Modeling and simulations of DC and RF atmospheric pressure non-thermal micro plasma discharges

Atmospheric pressure non-thermal plasma discharges are attractive for a wide range of applications due to their operational flexibility. Among the different atmospheric pressure nonthermal plasma sources, atmospheric pressure non-thermal micro plasma discharge is a very recent development. However, the micron scale size of these discharges makes it difficult to measure basic plasma characteristics (species density, gas and electron temperature, electric field etc) and also to analyze the different interplaying physico-chemical processes. In this work comprehensive multi-dimensional hybrid models were developed to simulate DC and RF atmospheric pressure non-thermal plasma discharges, and validated against experimental data. The basic plasma characteristics and different physico-chemical processes were explored by performing systematic parameter variations. The developed discharge models included detailed discharge physics, gas phase chemistry, surface chemistry and external circuit model. DC micro plasma discharges in argon, hydrogen and methane-hydrogen gas were simulated. The effect of the external circuit was found to be crucial in predicting the discharge characteristics accurately. The simulations indicated the discharge to be operating as a 'normal' glow discharge. Predictions from the model compared favorably to the experimental measurements. A detailed surface chemistry model was developed for a DC methane-hydrogen micro glow to study the possibility of using these micro plasma discharges in plasma enhanced chemical vapor deposition. RF plasma discharges in argon gas together with an extensive external circuit was simulated; special attention was devoted to the effect of external circuit parameters on the discharge characteristics. The circuit elements were found to trigger change in the mode of operation. An atmospheric pressure plasma jet in helium-oxygen feed gas was also simulated to study the possibility of surface decontamination applications. To the author's knowledge, this is the first attempt where detailed simulation of atmospheric pressure micro plasma discharge has been conducted together with an external circuit. The discharge models were used to investigate the plasma characteristics, physicochemical processes and study the effect of the external circuit and process parameters on the discharge. Better understanding of these processes will enable the tailoring and optimization of the operating conditions.