Klystron performance using a multistage depressed collector

A multistage depressed collector design has been developed that returns few electrons to the klystron circuit and, consequently, allows normal klystron operation while providing enhanced efficiency. (1) This design has been evaluated and the results are reported here. The collector design uses four depressed stages operating at equally spaced potentials. It is incorporated on a 60 kW 5 cavity klystron operating at 800 MHz with 51% electronic efficiency. The current distribution to the collector electrodes has been measured and the power recovery determined. Collector efficiency data is presented as a function of RF output power for various operating conditions. The magnitude of regeneration signals has been determined and the effectiveness of secondary electron suppression is noted. The performance results indicate 74% power recovery with no RF output reducing to 57% at saturation, representing an overall efficiency of 71%. Regeneration was low enough to allow stable operations with up to 60 dB gain.