The effects of electron mass on ion-acoustic solitons

It is usual in studies of solitons and double layers in fluid plasmas to make the assumption of Boltzmann electrons, i.e. because of their high mobility, the electron mass is neglected. In a recent paper it has, however, been suggested that electron inertia effects on ion-acoustic solitons may exceed relativistic effects. The purpose of this study is to determine finite electron mass effects on the amplitudes and existence domains of ion-acoustic solitons. We consider a plasma consisting of cold hydrogen ions and two isothermal electron fluids at different temperatures. The electron density distributions are determined using the plasma fluid equations, thus introducing the electron mass. Instead of using the small-amplitude KdV equation we carry out arbitrary-amplitude calculations from the fluid equations. The existence of a soliton is deduced from the form of the Sagdeev pseudopotential. Our main result is that particularly in the case of rarefactive solitons, the existence domain is considerably over-estimated by the Boltzmann electron model.