Ambipolar diffusion is a misnomer

In this paper we examine critically when the term diffusion is an appropriate description of the transport processes occurring in steady state active plasmas. It is suggested that ambipolar flow is a more correct and general expression. The paper examines in detail the situations in: (a) conventional active low temperature electropositive plasmas generated by electron impact such as the positive column of a d.c. gas discharge; (b) such plasmas where the electrons are magnetized and the ions not; (c) electronegative plasmas such as those used in plasma processing where there is separation into an ion–ion core and an outer electron–ion plasma.