Abstract
In this paper, through a one-dimensional fluid model, we investigate the influence of oxygen on the multiple-current-pulse (MCP) behavior in an atmospheric homogeneous dielectric barrier discharge (HDBD) in helium with air impurities. From the simulation results, we find that the O2 Penning ionization plays a leading role in the discharge characteristics. As the air content increases from 0 ppm to 5000 ppm, the current waveforms show a transition from a single-pulse mode to MCP mode, and the number of current pulses ( $N_{\mathrm {p}}$ ) also increases. Through analysis, we find that although $N_{\mathrm {p}}$ increases monotonically, the evolution mechanism of the MCP discharges under different ranges of air content is different. At lower air concentration (less than 500 ppm here), we find the similar explanation as that reported in our previous work on the MCP behavior only considering N2 impurity. However, when the air content is higher, we find that the seed electron density ( $n_{\mathrm {e0}}$ ) remains basically unchanged, not like the sharp drop at lower air concentration. Further analysis reveals that the rapid growth of direct ionization during a small period before the breakdown helps generate MCP discharges. In addition, the attachment reaction of O2 is analyzed. Results show that at higher air content (above 5000 ppm here), the O2 attachment reaction will provide more possibilities of successive ignitions after the first pulse with the assistance of the applied voltage, implying a stimulative effect of the oxygen on MCP discharges.
Highlights
In recent years, atmospheric dielectric barrier discharges have been widely used for plasma generations in pollution control [1], surface modification [2]–[4] and biomedical sterilization [5]–[8]
The MCP behavior appears in the case of 100 ppm and shows an intensification with a further increase in air content
(2) At lower air concentration, we find the similar explanation as that reported in our previous work on the MCP behavior only considering N2 impurity [23]
Summary
Atmospheric dielectric barrier discharges have been widely used for plasma generations in pollution control [1], surface modification [2]–[4] and biomedical sterilization [5]–[8]. Among various types of discharges, a homogeneous dielectric barrier discharge (HDBD) at atmospheric pressure is usually adopted as it can provide a uniform and stable low-temperature plasma, reducing filaments which are harmful to the sensitive surface in practical applications [9]–[13]. Previous studies have reported a different discharge mode which exhibits two or more pluses in each half cycle under some specific conditions [14]–[17]. This type of discharge phenomenon, which is denoted by ‘multiple-current-pulse (MCP) behavior’ hereafter, has been proved to be disadvantageous to practical applications because of its violent oscillations and instabilities [9], [11]–[13], [18]. A relatively longer effective treatment time per half cycle, during which the density of reactive species and the average
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