Design and Experimental Evaluation of Dual-Anode Electron Gun and PPM Focusing of Helix TWT

A dual-anode convergent electron gun with a perveance of 0.14 μp has been designed and developed for a high-efficiency helix traveling-wave tube (TWT), which would ultimately have application in a satellite communication system. The electron gun with an isolated beam forming electrode and an M-type dispenser cathode of 3.1-mm button diameter has been designed using EGUN, OMNITRAK-3-D, and OPERA-3-D codes. It consists of two isolated anodes, namely, control anode and ion-barrier anode, in addition to a ground accelerating anode to meet the requirement of long life and high reliability. Initially, in cathode selection, life considerations are ignored, and the gun is designed with the available cathode. Periodic permanent magnet (PPM) focusing has been designed using a Sm₂Co₁₇ high-intensity magnet in order to reduce the size and the weight of the overall TWT. Confined flow beam focusing has been adopted. A compact, small-size electron gun assembly has been designed using a ceramic insulator and a suitable support structure with due considerations for high-voltage and thermal requirements. A high-voltage analysis has been carried out using ESTAT code, and a thermal analysis has been carried out using ANSYS code. Designed electron gun and PPM focusing has been experimentally validated by developing and testing a beam-stick tube with the application of rated potentials at various electrodes in a gun and a collector. The design and experimental results for the electron gun and PPM focusing have been found in close agreement.