Multi-megawatt hybrid TWT's at S-band and C-band

The extensive theoretical and practical data available on high gain high power klystrons on the one hand and on wide band traveling wave tubes on the other has induced many microwave tube workers to attempt hybrid design combinations, with the objectives of achieving various operational advantages. In the past, Doehler, Huber, Kleen, Warneke, Gittens, Yadavali, Lichtenberg, and others have experimented with such tubes. At Varian, efforts have centered around the S-band VA-145A and the C-band VA-146A multi-megawatt pulse power hybrid tubes. These devices have been called variously hybrid TWT's, traveling wave klystrons, TWK's, and Twystron hybrid TWT's. Perhaps the most interesting feature of these tubes is the compatibility achieved between the broadband klystron RF driver input circuit and the TWT forward fundamental extended interaction RF output circuit, leading to unique and desirable combinations of wide bandwidth, high gain, high power, high operating efficiency, and relative uniformity of operating characteristics. The general operational performance exceeds that possible with broadband pulse power beam tubes of prior art. This report presents recent test results outlining the operating characteristics of these tubes. Some of the important tube design features will be presented as background material.