Influence of the Angular Distribution of Langmuir Waves on the Directivity of Radio Emission at Double Plasma Frequency

Abstract

The directivity of transverse electromagnetic waves generated in a plasma at a double plasma frequency during the coalescence of plasma waves is calculated for various angular distributions of these waves. It is shown that the directivity of the generated electromagnetic waves is determined by the angular distribution of the spectral energy density of the Langmuir waves and is practically independent of the turbulence spectrum. The case of axial symmetry of emitting area is considered. If the angular distribution of Langmuir waves is proportional to cosδ ϑ, where ϑ is the angle between the direction of the wave vector of the Langmuir wave and the axis of the symmetry of the emitting region, the maximum of the generated transverse waves corresponds to viewing angles of α = 30°–45°, where the viewing angle is the angle between the line of sight and the axis of the emitting-area symmetry. In this case, the ratio of the maximum intensity of the generated radiation to the minimum can reach 3. If the angular distribution of turbulence is proportional to sinδ ϑ, then the radio-emission maximum corresponds to viewing angles of α = 60°–120°. This anisotropy of the solar plasma radiation can be measured with radio observations, which will make it possible to draw a conclusion about the nature and source of Langmuir turbulence in the solar plasma.