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

2020 ◽  
Author(s):  
Catherine Krafft ◽  
Alexander Volokitin
Keyword(s):  
Electromagnetic Waves ◽  
Langmuir Wave ◽  
Density Fluctuations ◽  
Radiation Efficiency ◽  
Wave Turbulence ◽  
Radiation Mechanism ◽  
Constant Frequency ◽  
Electrostatic Wave ◽  
Electromagnetic Emissions ◽  
Solar Plasmas

<p>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<sub>p</sub> 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<sub>p</sub> 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.</p>

Dynamics of Langmuir Wave Spectra in Randomly Inhomogeneous Solar Wind Plasmas

2021 ◽  
Vol 923 (1) ◽  
pp. 103
Author(s):  
C. Krafft ◽  
A. S. Volokitin
Keyword(s):  
Diffusion Processes ◽  
Langmuir Wave ◽  
Density Fluctuations ◽  
Wave Turbulence ◽  
Quasi Particle ◽  
Potential Fluctuations ◽  
The Earth ◽  
Self Consistent ◽  
Electromagnetic Emissions ◽  
Non Gaussian

Abstract Solar coronal and wind plasmas often contain density fluctuations of various scales and amplitudes. The scattering of Langmuir wave turbulence on these inhomogeneities modifies the properties of the radiated electromagnetic emissions traveling from the Sun to the Earth. This paper shows the similarities between the physical results obtained by (i) a model based on the Zakharov equations, describing the self-consistent dynamics of Langmuir wave turbulence spectra in a plasma with external density fluctuations, and (ii) a modeling, within the framework of geometric optics approximation, of quasi-particles (representing plasmon quanta) moving in a fluctuating potential. It is shown that the dynamics of the Langmuir spectra is governed by anomalous diffusion processes, as a result of multiple scattering of waves on the density fluctuations; the same dynamics are observed in the momenta distributions of quasi-particles moving in potential structures with random inhomogeneities. These spectra and distributions are both characterized by a fast broadening during which energy is transported to larger wavevectors and momenta, exhibiting nonlinear time dependence of the average squares of wavevectors and quasi-particle momenta as well as non-Gaussian tails in the asymptotic stage. The corresponding diffusion coefficients depend on the time and are proportional to the square of the average level of density (or potential) fluctuations. It appears that anomalous transport and superdiffusion phenomena are responsible for the spectral broadening.

scholarly journals Fundamental Electromagnetic Emissions by a Weak Electron Beam in Solar Wind Plasmas with Density Fluctuations

2022 ◽  
Vol 924 (2) ◽  
pp. L24
Author(s):  
C. Krafft ◽  
P. Savoini
Keyword(s):  
Electron Beam ◽  
Electromagnetic Radiation ◽  
Inhomogeneous Plasma ◽  
Langmuir Wave ◽  
Density Fluctuations ◽  
Electromagnetic Energy ◽  
Langmuir Waves ◽  
Harmonic Emission ◽  
Electromagnetic Emissions ◽  
Weak Electron

Abstract The generation of Langmuir wave turbulence by a weak electron beam in a randomly inhomogeneous plasma and its subsequent electromagnetic radiation are studied owing to two-dimensional particle-in-cell simulations in conditions relevant to type III solar radio bursts. The essential impact of random density fluctuations of average levels of a few percents of the background plasma on the characteristics of the electromagnetic radiation at the fundamental plasma frequency ω p is shown. Not only wave nonlinear interactions but also processes of Langmuir waves’ transformations on the density fluctuations contribute to the generation of such emissions. During the beam relaxation, the amount of electromagnetic energy radiated at ω p in a plasma with density fluctuations strongly exceeds that observed when the plasma is homogeneous. The fraction of Langmuir wave energy involved in the generation of electromagnetic emissions at ω p saturates around 10−4, i.e., one order of magnitude above that reached when the plasma is uniform. Moreover, whereas harmonic emission at 2ω p dominates over fundamental emission during the time evolution in a homogeneous plasma, fundamental emission is strongly dominant when the plasma contains density fluctuations, at least during several thousands of plasma periods before being overcome by harmonic emission when the total electromagnetic energy begins to saturate.

