Ion Oscillations in Electron Beam Tubes; Ion Motion and Energy Transfer

This paper refers briefly to some of the deleterious effects that often arise when positive ions are trapped in electron beams. Calculations aimed at establishing a useful picture of ion oscillations in gridded drift tubes are presented, and a plausible physical picture of some possible ion motions is obtained. In consequence of these motions, the electric field inside the drift tube undergoes one or more space reversals. When a beam of fast electrons traverses such a region, beam loading may be negative; this is calculated in some detail, both for ions and for a simple LC circuit. Thus a mechanism for energy transfer from the electron beam to the oscillating ions has now been found. The question of whether or not this energy is sufficient to sustain oscillations is examined in a preliminary way. The importance of secondary electrons in some cases is discussed. Comparison between experiment and theory shows that a good qualitative understanding now exists of such observed phenomena as continuous oscillations. The occurrence, however, of fluctuating ion oscillations is not predicted by the present theory.