Optimization of lanthanum hexaboride electrodes for maximum thermionic power generation

Experimental research activities relating to thermionic energy conversion were initiated at the Aero Propulsion Laboratory (APL) of Wright Research and Development Center (WRDC) with the acquisition of several test stations from NASA Lewis Research Centre through Arizona State University. The diode test stations have been provided with new cooling systems, a new data processing/acquisition system and an output load circuit with a biasing power supply. Tests are currently being conducted manually by controlling the electrode and cesium reservoir temperatures between data points using their respective cooling and heating systems. Each performance test consists of driving the diode at fixed electrode temperatures from a positive bias voltage to ignition and further on to a fixed negative bias voltage, then tracing the path back to the original starting positive bias voltage. Optimization tests were conducted in which emitter and collector temperatures were maintained constant at 1700 K and 900 K respectively and the cesium reservoir temperature was varied from 350 to 550 K in suitable intervals. The performance peaked at a cesium reservoir temperature of 485 (± 10) K. Similar optimization tests on the collector revealed an optimum collector temperature of 885 (± 10) K. The optimim emitter temperature was limited to 1700 K due to bonding strength problems. (author)