Electron-acoustic solitons in an electron-beam plasma system

Electron-acoustic solitons exist in a two electron temperature plasma (with "cold" and "hot" electrons) and take the form of negative electrostatic potential pulses. They develop on a spatial scale of a few Debye lengths and propagate at the electron-acoustic velocity which is intermediate between the two electron thermal velocities. They correspond to local enhancement of the cold electron density. It is shown that the introduction of an electron beam in such a plasma allows the existence of new electron-acoustic solitons with velocity related to the beam velocity. Depending on the beam density and temperature and below a critical velocity of the electron beam, they often have a positive potential signature. In such conditions they correspond to electron density holes for the cold electron population. The properties of these solitons are studied in detail. These results suggest that further analysis of recent observations of electron density holes might provide the means to identify these structures in the magnetospheric plasma.