Acoustic Wave Propagation in a Gas Discharge

Abstract

When ordinary sound propagates in a weakly ionized gas, the wave motion of neutral particles controls that of charge carriers. The ion-density, electric-field, and electron-temperature responses to a given gas-density perturbation are calculated by means of linearized hydrodynamic equations for the case of wave propagation along the axis of a discharge. The equations include ionizing collisions, ambipolar diffusion, wall recombination, and collisions leading to intercomponent momentum and energy transfer. Because of competing effects of ions and electrons, no observable wave amplification can result from intercomponent momentum transfer. In addition to previously reported consequences of elastic collisions, the calculated dispersion relation contains an amplification term characterized by a time constant τν which is approximately the reciprocal ionization frequency (per electron) times the gas-to-plasma pressure ratio.

Acoustic Instability in Inhomogeneous Gas-Discharge Plasma

“…The presence of a sound wave in weakly ionized plasma affects the behavior of electrons and ions; this, in turn, causes the dispersion equation to vary somewhat and, thereby, affects the sound wave propagation. According to Ingard et al [1][2][3][4][5], the inclusion of, for example, the transfer of energy from electrons to colder neutrals may bring about an amplification of sound waves (acoustic instability). The theoretical prediction of the development of acoustic instability [1][2][3][4][5] in weakly ionized plasma was supported by numerous experimental investigations [6][7][8][9][10] in which the amplification of sound waves was observed in ordinary laboratory dc glowdischarge plasma at a gas pressure higher than 1 torr.…”

“…According to Ingard et al [1][2][3][4][5], the inclusion of, for example, the transfer of energy from electrons to colder neutrals may bring about an amplification of sound waves (acoustic instability). The theoretical prediction of the development of acoustic instability [1][2][3][4][5] in weakly ionized plasma was supported by numerous experimental investigations [6][7][8][9][10] in which the amplification of sound waves was observed in ordinary laboratory dc glowdischarge plasma at a gas pressure higher than 1 torr. Note, however, that the experimental results in the amplification of sound in gas-discharge plasma cannot be explained using the theory of Ingard et al Indeed, one can readily check that the criterion of sound amplification obtained, for example, in [2] is not valid for the values of parameters of plasma and frequency of sound waves that correspond to the experimental investigations in which the amplification of sound waves was observed.…”

“…It is known that acoustic waves in weakly ionized plasma represent a distorted form of ordinary sound waves in neutral gas and, under certain conditions, may become unstable [1][2][3][4][5]. The presence of a sound wave in weakly ionized plasma affects the behavior of electrons and ions; this, in turn, causes the dispersion equation to vary somewhat and, thereby, affects the sound wave propagation.…”

Propagation characteristics of audible noise generated by single corona source under positive DC voltage

“…(11) and can be expressed as S 0 = P 0 e −ikr 1 e −0.1151γr 1 4πr 1 (12) where P 0 is the frequency domain result of sound pressure at the known position. Once the sound source strength is known, the sound pressure at arbitrary positions can be calculated by Eq.…”

“…Then, in 1967 and 1969 Ingard presented the results of wave modes in weakly ionized and acoustic wave propagation in a gas discharge respectively. 11,12 In 1969 and 1972, Fitaire and Mantei published three papers to investigate the sound waves generation, amplification and propagation in a weakly ionized gas. 13,14 Their results showed contributions of electrons and applied electric field on the generation of sound source.…”