Efficiency of Electromagnetic Emission by Electrostatic Turbulence in Solar Wind and Coronal Plasmas with Density Inhomogeneities

Abstract

We present a new method to semianalytically calculate the radiation efficiency of electromagnetic waves emitted at specific frequencies by electrostatic wave turbulence in solar wind and coronal plasmas with random density fluctuations. This method is applied to the case of electromagnetic emission 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. The radiation efficiency (emissivity) of such a process is larger than that obtained in the framework of models where the low frequency density fluctuations and the corresponding ion sound waves are not external but produced by the electrostatic wave turbulence itself through nonlinear wavewave interactions. Results show that the radiation efficiency of Langmuir wave turbulence into electromagnetic emissions at ω p is nearly constant asymptotically, with 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.

Second Harmonic Electromagnetic Wave Emissions from a Turbulent Plasma with Random Density Fluctuations

“…However, the correction provided by δn/n 0 turns out to be small and can be omitted, as one can verify by a simple estimation and as proven by the simulations presented below. Further, similarly to calculations performed for electromagnetic wave radiation at the fundamental plasma frequency ω p (Volokitin & Krafft 2020), we calculate the growth rate of the energy of electromagnetic waves generated by electric currents with a modulation frequency of 2ω p .…”

“…where the second right-hand side term is a particular solution of (4). Equation (7) can be solved analytically by using the method provided by the authors in a previous work (Volokitin & Krafft 2020), as shown below.…”

“…Indeed, we take into account the significant modifications of Langmuir spectra due to the waves' transformations on the density fluctuations, which strongly influence the harmonic electromagnetic radiation. Moreover, the model provides a first-order differential equation that can be integrated numerically with a method developed by the authors (Volokitin & Krafft 2020), enabling for the first time to obtain the radiation rate (emissivity) of the harmonic electromagnetic waves in a randomly inhomogeneous plasma, as well as its dependence as a function of the average level of density fluctuations, the electron plasma temperature, and the Langmuir waves' and density fluctuations' spectra. Finally, this work allows for generalization of the scaling laws provided by the weak and strong turbulence theories, developed for homogeneous plasmas, and it extends their applicability to new situations.…”

Particle-in-cell simulations of the plasma emission in type III solar radio bursts

“…黑色虚线代表二次谐波的色散关系, 即 n = 2 时高次 谐波的理论色散关系 [36] : [37] , 其中的非线性耦合效应可显著增强静电波 向电磁波的转化效率 [38][39][40] . [41] .…”

Numerical simulations of a continuously injected relativistic electron beam relaxation into a plasma with large-scale density gradients

“…Different density gradients are considered in Kontar [21,22], and Kontar and Pécseli [23]. Kraft and Volokitin [24][25][26][27][28][29] actively study influence of random plasma density inhomogeneities on plasma oscillations and solar radio bursts generation in Hamiltonian approach whereby the dynamics of the background plasma particles, Langmuir and ion-acoustic wave fields are described by the Zakharov equations. Main prediction of quasilinear theory and hamilton model are confirmed by particle-in-cell (PIC) simulations [30].…”