Evaluation of the real space electron drift velocity in gases using moment equations performed in velocity space

The centroid drift velocity and the mean electron velocity of electron swarms in gases have different values even under the same electric field when electron-impact ionization and/or electron attachment processes are present. A new evaluation technique for is proposed based on moment equations, in which the quantitative difference between and is described as a function defined in velocity space. values are derived from calculations using a propagator method performed in velocity space without the electron distribution in real space. The effects of ionization and attachment on are quantitatively analysed for and , and the mechanism producing the difference between and is illustrated.