Electron Streams in a Diode

T HE theory of an electron stream flowing in a diode has received much attention; 1 - 1 3 because the tetrodes, pentodes and other modern tubes are cascade arrangements of individual diodes. The theory of the diode is the foundation for considering the circuit characteristics and the noise characteristics of these tubes. In earlier days when communication channels were confined to relatively low frequencies, an electron could traverse a diode in a short period of time compared to an oscillation of any electrical signal, and the theory could be developed rather simply from the known d-c equations. But in these days of high and ultra-high frequencies, the situation is quite different. A signal voltage may oscillate several times while an electron is traversing a diode, and the electron stream flows in bunches or waves. The present article is primarily concerned with this more complicated type of flow. It is confined to the case of parallel plane electrodes, and developed under the usual assumption that the electron velocity is a single valued function of space and time. It is shown to be an approximate solution for physical electron streams over a wide range of conditions. Particular solutions for an electron stream under small signal conditions are given in various published articles. These theories approach the subject in two different manners. In one approach attention is confined to the motions of electrons as individual particles, 1-3 and the other approach may best be described as a wave theory of electron streams.