The transition from collisionless to collisional in active low-temperature plasmas with more than one species of positive ion generated by electron impact and the Bohm criterion

The fluid model for low-temperature plasmas with a constant ion collision frequency is examined in the plasma approximation in the situation where there is more than one species of singly charged positive ion present.

The parameter range considered allows one to cover the transition from collisionless to fully collisional. Thus it is possible to predict for two species when both will be close to their own Bohm speed at the plasma edge, when one species will be close to its Bohm speed but the other not, and when both species differ from their respective Bohm speeds by factors as much as two.

It is assumed specifically that the plasma is generated by electron impact with a constant but different ionization frequency for each species, and by low temperature we mean that the electron temperature (kT_e) is less than the first ionization potential (eV_iq) of each species `q'.