Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines
2011 (English)In: Physics of Plasmas, ISSN 1070-664X, Vol. 18, no 15, 052107-052114 p.Article in journal (Refereed) Published
Observations by, for instance, the EISCAT Svalbard Radar (ESR) demonstrate that the symmetry of the naturally occurring ion line in the polar ionosphere can be broken by an enhanced, nonthermal, level of fluctuations (naturally enhanced ion-acoustic lines, NEIALs). It was in many cases found that the entire ion spectrum can be distorted, also with the appearance of a third line, corresponding to a propagation velocity significantly slower than the ion acoustic sound speed. It has been argued that selective decay of beam excited primary Langmuir waves can explain some phenomena similar to those observed. We consider a related model, suggesting that a primary nonlinear process can be an oscillating two-stream instability, generating a forced low frequency mode that does not obey any ion sound dispersion relation. At later times, the decay of Langmuir waves can give rise also to enhanced asymmetric ion lines. The analysis is based on numerical results, where the initial Langmuir waves are excited by a cold dilute electron beam. By this numerical approach, we can detect fine details of the physical processes, in particular, demonstrate a strong space-time intermittency of the electron waves in agreement with observations. Our code solves the full Vlasov equation for electrons and ions, with the dynamics coupled through the electrostatic field derived from Poisson's equation. The analysis distinguishes the dynamics of the background and beam electrons. This distinction simplifies the analysis for the formulation of the weakly nonlinear analytical model for the oscillating two-stream instability. The results have general applications beyond their relevance for the ionospheric observations.
Place, publisher, year, edition, pages
2011. Vol. 18, no 15, 052107-052114 p.
plasma fluctuations, plasma instability, plasma Langmuir waves, plasma nonlinear waves, plasma oscillations, plasma simulation, plasma sources, plasma turbulence, Poisson equation, Vlasov equation; Nonlinear phenomena: waves, wave propagation, and other interactions, Fluctuation and chaos phenomena, Electrostatic waves and oscillations, Fokker-Planck and Vlasov equation, Plasma turbulence, Transport properties
Research subject Physics
IdentifiersURN: urn:nbn:se:umu:diva-50788DOI: 10.1063/1.3582084OAI: oai:DiVA.org:umu-50788DiVA: diva2:468839