Abstract

The speed distributionP(v, t) of electrons moving in an electric field through a background gas of normal atoms is obtained by a simple random-walk analysis of the problem. The limits of validity of the Fokker-Planck equation forP(v, t) are discussed. Important quantities, such as the rates of change of electron speed (energy) per collision and per free path, are derived and compared with some corresponding formulae in the literature. Previous derivations of the electron energy distribution leading to results disagreeing with those of Druyvesteyn are examined and the causes of the discrepancies are indicated. The problem of deriving an accurate formula for the electron drift speed when electrons undergo inelastic collisions also is widely studied. The results following from a new and very recent theory of the electron drift velocity are obtained and compared with commonly accepted formulae; the conditions for their coincidence are found. A new formula is then proposed for the electron drift speed, valid when inelastic scattering processes are not isotropic.

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