Electromagnetic surface waves supported by a half-space of a counterstreaming plasma

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi-infinite region of free space from another semi-infinite region consisting of a plasma counterstreaming parallel to the interface are investigated for the case in which the wave is progressing parallel to the direction of the streams. The behaviour of the surface waves is quite different from the case in which the plasma is stationary. The surface waves exist for all frequencies. The phase velocity of the surface wave is equal to the electromagnetic wave velocity in free space for very low frequencies, decreases monotonically as the frequency is increased and asymptotically approaches the velocity of the stream for very high frequencies. The surface waves are always stable. In contrast to on unbounded counterstreaming plasma which gives rise to instability for the plane longitudinal wave progressing parallel to the streams, a half-space of counterstreaming plasma does not give rise to any instabilities for waves progressing parallel to the streams.