射频/直流驱动大气压氩气介质阻挡放电的一维仿真研究

One-dimensional simulation of Ar dielectric barrier discharge driven by combined rf/dc sources at atmospheric pressure

采用一维自洽耦合流体模型理论研究了射频(rf)/直流(dc)驱动大气压氩气(Ar)介质阻挡放电特性,仿真得到了不同直流电压下,射频最小维持放电电压变化情况、周期平均电子密度平均值随周期平均气体电压平均值变化情况、电子产生率及电子密度的时空分布.分析表明:直流电压通过改变介质表面电荷密度来影响气隙电压,从而控制放电过程.直流电压较小时放电被抑制,直流电压较大时放电得以恢复.随着直流电压的增大,射频最小维持放电电压振幅随之呈现先增大后减小的变化趋势.另外,当射频电压振幅高于最小维持放电电压振幅时,射频电源驱动与射频/直流驱动时的气隙电压相同,射频电源控制放电.进一步发现在α模式下,随着直流电压的增大,鞘层逐渐形成,电子产生区域从接地电极附近转变为两侧鞘层和主等离子体区边界处;在γ模式下,当射频电压振幅高于最小维持放电电压振幅时,电子产生和分布不受直流电压影响.

We present the dielectric barrier discharge(DBD)mechanism of argon(Ar)plasma driven by a combination of radio frequency(rf)voltage source and direct current(dc)voltage source at atmospheric pressure,based on one-dimensional self-consistent coupled fluid model.Using the finite element method(FEM)to numerically calculate the model,the average value of period average electron density varying with the average value of period average gas voltage in one rf period,and the variation of the minimum rf sustaining voltage are obtained under different dc voltages.In addition,the spatiotemporal distribution of the electron density and electron generation rate,the spatial distribution of electron temperature,and the time-domain variation of electron conduction current flowing to the dielectric are studied.The results show that the introduction of the dc voltage source has a significant effect on the rf discharge process of atmospheric pressure Ar gas,and the parameters of the plasma state are changed correspondingly.The discharge process is mainly controlled by the air gap voltage,and the dc voltage affects the gap voltage by changing the charge density on the dielectric surface.The minimum rf sustaining voltage V_(rf,min)first increases and then decreases with the increase of dc voltage.The amplitude of rf minimum sustaining discharge voltage is changed by the dc voltage.And when the amplitude is reached or exceeded,the discharge is controlled by the rf power supply.On the one hand,in the a mode,when the dc voltage is low,electrons are generated near the ground electrode.The electric field intensity in the ionization area is too small to maintain ionization.When the dc voltage is high,the sheath is formed,and electrons are generated near the rf sheaths on both sides and the boundary of the plasma region.In theγmode,when the rf voltage amplitude is equal to or greater than the rf minimum sustain discharge voltage amplitude,i.e.V_(rf)≥V_(rf,min),the generation and distribution of electrons are almost unaffected by the dc voltage.On the other hand,in the a mode,the ionization cannot be sustained for the low dc voltage,resulting in the failure to form the main plasma area.Therefore,the electron temperature is generally high.Owing to the high electron density near the ground electrode,the electron temperature is higher.The electron density near the dielectric is less than that near the electrode,so the temperature is lower.When the dc voltage is getting larger,the sheath and the main plasma region are formed.The dc voltage significantly affects the electron temperature by controlling the sheath voltage and the length of the main plasma region.Finally,in the a mode,the electron density near the medium is very low and the air gap voltage is negative for the low dc voltage.As a result,few electrons can reach the surface of the dielectric,and the conduction current of electrons flowing to the medium is very small.With the increase of the dc voltage,the electric field across air gap increases,and electrons,under the action of the electric field,flow from the dielectric surface.The sheath having formed,some speedy non-localization electrons that have reached the dielectric surface are reflected back to the sheath,resulting in a significant reduction in the number of electrons that can reach the dielectric surface.