Abstract :
The paper outlines the influences of the anode aperture, disregarded in the theory of the Pierce gun, which lead to an unsatisfactory functioning of such electron guns, particularly in the case of a high perveance. These influences are taken into consideration by imposing a rectilinear boundary on the beam, so that the space charge potential can be simply determined in the electrolytic tank. For this purpose, the anode is made tubular and sharp edged, and besides the Wehnelt electrode, an additional electrode of substantially the same potential is introduced, being mounted in the immediate vicinity of the anode aperture. Simple electrode forms and their favourable positions are given for a wide range of dimensioning. By the introduction of corrections, the dimensioning rules are extended to high perveance values. The magnitude of the current leaving the assumed boundary of the beam because of its initial thermal velocity is determined.
