Efficiency of electromagnetic emission by electrostatic turbulence in solar plasmas with density inhomogeneities

A new method to calculate semi-analytically the radiation efficiency of electromagnetic waves emitted at specific frequencies by electrostatic wave turbulence in solar plasmas with random density fluctuations is presented. It is applied to the case of electromagnetic emissions radiated at the fundamental plasma frequency ω_p by beam-driven Langmuir wave turbulence during Type III solar bursts. It is supposed that the main radiation mechanism is the linear conversion of electrostatic to electromagnetic waves on the background plasma density fluctuations, at constant frequency. Due to the presence of such inhomogeneities, the rates of electromagnetic radiation are modified compared to the case of uniform plasmas. Results show that the radiation efficiency of Langmuir wave turbulence into electromagnetic emissions at ω_p is nearly constant asymptotically, the electromagnetic energy density growing linearly with time, and is proportional to the average level of density fluctuations. Comparisons with another analytical method developed by the authors and with space observations are satisfactory.