Electrically efficient production of reactive species in a diffuse nonthermal atmospheric plasma

Summary form only given. Nonthermal atmospheric pressure gas discharges operated in the diffuse mode have commanded increasing interest largely because their low gas temperature, spatial uniformity, and temporal stability are highly desirable for many materials processing applications. Most such plasmas are generated capacitively with a sinusoidal excitation voltage, and their electrical signature has a distinct characteristic of having one discharge current pulse every half cycle. Of particular interest is that the width of the discharge current pulse is a small fraction of half period of the applied excitation voltage and that the current pulse usually precedes the peak of the excitation voltage in any given half cycle. This suggests that for a very significant part of its application the excitation voltage may not contribute to the production of electrons and that of reactive species, both of which are important for surface modifications required for many materials processing applications. Therefore it is of interest to explore whether this potentially inefficient use of the input electric power can be remedied by, for example, appropriate shaping of the waveform of the excitation voltage. To study this, we have developed a simple numerical model and its associated computer code for one-dimensional simulation of atmospheric pressure helium discharges. To compare to the usual route of using sinusoidal excitation, we consider three pulsed excitation voltage waveforms, namely (1) peak-leveled sinusoidal, (2) square wave, and (3) Gaussian. For each case, plasma voltage and current are computed to identify the parametric range within which the generated atmospheric plasmas are diffuse and nonthermal discharges.