Propagation of Electron-Acoustic Waves
Electron-acoustic waves are observed in space plasmas such as the Earth’s magnetosphere where two distinct electron populations exist, namely cool and hot electrons. The observations of the auroral broadband electrostatic noise emissions revealed that the hot electron distribution often has a long-tailed suprathermal (non-Maxwellian) form. The main goal of his Master project was to investigate how various plasma parameters modify the electron-acoustic structures.
Over 2009 Ashkbiz Danehkar studied linear and nonlinear structures of electron-acoustic solitary waves in a collisionless and unmagnetized plasma consisting of cool inertial electrons, hot suprathermal electrons, and mobile ions. A linear dispersion relations was obtained for electron-acoustic waves, which depicts a strong dependence of the charge screening mechanism on excess suprathermality. A nonlinear (Sagdeev) pseudopotential technique was employed to investigate the existence of electron-acoustic solitary waves, and determine how their characteristics depend on various plasma parameters.
His results indicate that the thermal pressure deeply affects the electron-acoustic solitary waves. Only negative polarity waves were found to exist in the one-fluid model, which becomes narrower as deviation from the Maxwellian increases, while the wave amplitude at fixed soliton speed increases. However, for a constant value of the true Mach number, the amplitude decreases for increasing suprathermality. It is also found that the ion inertia has a trivial role in the supersonic domain, but it is important to support positive polarity waves in the subsonic domain.