Experimentelle Untersuchungen über den Einfluß der Wand-Raumladungsschicht bei der Extraktion positiver Ionen

Abstract

The mechanism of ion extraction from a weakly ionized plasma has been investigated using a quadrupole mass spectrometer. The plasma was generated in a flow system by means of a high frequency discharge. It could be shown that the picture given by PAHL has to be extended by considering a space charge sheath spread over several mean free ion paths in front of the plane extraction probe, used. Two effects, resulting from the space charge, have been found observing the behaviour of nitrogen ions. First, the directional distribution of the extracted ions may be different for different ions. Second, ion-molecule reactions may be caused by the field strength within the sheath varying with both ion number density and probe voltage. In the case of N₄ ⁺ ions the Varney reaction seems already to start in the static sheath. In order to minimize influences from the space charge, it is suitable to apply a slightly positive potential with respect to the container wall.