Description of Apparatus Diminiode Construction The base of the diminiode consists of three concentric conductors bonded together with aluminum oxide insulation between each layer. The conductors were bonded to the insulators by the Hot Isostatic Pressing Process (HIPP). The center and second steps at the bottom of the diminiode base served as the electrical taps for the collector and guard. The electron bombardment target was located on the machined shoulders of a standard tantalum tube. The tube was attached to the diminiode base and served as the cesium reservoir. Cesium was sealed in the tube after internal degassing. The cesium reservoir was sealed by copper brazing a tantalum ball at the neck of the cylinder. The collector and guard were cut from the same material and were attached to the diminiode base by high temperature brazing. Thermocouples measured the cesium reservoir, collector and guard temperatures. The emitter was heated by electron bombardment and the thermal control coils were used to adjust the temperature of the guarded collector and cesium reservoir. The interelectrode gap was maintained at 0.25 mm. Optical pyrometry was used to measure the electron bombardment target temperature which was then converted to the emitter temperature as follows: Pyrometer Output Calibration and Analysis. A manually balanced disappearing filament pyrometer was used to measure emitter temperature. Measuring the emitter temperature was accomplished by focusing the pyrometer on the black-body cavity located in the electron bombardment target. A voltage signal corresponding to the temperature of the electron bombardment target was sent to the data acquisition system from the pyrometer. The data acquisition system was programmed to sense this voltage signal, convert it to digital form and send it to the computer. A computer program corrects the voltage signal for several factors causing attenuation, such as the energy scatter created by the sapphire viewport, the temperature gradient between emitter and target, etc. The correction was accomplished with several equations generated by analytical curve fitting techniques. This allowed the emitter temperature to be read directly from the computer screen. Figure 1 represents the final correlation between emitter temperature and pyrometer output voltage for the three scales representing the entire temperature range over which the emitter could possibly be heated. The temperature corresponding to the three scales were: Scale—1: 700°C to 135O°C Scale—2: 1350°C to 1850°C Scale—3: 1850°C to 2500°C. Though calibration data were not available over the entire range of each scale, extrapolation should not introduce any large systematic errors. Figure 1 is the outcome of three stages of conversions, viz. (a) conversion of output voltage to pyrometer temperature, (b) conversion of optical pyrometer temperature to target temperature and (c) conversion of target temperature to emitter temperature. Only the final calculated values after conversion are indicated in the figure, for each of the three scales. The corresponding analytical results were represented by the following relations:
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