Design and performance verification of advanced multistage depressed collectors

In a joint USAF-NASA Program, Lewis Research Center is carrying out an efficiency improvement program on TWTs for use in ECMs by applying multistage depressed collector (MDC) and spent beam refocusing techniques developed at Lewis. In the analytic part of the effort, 3-D electron trajectories are used throughout the 10-18% (electronic) efficient, 4.8-9.6GHz bandwidth, 400-600 W CW TWT, the spent beam re-focuser and the depressed collector. Collector efficiency, collector losses and overall efficiency are identified and computed. On the experimental side, tube performance is evaluated first without the MDC, then the spent beam is analyzed for symmetry, circularity and the velocity spread. Finally, the MDC is attached and its performance optimized and evaluated. Theory predicts a MDC-efficiency of 84% for a 4 stage, 3"\times2" size MDC which can be achieved with symmetric and circular beams.