Experimental data obtained on audio frequency (100–10000 Hz) discharge in argon at four pressures 50, 60, 70, and 80 mTorr are presented. The data show significant changes of the discharge current waveform with frequency. These changes seem to be associated with the glow discharge profile and colour. An empirical model based on the assumption of a frequency-dependent breakdown voltage is used to describe the experimental data.

To add more details about the effect of the axial magnetic field on the plasma profile, the breakdown voltage of air was investigated at low pressure (9-15 Pa) in the presence of axial magnetic field (0.01-0.04T). The air was ignited by a DC voltage between two plain electrodes of aluminum separated by a distance (8.5cm). The measurements showed that the discharge voltage decreases to a minimum value, then returns to increase over the minimum with increasing the magnetic field strength, at all pressures in the range. It was also observed that a maximum decrease in the discharge voltage is obtained near the minimum of  Paschen curve from the right side. The decrease in the discharge voltage was caused mainly by the effect of magnetic flux density on the diffusion of charged particles to the walls, especially on that of free electrons which were borne during the breakdown process.

In the present study experimental measurements have been carried out to investigate the variation of air discharge voltage (V) and current (I) as a function of working pressure (p), in the ranges (300-500 V), (2-15 mA) and (0.09-0.13 Torr) respectively. Two thick, flat and circular electrodes of radius  (4 cm) of Aluminum with a Pyrex cylinder tube of length (10 cm) and radius  (3.5 cm) were used to generate the air glow discharge modes. The (V-p) characteristics have shown that an increasing in the discharge voltage of normal mode and reduction in that of abnormal mode with increasing the working pressure. It also displayed that the range of upper voltage from breakdown to abnormal glow has a minimum value (15.7 V) at  (0.117 Torr). In addition to that, it is found that  the (I-V) characteristics of air glow discharge modes  are consistent with those reported in the literature for other gases, as argon, hydrogen and oxygen. It is expected that these observations can help to reduce the voltage needed to get an intense abnormal glow discharge in the air, and to understand well the behavior of two modes of glow discharge, that is important in various applications.   http://dx.doi.org/10.25130/tjps.24.2019.090

An experimental investigation of the variation of argon discharge current with a glow and afterglow time intervals of a square discharge voltage was carried out at low pressure (6-11 mbar). The discharge was created between two circular metal electrodes of diameter (7.5 cm), separated horizontally by a distance (10 cm) at the two ends of a Pyrex cylindrical tube. A composite of two Gaussian functions has been suggested to fit and explain the variation graphs clearly. It is shown that the necessary times of glow and afterglow needed to attain a maximum discharge current are (70 us) and (60 us), respectively. The discharge current is observed to drop to the lowest value when the two times are serially longer than (85 us) and (72 us). Furthermore, the difference between the two times required to obtain a maximum rate of change in the discharge current, or a maximum discharge current, is deduced to be comparable to the breakdown time delay of gases reported in the literature. These observations can be useful for the design of plasma devices requiring specialized engineering.

The incomplete response of a nonlinear oscillatory system to a periodically driving force called periodic pulling oscillation. In the present study, this phenomenon is observed in the discharge current of airglow discharge that generated at low pressure (55-85 mTorr) by a periodically driving force (a sinusoidal voltage) of the period (3.33 mSec). The glow discharge is created between two plan electrodes of Aluminum, sited parallel inside a Pyrex cylindrical tube at the distance (9.5 cm). It has been observed that the periodic pulling waveform and amplitude changed with the discharge pressure and voltage. A maximum periodic pulling is obtained at a moderate discharges voltage and pressure, namely at normal glow discharge voltage and pressure that coincides with the pressure of the Paschen curve minimum. Furthermore, it is observed that the periodic pulling oscillation is weak and disappear at a higher discharge voltage and /or discharge pressure within the range.