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Title: Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering

Abstract

This paper presents a numerical study of the effect of Langmuir turbulence on incoherent scatter spectra. The Langmuir turbulence is driven by low energy beams of electrons in the Earth's upper ionosphere above 300 km. The nonlinear coupling between Langmuir waves and ion-acoustic waves is governed by the Zakharov system of equations. The model is enhanced with stochastic forcing in order to estimate by how much over the thermal level the spectrum seen by an incoherent scatter radar will be enhanced. This also allows us to directly compare the modeled spectra to the observed spectra collected by the incoherent scattering technique, as well as to statistically investigate the signature of the modeled spectra through an exploratory data analysis. Results for different beam energies are presented, covering the regimes of weak as well as strong turbulence. The incoherent scatter spectra signature is discussed in light of these regimes. It is shown that incoherent scatter radar observations of enhanced ion-acoustic and/or Langmuir waves compared to thermal level can provide good estimates of the beam parameters and of the type of turbulent regime. The cascade regime leads to strongly asymmetric spectra with enhancements over a limited range of wave numbers. The cavitation regimemore » leads to marginally asymmetric spectra, with enhancement over a wide range of wave numbers, and features a central peak for a limited range of wave numbers. Finally, it is shown that the Langmuir turbulence should be preferentially observed for scattering wavelengths large compared to the Debye length.« less

Authors:
;  [1];  [2]
  1. Physics Department, University of Oslo, N-0316 Oslo (Norway)
  2. (France)
Publication Date:
OSTI Identifier:
20860452
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 12; Other Information: DOI: 10.1063/1.2402145; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASYMMETRY; BEAM-PLASMA SYSTEMS; COMPARATIVE EVALUATIONS; COUPLING; DATA ANALYSIS; DEBYE LENGTH; ELECTRON BEAMS; ELECTRONS; INCOHERENT SCATTERING; ION ACOUSTIC WAVES; IONOSPHERE; IONS; NONLINEAR PROBLEMS; NUMERICAL ANALYSIS; PLASMA; PLASMA SIMULATION; STOCHASTIC PROCESSES; TURBULENCE; VISIBLE RADIATION

Citation Formats

Guio, P., Forme, F., and CETP, University of Versailles, F-78140 Velizy. Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering. United States: N. p., 2006. Web. doi:10.1063/1.2402145.
Guio, P., Forme, F., & CETP, University of Versailles, F-78140 Velizy. Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering. United States. doi:10.1063/1.2402145.
Guio, P., Forme, F., and CETP, University of Versailles, F-78140 Velizy. Fri . "Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering". United States. doi:10.1063/1.2402145.
@article{osti_20860452,
title = {Zakharov simulations of Langmuir turbulence: Effects on the ion-acoustic waves in incoherent scattering},
author = {Guio, P. and Forme, F. and CETP, University of Versailles, F-78140 Velizy},
abstractNote = {This paper presents a numerical study of the effect of Langmuir turbulence on incoherent scatter spectra. The Langmuir turbulence is driven by low energy beams of electrons in the Earth's upper ionosphere above 300 km. The nonlinear coupling between Langmuir waves and ion-acoustic waves is governed by the Zakharov system of equations. The model is enhanced with stochastic forcing in order to estimate by how much over the thermal level the spectrum seen by an incoherent scatter radar will be enhanced. This also allows us to directly compare the modeled spectra to the observed spectra collected by the incoherent scattering technique, as well as to statistically investigate the signature of the modeled spectra through an exploratory data analysis. Results for different beam energies are presented, covering the regimes of weak as well as strong turbulence. The incoherent scatter spectra signature is discussed in light of these regimes. It is shown that incoherent scatter radar observations of enhanced ion-acoustic and/or Langmuir waves compared to thermal level can provide good estimates of the beam parameters and of the type of turbulent regime. The cascade regime leads to strongly asymmetric spectra with enhancements over a limited range of wave numbers. The cavitation regime leads to marginally asymmetric spectra, with enhancement over a wide range of wave numbers, and features a central peak for a limited range of wave numbers. Finally, it is shown that the Langmuir turbulence should be preferentially observed for scattering wavelengths large compared to the Debye length.},
doi = {10.1063/1.2402145},
journal = {Physics of Plasmas},
number = 12,
volume = 13,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • The damping of ion-acoustic waves in a plasma with a high level of Langmuir turbulence is investigated. The dependence of the damping rate on the turbulent energy density is given analytically. (AIP)
  • The purpose of this work is to investigate the linear and nonlinear properties of the ion-acoustic waves (IAW), propagating obliquely to an external magnetic field in a weakly relativistic, rotating, and magnetized electron-positron-ion plasma. The Zakharov-Kuznetsov equation is derived by employing the reductive perturbation technique for this wave in the nonlinear regime. This equation admits the solitary wave solution. The amplitude and width of this solitary wave have been discussed with the effects of obliqueness, relativity, ion temperature, positron concentration, magnetic field, and rotation of the plasma and it is observed that for IAW these parameters affect the propagation propertiesmore » of solitary waves and these plasmas behave differently from the simple electron-ion plasmas. Likewise, the current density and electric field of these waves are investigated for their dependence on the above-mentioned parameters.« less
  • Bifurcations of nonlinear propagation of ion acoustic waves (IAWs) in a magnetized plasma whose constituents are cold ions and kappa distributed electron are investigated using a two component plasma model. The standard reductive perturbation technique is used to derive the Zakharov-Kuznetsov (ZK) equation for IAWs. By using the bifurcation theory of planar dynamical systems to this ZK equation, the existence of solitary wave solutions and periodic travelling wave solutions is established. All exact explicit solutions of these travelling waves are determined. The results may have relevance in dense space plasmas.
  • In this article, we present how ion acoustic waves can be unambiguously identified and can be used to definitely demonstrate the existence of the Langmuir decay instability (LDI) of electron plasma waves associated with stimulated Raman scattering. This observation is very important in the context of inertial confinement fusion because the LDI is a mechanism that may influence the stimulated Raman scattering saturation and growth. The experimental identification of those waves relies on Thomson scattering of a short wavelength probe beam. The Thomson scattered light was analyzed by two sets of spectrometer and streak camera providing information on the densitymore » fluctuations associated with the electron plasma waves and ion acoustic waves with temporal and spectral resolutions. Selection of a narrow range of angles (4 degree sign of aperture) inside the probe and scattered light apertures provided necessary resolution in wave vector. The method used for the design of the Thomson scattering diagnostic is described as well as the technique used to clearly identify the observed ion acoustic waves as one of the Langmuir decay instability products. (c) 2000 American Institute of Physics.« less
  • Both Zakharov equations and Vlasov equations are solved numerically to study the strong Langmuir turbulence developed in a plasma driven by an external pump field oscillating at the plasma frequency. A steady state turbulence in Vlasov simulations is reached by using open boundary conditions under which hot particles generated by strong caviton fields are replaced by initial cold Maxwellian particles when they cross the boundaries of simulation domain. A similar steady turbulent state in Zakharov simulations is easily achieved by implementing a phenomenological damping model and using periodic boundary conditions. Simulation results of these two different models are compared andmore » investigated. {copyright} {ital 1996 American Institute of Physics.}« less