During this reporting period basic analytical and experimental exploration was conducted on several types of advanced thermionic energy converters, and preliminary analysis was performed on systems utilizing advanced converter performance. The Pt-Nb cylindrical diode which exhibited a suppressed arc drop, as described in the preceeding annual report, was reassembled and the existence of the postulated hybrid mode of operation was tentatively confirmed. Initial data obtained on ignited and

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... ted triode operation in the demountable cesium vapor system essentially confimed the design principles developed in earlier work, with a few exceptions. Three specific advanced converter concepts have been selected as candidates for concentrated basic study and for practical evaluation in fixed-configuration converters. Test vehicles and test stands for these converters and a unique controlled-atmosphere station for converter assembly and processing were designed, and procurement has been initiated. System analysis has shown that the thermionic heat exchanger concept for topping of electric power plants is economically sind technically attractive if 2nd generation converter perfonaance is achieved, and if identified structural, heat transfer and output coupling innovations are reduced to engineering practice.