Plasma boundary layer in the presence of fast primary electrons

The fluid equations are solved for a three component plasma in contact with a conducting surface. The plasma consists of cold ions, monoenergetic primary electrons with an isotropic distribution and thermal electrons with a Maxwellian distribution. The rate of ionization β is assumed to be proportional to the local number density p of the primary electrons. The boundary is at floating potential so that no net electrical current flows to it. The onset of the spatial space charge oscillations can be explained as follows: As the potential drops toward the boundary first the secondary electron density decreases rapidly while the density of the primary electrons remains nearly constant provided their energy is sufficiently large. If the ion density decreases sufficiently rapidly due to acceleration in the potential gradient a local net negative space charge may be formed by the excess primary electrons. It turns out that beyond this point the potential oscillates in space around the quasineutral potential solution. This behaviour is similar to that of the well-known BGK-solutions