfections. However, due to the high power of radio-frequency, the discharge is easily transferred from glow to arc, which limits the applications of radio frequency atmospheric pressure. To solve the confliction between the intensity and stabilization of discharges, researchers found a new method namely the pulsed-modulated radio-frequency atmospheric pressure dielectric-barrier glow discharge. This method, by controlling the pulse power on and off time, could achieve high intensity and stabilization discharges. Many experiments have been carried and proven the advantages of pulse-modulated discharge. However, there are still many phenomena in the experiments that cannot be explained now, requiring many simulations work to explain these.In this thesis, we adopt the fluid model to investigate the pulse-modulated radio-frequency atmospheric pressure dielectric-barrier glow discharge. The characteristics of pulse-modulated discharge and the influences of main factors on the discharge characteristics are analyzed in detail.In the first place, we adopt a one-dimensional collision-less fluid model to study the slab discharge device. The simulation results show the current-voltage characteristics, time evolution of particle densities of different species and the influences of the gas gap and temperature on these characteristics at a duty cycle of 80%. The current-voltage waveform is the same with RF discharge during the power on, and the current decreases rapidly with the power off. The particle densities of different species change slowly comparing with the current during the power off. The majority of electrons generated during one discharge event remains in the gas gap and acts as seed electrons for the ignition of the next discharge event. The mode transition is familiar with conventional RF-APGD without pulse modulation. And the discharge current increases as the gas gap reduces.In the second place, we study the influences of pulse modulation on discharges. Two different glow modes can be achieved with the change of duty cycle. The discharge current magnitude increases with the frequency of RF. And the diffusion of electrons varies with different duty cycles during the power off time. After that, we also find that the pulsed modulation frequency does not affect the magnitude of discharge current at a duty cycle of 80%. In the end, we use a two-dimensional fluid mode to investigate the pulse-modulated radio-frequency dielectric-barrier discharge. The results of discharge current and particle densities are the same as those obtained in one-dimensional simulation model. This proves the validity of our two-dimensional model. And we also analyze the evolution of discharge current, electron density and electric field during the power off time. Because the two-dimensional model is close to the real glow discharge device, the work of this part contributes the solid basics for the application of atmospheric pressure pulse-modulated discharge.