Results of experiments with a 2-cavity extended interaction klystron will be given. The tube is nominally capable of 1 KW - CW at S-band and consists of two five-gap short-slot-coupled or floating drift tube type cavities coupled to the input and output lines by means of a TWT matching section with an adjustable mismatch. The unusual features of the tube are: (1) the length of extension of the resonant cavities (5 electron ballistic wavelengths) and, (2) the incorporation of different and controllable beam-circuit synchronism conditions for the input and output cavities. The results of principal interest which will be described are: (1) the low velocity spread in the spent beam entering the collector, (2) the high total conversion efficiency (65%) obtainable by depression of the collector, which is of standard geometry, and (3) gain in excess of 20 db. Some theoretical treatment of the relationship of efficiency and oscillation stability will be given, as well as comments on the usefulness of such a design for high power mm wave amplification.
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