Innovative Feedthrough Technology for Collector Efficiency Enhancement in Space Travelling Wave Tubes

Multistage depressed collector (MDC) plays a dominant role in efficiency enhancement of space travelling wave tubes (TWTs). Although MDCs are typically designed to achieve high collector efficiencies exceeding 90%, realising such levels in practice remains challenging. The primary limiting factor is the high-voltage breakdown issues occurring in the collector region, leading to electrical arcing, particularly between the last highly depressed electrode and ground. These breakdown events deteriorate the collector performance and prevent the attainment of the designed collector efficiency. A detailed investigation has identified the feedthrough assembly as the root cause of the breakdown problems. To address this, an innovative modification of the feedthrough assembly has been proposed, where individual feedthrough insulators are replaced by a single insulator with multiple feedthrough pins. This redesign substantially enhances the breakdown strength of the MDC, thereby enabling the application of intended low depressed potentials. Consequently, a 20% increase in collector efficiency has been demonstrated practically by this modification. In addition to the performance benefits, the proposed technological solution is simple, cost-effective, and employs only half the number of components. It also minimises the number of brazing operations, thereby drastically lowering the fabrication time and reducing the thermal cycles. Overall, the modified feedthrough technology markedly improves the manufacturing yield of MDCs.