Definition of thermion in US English:



  • An ion or electron emitted by a substance at high temperature.

    • ‘Another theory is that, since energy is required to extract electrons from the heated material, there should be cooling when thermions are emitted.’
    • ‘Alloyed thorium enhances the emission of thermions by lowering the work function barriers.’
    • ‘When the main power supply of the X-ray tube is on, the cathode emits thermions as it is heated by a heater.’
    • ‘If the ionization electrode is located at an appropriate position in the vicinity of the evaporation source and a positive voltage with respect to that of the evaporation source is applied to the electrode, thermions and secondary electrons from the evaporation source migrate toward the ionization electrode.’
    • ‘He discovered the Schottky effect, an irregularity in the emission of thermions in a vacuum tube and invented the screen-grid tetrode tube.’


Early 20th century: from thermo- ‘of heat’ + ion.