There has been considerable interest in non-thermal atmospheric pressure discharges over the past decade due to the increased number of industrial applications. Diverse applications demand a solid physical and chemical understanding of the operational principals of such discharges. This paper focuses on the four most important and widely used varieties of non-thermal discharges: corona, dielectric barrier, gliding arc and spark discharge. The physics of these discharges is closely related to the breakdown phenomena. The main players in electrical breakdown of gases: avalanches and streamers are also discussed in this paper. Although non-thermal atmospheric pressure discharges have been intensively studied for the past century, a clear physical picture of these discharges is yet to be obtained.

The dielectric barrier discharge (DBD) has a number of industrial applications and has been a subject of research for many years. Many studies have been carried out to understand the underlying DBD physics. Despite the fact that much progress has been made, some important issues are still far from being clear. In this work, we summarize the basics of DBD physics and introduce innovative concepts of discharge behavior that were discovered recently.

The two-dimensional spatial distribution of microdischarges in atmospheric pressure dielectric-barrier discharges (DBDs) in air was studied. Experimental images of DBDs (Lichtenberg figures) were obtained using photostimulable phosphors. The storage phosphor imaging method takes advantage of the linear response of the phosphor for characterization of microdischarge intensity and position. A microdischarge interaction model in DBDs is proposed and a Monte Carlo simulation of microdischarge interactions in the discharge is presented. Comparison of modelled and experimental images indicates interactions and short-range structuring of microdischarge channels.

The stability and uniformity of a radio-frequency (RF) discharge is limited by a critical power density. Beyond this critical power density, instability occurs in the form of physical changes in the plasma (such as contraction due to arcing). The RF discharge used in this study is the non-equilibrium Atmospheric Pressure Plasma Jet (APPJ ® ) developed by Apjet, Inc. This discharge is known to operate uniformly in helium gas. However, for some proposed applications such as surface modification, there is a need to operate with reactive gases such as O 2 . Our experimental studies show that addition of molecular gas to a discharge operating in helium increases its power density (W cm −2 ), until it reaches the critical unstable arcing limit. Moreover, an increase in the frequency of operation (from 13 to 27 MHz) allows the plasma to sustain higher molecular gas concentrations and power densities before instability occurs. Further, it is observed that this critical power density is dependent on the type of molecular gas added. These results provide a motivation for the development of a mathematical model that can provide insight into the causes of instability and potential methods of suppression. The two commonly studied modes of instability are (1) thermal instability (TI) and (2) α-γ -arc mode transition. For the APPJ ® discharge conditions, the development time scales of TI are much longer (∼1 ms) as compared with discharge oscillation period (∼100 ns). Hence, if the instability was indeed thermal, discharge frequency increase would have no consequence, contrary to experimental findings. A 1D fluid model based on the local field approximation is developed to study instability in APPJ ® discharge. The analysis of modeling results confirmed our hypothesis that the instability development actually takes place via breakdown of sheath i.e. α-γ -arc mode transition and not by TI.

Although microdischarges in dielectric-barrier discharges (DBDs) have been studied for the past century, their mutual interaction was explained only recently. 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. This paper presents the results of study of regular microdischarge pattern formation in DBD in air at atmospheric pressure. Experimental images of DBD (Lichtenberg figures) were obtained using photostimulable phosphors. 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 and comparison indicates the presence of interaction between microdischarges. Analysis of microdischarge patterns shows that regularity of the patterns increases with the number of excitation cycles used to produce the pattern.