Thermionic Emission from Tungsten and Thoriated Tungsten Filaments

Abstract

The electron emission from pure and thoriated tungsten filaments has been investigated as a function of the applied potential over the entire range from a few volts retarding to 1400 volts accelerating including careful studies at zero field. The filaments were heated with pulsating currents from thyratrons to eliminate during the measurements any drop in potential along the filament. The energy distribution of electrons was found to be deficient in slow electrons. An empirical reflection factor of $R({p}_{x})=\mathrm{exp}\ensuremath{-}\frac{p_{x}^{}{}_{}{}^{2}}{2m\ensuremath{\omega}}$, where $\ensuremath{\omega}$ is a constant 3.05\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ erg, represents the observed data for all temperatures and all states of activation for the thoriated tungsten. Analysis shows that there is no disagreement between the new results and the experiments of Germer. Zero-field Richardson plots show that the reflection effect alters both the $A$ and $b$ of Richardson's equation. The resulting values after correcting for reflection are $A=204$ and $b=55,100$ for pure tungsten. This value of $A$ indicates a negative temperature coefficient of the work function of 4.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ volt per degree, which has been verified by an independent experiment. New data on the electron emission in accelerating fields are given for many states of activation, showing that there are large deviations from the Schottky mirror image theory. Becker's patch theory is discussed briefly and a simpler strip theory is developed which serves to represent the observed data as an empirical result. This analysis shows that the patch theory is not suitable to explain the reflection effect since it is independent of the state of activation of the filament.