INVESTIGATION OF CLOSE-SPACED THERMIONIC CONVERTER
ITT INDUSTRIAL LABS FORT WAYNE IN
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Difficulties in realizing a very small anodecathode spacing, due to uneven thermal expansion and warping, have led to a feasibility study of a subliming anode surface that automatically maintains the proper spacing from the cathode. Barium was chosen as a subliming metal since it serves also to activate the cathode. This required that all parts of the vacuum enclosure be held above 500 degrees C. Effects of barium corrosion at high temperatures were studied. Four test models were made and tested. By holding the temperature of the barium reservoir constant and varying the cathode temperature, the maximum of the Taylor-Langmuir emission S-curve was repeatedly traversed. Starting with an anodecathode spacing of 0.007 inch and a heated bari m reservoir, the spacing was reduced by build-up of barium on the anode. A metallic connection between anode and cathode then developed. This was removed by rising the cathode above 1000 degrees C and the anode above 500 degrees C. The characteristic thermionic current-voltage curves were then seen again, but with currents 12 times larger than those obtainable with the original spacing. This proved that build-up of barium had reduced the anode-cathode spacing. Since the temperature distribution in the anode was non-optimum, suggestions are made for further studies with improved anode design.
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