Self-organization of microdischarges in DBD plasma

Dielectric-barrier discharge, also referred as a silent discharge, combine the ease of atmospheric pressure operation with non-equilibrium plasma conditions suited for many plasma chemical processes. Numbers of interesting industrial applications in addition to the well know ozone generation was found. In particular, it is very effective in plasma treatment of polymer surfaces to promote wettability, printability and adhesion [1, 2]. In air at atmospheric pressure the discharge consist of large number of filaments that can form at regular pattern. Different types of periodic patterns were observed experimentally. Their properties were analyzed in detail. Microdischarge interaction model in dielectric-barrier discharge was proposed in order to explain experimentally observed patterns. Monte-Carlo simulation of microdischarge interaction in discharge gap based on proposed model was developed. Comparison between modeled and experimental patterns was performed by several methods. Effect of different driving voltage on observed patterns was evaluated. Gas phase discharge chemistry was calculated; impact of patterns on chemistry was investigated. For patterns analyze and comparison 2D correlation function of the pattern averaged over the observed space, Voronoi Polyhedron approach as well as two dimensional Fourier transform was used.M.S., Mechanical Engineering -- Drexel University, 200

Stability of atmospheric pressure glow discharges

There has been a considerable interest in non-thermal atmospheric pressure discharges over the past decade due to increased number of industrial applications. Although non-thermal atmospheric pressure discharges have been intensively studied for the past century the clear physical picture of these discharges is far from being complete.Spontaneous transition of non-thermal atmospheric pressure discharges to thermal discharge and discharge filamentation are among least understood plasma phenomena. The discharge stability and reliable control of plasma parameters are highly desirable for numerous applications. This study focuses on stability of atmospheric pressure glow discharges with respect to filamentation and arcing.Atmospheric pressure glow discharge (APG) is the newest and the most promising addition to the family of non-thermal atmospheric pressure discharges. However this discharge is very susceptible to thermal instability which causes arcing, loss of uniformity and significant damage to electrodes. Suppression of thermal instability and effective control of discharge parameters is critical for industrial applications.A model was developed to understand transition to arc in atmospheric pressure glow discharges. APG discharges that operate in pure helium and in helium with addition of oxygen and nitrogen were considered in these studies. Simulation results indicate that arcing is the result of sheath breakdown rather than thermal instability. It was shown that although sheath breakdown is always followed by overheating the transition to arc in atmospheric glow discharges is not a result of thermal instability.In second part of this research interaction between plasma filaments in dielectric barrier discharges has been studied. This interaction is responsible for the formation of microdischarge patterns reminiscent of two-dimensional crystals. Depending on the application, microdischarge patterns may have a significant influence on DBD performance, particularly when spatial uniformity is desired. A microdischarge interaction model is proposed and a Monte-Carlo simulation of microdischarge interactions in the discharge is presented.A new method for analysis of microdischarge patterns that allow measuring the degree of pattern regularity was developed. Simulated and experimental patterns were compared using the newly developed method. Analysis of microdischarge patterns shows that regularity of the patterns increases with the number of excitation cycles used to produce the pattern.Ph.D., Mechanical Engineering -- Drexel University, 200