Ion Acoustic Waves in a Collisional Plasma

The damping of the ion acoustic waves by Coulomb collisions is studied by using the Fokker-Planck equation of Rosenbluth et al. for both the species constituting the plasma, namely, the electrons and the ions. In a plasma with weak collisions and in the absence of any external field, one finds that irrespective of the ratio T of the ion temperature to the electron temperature, the characteristic frequency gets affected only by the electron-ion collisions. However, as far as the collisional damping is concerned, both the ion-ion and the electron-ion collisions play a somewhat equally important role; the electron-electron and the ion-electron contributions are negligible compared to the other two. The damping increases with increase in the collision frequency but decreases with increase in T.