Some Experimental Results on Acoustic Wave Propagation in a Plasma

Three aspects of the theory of propagation of sound in a plasma are experimentally confirmed. It is shown: (1) That the source term for the generation of sound in the neutral gas is proportional to the time derivative of the power input to the electrons from an externally applied electric field, (2) that at low frequencies the electronic and neutral fluid components move together approximately in phase when an acoustic wave propagates through the plasma, and (3) that the resonance curve of an acoustic cavity is sharpened by the presence of plasma; the latter effect is attributed to the collisional transfer of energy from the electrons to the neutrals.