Modulational Instability of Ion-Acoustic Waves in a Plasma with Warm Ions, Nonthermal Electrons and Nonthermal Positrons

The modulational instability and envelope solitons of ion-acoustic waves have been investigated in an unmagnetized collisionless warm electron–positron–ion (e-p-i) plasma with both the electrons and positrons having nonthermal distribution. Using standard multiple scale perturbation technique a nonlinear Schrödinger equation (NLSE) governing nonlinear evolution of the wave envelope has been derived. Using this equation we have shown through numerical analysis that the presence of nonthermal electrons and positrons plays significant role on the formation and the structure of ion-acoustic envelope solitons.