Bound Waves in Compressible Plasma Gaps†

It is shown that a planar gap in a plasma medium is an appropriate idealized model for studying electromagnetic and plasma waves in a variety of situations, including plasma sheaths and ionospheric layers. A uniform, isotropic, lossless, warm plasma gap is investigated and is found to support both surface and interface waves which consist of an electromagnetic mode coupled to a plasma pressure mode. The surface waves are fast and they occur primarily at frequencies below the plasma frequency, whereas the interface waves are slow and are present at all frequencies ; in both cases, the waves may be either of the forward- or backward-travelling variety. In addition, the presence of leaky waves of the spectral type is demonstrated at frequencies above the plasma frequency. Dispersion curves are calculated for o large range of the parameters involved and the results are compared to those for surface waves along a dielectric slab which, in certain respects, represents a configuration analogous to the plasma gap if pressure effects are neglected.