Design of four-stage depressed collector for a high efficiency helix TWT

Summary form only given. A four-stage axisymmetric depressed collector was successfully designed and developed to recover nearly 80% of the spent beam kinetic energy for a high efficiency C-band 60 W space TWT. The PIERCE program [LK-MTRDC] was used to optimize shape, size and operating depressed voltage of each electrode of the 4-stage depressed collector for achieving optimum energy recovery from the spent electron beam with minimum loss of collector efficiency caused by secondary electrons from back streaming. The program uses geometrical parameters of the electrodes and the spent beam trajectories data. The electron beam trajectories data were generated from the SUNRAY-3D large-signal model [VS-CEERI] and SUNBRS program [VS-CEERI] for the TWT operating at saturation output power at centre frequency 3.90 GHz. The SUNBRS code was used for analyzing the spent beam passing through the beam refocusing section (BRS) which was used before the collector for improving its performance. Radial velocities in the spent beam were reduced by decreasing PPM focusing magnetic field along the BRS.