Xenon induced changes of plasma drop and electron temperature of a thermionic converter

Abstract

The I–V curves of a thermionic converter were measured for several cesium pressures and various electrode distances, and partial pressures of added xenon as well. The minimum internal voltage drop across the electrode gap was determined and correlated with cesium pressure, spacing and xenon pressure. Without xenon added this voltage drop shows the well-known minimum at an optimum pressure-spacing product ofp _Cs d=5·10⁻²cm·Torr. Only for smaller values of the pressure-spacing product the internal voltage drop can be reduced by the addition of xenon.

An interpretation is achieved by a comparatively simple model assuming a uniform electron temperature in the electrode gap. Using this model, the electron temperatures were calculated for various spacings and xenon pressures. Comparing the experimental data of the internal voltage drop and the correspondingly calculated electron temperatures it turns out that, within the framework of the model used, the internal voltage drop is represented by the electron temperature. The electron temperature itself is determined by the ion balance.