846 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



3.0 



0.5 



Fig. 2 — Values of efficiency/C as a function of QC andyro at the voltage giving 

 maximum gain per unit length. The shaded contours and triangular points are 

 from the computations^ of Tien, Walker and Wolontis. The circled points are from 

 the measurements and the line contours are estimated lines of constant efficiency. 

 The most significant difference is for large beam radii, where the RF field varies 

 over the beam radius in a way not accounted for in the computations. 



SPENT BEAM CHARACTERISTICS 



The scale model traveling wave tube was followed by a velocity an- 

 alyzer as sketched in Fig. 5 and described in the Appendix. A sample of 

 the beam at the output end of the helix is passed through a sweep cir- 

 cuit to separate electrons according to phase, and crossed electric and 



