Emissivity of a multibeam electron gun with a glassy carbon field-emission cathode

A multibeam triode electron gun with a glassy carbon field-emission cathode that is intended for an O-type microwave amplifier is studied. The electric field strength and the current density at the microtips versus the distance to the center of a cell of the cathode–grid unit are calculated. Calculation data are compared with experimental results. It is shown that about 70% of the cathode current in each cell is accounted for by microtips arranged in a circumferential ring no wider than 20 $\mu$m. The field-emission current density inside the ring exceeds 40 A/cm$^2$, and the current per microtip equals 43.1 $\mu$A.