Secondary Electron Emission Produced by Positive Caesium Ions

Abstract

Number of electrons emitted from a Cs covered grid and plate per positive Cs ion striking them.---The source of the positive caesium ions, a short tungsten filament maintained at about 1200\ifmmode^\circ\else\textdegree\fi{}K in the presence of caesium vapor, was mounted on the axis of a long cylindrical grid and plate. The plate current and total positive ion emission current were observed for each of several negative grid potentials as the plate potential was varied from +50 to -650 volts. From these observations the number of electrons that were emitted from the caesium covered grid and plate per positive ion was calculated. This number increased uniformly from 0.01 at approximately 100 volts to 0.15 at 600 volts.Calibration of tube.---After corrections for the emission of secondary electrons were made, the ratio of the positive ion current to the plate to the total emission current was found to be independent of the plate and grid potentials for plate potentials greater than 0.2 of the grid potential. This ratio, 0.72, is the same as the ratio between the total area of the plate less the projected area of the grid, and the total plate area. Assuming the same distribution of electrons as positive ions, we can calculate the ratio of the plate current to the grid current in this type of tube.