| With the wide applications of the non-thermal plasmas in various fields, the generation of homogeneous non-thermal plasmas through gas discharge at atmospheric-pressure has become one of the most attractive researches in the field of gas discharge and non-thermal plasmas. Dielectric barrier discharge (DBD) is considered as an effective method to generate the atmospheric-pressure non-thermal plasmas and has attracted much attention. For the reported studies on atmospheric-pressure DBD, continuous sinusoidal voltage is usually used as a driving source. With the development of pulsed power technology, the atmospheric-pressure DBD excited by repetitive voltage pulses (pulsed DBD) presents its particular advantages. Although some studies on atmospheric-pressure pulsed DBD have been made experimentally and numerically in recent years, there are many problems to need solving, such as the reasonable and general explanation for the mechanism of the discharge, the more knowledge for some discharge behaviors, and the relationship between characteristics of discharges and conditions.To this end, in this thesis the atmospheric-pressure pulsed DBD has been systematically investigated by means of numerical simulation with the use of a one-dimensional fluid model, and the main contents and results are summarized as follows:(1) The time evolutions of the characteristic quantities of the pulsed DBD in pure helium at atmospheric-pressure have been simulated in detail. These characteristic quantities refer to discharge voltage, discharge current density, and particles density, and they as a function of time have been given. In addition, the spatial distributions of ion density, electron density, and electric filed at different time points have been obtained. Based on the above, the characteristics and mechanism of the discharge have been analyzed, and the following are obtained. For the DBD excited by the repetitive voltage pulses with small pulse width, the time evolution of the discharge occurring at the rising edge of applied voltage pulse is similar to that occurring at the falling edge. For the spatial distribution of electron density, only one peak appears nearby the momentary cathode (MC) in the first discharge, and there are two peaks nearby both the MC and the momentary anode (MA) in the second discharge. In addition, the peaks of the spatial distribution of averaged electron temperature appear nearby the MC in the two discharges.(2) The influences of the parameters of the applied voltage pulse on the characteristics of atmospheric-pressure pulsed DBD have been systematically investigated. These parameters include amplitude, pulse width, frequency, rising time, and falling time. When the amplitude of the applied voltage pulse increases, both the amplitude of current density in each discharge and the electron density in the gap increase, the cathode sheath becomes thinner, and the averaged electron temperature in cathode sheath increases obviously. When the rising and falling times of the applied voltage pulse decrease, the dependences of the characteristic quantities of the discharge on these two times are similar to those due to decrease of the amplitude of the applied voltage pulse, the multi-peak behavior can be observed, and the quasi-neutral plasma bulk in the discharges decreases gradually and disappears eventually. Moreover, when the pulse width or frequency of the applied voltage pulse changes, the electron density and averaged electron temperature nearby both edges of the gap change evidently, and those in the middle area change slightly.(3) The influences of the parameters of the discharge configuration on the characteristics of atmospheric-pressure pulsed DBD have been systematically investigated. These parameters include secondary electron emission coefficient, dielectric thickness, the relative permittivity of the dielectric, and the gap width. The following are shown. When the secondary electron emission coefficient increases, the amplitude of discharge current density increases, large averaged electron density can be obtained by small averaged dissipated power density. In addition, in the discharge the cathode sheath gets thinner, the peak value of the spatial distribution of electron density nearby the MC increases, but the averaged electron temperature in the cathode sheath decreases. With the increase of the gap width, the amplitude of the discharge current density in the first discharge decrease, there is the peak value for that in the second discharge, and in the discharge both the peak value of the spatial distribution of electron density nearby the MC and the averaged electron temperature in the cathode sheath decrease. Decreasing the relative permittivity of the dielectric or the dielectric thickness increases, the amplitudes of the current densities in the two discharges increase, and in the discharge the cathode sheath becomes thinner and the averaged electron temperature becomes larger.(4) The investigation on the generation and characteristics of multi-peak behavior in atmospheric-pressure pulsed DBD has been carried out, and the influences of the discharge conditions on multi-peak behavior have been systematically analyzed. For a given applied voltage amplitude, the number of discharge current pulses increases with decreasing voltage growth rate, and when voltage growth rate is small, its effect on the number of current pulses is more evident, and the dependence of the amplitude of each current pulse on voltage growth rate is different. When the voltage growth rate is not larger, the spatial distributions of ion density and electron density in the discharge are similar to those in Townsend discharge. For a given voltage growth rate, the number of discharge current pulses increases with increasing amplitude of the applied voltage pulse, but the amplitude of each current pulse changes little. The increase of the pulse width or frequency can induce not only later appearance of current pulses and smaller amplitude of the last current pulse at the rising edge of the applied voltage pulse but also larger amplitude of the last current pulse at the falling edge of the applied voltage pulse. With the decrease of the relative permittivity of the dielectric or with the increase of dielectric thickness, the amplitudes of discharge current densities decrease and the number of discharge current pulses increase.(5) The effects of N2impurity amount on the characteristics of atmospheric-pressure pulsed DBD in He-N2admixture gas have been investigated, and the comparison between the characteristics of the pulsed DBD and the DBD excited by continuous sinusoidal voltages in He-N2admixture gas at atmospheric pressure at small N2impurity amount has also been made. For small N2impurity amount in He-N2admixture gas, in two types of discharge, i.e., the pulsed DBD and the DBD excited by continuous sinusoidal voltages, the electrons are mainly generated through direct ionizations when the discharge occurs and through penning ionizations in the later stage of the discharge or after the discharge, but the reaction rates of both direct ionizations and penning ionizations in the pulsed DBD differ obviously from those in the DBD excited by continuous sinusoidal voltages. For the pulsed DBD in He-N2admixture gas at atmospheric-pressure, with the increase of N2impurity amount, the averaged density of He2+keeps decreasing, there are the maximum value for the averaged density of N2+and N4+, and He2+, N2+, and N/play a dominating role in the discharge. With the increase of N2impurity amount, the amplitudes of the current densities in the two discharges are in no monotonous variety, and those in the second discharge present complex variety. For the different rising times and falling times of the applied voltage pulse, the dependences of averaged electron density, dissipated power density, and the amplitudes of the two discharge current densities on N2impurity amount are similar for each other. When N2impurity amount is larger than a certain ppm under the given discharge parameters, the N2impurity amount corresponding to the maximum value of the amplitude of the first discharge current density decreases with increasing rising and falling times of applied voltage pulse. |
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