Multistage Depressed Collector With Novel Dual Aperture Electrodes for Space Traveling Wave Tubes

Traveling wave tubes (TWTs) employed in communication satellites as power amplifiers have stringent requirements of high efficiency, low weight, compact size, etc. In order to achieve high overall efficiency, the interaction structure is designed for very high electronic efficiency, which, in turn, causes the spent-electron beam to be highly chaotic with wider velocity spread, thereby making the efficient collection of the electron beam a challenge. To address this challenge, the authors have designed a four-stage depressed collector with novel dual aperture electrodes, keeping ease of fabrication in mind. Each electrode is designed with dual taper structures, with each taper section comprising a positive slope structure followed by a zero-slope cylindrical structure. Additionally, the leakage magnetic field from the beam refocusing section has been optimized to achieve maximum collector efficiency without using any additional magnets. As the collector optimization involves many parameters that are non-linearly interdependent, a genetic algorithm-based approach has been employed to attain better results. Further, electrode materials with low secondary electron emission yield have also been explored. Adopting the combination of these approaches - novel geometry modification, employing leakage magnetic field, optimization of collector parameters using genetic algorithm, and using low secondary electron emission yield material has resulted in a high collector efficiency of 85.24%. This offers a significant increase of 5.54% in the collector efficiency as compared to its conventional counterpart, thereby resulting in a tremendous saving in the launch cost of the communication satellite.