Contrasting Plasma Dynamics in Barrier-Free and Dielectric-Barrier Glow Discharges in Atmospheric Helium

Summary form only given. Near room-temperature atmospheric discharges are usually produced using either dielectric insulation to the electrodes or high excitation frequencies above 1 MHz. The first technique is key to atmospheric dielectric-barrier discharges (DBD) that operate typically at frequencies of 1-100 kHz and have been the most commonly studied atmospheric pressure glow discharges (APGD). Recently we have observed a novel kilohertz atmospheric pressure glow discharges between two bare stainless steel electrodes without any dielectric insulation. This is scientifically intriguing since dielectric barrier has long been believed to be essential for sustaining atmospheric glow discharges at kilohertz frequencies. From an application standpoint, this is also significant since open-air operation of large-scale APGD systems is likely to introduce foreign particles (such as dust) to the dielectric barriers and such environmental influences can critically alter performance characteristics of atmospheric DBD. The removal of the dielectric barrier can at least minimize such influences. Yet little is known of ionization dynamics in atmospheric barrier-free discharges. In this contribution, we present an experimental study of plasma dynamics in a helium atmospheric barrier-free discharge using current-voltage characteristics, nanosecond imaging and emission spectroscopy. Results of this study are then compared to a similar study of a comparable atmospheric DBD in helium to contrast out their dynamic behaviors and hence their ionization mechanisms. To further support this, a fluid model is used for numerical simulation of both types of atmospheric helium plasmas. The synergistic interplay of these studies offers a systematic evaluation of the similarity and difference between atmospheric barrier-free discharges and atmospheric dielectric-barrier discharges