Electromagnetic plasma emission during beam-plasma interaction: Parametric decay versusinduced scattering

摘要

1 Two-dimensional electromagnetic particle-in-cell simulations are performed forexamination of electromagnetic plasma emission at twice the electron plasma frequency.Electromagnetic "2f_p" waves are considered to be excited by nonlinear three-waveprocesses in beam-plasma interactions. In this paper, nonlinear development of anelectron-beam-plasma instability is studied as an initial value problem. The presentsimulation result confirmed that electromagnetic 2f_p waves are strongly enhanced by thewave-wave interaction between forward and backward Langmuir waves, which is inagreement with the previous studies. It is also demonstrated that large-amplitude forwardLangmuir waves decay into backward Langmuir waves and ion acoustic waves via aparametric decay and that electromagnetic 2fp waves are also enhanced by the decay ofLangmuir waves. However, the growth rate of the electromagnetic 2fp waves due to theparametric decay of Langmuir waves is not as high. It should be noted that inducedbackscattering of Langmuir waves by enhanced thermal fluctuations of ions cannot beneglected in the excitation of backward Langmuir waves. Hence, low-noise simulationsare necessary to suppress the effect of enhanced thermal fluctuations in the particle-in-cellmethod.