The influence of electrons reflected from the anode on ionization

In modeling of electron energy distribution functions measured in a special experiment it has been shown that it is necessary to include both reflected and secondary electrons produced at the anode to be able to fit the experimental data. In this paper the degree of ionization, described through multiplication, due to reflection of electrons is studied. Multiplication (M) is the number of electrons reaching the anode per initial electron at the cathode. Typically, 10 000 to 1 000 000 initial electrons are used in these calculations. A complete set of cross sections for argon, shown to give an excellent fit to the transport coefficients is used in the present simulation. The data for graphite is used even though reflection from graphite is small. Spatial profiles of ionization rates (direct and total) at several values of E/N indicate that the contribution of reflection is significant already at several kTd. The data from the profiles of multiplication should be used in modeling the breakdown rather than the data for direct electrons only and the effect on determination of secondary yields may be quite large. The actual values of the multiplication factors are also presented