The increase of thermionic currents from tungsten in strong electric fields

Abstract

Schottky has pointed out that there should be an increase in thermionic currents above the saturation value with the application of strong electric fields. His theoretical expression is based on the assumption that an electron is prevented from escaping by the attraction of its electric image in the emitting wire, and that the external field neutralises part of this image force field. In the same paper he reports an approximate experimental verification of his theoretical law, though the details are lacking. Since that paper, reference has been made to this increase in current, and it has been applied as a correction in determining the thermionic work function. Becker and Mueller have discussed the problem, but apparently assume the correctness of Schottky’s expression. Under the circumstances it seemed that an experimental investigation was needed, all the more because Schottky’s theoretical expression seems open to question on certain points. Let us suppose that a single electron is escaping from a plane electrode, and that the image force alone is acting upon it.