Positive ion flux from a low-pressure electronegative discharge

We compute the flux of positive ions exiting a low-pressure, planar, electr onegative discharge as a function of the negative ion concentration and tem perature. The positive ions are modelled as a cold, collisionless fluid, wh ile both the electron and negative ion densities obey Boltzmann relations. For the plasma approximation, the plasma edge potential is double-valued wh en the negative ions are sufficiently cold. When strict charge neutrality i s relaxed, spatial space-charge oscillations are observed at the edge of th e plasma when the flux associated with the low tin absolute value) potentia l solution is less than that of the high potential solution. However, the f lux is always well defined and varies continuously with the negative ion co ncentration. We demonstrate that the correct solution for the plasma approx imation is that having the greater flux.