185 / 2018-08-29 10:05:19

Investigation of Surface Charge Distribution and Its Influence on Self-stabilized Discharge Filaments at Atmospheric Pressure

dielectric barrier discharge (DBD); surface charge; Pockels effect; fluid model

Dielectric barrier discharge (DBD) with a broad range of technological applications is a hot topic in the field of gas discharge. In recent years, the dynamic distribution of surface charges on the dielectric barrier has been known as an important influence factor on the discharge characteristics of DBD at atmospheric pressure. In some conditions, the discharge mode of DBD tends to be self-stabilized discharge filaments. In order to understand the physical mechanism of that, it’s quite necessary to investigate the dynamic accumulation and decaying of surface charges in DBD.
In this paper, a comprehensive measurement system of surface charge and discharge pulse current based on Pockels effect was established. The BSO crystal was used as a transducer to transfer surface charge density distribution to light phase retardation. With the pictures recorded by two ICCDs, the surface charge density on the dielectric barrier was displayed with two-dimensional chromatic graph. A DBD structure with specific discharge gap was specially designed, in which the BSO crystal covered by a polyethylene film with thickness of 6um acted as the dielectric barrier. The crystal was fixed on a BK7 substrate with ITO coatings on the other side as the ground electrode. The discharge structure was put into an environmental chamber and it coupled with the optical components outside the chamber through a transparent window. With the measurement system, the distribution of surface charge during DBD can be measured under the condition with different voltage frequency, gas atmosphere and voltage amplitude.
In the experiment, a single self-stabilized discharge filament was achieved under high-frequency sinusoidal voltage at atmospheric pressure. With the measurement system mentioned above, surface charge distribution during a single discharge pulse was obtained. Besides, the development process of a single self-stabilized discharge filament in the gas gap was observed using an ICCD. So the volume and surface process during a single DBD pulse can be gained at the same time, which can promote a better understanding of the whole discharge process.
The residual surface charge dynamic distribution after each discharge pulse was also measured. The variation rule of residual surface charges during the period from the initial discharge to the stabilized discharge was summarized. With that, the contributions that surface charges make to the development process from unstable discharge mode to self-stabilized discharge filament can be well understood. Moreover, the influence that different factors have on the distribution of surface charges during DBD was also investigated. With the variation of experimental conditions, the stability and the number of self-stabilized discharge filaments can experience a subtle change, which can be perfectly explained using the surface charge distribution.
In addition to experimental measurement, a mathematical model based on charge fluid equations was established to simulate the development process of the self-stabilized discharge filament. The spatial-temporal distribution of surface charges and electrons was obtained. The influence that different amplitude and frequency of the applied voltage have on the characteristics of DBD was investigated and discussed. It shows that the simulation results about the features of surface charges distribution agree with that of experiment, which makes it easier to understand the behaviors of DBD.