. La rivista tecnica Bell System . a questo punto si vuole dire che trasformiamo i nostri coordinatida un sistema fisso a uno che ruota con il campo e si domandano se una soluzione è possibile dove a il movimento angolare è sempre piccolo. Egli scopre che tale asoluzione è effettivamente possibile e che per il movimento elettronico essere stabile il valore di a deve essere tale che gli elettroni sono in qualche modo dietro la linea per cui il campo ha il suo valore di ritardo massimo. Gli elettroni sono quindi in grado di perdere energia al campo e di spiralarsi verso l'anodo. Posshumo ha definito il valore degli elettroni veloci radiali
1308 x 1911 px | 22,1 x 32,4 cm | 8,7 x 12,7 inches | 150dpi
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. The Bell System technical journal . at this is to say that we transform our coordinatesfrom a fixed system to one rotating with the field and inquire if a solutionis possible where a the angular motion is always small. He finds that such asolution is indeed possible and that for the electron motion to be stable thevalue of a must be such that the electrons are somewhat behind the line forwhich the field has its maximum retarding value. The electrons are thusin a position to lose energy to the field and to spiral out toward the anode. Posthumus defined the value of the electrons radial velocity squared atthe anode as P and the total velocity squared at the anode as Q. Nor-malized plots of these two parameters are shown in Fig. 15 as a function offrequency. The upper plot shows the radial velocity. Obviously for elec-trons to reach the plate at all they must have a positive velocity at the plate.Electrons can therefore reach the plate with any given field value, say Z = 2, ELECTRON BALLISTICS IN HIGH-FREQUENCY FIELDS 349. -0-5 -10 10077m- rsxVo Cx» Fig. 15—Electron velocities in the magnetron according to Posthumus. that is with a field equal to twice the cutoff value, for all frequencies lessthan the equivalent value defined by the intercept of the Z = 2 line with 350 BELL SYSTEM TECHNICAL JOURNAL the abscissa axis. The hne for P = 0 appears on the lower curve as thedotted hne s. Here the ordinate is the total velocity squared, normalizedwith respect to the value without oscillation. Efficiencies can therefore beput on the plot directly as shown by the right-hand scale in per cent. Theline 5 is therefore a plot of the maximum possible efficiency. This refersto what we might call the electronic efficiency since no account is taken ofcircuit losses. Now in any physical device there are some circuit losses andhence a lower value of electronic efficiency for which sustained oscillationsare not possible. The dotted line p is Posthumus experimental value forthis lower
