In this paper we suggest a simple technique for validating the Goldstein-Wehner law for a stratified positive column of dc glow discharge while studying the properties of gas discharges in an undergraduate laboratory. To accomplish this a simple device with a pre-vacuum mechanical pump, dc source and gas pressure gauge is required. Experiments may be performed in nitrogen or even in air. First you need to photograph the discharge tube with striations at different gas pressure values and then you need to determine the thickness of the first striation on a computer monitor.

This paper studies the normal and abnormal regimes of a weak-current rf discharge in ammonia, nitrogen, hydrogen and N 2 O for the rf electric field frequencies of 13.56 and 27.12 MHz. We reveal that only the abnormal regime of burning is observed at low pressures when the current growth is accompanied by an rf voltage increase while the surface of the electrodes is completely covered with the discharge. The normal regime occurs at higher gas pressures when the current growth is due to the increase in the surface area occupied by the discharge on the electrodes. The discharge burns in the abnormal mode after the surface of the electrodes is completely covered with the discharge. We demonstrate that the normal current density is directly proportional to the gas pressure and it depends approximately on the square of the rf electric field frequency. We present an analytical model for two limiting cases: constant free path length and constant mobility of positive ions furnishing a satisfactory description of the experimental data.

It is established which of the Child-Langmuir collision law versions are most appropriate for describing the processes in the cathode sheath in the N 2 O. At low pressure (up to 0.3 Torr), the Child-Langmuir law version relating to the constant ion mobility holds. At N 2 O pressure values starting from 0.75 Torr and above, one has to employ the law version for which it is assumed that the ion mean free path within the cathode sheath is constant. In the intermediate pressure range (between 0.3 and 0.75 Torr), neither of the Child-Langmuir law versions gives a correct description of the cathode sheath of the glow discharge in the N 2 O.

We studied the positive column of the dc discharge through analytical modeling. We considered the ambipolar regime when the balance of charged particles is determined only by direct ionization of molecules by electrons and ambipolar escape of them to the discharge chamber walls. The approximation chosen permitted us to solve the balance equation and to obtain simple formulas for the reduced electric field. Our calculation data for the positive column in hydrogen agree well with experimental and theoretical data of other authors.