The Evolution of Instabilities Driven by a Drift Between Ions and Electrons in Nonmagnetized Plasma

The electron-ion beam instability is studied by one-dimensional electrostatic particle-in-cell simulation. When the relative drift velocity between the electron and ion is sufficiently less than the electron thermal speed, the dominant mode is the Langmuir wave; the ion-acoustic instability is very weak; the Buneman instability is not excited. When the relative drift speed is equal to the electron thermal speed, the Langmuir wave, the ion-acoustic and the Buneman instability nearly exist simultaneously. The three instabilities now appear to have al- most equal intensities. When the relative drift speed exceeds the electron thermal speed, the ion-acoustic instability turns into the Buneman instability which appears to have much higher intensity than the Langmuir wave.