NATURE OF POWER SATURATION IN TRAVELING WAVE TUBES 861 



where the parameters are all obtained from a single velocity curve, and 



is field strength in volts meter at phase $ 



is the value of the ordinate of the velocity characteristic of 



of interest (Figures 7 to 10) and 



is the ^'alue of the ordinate corresponding to the wave 



velocity. (To be precise, the wave velocity at the associ- 

 ated output level, but to a reasonable approximation, that 

 of the wave velocity at low levels. (This value is indicated 

 by Vw in the velocity curves.) 



i The total electric field has been computed for the case of Figs. 8(a) and 

 (b) and is given in Figs. 11(b) and 12(b) together with the circuit field 

 .calculated for the associated power level and plotted with an arbitrarily 

 chosen phase. In each case it is seen that the space charge field is com- 

 parable in magnitude to the circuit field, is far from sinusoidal, and 



z 



UJ 



cr 

 q: 



D 

 O 



UJ 

 > 



111 



cc 



u u 



UJ 



-J I 



UJ H 



o 



> UJ 



I- tc 



< H 



CE 9 



■180 



-120 



-60 60 



RELATIVE PHASE IN DEGREES 



120 



180 



Fig. 12 — AC current and electric field in the beam deduced from Fig. 8(b). 

 The greater space charge results in a less defined bunch, and smoother space 

 charge field than in Fig. 11. 



