Atomic Battery - Thermal Converters

Thermal Converters

Thermionic converter

A thermionic converter consists of a hot electrode which thermionically emits electrons over a space charge barrier to a cooler electrode, producing a useful power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply (by surface contact ionization) to neutralize the electron space charge.

Radioisotope thermoelectric generator

A thermoelectric converter connects pairs of thermocouples in series. Each thermocouple is formed by the junction of two dissimilar materials. One of each pair is heated and the other cooled. Metal thermocouples have low thermal-to-electrical efficiency. However, the carrier density and charge can be adjusted in semiconductor materials such as bismuth telluride and silicon germanium to achieve much higher conversion efficiencies.

Thermophotovoltaic cells

Thermophotovoltaic cells work by the same principles as a photovoltaic cell, except that they convert infrared light (rather than visible light) emitted by a hot surface, into electricity. Thermophotovoltaic cells have an efficiency slightly higher than thermoelectric couples and can be overlaid on thermoelectric couples, potentially doubling efficiency. The University of Houston TPV Radioisotope Power Conversion Technology development effort is aiming at combining thermophotovoltaic cells concurrently with thermocouples to provide a 3 to 4-fold improvement in system efficiency over current thermoelectric radioisotope generators.

Alkali-metal thermal to electric converter

The alkali-metal thermal to electric converter (AMTEC) is an electrochemical system which is based on the electrolyte used in the sodium-sulfur battery, sodium beta-alumina. The device is a sodium concentration cell which uses a ceramic, polycrystalline β-alumina solid electrolyte (BASE), as a separator between a high pressure region containing sodium vapor at 900 - 1300 K and a low pressure region containing a condenser for liquid sodium at 400 - 700 K. Efficiency of AMTEC cells has reached 16% in the laboratory and is predicted to approach 20%.

Stirling radioisotope generator

A Stirling engine driven by the temperature difference produced by a radioisotope.