Numerical computation of the emission current in electron guns

Abstract

A computer program for evaluating the emission current in electron guns has been developed, and good agreement between evaluations and experiments has been achieved. The computational model is based on the statistical theory of thermal electron emission, and the potential distribution in front of the cathode is equivalent to that of an infinite planar diode in which the longitudinal thermal velocity effect (LTVE) is taken into account.

From the results evaluated by the computer for several different cases, the conclusions are shown as follows:

• 1. In cathode ray tube (CRT) guns, the LTVE must be taken into account. The emission current values estimated by the program are greater than those calculated by the 3/2 power law. The former values are closer to the measured values than the latter ones.

• 2. In high perveance guns, the LTVE is noticeable when the operating potentials are low, but this influence of the LTVE is much smaller than in CRT guns.

• 3. The LTVE becomes significant as the ratio of the saturated emission current density delivered from the cathode to the actual emission current density increases, and remains unchanged when the ratio is beyond a certain value.