Design considerations for no discharge in space TWTs for long life & reliable satellite communication

Space Travelling-Wave Tube (TWT) for satellite communication is the most critical ultra-high vacuum device. Long life (>15 years) and high reliability are the prime requirements of a space TWT. Because of the continuous long life CW operation, special design and technological considerations are used to avoid any discharge in a tube. All electrical insulators in gun and collector assemblies of a space TWT are selected of highest purity and sufficient high voltage margin (more than twice the operating voltages). Also, special precautions are taken to avoid charging of high voltage ceramic insulators due to any stray electron. High purity and low loss alumina (99.5%) insulators are used for RF window and all ceramic to metal joints in multi-electrodes gun and multi-stage depressed collector assemblies. All ceramic to metal joints are designed to minimize the triple-junction effects, and are brazed using Cu or Cu-Au alloys. For RF output coupler in a tube, there is sufficient design margin of multipactor discharge of at least four times the operating RF power output. Some of the critical technologies issues related to no discharge in space TWTs for long life operation are presented.