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The emission of multi-component waves by sources in non-uniform media of arbitrary spatial dimensions is discussed. If the emission occurs in the vicinity of a mode conversion region—i.e., a region where the local dispersion relations for two polarizations become nearly degenerate—the far field is very complex. The special case of plane-wave sources was analyzed in detail in [1] and it was shown that the qualitative nature of the far field is completely determined by the ray geometry of the un-coupled modes. The numerical simulations were conducted for a model problem involving two interacting 1-D wave modes excited in a non-stationary and non-homogeneous medium. The qualitative picture of emission agrees with the theoretical predictions.

An important feature of nonuniform media is the possibility of linear mode conversion due to the near-degeneracy of the dispersion relations of two wave modes in localized regions of the plasma. Wave emission from mode conversion regions has been a subject of a discussion in several recent publications (see, e.g. Swanson, Rev. Mod. Phys. 64, 837 (1995)). Here we present a new approach to this problem which is based on the ray tracing technique of Tracy et al., Phys. Plasmas 2, 4413 (1995), extended to mode conversion regions, as discussed in Friedland and Kaufman, Phys. Fluids 30, 3050 (1987). This extension allows one to connect the local wave field emitted by a source to rays outgoing from the conversion region. The analysis is performed for both positive- and negative-energy waves in arbitrary dimensions.