Results from the advanced thermionic technology program

A thermionic energy converter (TEC) is a direct energy conversion device, which converts heat to electricity with no moving parts. In the past, application of thermionic converters has been limited to space power systems, because of their high operating temperature and relatively low efficiency. In addition, fabrication and operation of TEC's has been difficult and expensive. Several recent advances in thermionic energy conversion technology have greatly improved the efficiency of these devices. A research program was undertaken to independently confirm these advances, and to extend them to converters with practical geometry. The recent development of a stable cesium/oxygen vapor source has led to a significant improvement in performance. The addition of a small amount of oxygen to the cesium vapor can increase the emission current by a factor of three. The beneficial effects of oxygen are stable and reproducible. A TEC with a cold seal has been invented, which greatly simplifies construction, operation, and maintenance of the TEC. Electron reflection from the collector has been shown to reduce the performance of TEC's. Reflection suppressing materials were produced and tested. One sample showed evidence of reflection suppression, increasing the average output voltage by 0.16 V. Another sample did not. Research in this area is ongoing.