Abstract
THE electron emission from thermionic cathodes of the alkaline-earth oxide-coated type when under electron bombardment has been investigated recently by Johnson1 and by Pomerantz2. Johnson concluded that the secondary-electron emission produced by the bombardment changed little with the cathode temperature, that at 850° C. the maximum value, δm, of the secondary to primary ratio was about 5, and that the bombardment produced a temporary improvement in the thermionic activity of the cathode, which gave an ‘enhanced thermionic emission'. Pomerantz, on the other hand, concluded that the secondary-electron emission increased exponentially with the cathode temperature, and deduced from extrapolation of the results obtained at lower temperatures that, at 850° C, δm exceeded 100. The effect which Johnson interpreted as "enhanced thermionic emission" was also observed ; but that interpretation was not accepted. It has been suggested3 that "enhanced thermionic emission" rather than secondary-electron emission enables the anode current in a magnetron to exceed the thermionic emission provided by the unbombarded cathode. The experiments the results of which are indicated below were designed to throw light on the disagreement in the conclusions of the above investigators regarding the temperature dependence of the secondary-electron emission, and on the nature of the "enhanced thermionic emission" effect.
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References
Johnson, J. B., Phys. Rev., 66, 352 (1944); 69, 693 and 702 (1946).
Pomerantz, M. A., Phys. Rev., 70, 33 (1946); J. Franklin Inst., 241, 415 (1946); 242, 41 (1946).
Fisk, J. B., Hagstrum, H. D., and Hartman, P. L., Bell Syst. Tech. J., 25, 257 (1946).
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JONES, T. Electron Emission from Oxide-coated Cathodes under Electron Bombardment. Nature 161, 846 (1948). https://doi.org/10.1038/161846a0
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DOI: https://doi.org/10.1038/161846a0
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