ISSN 1063-7842, Technical Physics, 2011, Vol. 56, No. 1, pp. 55–60. © Pleiades Publishing, Ltd., 2011. Original Russian Text © E.A. Bogdanov, A.A. Kudryavtsev, A.S. Chirtsov, 2011, published in Zhurnal Tekhnicheskoі Fiziki, 2011, Vol. 81, No. 1, pp. 59–64. 55 Scientific and applied interest in the high-pressure glow discharge is largely due to the fact that it does not need expensive and bulky vacuum equipment. As a result, facilities using this type of discharge are much cheaper and easier to operate. In experiments, high-pressure discharges are maintained only if their size is small. Reasons are the following. It is known (see, e.g., [1]) that optimal con- ditions for glow discharge initiation and maintenance are near a minimum in the Paschen curve (Stoletov point), where pL = 0.5–5.0 cm Torr (p is the gas pres- sure and L is the interelectrode gap). Therefore, when the pressure is low (p ~ 1 Torr), the size of the dis- charge region is typically equal to several centimeters or more, while at a high pressure (p = 100–760 Torr), the discharge region shrinks to several millimeters or even micrometers. Such microdischarges (see, e.g., [2, 3]) are characterized by an elevated energy deposit, all other things being the same. Since heat removal conditions grow worse at a high pressure, the gas is heated more strongly than in low-pressure discharges [1–3]. That the gas temperature in high-pressure dis- charges (in which charges are lost in volume processes rather than at walls or electrodes) rises is well known and well studied for extended discharges with a posi- tive column (see, e.g., [1, 4]). It has been found in many experiments that developing thermal instabili- ties lead, in this case, to a descending voltage–current characteristic of the column and, consequently, make the discharge unstable. 1 1 In practice, extended high-pressure discharges (that is, those having a positive column) can be initiated only using special means, such as gas pumping, pulsed power supply, etc. Therefore, stable high-pressure discharges with an ascending voltage–current characteristic, which are used in practice, usually have a length such that pL < 10–20 cm Torr, in which case a distinct positive col- umn is absent [2, 3]. When the length of such dis- charges (microdischarges) exceeds the size of the cathode region consisting of a cathode sheath, nega- tive glow, and Faraday dark space, one can speak of the transition positive column region, in which the elec- tric field is distributed nonuniformly. Unfortunately, despite much practical interest in the microdischarge because of its stability, the effect of gas heating on its characteristics has been poorly understood. In this work, we carried out 1D simulations of the microdischarge in argon at p = 300 Torr and two inter- electrode gap widths, L = 0.100 and 0.333 mm. It is shown that, as a result of heating the gas and a decrease in its density, the discharge takes the form of the obstructed discharge (in other words, as the current rises and heats up the gas, the discharge initiated in the right-hand branch of the Paschen curve passes to its left-hand branch, i.e., takes another form of the volt- age–current characteristic). Under such conditions, the voltage–current characteristics of the discharge behave paradoxically: as the voltage grows, the current not only remains the same but may even decrease. When simulating, we used a version of the com- bined model used earlier in 1D and 2D simulations of gas discharges [5–8]. For heavy particles, the continu- ity equations using the diffusion–drift approximation of charge transfer are solved with allowance for charge loss and generation in the volume. In the plasma- chemical model of argon, we took into consideration three effective excited atomic levels, two excimer lev- Transition to the Obstructed Discharge and a Sharp Change in the Voltage–Current Characteristic as a Result of Gas Heating in a Short (Positive-Column-Free) High-Pressure Glow Discharge E. A. Bogdanov, A. A. Kudryavtsev*, and A. S. Chirtsov St. Petersburg State University, Universitetskii pr. 28, Staryi Peterhof, St. Petersburg, 198504 Russia *e-mail: akud@ak2138.spb.edu Received April 13, 2010 Abstract—The formation of a high-pressure glow discharge is studied under conditions when the discharge evolves from the normal glow to the abnormal glow. It is shown that the transition to the voltage–current characteristic of the obstructed discharge may take place as a result of heating the gas and a decrease in its density. The obstructed discharge follows the left-hand branch of the Paschen curve and features a sharp volt- age rise and current density limitation. DOI: 10.1134/S1063784211010051 GAS DISCHARGES, PLASMA