Numerical Simulation Of Radio Frequency Atmospheric Glow Discharge In Argon

Radio Frequency (RF) Atmospheric Pressure Glow Discharge (APGD) has advantages of high discharge stability and plasma species density. Therefore it attracts widespread interesting in domains of plasma etching, surface modification and environment purification research. The excitation frequency scope of RF APGD is generally in mega-hertz range. As a result reactive species, such as electrons and ions can sustain during one RF time period, which are trapped in the discharge space. It is the reason of high plasma density, low breakdown and sustaining voltage in RF APGD. Moreover, gas temperature in the discharge is also high because of thermal accumulation. With increasing discharge current density, mode transition of discharge occurs, transiting from the volumetric glow discharge of a mode to the unstable constricted discharge column ofγmode. Recently, the studies of discharge characteristics and mechanism are the most important issues in RF APGD.The numerical simulation is proposed to be an important method, which helps to understand the characteristic and mechanism of discharge and also the optimization of discharge processing. The studies of numerical simulation carried out in the paper are presented as following.Here a one-dimensional, self-consistent fluid model of argon atmospheric pressure radio frequency glow discharge is developed, based on the transport equations of electron and ion, which combines with the Poisson equation for electric field calculation. The numerical model considers the continuity equation, momentum equation of charged particles and metstables with drift-diffusion approximation, coupled with the current balance equation. The simulated results provide the spatio-temporal evolution of RF APGD in argon, which helps the discussion of discharge mechanism and stability control.It has been demonstrated that there were different operation modes in argon RF APGD, namely a mode and y mode. When the discharge operates in a mode, the ionization events occur in the entire discharge region, the voltage gradually grows with current density. The current-voltage characteristics show positive differential conductivity. However the ionization in y mode is mainly located in the boundary region between discharge bulk region and sheath region. The sheath characteristics are used to demonstrate the mechanism of mode transition in argon RF APGD. Further studies on radio frequency excitation frequency, electrode spacing and dielectric-barrier are carried out and given as following:.(1) The discharge characteristics of argon RF APGD under different radio frequency excitation frequencies of 6.78 MHz,13.56 MHz and 27.12 MHz show that with growing radio frequency excitation frequency, the stable operation region of a mode expanses. It suggests that the argon APGD is more stable under higher excitation radio frequency; also the produced plasma intensity is found to be higher.(2) Under different discharge spacing of 0.8 mm,1.2 mm and under 2.4 mm, the stable operating region of argon RF APGD expands intensively and the current density of stable discharge improves. It proposes that higher stable discharge obtains under smaller spacing. (3) By introducing the dielectric barriers, the stability of argon APGD has effective enhancement while maintaining the fundamental characteristics. The dielectric barriers play an important role on limiting the quick growth of discharge current density, which stabilizes the discharge, especially inγoperation mode.