Electron Images of Recording Storage-tube Cathodes: A New Technique for Cathode Study†

It is shown that in a recording storage tube there are four general dielectric-to-cathode potential regions for storing cathode images and that images stored ill each of these regions give different information. Beam current density is given directly by the image stored at the potential for maximum beam acceptance and also by the image stored substantially above the first crossover. Electron energy spread and cathode surface potential are obtained from a series of images stored near the first crossover. The probability of elections landing on low-potential surfaces is shown by an image stored just above the cathode potential. The energy distribution in the electron beam can be obtained by combining the information in the current-density and electron-energy images. Cathode images from five tubes, stored in the several dielectric-to-cathode potential regions of interest, exhibit cathode patch potentials which are not in accord with theory. A model of the oxide-coated cathode is proposed to explain the observations.