Electrostatic waves in an electron-beam plasma system

A one-dimensional (1D) electrostatic particle-in-cell simulation was performed to study wave excitation processes due to a tenuous electron beam in a plasma system, which is composed of hot and cold electron components. In this case, three types of electrostatic waves are excited, namely, Langmuir waves, electron-acoustic waves, and beam-driven waves. The beam-driven waves have a broad frequency spectrum, which extends from (0.1-0.2)omega(pe) (omega(pe) is the electron plasma frequency) to (1.5-2.5)omega(pe), with phase speeds close to the speed of the electron beam. The interactions among these waves are investigated for different values of density, temperature, and speed of the electron beam, etc. One special case is that when the density of the electron beam is sufficiently high, compressive solitary waves with bipolar structure of the electric field are generated. The generation mechanism of these solitons is mainly due to the trapping of a fraction of the beam electrons by the potential well of the enhanced beam-driven waves, as shown by the holes that are formed in phase-space plots. The relevance of these excited electrostatic waves to the intense broadband electrostatic noise observed in the Earth's auroral region is also discussed. (C) 2005 American Institute of Physics.