Optimum Design and Performance of an Electron Gun for a Ka-Band TWT

This paper deals with optimum design and development of a thermionic electron gun to meet specified beam requirements within defined electric and geometric constraints for a Ka-band traveling wave tube (TWT) for space applications. The electron gun design is based on the Pierce method and carried out according to the iterative process indicated by Vaughan. The design of a periodic permanent magnet (PPM) beam focusing system for the stability of the beam is also required. A sensitivity analysis, by varying electric parameters and geometric parameters, is presented and taken into account as a fundamental role to the aim of optimizing the design of the Pierce gun. A cathode current value of 550 mA at a cathode voltage value of 20 KV with a beam diameter value of less than 0.55 mm, as a result of the analysis, is imposed as a goal design parameter, to obtain a TWT output power value more than 500 W. The simulated results show very good agreement with the beam tester experimental results. The body current measured value, in excellent agreement with the simulated one, shows the effectiveness of the design procedure. Data from the experimental beam tester demonstrate 98% beam transmission to the collector.