Acoustic wave interaction with plasma

Experiments have been conducted to find the variation of the velocity of an acoustic wave propagating through air plasma. It is found that the velocity of sound increases with increasing charged particle density in the plasma. Also it has been observed that as the frequency of the acoustic wave through the plasma increases, the perturbed variation in charged particle density and the electron-neutral atom elastic collision frequency remain constant as long as the frequency of the sound wave is less than the ionisation frequency of the plasma. However, for further increase in the wave frequency equal to, or greater than, the ionisation frequency of the plasma, the change in the number density reduces to a minimum value while the elastic collision frequency of the plasma increases. (author)