. The Bell System technical journal . type. With the very close spacings encountered in the Bell 619 620 BELL SYSTEM TECHNICAL JOURNAL Laboratories 1553 triode^^ the theoretical analysis no longer represents avalid approximation. Let us consider curve c in greater detail. The fact that electrons are emittedwith a Maxwellian velocity distribution, instead of being emitted at zerovelocity as in the Childs law or complete space charge case, means that moreelectrons are introduced in the space between the electrodes than can flowto the anode in accordance with Childs law. The surplus electrons dep
. The Bell System technical journal . type. With the very close spacings encountered in the Bell 619 620 BELL SYSTEM TECHNICAL JOURNAL Laboratories 1553 triode^^ the theoretical analysis no longer represents avalid approximation. Let us consider curve c in greater detail. The fact that electrons are emittedwith a Maxwellian velocity distribution, instead of being emitted at zerovelocity as in the Childs law or complete space charge case, means that moreelectrons are introduced in the space between the electrodes than can flowto the anode in accordance with Childs law. The surplus electrons depressthe potential in front of the cathode to a value below that of the potential minimum is indicated by Vm in the figure. Electrons whichhave insufficient energy to cross this barrier return to the cathode. In the space between the cathode and the potential minimum, electronsare found traveling with various velocities in both directions. Between thepotential minimum and the anode, electrons travel in one direction only,. Fig 1—Potential distributions in a diode toward the anode, but with multiple velocities. With close spacings andhigher frequencies the distance between the cathode and the potentialminimum may be an appreciable part of the total cathode-anode spacing,with the result that the electrons returning to the cathode may absorb asubstantial amount of power from the high-frequency held. This argument also applies to the cathode-grid region of a microwavetriode such as the 1553. In order to increase the transconductance of thetriode, it is desirable to locate the grid as close to the cathode as close spacing, however, leads to a greater loss of power to the returningelectrons, which prevents a realization of the full benefits expected from thereduced spacing. All of these difficulties are a result of the Maxwellian veloc-ity distribution of the emitted electrons. In view of the importance of electron stream admittances in the designof microwa
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