The generation of high-frequency oscillations by hot-cathode discharge tubes containing gas at low pressure

A brief account is given of some experiments on the generation of plasma electron oscillations by the discharge from a hot filament through ionized mercury vapour, argon and other gases at low pressures. These are produced both with bare metal cathodes and oxide-coated cathodes. The vacuum wavelengths of the electromagnetic waves produced have ranged from 5 cm to 2 m. Using bare cathodes, they have been detected both below the saturation current and on the saturation section of the tube characteristic. Using oxide-coated cathodes, they have been detected over wide sections of the tube characteristic. Data are given for the variation of wavelength and intensity with operating conditions for some tubes, and with position of an exploring electrode in the tube and on the outside of the tube wall. Under favourable conditions 1% of the anode power can be converted into energy of oscillation in an external circuit coupled with the tube. The observations are in the main consistent with the existence of restricted regions of oscillating plasma, in traversing which the primary electron beams undergo velocity modulation. Suggestions are made as to how the oscillations may be confined within a tube.