  Electron-acoustic waves occur in space and laboratory plasmas where two
distinct electron populations exist, namely cool and hot electrons. The
observations revealed that the hot electron distribution often has a
long-tailed suprathermal (non-Maxwellian) form. The aim of the present study is
to investigate how various plasma parameters modify the electron-acoustic
structures. We have studied the electron-acoustic waves in a collisionless and
unmagnetized plasma consisting of cool inertial electrons, hot suprathermal
electrons, and mobile ions. First, we started with a cold one-fluid model, and
we extended it to a warm model, including the electron thermal pressure.
Finally, the ion inertia was included in a two-fluid model. The linear
dispersion relations for electron-acoustic waves depicted 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 to determine how their characteristics
depend on various plasma parameters. The 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 become
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.
