Arbitrary amplitude ion-acoustic waves in a plasma with nonthermal electrons

We investigated the effect of the presence of a nonthermal electron population on the electrostatic nonlinear waves. We considered positively charged ions with two electron populations. Using the fluid equations for the unmagnetized case and the Sagdeev pseudo-potential approach the nonlinear ion-acoustic waves are studied. The cold electrons are in thermal equilibrium while the hot electron population follows a nonthermal distribution. Numerical investigation shows the importance of the presence of small amount of cold electrons that make it possible for the plasma to support nonlinear waves. We obtained the minimum cold electron density necessary to sustain these nonlinear waves. The relevant situation corresponds to the upper ionosphere where energetic electrons have been observed.