Theoretical Study On The Characteristics Of Atomospheric Dielectric Barrier Discharges

For the non-equilibrium plasma produced at atmospheric pressure, its electrons are of higher energy and its ion energies are lower. Especially, it contains a lot of active particles. These particles can reduce the threshold of chemical reactions with other corresponding matters. Therefore, many chemical reactions can occur in low temperature as well as in room temperature in the non-equilibrium plasma. Due to the above, the non-equilibrium plasma is widely used in industrial applications and the plasma physics scientific community has paid much attention to the development of atmospheric pressure non-equilibrium plasma.In recent years, many studies on the homogeneous dielectric barrier discharge at atmospheric pressure have been made experimentally and numerically, and some preliminary insights into this discharge have been obtained. However, following these studies the complexity of this discharge, which is located in the dissipative system with strong nonlinearity, has also been understood. In addition, there is the poor knowledge for some discharge behaviors, reasonable and general explanation for some phenomenon occurred in the discharges has not been given, the dependence of the non-equilibrium plasma on the parameters governing the discharge is not well known, and the physical and chemical processes in the discharge is not clear. By reason of these, many aspects of the discharge remain the subject of great interest. In this thesis, the characteristics of the homogenous dielectric barrier discharge at atmospheric pressure in helium and in helium-nitrogen mixture are investigated numerically with the use of a one-dimensional fluid model. The main contents and results are summarized as follows:1. In chapter1, background and significance for the studies on the dielectric barrier discharge at atmospheric pressure are briefly introduced, and the systematic analyses on the situations concerning with this study are made.2. In chapter2, using helium as working gas, the characteristics of the homogeneous dielectric barrier discharge with single pulse at atmospheric pressure is studied. The effects of several parameters on the homogeneous dielectric barrier discharge at atmospheric pressure are explored. These parameters are the amplitude and frequency of the applied voltage, the thickness of dielectric plate, and the permittivity of dielectric. A method of estimating the pulse width of the discharge by calculating the time interval between the breakdown voltage and extinguishing voltage is proposed. Further, the effect of the amplitude and frequency of the applied voltage on the pulse width of the discharge is investigated, giving the principle of restraining the transition from the glow mode to filamentary mode so as to obtain the homogeneous dielectric barrier discharge.3. In chapter3, the homogeneous dielectric barrier discharge with multiple current pulses at atmospheric pressure in helium is investigated numerically. The influences of the parameters, i.e. the amplitude and frequency of the applied voltage, the thickness of dielectric plate, and the gap width of discharge configuration, on the discharge characteristics are analyzed systematically. The characteristics include the number of discharge current pulses and the time interval between two successive discharge current pulses. Moreover, an approach by means of linear fitting is given for estimating the starting voltage and frequency for the formation of a new discharge current pulse. This estimation could provide theoretical references for experimental study on the multiple-pulse discharge.4. In chapter4, based on the method used in the radio frequency discharge, a procedure of keeping the constant power in the processes of the discharge by adjusting the amplitude of the applied voltage is proposed and the corresponding iterative formula is given. These extend the constant power method used in the radio frequency discharge into the study on the constant power in the homogeneous dielectric barrier discharge at atmospheric pressure. Under the constant power, the effects of both the frequency of the applied voltage and the gap width of discharge configuration on the characteristic quantities, such as the current density, the discharge pulse width, the electron density, and the charge density, have been investigated systematically, providing theory for high efficiency and for optimization of discharge configuration in the homogeneous dielectric barrier discharge at atmospheric pressure.5. In chapter5, the influence of different amounts of nitrogen impurity on the barrier discharge at atmospheric pressure in He-N2admixture gas has been numerically studied. The characteristic of the current density versus N2impurity amount shows a transition point. The influence of the amplitude and frequency of the applied voltage on both N2impurity amount and the current density at the transition point has been particularly investigated. The following conclusions are given. For fixed frequency of the applied voltage, both N2impurity amount and the current density at the transition point increase with increasing amplitude of the applied voltage. Fixing the amplitude of the applied voltage, N2impurity amount at the transition point increases with increasing frequency of the applied voltage, but the minimum value of the current density is not evidently affected by the frequency. In particular, the Townsend discharge mode is observed at the transition point under the present simulation conditions.