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On the periodicity of ion-acoustic waves in an inhomogeneous plasma

The existence of periodic ion-acoustic waves propagating through an inhomogeneous moving plasma is studied. For supersonic flow speeds it is shown that periodic excitations result in periodic responses independent of the nature of the media properties and the initial conditions. For subsonic flow speeds, periodic responses exist only under certain restrictions on the media and the initial conditions. However, most cases of physical interest are in the class of problems for which periodic or asymptotically periodic responses exist.