Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh12a0404l&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SH12A-0404
Other
7534 Radio Emissions, 7839 Nonlinear Phenomena, 7843 Numerical Simulation Studies, 7867 Wave/Particle Interactions, 7868 Wave/Wave Interactions
Scientific paper
Nonlinear electrostatic Langmuir decay is important for type III solar radio emissions, and other emissions in space plasmas. For instance, to generate the observed levels of emission in type III bursts, it is important to produce backscattered Langmuir waves to participate in the emission of radiation at the second harmonic of the electron plasma frequency, and ion-acoustic waves to stimulate fundamental emission. In this work, the evolution of Langmuir waves and ion-acoustic waves in time, space and wave number, stimulated by a hot electron beam and coupled by Langmuir decay processes in an initially homogeneous plasma is investigated numerically using kinetic theory. The nonlinear dynamics of Langmuir waves and ion-acoustic waves for parameters appropriate to the solar wind at 1AU is studied in detail. Nonlinear Langmuir decay is observed to effectively scatter the beam-driven Langmuir waves out of resonance. The scattered Langmuir waves then undergo further decays and condense sequentially toward small wave numbers, until decay is prohibited kinematically. At a given spatial location, the levels of the product Langmuir waves initially are lower than those of the resonant Langmuir waves, they increase and eventually reach as high as or exceed those of the beam-driven Langmuir waves, which become weaker as the beam passes this position. The ion-acoustic waves generated are relatively weak and subject to damping at large times. Fine structures in scattered Langmuir waves and ion-acoustic waves are observed, due to the depletion of their energy when decay and coalescence processes proceed. Furthermore, quasilinear relaxation of the beam is not affected significantly by the decay, and hence the main features of resonant Langmuir waves are very similar to those when nonlinear decay is absent. The decay process is thus slaved to the primary beam-plasma evolution, as assumed in previous works. We investigate also the effects of varying beam and ion parameters. We found that the electron to ion temperature ratio affects not only the intensity of the ion-acoustic waves through effects on the damping rate, but also the dynamics of a decay processes via effects on the decay rate, which was usually overlooked in previous studies. These results for the Langmuir and ion-acoustic waves will be used as input to calculate electromagnetic emission in type III bursts using wave-wave interaction theory, with further inclusion of spatial inhomogeneity in the background plasma.
Cairns Iver H.
Li Baowen
Robinson Adam P.
Willes Andrew
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