The QKH 2244 is intended to operate as a free running oscillator in the proposed demonstration of beamed power transmission. However, it is easy to convert its operation into that of a high-gain, phase-locked amplifier with external circuitry. The operation then is closely analogous to its use in the transmitter of the Solar Power Satellite as shown in Figure 1. The major design items that are novel in the QKH 2244 are the radiating fin and the magnetic field circuit. Design and Testing of the Radiating Fin The design of the fin was dependent upon the specified microwave power output for the proposed demonstration, the efficiency of the magnetron, and the temperature at which the fin could be operated. The required power output was 250 watts. At a nominal efficiency of 60%, this would require the fin to radiate 167 watts. A maximum operating temperature of the anode of the tube of 300 degrees Celsius was also assumed, but this selection is somewhat arbitrary and conservative. To make the design itself conservative, the objective dissipation of the fin was taken to be 240 watts, and the fin was evaluated at this level. The end objective of the fin design is to minimize the radiating area and the mass of the fin. To attain this objective, the material of the fin should have a very high ratio of heat conductivity to its density, and its surface should have a very high emissivity. Also tapering of the thickness of the fin can reduce the mass. As was pointed out, pyrolytic graphite with its low density, very high heat conductivity, and near black body emissivity is an ideal material for a radiating fin. However, in the context of the modest funding available for the tube construction, its high cost prohibited its use. It was therefore necessary to look for alternative materials in designing the fin. After a literature study of various materials and their treated surfaces was made it was decided to experimentally evaluate a black dyed anodized surface on aluminum that was available from a local vendor, this turned out to be a fortuitous choice but at the time of procurement it was not known whether such a surface would hold up at an operating temperature of 300 degrees Celsius in vacuum or if it would degas to such an extent as to ruin the exhaust system in which it was inserted. To expedite the procurement of anodized disks, the disks to be anodized were fabricated in the most expedient way without regard to such refinements as tapering. Further, the diameter was limited by machining considerations to a diameter of 9 3/4". These test disks, however, gave a performance that met the radiation objective of 240 watts of heat at a temperature below the specified 300 degrees Celsius and so, in the interests of cost and time saving, they became incorporated into the final design of the tube. However, the design of the fin is far from being optimized. In particular the fin thickness is much greater than it has to be, but the fin was left thick so that the radiating temperature over the fin would tend to be
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