Excitation and Damping of Continuous Pseudo Acoustic and Ion Waves in a Plasma

The continuous sinusoidal pseudo waves excited by a grid are studied experimentally and theoretically. For the small exciting voltage the received signal contains an ion wave. For the large exciting voltage the signal of the pseudo wave is dominant. The velocity of the pseudo wave is given by α(2 e V p–p / M ) 1/2 empirically. The reduction factor α is explained by the transit time effect which occurs when the ions are accelerated by an alternating electric field in the sheath surrounding the exciting grid. It is shown that pseudo waves may be excited even if the damping ratio δ/λ is larger than the value given by Hirshfield and Jacob. The effect of the ion-atom collision and the electric current for waves are studied. In this experiment the plasma is generated by the funnel-typed source which is the differentially pumped one for producing a quiescent plasma and is able to control the various plasma parameters.