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Propagation of sound in a medium where the rate of local heat addition is a function of gas density is analysed theoretically and the results are applied for modelling the experimentally observed effect of amplification of acoustic waves by an extended glow discharge in air. The model adequately describes the experimental dependences of the gain on the wave frequency and discharge power density and predicts that the amplification of sound by an unconfined glow discharge in air increases with discharge current density but does not change noticeably with gas pressure when the current density is kept constant. Quantitative estimates indicate that a gain of as high as 1 m−1 (or 9 dB for a 60 dB wave passing through 1 m of plasma) could be realized using a discharge in air with a current density of 100 mA cm−2.

The evolution of a vortex in glow discharge plasma is studied analytically. Specifically, the mechanism of local energy deposition into the flow by the plasma is considered and its effect on the structure of an inviscid vortex is analyzed. The vortex is modeled by a set of Euler’s equations while the energy transferred by the plasma into the gas is represented by Rayleigh mechanism. In this mechanism, the amount of heat addition is a function of local gas density. The analysis indicates that the plasma can have a considerable effect on the structure of a vortex. The inviscid calculations show that in a uniform discharge, a 1 cm vortex dies out in a fraction of a second.

A phenomenological analysis is carried out to investigate the propagation of sound wave in the positive column of a glow discharge plasma. Specifically, the effect of local energy transfer from the discharge into the gas is studied. The analysis shows that the density fluctuations cause variations in the energy transfer rate. This effect is found to be a function of the plasma parameters and acoustic wave frequency thus leading to acoustic dispersion. The conclusion confirms earlier mathematical treatment of the problem [Kolosov et al., AIAA Paper No. 99-4882, 1999] and provides a physical explanation of the phenomenon.

An analysis is carried out to determine radial temperature distributions in the cylindrical positive column of a glow discharge formed in air in free space without confining walls. The analysis considers discharge with current densities lower than 100 mA/cm2 and at gas pressures of several tens of Torr. The plasma is represented by a set of hydrodynamic equations that include the balances for electron number density, translational energy, and the vibrational energy. The equations are solved using an iterative method to obtain gas temperatures for a range of plasma conditions. The results show that increasing discharge current densities lead to higher gas temperatures on plasma axis, however, unlike in the case with glow discharge restricted by dielectric walls, increased current densities also lead to wider radial profiles of temperature. Increased gas pressure, while leading to higher on-axis gas temperatures, results in narrower temperature profiles, mainly due to the reduced diffusion rates and vibrational-translational energy relaxation times. At low gas pressures and current densities, the electron density profiles are found to be significantly narrower than those for temperature while at higher values of these parameters, the width of the two are comparable. The characteristic radius of the predicted gas temperature distribution is in a good agreement with recent experimental findings.