NATURE OF POWER SATURATION IN TRAVELING WAVE TUBES 843 



saturation, but still involve questionable approximations which make it 

 desirable to compare predictions with the actual situation. 



Theoretical considerations of the effects of attenuation upon efhciency 

 have not led to conclusions coming even close to the observed results. 

 Measured characteristics^^' ^^ show that the effect of attenuation is very 

 large, but that attenuation may be appropriately distributed to attain 

 stability and isolation between input and output of the tube without de- 

 grading the output power. 



There are also several papers in the French and German periodicals 

 which deal with the question of traveling wave tube efficienc3^ Some 

 of these are listed in References 12 through 20. 



This paper describes measurements of efficiency and of beam modula- 

 tion made on a traveling wave tube scaled to large size,* and low fre- 

 quencies. The construction of the tube, shown in Fig. 1, and the measure- 

 ment of its parameters were much more accurate than is usual in the 

 design of such tubes. The results are believed to be generally applicable 

 to tubes having similar values of the normalized parameters. 



OUTPUT 

 TERMINATION 



INPUT 

 TERMINATION 



INTERMEDIATE 

 TAP 



VACUUM HEADER 



/ 



^ VELOCITY 

 ANALYZER 



SAMPLE 

 OF HELIX 



SUPPORTS 



SECTION OF 

 FOCUSING SOLENOID 



Fig. 1 — The scale model traveling wave tube. The tube is 10 feet long with a 

 c-opper helix supported by notched glass tubing from an aluminum cylinder over- 

 wound with a focusing solenoid. It is continuously pumped and readilj^ demount- 

 able. 



See Appendix. 



