MICROWAVE-DISCHARGE WITH NEGATIVE-IONS AT MODERATE PRESSURES

The properties of an electrode boundary layer in a microwave discharge at a moderate pressure are analyzed for electronegative gases. The structure of the electrode boundary layer depends on the ratio between the attachment frequency of the electrons and the time of ion motion through the layer. When the attachment frequency is very high or small, the electrode boundary layer is similar to the layer in a two-component plasma. However, for highly electronegative gases, the intermediate case is more typical. This case is characterized by the fact that the attachment frequency and the inverse time of the ion motion through the layer are comparable. This corresponds to small layer thicknesses in comparison with those in electropositive gases. In this case, the layer thickness grows proportionally to the current. The jumps or peaks in the ion density arise at the plasma-layer boundary depending on the ratio between the ambipolar diffusion and the ion velocity in the layer.