Investigation of an atmospheric pressure radio-frequency capacitive plasma jet

We have constructed a large area atmospheric pressure plasma jet (LAAPPJ) composed of two planar electrodes with an area 38 cm(2) at a distance of 2.5 mm. The LAAPPJ was operated with helium at a gas flow rate of 1.5 mmol/s. The electrical properties of the discharge were studied by measuring the voltage and the discharge current simultaneously using a high voltage probe, a current probe and a digital oscilloscope. Pictures of the discharge were taken with a digital camera. Two discharge modes can be sustained within certain limits. At RF input powers of 50-420 W an a-discharge can be sustained, however, below approximately 300 W the electrodes are only partially covered with the glow. At higher powers a breakdown occurs and a transition to a gamma-discharge takes place, whereby the alpha-discharge dies out. The gamma-discharge only covers a part of the electrodes and can be sustained down to powers of 50 W. Below this power the discharge extinguishes. (c) 2005 Elsevier Ltd. All rights reserved.