Glow Discharges Observed in Capacitive Radio‐Frequency Atmospheric‐Pressure Plasma Jets

Abstract

Summary: The APPJ is the subject of intensive recent research. Basically, the APPJ consists of an atmospheric‐pressure RF discharge between two bare metallic electrodes and of a superimposed gas flow consisting predominantly of a rare gas. In its usual operating regime, a uniform glow discharge, which was identified as the α mode of a RF discharge, can be sustained over a wide range of gap spacings and RF powers. Maximum electron densities of 0.22 × 1012 cm−3 were assessed for helium and of 2.75 × 1012 cm−3 for argon by evaluation of electric measurements using a simple equivalent circuit model. At low RF powers, only partial coverage of the electrodes was observed. At high RF powers, a breakdown of the α sheath occurred, and a transition to either a pure γ mode or a coexisting α and γ mode took place. The γ mode covers only a small fraction of the electrode surface. In helium, it was easy to ignite directly a pure α discharge, but not in argon. Due to the high over‐voltage needed, the ignition in argon mostly led to a coexisting α and γ mode. However, through RF power reduction a transition to a pure α discharge can be initiated.

Instability control in microwave-frequency microplasma

“…In contrast, one observes that 13.56 MHz rf capacitive microdischarges have much larger electrode potentials. Those high voltage microdischarges may have stability issues due to the transition from the E-field driven α mode to the secondary electron driven γ mode [40]. In this work, only the α discharge mode was observed and there is never an intense plasma layer near the electrodes due to secondary electrons.…”

Separation of VUV/UV photons and reactive particles in the effluent of a He/O2atmospheric pressure plasma jet

“…Measurements and modelling have been reported for a coaxial jet with 1 cm diameter inner electrode and 1 mm electrode gap [17], parallel plate jet with 1 mm electrode separation and 1 mm electrode width [13], or for sources with electrode width larger than 1 mm [13,18]. The plasma dynamics and plasma chemistry in these discharges have also been modelled by several authors [19,20].…”

Recent Advances in the Research on Non‐Equilibrium Atmospheric Pressure Plasma Jets

“…With increasing current, arcing was reported 30. However, considering the pictures presented by Yalin et al30 and the experiences made with the APPJ, the discharge patterns are most probably a consequence of the occurrence of γ ‐mode 33. It could be argued that this device is an APPJ with a very specific geometry.…”

“…However, operation is restricted to a feedstock gas consisting predominantly of a rare gas with only a small admixture of a molecular gas. The uniform discharge in the APPJ was identified as the α ‐mode of an RF‐discharge 33–35. Since the introduction of the APPJ, quite a few investigations have been reported 34–70.…”

“…The most frequently used design consists of two solid parallel planar electrodes (Figure 2b). 33–35, 41, 42, 56, 57, 61 The gas flows along the electrodes through the rectangular cross section between them. Since the electrodes may be rather large, this design is sometimes referred as large area APPJ 35.…”