The Study On Discharge Characteristics And Physical Mechanisms Of Atmospheric-pressure Glow Discharge

Atmospheric-pressure glow discharges (APGDs), due to their desirableuniformity, sufficient reactive species, and avoidance of complex vacuum system,have recently been widely used in many fields, including thin film deposition,environmental pollution control, surface modification, and biomedical engineering.As the two main methods to produce APGDs, dielectric-barrier discharge (DBD) anddirect-current (DC) discharge have attracted much attention. The study on the twodischarge approaches allows us to preliminarily understand the formation andevolution discipline of plasma and arrive at the basic knowledge of how to acquireand control the atmospheric-pressure homogenous plasma. Since the plasma sourcesare usually equipped with different electrode configurations and driven by variouspower supplies, manifold physical mechanisms and complex chemical reactionprocesses are involved in the plasma. Thus, there is little chance for people to have acomprehensive and systematic understanding of APGDs. In view of this, we proceedwith the theoretical and experimental study on the dielectric-barrier glow dischargeand DC glow discharge, respectively. The specific research contents and results areas follows.First, we study the influence of alternative-current (AC) parameters ondischarge mode and current pulse number in one dimensional fluid model. Theresults show that when the driving frequency is maintained at a level where the glowmode appears in one period with the amplitude of external voltage unvaried (1.8kV),the current pulse number decreases with the increasing frequency and there is atendency of transition from the Townsend mode to the glow mode for the dischargeboth at the current peaks and troughs; The discharge in the whole period can allalong operate in the glow mode with the driving frequency increased above40kHz;the increasing amplitude of external voltage benefits to the increase of the currentpulse number and the transition from the Townsend mode to the glow mode in thewhole period with the diving frequency fixed at40kHz, accompanied by thedisappearance of the residual peak in this process.Second, through a two-dimensional axisymmetric model simulation, we find aspecial spatiotemporal nonlinear behavior in atmospheric-pressure dielectric-barrierglow discharge: the symmetric evolution of discharge current and the asymmetrical spatial discharge structure with its compensation effect over the whole period. Theformation and evolution of the spatial discharge structure (the spatial distributions ofelectric field, electron density, and ion density) in one cycle have been analyzed andthe underlying reason for the reverse of spatial discharge structure has beenaddressed. The results show that: the emergence of the residual discharge plays a keyrole in the reverse of spatial discharge structure; this discharge behavior, whichoccurs only in a limited driving frequency range, can compensate the spatialnon-uniformity of discharge that is originated from the spatial nonlinearity.Finally, we conduct an experimental study of a magnetic-field-assisted plasmajet generated by dielectric-barrier discharge enhanced DC glow discharge atatmospheric pressure and develop a unique and novel plasma generator. Theexperimental results show that the introduction of a magnetic field can significantlyimprove the performance of the plasma jet, including the reduction of the dischargepower and plasma temperature, enhancement of the chemical activity, enlargementof the plasma volume, and optimization of the plasma uniformity. The improvementof the plasma jet performance is attributed to the enhancement of ionization in thecurved and lengthened electron path and the dispersion of discharge domains.The formation and evolution of atmospheric-pressure glow discharge, as well asthe discharge characteristics, have been investigated by using the numericalsimulations and experimental measurements. This work not only further improvesthe theoretical model of atmospheric-pressure glow discharge, but also lays atheoretical base to design and optimize the electrode structure andworking-parameter control strategy for the low-power, high-efficiency plasmagenerator, and provides a technical guidance for the practical application ofatmospheric-pressure glow discharge in the field of surface modification.