Cathode fall characteristics in a dc atmospheric pressure glow discharge

Copyright 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the authors and the American Institute of Physics. This article appeared in the Journal of Applied Physics and may be found at: http://link.aip.org/link/?JAPIAU/94/5504/1Atmospheric pressure glow discharges are attractive for a wide range of material-processing applications largely due to their operation flexibility afforded by removal of the vacuum system. These relatively new atmospheric plasmas are nonequilibrium plasmas with gas temperature around 100 °C and electron temperature in the 1–10 eV range. Their appearance is characteristically diffuse and uniform, and their temporal features are repetitive and stable. Of the reported numerical studies of atmospheric glow discharges, most are based on the hydrodynamic approximation in which electrons are assumed to be in equilibrium with the local electric field. Spectroscopic and electrical measurements suggest however that the cathode fall region is fundamentally nonequilibrium. To this end we consider a hybrid model that treats the cathode fall region kinetically but retains a hydrodynamic description for the region between the thin cathode fall layer and the anode. Using this hybrid model, a helium discharge system excited at dc is studied numerically for a very wide current density range that spans from Townsend dark discharge, through normal glow discharge, to abnormal glow discharge. Numerical results confirm many distinct characteristics of glow discharges and compare well with that of low-pressure glow discharges. Generic relationships, such as that between the electric field and the current density, are also established and are in good agreement with experimental data. This hybrid model is simple and insightful as a theoretical tool for atmospheric pressure glow discharges

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas

Charge densities in the electrolyte cathode atmospheric glow discharges (ELCAD)

In a normal and an abnormal ELCAD plasmas the density of electrons and positive ions were estimated from the earlier measured values of the cathodic current density, the cathode fall, the electric field, the length of cathode dark space, the kinetic energy, the last free path of positive ions hitting the cathode and the rate of secondary electron emission. In a normal ELCAD, the density of positive ions forming the space charge: $n_{sp}^{+}$ ≈ 5.7×1012 cm-3, the density of positive ions hitting the cathode: n+ ≈ 1.1×1012 cm-3, the electron density at the cathode: $n_{e,c}$ ≈ 3.7×1011 cm-3, the electron density at the end of cathode dark space: ne ≈ 5.7×1012 cm-3 and the multiplication of electron in cathode dark space M ≈ 15.3 were obtained. In an abnormal case, $n_{sp}^{+}$ ≈ 2.1×1013 cm-3, n+ ≈ 4.3×1012 cm-3, $n_{e,c}$ ≈ 3.9×1012 cm-3, ne ≈ 2×1013 cm-3, M ≈ 5.17 were received