Modeling of thermionic devices with nonequilibrium inert gas plasmas

A novel concept of thermionic energy conversion with inert gas filled cells is proposed. The low-pressure weakly ionized plasma in the cell eliminates the space charge limit on the current. Nonequilibrium ionization can allow the use of low-pressure inert gases instead of cesium vapor. Preliminary modeling of plasma dynamics and kinetics shows that under certain conditions the electric field-induced heating of plasma electrons can result in self-sustained ionization sufficient for the argon-filled device functioning without external ionization. The self-sustained nonequilibrium ionization regime is also characterized by oscillations of electron temperature and density. At relatively low voltages, the heating of plasma electrons is not sufficient to sustain the ionization, and repetitive short pulses can be used to operate the inert gas filled device.