DOE/JPL Advanced Thermionic Technology Program. Progress report No. 41

The primary long-term goal of the DOE effort is to improve TEC performance to the level that thermionic topping of fossil fuel steam powerplants becomes technically possible and economically attractive. An intermediate goal is to demonstrate an in-boiler thermionic module in the early 1980's. A short-term goal is the demonstration of the reliability of thermionic operation in a combustion environment. The focus of the JPL program is to develop thermionic conversion technology appropriate for nuclear electric propulsion (NEP) missions. These missions require operation at collector temperatures substantially higher than those associated with terrestrial applications. The DOE and JPL tasks for developing thermionic energy conversion (TEC) are complementary and synergistic. Converter performance improvement is an area in which one agency's program supports the effort of the other. Progress in the DOE program is reported including: (1) demonstration of over 3600 hours of stable operation (Quarter Scale Silicon Carbide Converter No. 1) in a combustion environment at emitter temperatures at, or above, 1600/sup 0/K; (2) calculation of a complete current density-voltage characteristics in the power quadrant which includes both double valued sheath effects at the emitter and the spatial distribution of electron temperature in the interelectrode plasma; and (3) successful operation of Converter No. 222 with a cesium-graphite reservoir. JPL program accomplishments reported include: (1) performance data have been obtained on three planar variable spaced converters with molybdenum emitters (Converter Nos. 223, 227 and 228); and (2) system calculations indicate that long term thermionic performance demonstrated at Thermo Electron should yield a power system specific mass less than 22 kg/kWe