The possibility of transfer of electricity in a thermionic convertor by negative ions

The transfer of electrons from the emitter or space charge region to the collector in a thermionic energy convertor by negative ions has been experimentally investigated. The region between the emitter and collector is filled with a low pressure gas whose molecules attach electrons in the space charge or become negative ions after contact with the emitter. The negative ions move to the collector by diffusion and mutual repulsion, or convective flow, where they deposit their electrons by collisional detachment. Strongly electron-attaching gases, Br₂, CF₂Cl₂, and SF₆, were tried, but they did not undergo collisional detachment and reacted with the tungsten emitter. The inert gases, He and A, had little or no effect on the collector current and were used for comparison. Very pure methane, CH₄, produced collector current increases of a factor of 10 or more when added to the thermionic converter. Experiments performed in a magnetic field showed that the collector current was due to the diffusion of negative ions, as well as electrons. An experiment having a mass flow of methane over the emitter to the collector showed the transfer of electricity by negative ions. Photoionization or photodecomposition did not account for the negative ion formation. The mechanism whereby CH₄ forms negative ions is unknown.