Figure 8 MPTS 5 kW Amplitron Parameters Figure 9 MPTS 5 kW Amplitron Power Budget Preliminary studies of the klystron indicated the 1.5 GHz to 3 GHz region would yield relatively low specific weight and cost designs as was the case for the amplitron. They also showed a possibility of purely passive cooling at power levels below 10 kW, but further study indicated all klystrons would require at least a heat pipe cooling scheme. Attention then shifted from low power, permanent magnet-focused tubes to higher power tubes of the solenoid-focused type where focusing power becomes less significant in the power budget. This trend is shown in Figure 10. A klystron design at 2.45 GHz representative of the higher power versions is shown in cross section for a 48 kW tube in Figure 11. Like the amplitron the tube would be open construction. Most power loss occurs at the collector where it is radiated at high temperature. However, removing beat from the body is a difficult challenge, solved in this example by using heat pipes which remain to be detailed in future studies. The tube incorporates a hot cathode which must be designed to achieve a life commensurate with a 30 year system life. Cold cathodes have not been demonstrated in klystrons as they have in amplitrons, although they might be realized by further development. The power budget and tube parameter summary in Figures 12 and 13 indicate that relative to the amplitron, efficiency is about four percent lower, specific weight is three hundred percent higher and specific cost is slightly higher. However, the klystron may have two potential advantages over the amplitron: (1) fewer, higher power tubes may simplify the orbital assembly task and (2) low noise and narrow bandwidth reduce radio frequency interference .
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