Abstracts of technical articles from Bell System sources

The Effect of Temperature on the Emission of Electron Field Currents from Tungsten and Molybdenum.
¹
A. J. Ahearn. Electron field currents from the cent ral portion of long molybdenum and tungsten filaments abo ut 2.7 = 10
⁻³
cm. in diameter have been studied. The field currents were first made stable to about 5 per cent by longcontinued conditioning treatments of temperature and high voltage under high vacuum conditions. Thermionic emission measurementsm gave the values 4.32 and 4.58 volts for the work function of the molybdenum and tun gsten, respectively, in good agreement with the accepted values for the clean met als. Emission measurements were then made at fields varying from about 5 = 10
⁵
volts/cm. to abo ut 1 = 10
⁶
volts/cm. and at temperat ures varying from 300° K. to about 2000° K. Down to abo ut 1600° K. th e therm ionic currents completely masked the field currents. Thermionic emission values below 1600° K. were obtai ned by ext rapolation. Thus the field currents at the lower temperatures were separated from the thermionic currents. Where necessary, corrections were made for the decrease in the voltage gradient accompanying the thermal expansion of the filament. The field currents were found to be independent of temperature to with in 5 percent from 300° K. to 1400° K. At temperatures higher than 1400° K. the data are consistent with the assumption that the current consists of a thermionic current plus a current which is independent of temperature. However, because of the exponential change of thermionic current with temperature a small effect of temperature on the field current could not be distinguished at temperatures higher than 1400° K. From the theory of Fowler an d Nordheim, β a factor introduced by surface irregularities, is found to be 120 for the tungsten cathode and 47 for the molybdenum one. Thus for tungsten, Houston's theory of the temperature effect is in approximate agreement with the negative results of these experiments.