Abstract
Two-dimensional electromagnetic particle-in-cell simulations are carried out to investigate the effect of ion-to-electron mass ratio on the evolution of warm electron beam-plasma instability. Four cases are considered: A: mi/me = 0 (two-electron stream instability); B: mi/me = 1 (pair plasma); C: mi/me = 100; and D: mi/me = 1000. It is shown that the generation of Langmuir waves in the fundamental mode of electron plasma frequency and the subsequent dynamics of large-amplitude solitons are not affected by the ion species. However, it determines the decay process of solitons and the excitation of electromagnetic waves in the second harmonic. In the first two cases, mi/me = 0 and 1, there is no sign of emission in the second harmonic, while the strongest emission in the second harmonic is found for the case of largest mass ratio, mi/me = 1000. This confirms the two-step wave-wave coupling mechanism for the generation of second harmonic electromagnetic waves, which requires the excitation of ion-acoustic waves in the first step. Moreover, the dispersion diagrams of all excited waves are presented.
Highlights
Electron beam-plasma interaction is a fundamental nonlinear plasma process that is frequently taking place in space environments and laboratory plasmas
Soucek et al [3] suggested an interpretation of these spectra as signatures of nonlinear decay of Langmuir waves to electron-sound and ion-sound secondary waves. e results of the Geotail waveform observation on the electrostatic plasma waves with their frequency close to the local electron plasma frequency in the tail lobe were presented by Kojima et al [4]. ere are some other studies that discussed other aspects of the beamplasma interaction such as beam heating and characteristics of Langmuir electric field waveforms [5,6,7]
It is thought that the intensity of emission in the second harmonic depends on the ion-to-electron mass ratio since strong ion-acoustic waves result in the effective backscattering of Langmuir waves
Summary
Electron beam-plasma interaction is a fundamental nonlinear plasma process that is frequently taking place in space environments and laboratory plasmas. Laser and Particle Beams theoretical study, Baumgartel [11] described a simple linear approach to the phenomenon of amplitude modulation of Langmuir waves in weak beam-plasma interaction and found out that the resulting waveforms in temporal representation are quite similar to those observed by the spacecraft. Umeda and Silin et al [14, 15], using Vlasov simulations, discussed the amplitude modulation and packet formation of Langmuir waves and the linear dispersion theory of the electron-beam interaction with plasma. It is thought that the intensity of emission in the second harmonic depends on the ion-to-electron mass ratio since strong ion-acoustic waves result in the effective backscattering of Langmuir waves. Is paper is structured as follows: the section describes the model and simulation setup, while the results and discussion are presented in the third section which is followed by a brief summary
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