Characteristics of Large-Area Cold Atmospheric Discharges from Radio-Frequency Microdischarge Arrays

Abstract

Uniform and homogeneous large-area cold atmospheric discharges were produced by arrays of radio-frequency (rf) microhollow cathode discharges. A high flow rate of helium through the cathode holes was necessary to maintain stable and uniform discharges. The rf power also played a key role in sustaining the homogeneous and uniform discharges due to its efficiency being higher than that of the dc or pulse discharges. The rf microdischarges under various conditions were characterized by optical emission spectroscopy and by measuring the electrode voltage with an oscilloscope. Due to the higher concentration of Ag contaminants in the plasma, the optical emission intensity from the discharge using silver paste as the cathode was lower than that using silver paste as the anode. The electron temperature and the plasma density increased with increasing rf power and helium flow rate. The dc self-bias of the rf-powered electrode for the atmospheric discharge could be either negative or positive depending on the plasma density. A mechanism was proposed to explain the positive self-bias characteristic of the atmospheric discharge. Using a third electrode powered by a pulse power supply (100 kHz, 50% duty cycle), the rf microdischarge sheet was extended into a stable and homogeneous volume discharge with the thickness increased from 3 mm to 20 mm.