Dark phase effect in the evolution of the positive column of a glow discharge in nitrogen
- PDF / 428,545 Bytes
- 16 Pages / 612 x 792 pts (letter) Page_size
- 55 Downloads / 210 Views
MA DIAGNOSTICS
Dark Phase Effect in the Evolution of the Positive Column of a Glow Discharge in Nitrogen N. A. Dyatkoa, Yu. Z. Ionikhb, A. V. Meshchanovb, A. P. Napartovicha, and A. I. Shishpanovb a
Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 Russia b St. Petersburg State University, Universitetskaya nab. 79, St. Petersburg, 199034 Russia Received October 21, 2010
Abstract—The characteristics of the initial stage of the formation of the positive column of a glow discharge in nitrogen at reduced pressures are studied experimentally and numerically. A dip in the plasma emission intensity in the initial stage of the discharge (the socalled “dark phase”) is observed experimentally at the positive polarity of the highvoltage electrode (the cathode is grounded). The dark phase is preceded by an ionization wave (IW). When the anode is grounded, neither an IW nor a dip in the discharge emission inten sity are observed. A theoretical model capable of describing the discharge development under the actual experimental conditions is constructed. It is shown that the dark phase effect may be caused by the high elec tron density (above the steadystate one) produced in the gas during the passage of the IW across the discharge gap. This mechanism of the dark phase formation differs from the mechanism proposed earlier to explain a similar effect in noble gases. Additional experiments carried out with pure argon, helium, and helium with a nitrogen admixture have shown that, in the case of a grounded cathode, gas breakdown is also accompanied by the passage of an IW, whereas in the case of a grounded anode, no IW is observed; however, the dark phase is present in both cases. It is shown using computer simulations that, in nitrogen (in contrast to noble gases), the mechanism resulting in the dark phase effect does not operate in the absence of an IW. DOI: 10.1134/S1063780X11050035
1. INTRODUCTION
ionization channels in discharges in noble gases is the process
The dark phase in the evolution of the positive col umn of a glow discharge was first observed in [1], where the initial stage of a glow discharge in helium with a small CO or nitrogen admixture was studied. In subsequent experiments [2–4], a similar effect was observed in pure helium, argon, and neon. The dark phase effect manifests itself as a dip in the plasma emission intensity, which occurs after a short bright radiation peak at the front of the discharge pulse and during which the intensities of all spectral lines and bands are nearly zero. Depending on the experimen tal conditions, the duration of the dark phase varies from several microseconds to several milliseconds. After this phase, the discharge luminosity usually undergoes several oscillations and then reaches a steadystate level. In order to observe this effect, it is necessary that the power supply voltage be sufficiently high. In this case, the discharge current is mainly determined by the ballast resistor (rather than the plasma resistance) and varies insignif
Data Loading...
