Partially constricted glow discharge in an argon-nitrogen mixture
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TEMPERATURE PLASMA
Partially Constricted Glow Discharge in an Argon–Nitrogen Mixture Yu. Z. Ionikha, A. V. Meshchanova, F. B. Petrova, N. A. Dyatkob, and A. P. Napartovichb aFock
Institute of Physics, St. Petersburg State University, Ul’yanovskaya ul. 1, Petrodvorets, St. Petersburg, 198904 Russia bTroitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 Russia Received March 14, 2008
Abstract—The characteristics of a glow discharge in Ar:N2 mixtures with a low content of nitrogen (0.02–1%) are studied experimentally. Most studies were performed at pressures higher than 10 Torr, at which the discharge constriction goes by a jump and the hysteresis effect is well pronounced. It is found that the time during which the discharge switches from the diffuse to the constricted mode (and back) can reach ~1 s. The transition between these modes begins with the development of a constriction at one end of the positive column. Then, the constricted part of the discharge extends toward the other end until it occupies the entire column. The reverse transition occurs in a similar way. By varying the parameters of the electric circuit during the transition, the constriction front can be stopped to form a steady-state partially constricted discharge. It is shown that this type of discharge corresponds to points lying inside the hysteresis loop of the conventional I–V characteristic measured without affecting the discharge during a transition. A comparative analysis of the discharge characteristics in Ar:N2 mixtures and in pure argon is performed. PACS numbers: 52.80.-s, 51.50.+v, 52.20.Fs, 52.20.Hv DOI: 10.1134/S1063780X08100085
1. INTRODUCTION The constriction of a glow discharge is the formation of one or several current channels. This manifests itself in the localization of the discharge glow in a volume that is much smaller than the volume of the discharge chamber. A sufficiently large increase in the gas pressure or/and the discharge current almost always leads to a transition of a diffuse glow discharge into the constricted mode. In some cases, this transition proceeds smoothly, i.e., the transverse size of the glowing plasma decreases gradually with increasing discharge current. However, more frequently, such a transition goes by a jump when the discharge current exceeds a certain critical value of Ic. The transition is accompanied by an abrupt increase in the current density and gas temperature in the discharge channel. Therefore, the constricted discharge can be considered as an intermediate state between a diffuse glow discharge and an arc [1]. Being a serious obstacle in creating large-volume plasmas, the constriction phenomenon has been actively studied in the past decades both experimentally and theoretically (see, e.g., reviews [2–4] and monographs [1, 5]). The discharge constriction can be regarded as a result of the onset of plasma instability against transverse perturbations of the electron density. Depending on the experimental conditions (first of all, on the sort of gas), instabilit
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