Analysis of the transverse energy distribution of HopFED

For HopFED applications without a flu spacer the normal energy distribution is less important than the energy distribution in the direction perpendicular to the propagation of the beam, the transverse energy Et. The transverse energy distribution of electrons leaving the exit hole of a hop spacer plate in a HopFED was measured experimentally and analyzed. These electrons were accelerated in a uniform field onto the anode screen. The luminance distribution of the spot on the screen was in our experimental set up largely determined by the transverse energy distribution of the electron beam. A directly grown carbon nanotube (CNT) field emitters as electron source was used. The system was positioned in a vacuum chamber with a glass window for viewing and measuring the electron spot. A digital camera recorded the luminance distribution of the electron spot on the phosphor screen. Software, which was originally developed for CRT spot size measurement, had to be improved for our luminance analysis. The analyses of the luminance distribution show that the transverse energy is rather low and that a HOPFED without a flu spacer will have good beam directionality.