Partial constriction in a glow discharge in argon with nitrogen admixture

Abstract

The constriction of the positive column of a glow discharge in argon with nitrogen admixture (0.02-1%) was studied. The discharge was maintained in a tube of 2.8 cm inner diameter and 75 cm length at intermediate pressures (several tens of Torrs), at which the discharge constriction goes by a jump and the hysteresis effect is well pronounced. It was observed that the constriction begins near one of the electrodes and then the constricted region boundary propagates toward the other electrode. The reverse transition occurs in a similar way. The transition time in Ar : N 2 mixtures appears to be essentially longer (up to 1 s) than that in pure argon. By varying the power supply voltage in the course of the transition, the boundary between the diffuse and constricted forms of the discharge could be stopped at some position between the electrodes. Such a partially constricted discharge (PCD) is stable and can exist for a long time. A PCD at various locations of the boundary can be formed, different locations being realized at different discharge voltages but at the same discharge current. This corresponds to a vertical segment in the voltage-current characteristic curve. It was found that this segment lies inside the hysteresis loop and connects two branches of the conventional I -V characteristic measured without affecting the discharge during the diffuse-to-constricted or reverse transitions. Plasma parameters in the diffuse and constricted positive columns are estimated and ionization mechanisms are analyzed. The possible reasons for the low velocity of the constriction front in Ar : N 2 mixtures and the mechanisms of the stabilization of the PCD are also discussed.

Dynamic contraction of the positive column of a self-sustained glow discharge in air flow

“…Presently, 1D models of current contraction in a tube are well developed. They take into account the kinetics of electrons, ions, and metastable particles, and provide reasonable agreement with the experiments [4][5][6][7][8].…”

“…Presently, 1D models of current contraction in a tube are well developed. They take into account the kinetics of electrons, ions, and metastable particles, and provide reasonable agreement with the experiments [4][5][6][7][8].There are a number of experiments stimulated by the development of powerful gas-discharge lasers and plasma-chemical reactors (see review [9]) where the current contraction phenomenon was observed when the discharge power exceeds a certain threshold level. However, this phenomenon in a plane duct in the presence of the gas flow is not well understood.…”

Influence of Nitrogen Admixture on Plasma Characteristics in a dc Argon Glow Discharge and in Afterglow

“…It was observed that at intermediate pressures a small additive of nitrogen to argon resulted in a noticeable decrease in the discharge voltage of a diffuse dc discharge. This effect was discovered in experiments with partially constricted discharges in Ar:N 2 mixtures [15,16,34]. Figure 2 shows current-voltage characteristics measured in pure argon and in Ar + 0.75%N 2 and Ar + 1%N 2 gas mixtures at gas pressure P = 40 Torr (R = 1.4 cm, interelectrode distance ≈ 75 cm).…”

“…At the same time, VACs in the constricted region go approximately along the same curve. As is shown in [16], it can be explained by the fact that, due to a very high electron density in a constricted discharge, N2 addition has very little influence on ionization mechanism which in Ar and Ar-N2 cases is mainly stepwise ionization of Ar metastables.…”

“…Over the past decades, many experimental and theoretical works have been carried out in which the effect of nitrogen admixture on the characteristics of an electric discharge in argon has been investigated. Various types of discharges have been studied: microwave [1][2][3], RF (magnetron, inductive, and capacitive) [4][5][6][7][8][9], surface [10], barrier [11][12][13], dc [14][15][16][17][18][19][20][21][22][23][24], and pulse-periodic [25][26][27] discharges. It is shown that nitrogen impurity can significantly change the electrical and spectral characteristics of the discharge, the plasma ion composition, and the population of argon energy levels.…”