NATURE OF POWER SATURATION IN TRAVELING WAVE TUBES 847 



magnetic fields to sort them according to velocity. The resulting beam 

 draws a pattern on a fluorescent screen as shown in Fig. 6 from which 

 charge density and velocity can be measured as a function of signal 

 phase. The velocity coordinate is determined by photographing the 

 ellipse with several different beam potentials, as in Fig. 6(a), and the 

 phase coordinate is measured along the ellipse. From pictures like this 

 a complete determination of electron behavior is obtained from the 

 linear region up to and above the saturation level. 



The results of such a run are plotted in Fig. 7. The upper lefthand 



2.0 



Fig. 3 — Values of efficiency/C as u function of QC and yro at elevated beam 

 voltage. Raising the beam voltage has little effect at large QC and small yro , 

 and less than expected anywhere. Again the triangular points are from Tien, Walker 

 and Wolontis,^ and the line contours are estimated from the measured data. 



