Design of multistage depressed collector for Ka-band 40W high efficiency helix TWT

Multistage depressed collector (MDC) plays an important role in enhancing overall efficiency of a space TWT. A high efficiency four-stage depressed collector has been designed for Ka band 40W high efficiency helix TWT using EGUN code coupled with In-house developed pre-processor, and post processor modules. The spent beam data has been used from In-house developed SUNRAY 2.5-D code, a large signal model. The collector electrodes geometries and different depressed potentials on four stages have been optimized to enhance the collector efficiency and minimize the back streaming current. Collector efficiency with 4-stage depression using high-density graphite electrodes (with secondary electron emission coefficient (¿) =0.6) has been achieved more than 81%. The back streaming current has also been controlled within 0.7mA, while the total beam current is 75mA. The variation in collector efficiency with the different operating power level of the tube has also been studied.