Study on discharge modes and characteristics of large-area plasma produced at atmospheric pressure

Abstract

The physical properties and application feasibilities were studied using atmospheric radio-frequency (RF) capacitive discharge sources. From the fundamental study of a typical RF capacitively coupled discharge source, a new type of atmospheric pressure discharge source was suggested for large-area plasma generation with low-breakdown voltage and low gas temperature. In addition, spectroscopic methods were developed and applied to the atmospheric plasmas for measuring plasma parameters. In an atmospheric pressure capacitive discharge, α and γ discharge modes of a helium discharge were investigated by varying the discharge gap distance between the two electrodes from 1~mm to 5~mm. As similarly observed in other experiments, the α- and γ-mode and the α-γ mode transition were observed with nearly 40% drop in the voltage, 67% drop in the phase angle between the voltage and current, and contraction of the plasma volume. The discharge voltage, at which the α-γ mode transition occurred, versus the inter-electrode gap distance showed a similar behavior with the Paschen curve for gas breakdown. Depending on the discharge gap distance, normal and abnormal glow regimes were observed in the α-mode. At 1 and 2~mm, the α-mode was remained in the abnormal glow discharge with a increasing current until the α-γ mode transition occurred. At 3mm, however, the α-mode was excited as a normal glow discharge with a constant current density (17 mA/cm²), then, it became an abnormal glow discharge as the current increased. At 4 mm, the α-mode was sustained as a normal glow discharge until the transition to the γ-mode occurred. Using a simple resistor-capacitor (RC) electrical circuit model and a α-sheath breakdown model, the discharge modes and the mode transition were studied. Based on these results, an atmospheric large-area capacitive discharge source consisted of a double electrode structure was developed. This discharge configuration provided stable and large ar...