Calculation of the Maximum Efficiency of the Thermionic Converter

A theoretical analysis of the efficiency of a thermionic converter is made in terms of the following parameters: Va, the potential difference between the top of the potential barrier in the interelectrode space and the Fermi level of the anode; VL, the potential drop across a load impedance in series with the converter; and Vl, the potential drop in the necessary electrical connection to the cathode. The analysis is carried out by developing an expression for the efficiency of the converter and then maximizing this expression with respect to VL and Vl. This method yields optimum values of load impedance, cathode lead geometry, and cathode work function in terms of Va, cathode temperature, cathode emission constant (usually denoted by A), and effective emissivity of the cathode. A hypothetical example is worked out numerically and the results show that (1) a low value of Va is required for high efficiency, and (2) relatively low values of cathode work function are required for maximum efficiency at ordinary cathode temperatures.