On the physical processes ruling an atmospheric pressure air glow discharge operating in an intermediate current regime

Abstract

Low-frequency (100 Hz), intermediate-current (50 to 200 mA) glow discharges were experimentally investigated in atmospheric pressure air between blunt copper electrodes. Voltage-current characteristics and images of the discharge for different inter-electrode distances are reported. A cathode-fall voltage close to 360 V and a current density at the cathode surface of about 11 A/cm 2 , both independent of the discharge current, were found. The visible emissive structure of the discharge resembles to that of a typical low-pressure glow, thus suggesting a glow-like electric field distribution in the discharge. A kinetic model for the discharge ionization processes is also presented with the aim of identifying the main physical processes ruling the discharge behavior. The numerical results indicate the presence of a non-equilibrium plasma with rather high gas temperature (above 4000 K) leading to the production of components such as NO, O, and N which are usually absent in low-current glows. Hence, the ionization by electron-impact is replaced by associative ionization, which is independent of the reduced electric field. This leads to a negative current-voltage characteristic curve, in spite of the glow-like features of the discharge. On the other hand, several estimations show that the discharge seems to be stabilized by heat conduction; being thermally stable due to its reduced size. All the quoted results indicate that although this discharge regime might be considered to be close to an arc, it is still a glow discharge as demonstrated by its overall properties, supported also by the presence of thermal non-equilibrium.

On the Gas Heating Mechanism for the Fast Anode Arc Reattachment in a Non-transferred Arc Plasma Torch Operating with Nitrogen Gas in the Restrike Mode

“…The discharge current density varied in the range 1-5 A/cm 2 , whereas the reduced electric field was about 30-40 Td. These values are in according to those reported for atmospheric pressure glowlike discharges in molecular gases [20,26]. For E/N larger than about 40 Td (corresponding to E [ 0.8 9 10 5 V/m), no stationary solution was found; thus indicating that the arc reattachment is essentiality a threshold process.…”

Modelling of an Atmospheric–Pressure Air Glow Discharge Operating in High–Gas Temperature Regimes: The Role of the Associative Ionization Reactions Involving Excited Atoms

“…Several kinetic schemes have been proposed in the literature for modelling atmospheric pressure nonequilibrium air discharges, such as streamers [1,2], low-current arc and glow discharges at rest (or in low gas flows) [3][4][5][6], glow discharges in fast gas flows [7][8][9], and high-current pulsed discharges [10][11][12][13][14][15]. It is found that the ionization by electron impact of O 2 and N 2 molecules dominates at low-gas temperature (T g is below the range of 1000-2000 K [10,14,15]), while the electron-impact ionization of NO molecules is written as: e + NO → NO + + e, (R3) (1) where R refers to the reactions used in the model.…”

“…It is found that the ionization by electron impact of O 2 and N 2 molecules dominates at low-gas temperature (T g is below the range of 1000-2000 K [10,14,15]), while the electron-impact ionization of NO molecules is written as: e + NO → NO + + e, (R3) (1) where R refers to the reactions used in the model. This electron-impact ionization is favored by its low ionization energy of 9.27 eV and dominates at high gas temperatures [3,4,14,15]. At T g > 4500 K, the associative ionization in ground-state atomic collisions can be shown as:…”

“…The ionization rate is independent of the reduced electric field, because the densities of both O( 3 P) and N( 4 S) depend only on T g [3,4,10,13,15], which becomes the dominant ionization mechanism in air. This transition leads to a sharp drop in the reduced electric field [10].…”

“…As a result, more efficient channels for associative ionization may appear [16]. However, despite the great interest and importance of ionization processes in hot air discharges, the influence of the electronically excited states of reactants on associative ionization processes is yet unclear, as they are not routinely considered in air kinetic models [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. To answer this question, it is necessary to carry out more comprehensive investigations.…”