338 



BELL SYSTEM TECHNICAL JOURNAL 

 Phase Focusing in a Reflex Tube 



It might be well to pause for a moment in our discussion of transit time 

 bunching to consider how the phase focusing diagrams can be applied to a 

 reflex tube. The elements of a modern reflex tube are shown in Fig. 8 







I 



Fig. 4- 



-The phase-focusing diagram of B ruche and Recknagel showing the analogy to 

 optical focusing. 



which was take«i from a recent I.R.E. paper by Dr. J. R. Pierce. Electrons 

 from the cathode pass through an input gap defined by two grids where they 

 are modulated in velocity. In traveling in the retarding field produced by 

 the repeller those electrons which passed the gap when the field was becom- 

 ing progressively less accelerated, become bunched; the faster electrons 



