Study of a laser-heated electron gun

Abstract

A method of cathode heating using a laser was studied for an electron gun. In order to observe the practicality of the heating system, the characteristics of the laser‐heated gun with a dispenser and LaB₆ thermionic cathodes have been experimentally investigated. The direct laser irradiation is so efficient that the gun is equipped without heat shielding, a cooling system, or an electrical circuit in the gun chamber for cathode heating. Modeling, based on the experimental data, indicates that the cathode temperature is proportional to one‐fourth power of the laser power and that laser power loss and conduction loss of heat in the gun assembly are negligible. An electron beam current density 0.48 A/cm² was measured with 26 W laser power for a dispenser cathode of 0.06 cm² emission area. Current density 0.16 A/cm² with 25 W was recorded for a LaB₆ cathode of area 0.12 cm². Electron beam emittance has been measured by using the typical pepper‐pot technique. It was observed that the growth of electron beam emittance was very small in the laser heating.