Negative electron mobility in a weakly ionized plasma: Dependence of the calculated quantities on the shape of the transport cross section

The electron energy distribution function f(u) and the electron drift velocity in an Ar-F2 mixture are studied numerically under the conditions corresponding to negative electron mobility. Two physical situations are considered: a steady plasma created by a fast electron beam and a decaying plasma created by a short ionizing pulse. The computations are carried out for two slightly different transport cross sections for Ar taken from the literature. It is shown that the calculated drift velocities depend strongly on the choice of the transport cross section for Ar, whereas the distribution function is almost independent of this choice. This result is explained by the fact that the balance between the positive (∂f/∂u<0) and negative (∂f/∂u>0) contributions to the mobility of electrons from different groups is sensitive to the shape of the transport cross section in the energy range in which f(u) is maximum. The possibility of observing negative electron mobility experimentally is discussed