4. 2 KLYSTRON The study of the klystron, a linear beam device, for the MPTS application was conducted by Shared Applications, Inc. , of Ann Arbor, Michigan under subcontract. Raytheon provided assistance in thermal analysis, magnetic design, weight and cost estimating as well as overall technical direction. In addition, the suggestions of Dr. Henry Kosmahl of Lewis Research Center were important factors in maximizing klystron capabilities for MPTS. The preliminary analysis indicated klystron designs could be implemented over ranges of 1-30 GHz and power to 150 kW with heat pipe cooling, and with powers to 10 kW with passive cooling. This resulted in initial design efforts centering on low power to achieve the simplicity of passive cooling. However, further study showed heat pipes would be needed at all powers, and design effort then was applied to higher power versions to reach maximum efficiency. Detailed design was undertaken at the nominal 2. 45 GHz frequency. Included in the study is a comparison of periodic permanent magnet (PPM) and solenoid, or electromagnetically (EM) focused klystrons. Simulations by computer have been used to determine the power capability and the efficiency of the PPM tube. Heat dissipation limits the power of both PPM and EM focused tubes, and heat-pipe cooling will be necessary for the body; indeed existing tubes are cooled by water or forced air when generating kilowatts of average power. The EM klystron is the clear choice for output power levels of 1 6 kW or more. It has higher efficiency, and at least three times the power output of the PPM tube for the same degree of body heating. Furthermore, the weight and cost per kilowatt generated fall appreciably with increasing power per tube. A nominal maximum of 43 kW initially was selected for the analysis, and this later was set at 48 kW, but the ultimate limit will depend on the extent of developments in heat-pipe technology. Previous research, published by the General Electric Company (2) and by Varian Associates (3) , has been directed at obtaining 7. 5 kW or less of continuous- wave output power per tube. The competing amplitron is recommended at 5 kW per tube. Thus, on the order of 1. 3 million such tubes would be needed for a 5 GW system. The high- power klystron provides an alternative system requiring, for example, only
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