CHAPTER XVII 

 CONCLUSION 



ALTHOUGH THIS BOOK contains some descriptive material con- 

 cerning high-level behavior, it is primarily a treatment of the linearized 

 or low-level behavior of traveling-wave tubes and of some related devices. 

 In the case of traveling-wave tubes with longitudinal motion of electrons 

 only, the treatment is fairly extended. In the discussions of transverse fields, 

 magnetron amplifiers and double-stream amplifiers, it amounts to little 

 more than an introduction. 



One problem to which the material presented lends itself is the calcula- 

 tion of gain of longitudinal-field traveling-wave tubes. To this end, a sum- 

 mary of gain calculation is included as Appendix VII. 



Further design information can be worked out as, for instance, exact gain 

 curves at low gain with lumped or distributed loss, perhaps taking the space- 

 charge parameter QC into account, or. a more extended analysis concerning 

 noise figure. 



The material in the book may be regarded from another point of view as 

 an introduction, through the treatment of what are really very simple cases, 

 to the high-frequency electronics of electron streams. That is, the reader may 

 use the book merely to learn how to tackle new problems. There are many 

 of these. 



One serious problem is that of extending the non-linear theory of the 

 traveling-wave tube. For one thing, it would be desirable to include the 

 effects of loss and space charge. Certainly, a matter worthy of careful in- 

 vestigation is the possibility of increasing efficiency by the use of a circuit 

 in which the phase velocity decreases near the output end. Nordsieck's work 

 can be a guide in such endeavors. 



Even linear theory excluding the effects of thermal velocities could profit- 

 ably be extended, especially to disclose the comparative behavior of narrow 

 electron beams and of broad beams, both those confined by a magnetic field, 

 in which transverse d-c velocities are negligible and in which space charge 

 causes a lowering of axial velocity toward the center of the beam, and also 

 those in which transverse a-c velocities are allowed, especially the Ikillouin- 

 type flow, in which the d-c axial velocity is constant across the beam, but 

 electrons have an angular velocity proportional to radius. 



Further problems include the extension of the theory of magnetron ampli- 

 fiers and of double-stream amplifiers to a scope comparable with that of the 



668 



