Isotropic graphite multistage depressed collectors - A progress report

A small isotropic-graphite-electrode multistage depressed collector (MDC) was designed, fabricated, and evaluated in conjunction with a 500-W CW 4.8-9.6-GHz TWT. The carbon electrode surfaces were used to improve the TWT overall efficiency by minimizing the secondary-electron emission losses in the MDC. The design and fabrication of the brazed graphite MDC assembly are described. The TWT and graphite-electrode MDC bakeout and processing (outgassing) characteristics were evaluated and found to be comparable to those for TWTs equipped with copper-electrode MDCs. The TWT and MDC performance was optimized for broadband CW operation at saturation. The average RF, overall, and MDC efficiencies were 14.9, 46.4, and 83.6 percent, respectively, across the octave operating band. A 1500-h CW test showed no gas buildup and excellent stability of the electrode surfaces.