The evaluation was simply instrumented by monitoring the power input to the magnetron and noting the temperature of the cooling fin. The power input was the power required to heat the filament to an electron emission temperature plus the product of the applied anode current and anode voltage. The temperature of the fin was monitored by a thermocouple placed at a distance of 1" from the outer edge of the fin. In addition a thermocouple was placed on the copper ring. A difference in temperature of the two thermocouples then represented the temperature drop between the copper ring and the cooling fin, plus the drop in fin temperature from inner to outer radii. The procedure in testing a new radiating fin was to increase the fin temperature at a rate at which the degassing of the fin did not saturate the pumping system. After this initial processing, which could require half an hour, the fin was ready for evaluation. The evaluation procedure was to suddenly apply a total input power of 240 watts and observe the transient buildup of temperature at the points A and B, as shown in Figure 12. Figure 12 indicates the transient response of temperature at A and B to the step function of 240 watts of power input to the anode. It is seen that the steady state fin temperature reaches a temperature of about 225 degrees Celsius, the time duration of the data shown in Figure 12 is 44 minutes, but in several cases the time period was extended to several hours without a change in temperature of the fin, indicating that the emissivity had not changed during those time intervals.
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