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Determination of e m from Measurements of Thermionic Currents

Determination of e m from Measurements of Thermionic Currents No. 2. DETERMINATION OF elm FROM MEASUREMENTS OF THERMIONIC CURRENTS.' By SAUL DUSHMAN. IN a recent paper on "The Effect of Space Charge and Residual Gases on Thermionic Currents in High Vacuum,"2 Dr. I. Langmuir has shown that the thermionic current from a heated metallic surface in high vacuum is limited by (a) temperature, (b) space charge. With a given potential difference between the electrodes, the current from the heated cathode increases with the temperature in accordance with the equation of Richardson, _b i = aV/eT. (.I ) However, above a certain temperature, this current becomes constant; further increase in temperature does not cause any corresponding increase in thermionic current. The temperature at which this limitation occurs increases with increase in anode potential. It was shown in the above paper that this effect is due to the existence of a space charge produced by the emitted electrons, and it was furthermore deduced that at a fixed cathode temperature, the electron current ought to increase with the three-halves power of the voltage (until the saturation current as defined by the Richardson equation is attained), that is, for electrodes of any shape, the space charge current i = k V3/2, http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review American Physical Society (APS)

Determination of e m from Measurements of Thermionic Currents

Physical Review , Volume 4 (2) – Aug 1, 1914
14 pages

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Publisher
American Physical Society (APS)
Copyright
Copyright © 1914 The American Physical Society
ISSN
1536-6065
DOI
10.1103/PhysRev.4.121
Publisher site
See Article on Publisher Site

Abstract

No. 2. DETERMINATION OF elm FROM MEASUREMENTS OF THERMIONIC CURRENTS.' By SAUL DUSHMAN. IN a recent paper on "The Effect of Space Charge and Residual Gases on Thermionic Currents in High Vacuum,"2 Dr. I. Langmuir has shown that the thermionic current from a heated metallic surface in high vacuum is limited by (a) temperature, (b) space charge. With a given potential difference between the electrodes, the current from the heated cathode increases with the temperature in accordance with the equation of Richardson, _b i = aV/eT. (.I ) However, above a certain temperature, this current becomes constant; further increase in temperature does not cause any corresponding increase in thermionic current. The temperature at which this limitation occurs increases with increase in anode potential. It was shown in the above paper that this effect is due to the existence of a space charge produced by the emitted electrons, and it was furthermore deduced that at a fixed cathode temperature, the electron current ought to increase with the three-halves power of the voltage (until the saturation current as defined by the Richardson equation is attained), that is, for electrodes of any shape, the space charge current i = k V3/2,

Journal

Physical ReviewAmerican Physical Society (APS)

Published: Aug 1, 1914

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