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.

This paper extends the recently reported one-dimensional model for sound propagation in glow discharge plasma to arbitrary mutual orientation of the plasma electric field and acoustic wave vectors. The results demonstrate that an acoustic wave in plasma may amplify, attenuate, or remain unchanged depending on the angle between these vectors and on the power input into the discharge. Quantitative evaluations indicate that for glow discharge plasma of a self-sustained discharge in air at the electric current densities of the order of 100 mA cm−2, a gain of as much as 1 m−1 at 0° angle between the vectors changes to similar strength attenuation for the 90° angle.

No abstract

The dispersion effects appearing during the propagation of acoustic waves through the plasma of a weakly ionized gas are studied. The main theoretical results are based on the equation of propagation of sound in the medium with the so called Rayleigh energy release mechanism, which has been obtained earlier.Unlike the previous investigations, the problem of propagation of a perturbation from a source and not the problem of propagation of the initial perturbation is solved. In particular, the sources of an N shaped shock wave and a wave in the form of a symmetrical step are analyzed in detail. It is shown that depending on the direction of wave propagation (along or across the electric field in a plasma), it degenerates either into a wave packet with a wave frequency lower than a certain frequency characterizing heating, or into a wave packet with a frequency higher than this value. In addition, a quantitative criterion is obtained, which makes it pos sible to estimate the plasma parameters for which it will be possible to observe the dispersion of acoustic waves in the plasma.

No abstract