Thermionic Converters Operating in the Ignited Mode. Part II: A Quasi-Equilibrium Model for the Interelectrode Plasma

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Abstract
A multistage ionization‐recombination model is proposed to describe the formation and loss of atomic ions in low‐energy cesium plasmas. Solutions of the ambipolar diffusion equation are investigated with due consideration given to these processes. The solutions indicate the existence of a state of quasi‐equilibrium throughout most of a low‐energy plasma in which the electron temperature is more than several hundred degrees above a critical ignition temperature. The assumption of quasi‐equilibrium in the interelectrode plasma of a thermionic converter operating in the collisional ignited mode is shown to result in a plasma model which correlates a wide variety of experimental data. Included in the successful correlations are electron random current density and temperature profiles as well as output‐current characteristics. The experimentally observed state of quasi‐equilibrium in thermionic converter plasmas is found to be near the Saha‐equilibrium limit. It is therefore concluded that the multistage ionization‐recombination processes in these plasmas involve numerous excited states.

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