A low-energy but high-perveance electron gun is displayed in the following plots. This gun was designed by Frost and Purl and was described in an article in the Proceedings of the IRE in 1962. Another capability of the program is the ability to generate separate trajectory and equipotential plots, as shown below.
Trajectories and electrode configuration for microperveance 1.9 electron gun.
Note that the beam passes very close to the extraction electrode. The original developers claim that the beam did not hit the electrode, but for some strange reason they later replaced the cathode with another one, which had a shorter radius. Adding the thermal distribution to this simulation (below) caused the beam to scrape this electrode.
Equipotentials for perveance 1.9e-6 electron gun.