Robust 500 We radioisotope power system

Planetary missions (e.g., Pioneer, Cassini, or Voyager) and applications with moderate power draw and increased mobility requirements (e.g., Curiosity) demand ~100s We-class continuous power sources with high reliability and robustness. To avoid the risks and challenges associated with mechanical-to-electrical energy conversion, including the use of working fluids and bearings, solid-state converters are preferred in many power generation applications as they can achieve reliable, high power-densities with moderate efficiency. State-of-the-art thermoelectric generators, for instance, achieve ~7% efficiency, and recent laboratory results are paving a route towards ~15% efficiency. To achieve higher efficiencies that can compete more directly with mechanical energy converters, however, higher operating temperatures are required, which essentially requires fundamental materials-discovery research for thermoelectrics. Project approach: Nanohmics Inc. proposes to develop a high-efficiency thermionic thermal-to-electric converter (TTEC) module based on nanostructured, high survivability emission materials. The TTEC device will offer higher energy conversion efficiency (greater than 25%), total power output of 500 We, and better resistance to high temperature and harsh environments (stable to about 2500 degrees F). Phase I tasks: Primary efforts under Phase I will be directed toward prototyping the proposed vacuum diode thermionic converter based on low-work-function thermally-stable emitter (hafnium carbide, zirconium carbide) and collector (lanthanum boride) materials, quantifying prototype device efficiency, and maturing emitter and standoff processing protocols to maximize operational lifetimes with an ultimate goal of multi-decade stability. Modeling and experimental efforts will lead to a wafer-scale thermionic device that will be evaluated at the end of the program. Commercial Applications and Other Benefits: Nanohmics Inc. is developing a novel high efficiency TTEC product that uses innovative nanostructured low-work-function emitters capable of high current thermionic electron emission. The primary application of this innovation is for radioisotope power systems (RPSs). There are other applications of this technology that present a more substantial commercial opportunity. These include applications within the combined cycle power generation market (topping cycles) and microwave vacuum electronics market. Key Words: Radioisotope power system, thermionic emission, thermal-to-electric converter.