Nonlinear beam generated plasma waves as a source for enhanced plasma and ion acoustic lines
- University of Michigan, Space Research Building, 2455 Hayward Street, Ann Arbor, Michigan 48109-2143 (United States)
- Department of Physics, University of Oslo, Box 1048 Blindern, N-0316 Oslo (Norway)
- Institute of Theoretical Astrophysics, University of Oslo, Box 1029 Blindern, N-0315 Oslo (Norway)
- Norwegian Water Resources and Energy Directorate, Drammensveien 211, Postboks 5091 Majorstua, N-0301 Oslo (Norway)
- Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
- Department of Physics, Linkoeping University, SE-58183 Linkoeping (Sweden)
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.
- OSTI ID:
- 21537789
- Journal Information:
- Physics of Plasmas, Vol. 18, Issue 5; Other Information: DOI: 10.1063/1.3582084; (c) 2011 American Institute of Physics; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BOLTZMANN-VLASOV EQUATION
ELECTRON BEAMS
FLUCTUATIONS
NONLINEAR PROBLEMS
PLASMA
PLASMA SIMULATION
PLASMA WAVES
POISSON EQUATION
TURBULENCE
TWO-STREAM INSTABILITY
BEAMS
DIFFERENTIAL EQUATIONS
EQUATIONS
INSTABILITY
LEPTON BEAMS
PARTIAL DIFFERENTIAL EQUATIONS
PARTICLE BEAMS
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
SIMULATION
VARIATIONS