practical purposes, the optimized emitter temperature was considered to be 1700 K. The outcome of the first stage series of optimization tests was that the optimum emitter, collector and cesium reservoir temperatures were 1700 K, 885 ±10 K and 485 ± 10 K respectively. In order to arrive at the optimized cesium reservoir and collector temperatures more accurately, a series of second stage optimization tests were conducted on the LaB6 diminiode. In these tests the cesium reservoir temperature was varied over a smaller temperature range from 465 to 505 K at intervals of 10°C and the collector temperature was varied over a range of 855-905 K at intervals of 10°C. Second Stage Optimization The results of the second stage performance optimization are shown in Figs. 14 and 15. Figure 14 indicates the output current density characteristics and output power density characteristics as a function of output voltage for various cesium reservoir temperatures. During these tests the collector was maintained at 885 K, and the emitter at 1700 K. It was found that the maximum short circuit current density occurred with a cesium reservoir temperature of 500 K but this was just about 1 A/cm2 more than the corresponding value at 475 K. However, the peak power density at 485 K was greater than that at 495 K. This observation, together with the fact that the spread in the experimental data exceeds ±0.5 A/cm2 provides sufficient evidence that the optimum reservoir temperature lies in the vicinity of 485 K but cannot be expressed with a resolution better than ± 10°C. Figure 15 gives the corresponding characteristics for the collector temperature optimization tests. From the short circuit current density values for the various collector temperatures, it can be seen that the maximum short circuit current density occurs with the collector at 855 K. However, there is a sharp drop in power density at this temperature above 0.4 V. This sharp drop was not observed at higher temperatures and given the spread in the experimental data, the most likely value of optimum collector temperature would be 875 K. The emitter temperature optimization was not
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