Plasma Ion Oscillations in Electron Beams

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Abstract
The frequency of the oscillations observed in ion-neutralized electron streams such as that of an ion-trapping gun or of a tetrode has been shown to agree well with the Langmuir-Tonks theory for plasma ion oscillations. The existence of a dipole mode of oscillation in addition to the longitudinal mode has been observed for a plasma column. A mechanism is proposed for the excitation of these self-sustained oscillations by which the secondary electron current from electrodes bounding the plasma is modulated by the vibration of the ions in such a way as to deliver energy to the ac field associated with the ion oscillations. Experimental observations verify this picture as far as the source of energy is concerned.