scholarly journals Turbulence and Microprocesses in Inhomogeneous Solar Wind Plasmas

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 69 ◽  
Author(s):  
Catherine Krafft ◽  
Alexander S. Volokitin ◽  
Gaëtan Gauthier
Keyword(s):  
Solar Wind ◽  
Energetic Electron ◽  
Langmuir Wave ◽  
Solar Wind Plasma ◽  
Density Fluctuations ◽  
Wave Radiation ◽  
Wave Turbulence ◽  
Small Scale ◽  
The Impact ◽  
The Waves

The random density fluctuations observed in the solar wind plasma crucially influence on the Langmuir wave turbulence generated by energetic electron beams ejected during solar bursts. Those are powerful phenomena consisting of a chain of successive processes leading ultimately to strong electromagnetic emissions. The small-scale processes governing the interactions between the waves, the beams and the inhomogeneous plasmas need to be studied to explain such macroscopic phenomena. Moreover, the complexity induced by the plasma irregularities requires to find new approaches and modelling. Therefore theoretical and numerical tools were built to describe the Langmuir wave turbulence and the beam’s dynamics in inhomogeneous plasmas, in the form of a self-consistent Hamiltonian model including a fluid description for the plasma and a kinetic approach for the beam. On this basis, numerical simulations were performed in order to shed light on the impact of the density fluctuations on the beam dynamics, the electromagnetic wave radiation, the generation of Langmuir wave turbulence, the waves’ coupling and decay phenomena involving Langmuir and low frequency waves, the acceleration of beam electrons, their diffusion mechanisms, the modulation of the Langmuir waveforms and the statistical properties of the radiated fields’ distributions. The paper presents the main results obtained in the form of a review.

Scattering of ordinary‐mode electromagnetic waves by density fluctuations in tokamaks

1993 ◽  
Vol 5 (12) ◽  
pp. 4299-4311 ◽  
Author(s):  
Gary R. Smith ◽  
Daniel R. Cook ◽  
Allan N. Kaufman ◽  
Arnold H. Kritz ◽  
Steven W. McDonald
Keyword(s):  
Electromagnetic Waves ◽  
Density Fluctuations ◽  
Ordinary Mode

Scattering of electromagnetic waves by anomalous fluctuations of a magnetized plasma

1990 ◽  
Vol 43 (2) ◽  
pp. 165-172 ◽  
Author(s):  
V. N. Pavlenko ◽  
V. G. Panchenko
Keyword(s):  
Cross Section ◽  
Electromagnetic Waves ◽  
Pump Wave ◽  
Density Fluctuations ◽  
Scattering Cross Section ◽  
Magnetized Plasma ◽  
Lower Hybrid ◽  
Scattering Cross ◽  
Parametric Decay ◽  
Ion Acoustic

Fluctuations and scattering of transverse electromagnetic waves by density fluctuations in a magnetized plasma in the presence of parametric decay of the pump wave are investigated. The spectral density of electron-density fluctuations is calculated. It is shown that the differential scattering cross-section has sharp maxima at the ion-acoustic and lower-hybrid frequencies when parametric decay of the lower-hybrid pump wave occurs. We note that scattering at the ion-acoustic frequency is dominant. When the pump-wave amplitude tends to the threshold strength of the electric field the scattering cross-section increases anomalously, i.e. there is critical opalescence.

scholarly journals Experimental signatures of localization in Langmuir wave turbulence

1991 ◽  
Vol 52 (1) ◽  
pp. 116-128 ◽  
Author(s):  
Harvey A. Rose ◽  
D.F. DuBois ◽  
David Russell ◽  
B. Bezzerides
Keyword(s):  
Langmuir Wave ◽  
Wave Turbulence
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