NATURE OF POWER SATURATION IN TRAVELING WAVE TUBES 873 



2.0 



1.8 



1.6 



1.4 



1.2 



1.0 



0.8 



0.6 



0.4 



0.2 



0.1 



0.2 



0.3 



0.4 



0.5 0.6 



QC 



0.7 



0.8 



0.9 



1.0 



1.1 



Fig. 18 — Increasing wave propagation factors used in interpreting the meas- 

 urements. These are the maximum value of x\ and the corresponding value of 6 

 and y\ for given values of QC. 



^ periment because a simple control of sensitivity was important in order 

 I to study velocity differences ranging from 1 per cent up to as much as 

 1 100 per cent of the dc beam velocity. 



The velocity analyzer is sketched in Fig. 5. It consists of an aperture 

 which transmits only a few microamperes of the electron stream; a mag- 

 netic pole piece (not shown) terminating the focusing field; a pair of 

 horizontal deflection plates; an electrostatic lens system; pole pieces and 

 j deflection plate to provide a region with crossed electric and magnetic 

 'fields; and finally a drift tube, a post deflection acceleration electrode 

 ,aiid fluorescent screen. The whole assembly is raised 1,000 volts above 

 the helix potential and the 0.001 " aperture is very close to the end of the 

 helix, so that the electrons are very quickly accelerated to a high voltage. 

 V>Y this means, the region of debunching outside of the helix field is kept 

 t)clow 1.4 radians transit angle and the velocity spread within the ana- 

 lyzer is reduced by a factor of four. Space charge within the analyzer is 

 <'iitirely negligible because of the small current transmitted. 



In order to discriminate in phase before the electrons are scrambled 



