A New Type of High-Frequency Amplifier 



By J. R. PIERCE and W. B. HEBENSTREIT 



This paper describes a new amplifier in which use is made of an electron flow 

 consisting of two streams of electrons having different average velocities. 

 When the currents or charge densities of the two streams are sutTicient, the 

 streams interact to give an increasing wave. Conditions for an increasing 

 wave and the gain of the increasing wave are evaluated for a particular geometry 

 of flow. 



1. Introduction 



IN CENTIMETER range amplifiers involving electromagnetic resonators 

 or transmission circuits as, in klystrons and conventional traveling-wave 

 tubes, it is desirable to have the electron flow very close to the metal circuit 

 elements, where the radio-frequency field of the circuit is strong, in order 

 to obtain satisfactory amplification. It is, however, difficult to confine the 

 electron flow close to metal circuit elements without an interception of elec- 

 trons, which entails both loss of efl&ciency and heating of the circuit elements. 

 This latter may be extremely objectionable at very short wavelengths for 

 which circuit elements are small and fragile. 



In this paper the writers describe a new type of amplifier. In this ampli- 

 fier the gain is not obtained through the interaction of electrons with the 

 field of electromagnetic resonators, helices or other circuits. Instead, an 

 electron flow consisting of two streams of electrons having different average 

 velocities is used. When the currents or charge densities of the two streams 

 are sufficient, the streams interact so as to give an increasing wave. Electro- 

 magnetic circuits may be used to impress a signal on the electron flow, or to 

 produce an electromagnetic output by means of the amplified signal present 

 in the electron flow. The amplification, however, takes place in the electron 

 flow itself, and is the result of what may be termed an electromechanical 

 interaction. '" 



While small magnetic fields are necessarily present because of the motions 

 of the electrons, these do not play an important part in the amplification. 



■ Some electro-mechanical waves with a similar amplifying effect are described in 

 "Possible Fluctuations in Electron Streams Due to Ions," J. R. Pierce, Jour. A pp. Plivs., 

 Vol. 19, pp. 231-236, March 1948. 



-While this paix;r was in preparation a classified report by .\ndrew V. Haeff entitled 

 "The Electron Wave Tube — A Novel Method of Generation and Amplification of Micro- 

 wave Energy" was received from the Naval Research Laboratory. Dr. Haeff 's report 

 (now declassified) contains a similar analysis of interaction of electron streams and in 

 addition gives experimental data on the performance of amplifying tubes built in ac- 

 cordance with the new principle. We understand that similar work has been done at the 

 RCA Laboratories. 



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