PBGUNS Output: Low Energy Electron Gun

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.

Equipotentials for perveance 1.9e-6 electron gun.

The fine matrix over the cathode region is shown above. The current density distribution and emittance plot near the beam waist are shown below for the non-thermal case. The current distribution is peaked at the outer radius of the beam, considerably more than the experimental device.

Current distribution near beam waist.

Emittance plot near beam waist.

While Frost and Purl state that there are no thermal effects, the simulation seems to indicate strong thermal effects; indeed, they dominate the current distribution in the beam. The plots below were obtained using a basic thermal distribution at the cathode. The current distribution fills in the center and adds a radial tail and now agrees quite well with their current distribution measurements.

Current distribution near beam waist with thermal particles added.

Emittance plot for thermal particles.