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 veloc ity in an Ar-F-2 mixture ate studied numerically under the conditions corre sponding to negative electron mobility. Two physical situations are conside red: 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 literatu re. It is shown that the calculated drift velocities depend strongly on the choice of the transport cross section for Ar, whereas the distribution fun ction is almost independent of this choice. This result is explained by the fact that the balance between the positive (partial derivative f/partial d erivative u < 0) and negative (partial derivative f/partial derivative u > 0) contributions to the mobility of electrons from different groups is sens itive to the shape of the transport cross section in the energy range in wh ich f(rr) is maximum. The possibility of observing negative electron mobili ty experimentally is discussed.