On the Efficiency of the Linear-mode Conversion for Generation of Solar Type III Radio Bursts

Abstract : Type III solar radio bursts are generated by streams of energetic electrons accelerated at the Sun during periods of solar activity. The generation occurs in two steps. Initially, electron beams generate electrostatic Langmuir waves and then these waves are transformed into electromagnetic emissions. Recent studies showed that the level of density fluctuations in the solar wind and in the solar corona is so high that it may significantly affect beam-plasma interaction. Here, we show that the presence of intense density fluctuations not only crucially influences the process of beam-plasma interaction, but also changes the mechanism of energy transfer from electrostatic waves into electromagnetic. Reflection of the Langmuir waves from the density inhomogeneities may result in partial transformation of the energy of electrostatic waves into electromagnetic around plasma frequency. We show that the linear wave energy transformation for the level of fluctuations of the order of 1% or higher is efficient enough to produce radio bursts with a brightness temperature of 10(14)-10(15) K.