EXCITATION OF COUPLED ELECTRO–ACOUSTICAL WAVES BY A RING SOURCE IN A COMPRESSIBLE PLASMA CYLINDER

Propagation of coupled electromagnetic and plasma waves (acoustical) excited by a magnetic ring current in an infinitely long compressible plasma cylinder surrounded by vacuum is studied. It is known that in an incompressible plasma a slow surface wave can propagate only when the electron–plasma frequency, ωP, is higher than the frequency, ω, of the source. However, in the present problem it is shown that under suitable conditions slow surface waves can propagate along the interface of the compressible plasma column and vacuum for values in the range either ωP > ω or ωP < ω. The surface waves for which ωp < ω are supposed to be a new phenomenon. Numerical results for these surface waves have been presented. In addition, an expression for a radiated field is obtained by the usual saddle-point method of integration. The possibility of the existence of leaky waves is also discussed for a special case.