Low-Noise Beams from Tunnel Cathodes

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Abstract
The tunnel cathode consists of a metal-insulator-metal sandwich in which the electrons tunnel through the insulator material. This paper presents an analysis of the noise associated with the space-charge waves of a beam emitted from such a cathode. The beam noise temperature for a refrigerated tunnel cathode is shown to be 2730 δ, where δ is the value in volts of a built-in energy window for the emitted electrons. The value of δ is adjustable by means of a dc potential. Assuming a beam noise temperature of 30°K, the current density is calculated for a variety of cathode parameters. A discussion is presented of the significance of the parameters and of the difficulties which would be encountered in constructing such cathodes for low noise.