A note on the Bohm criterion for electronegative gases

The Bohm criterion for electronegative gases is known to yield a multi-valued solution for certain plasma parameters. The prescription for the determination of the correct solution, in the original paper by Braithwaite and Allen (1988 J. Phys. D: Appl. Phys. 21 1733 ), was to choose the smaller value of the two possible potential drops in the quasi-neutral plasma. Several authors have recently questioned this procedure, but this paper affirms the correctness of the original method. It is a fact, however, that this application of the Bohm criterion becomes less useful than is normally the case, since it relates to only one part of the discharge plasma; it will not itself suffice to calculate the flux of positive ions leaving the entire system.