Dynamics of Langmuir Wave Spectra in Randomly Inhomogeneous Solar Wind Plasmas

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.

Automated summary

Research shows that Langmuir wave turbulence in solar coronal and wind plasmas is often scattered by density fluctuations, altering the properties of electromagnetic emissions radiated from the Sun to Earth. Anomalous diffusion processes govern the dynamics of Langmuir wave spectra, as a result of multiple scattering on density fluctuations, which is also observed in the momentum distributions of quasi-particles in fluctuating potential structures. These processes lead to fast broadening of spectra and distributions, with energy being transported to larger wavevectors and momenta, showing nonlinear time dependence and non-Gaussian tails in the asymptotic stage.