Experimental Observation of Amplification by Interaction 

 Between Two Electron Streams 



By A. V. HOLLENBERG 



The construction and performance of an amplifier employing the interaction 

 between two streams of electrons having different average velocities are de- 

 scribed. Gain of 33 db at a center frequency of 255 Mc has been observed 

 with bandwidth of 110 Mc between 3 db points. 



1. Introduction 



ANEW type of amplifier in which the gain is obtained by an interaction 

 between streams of electrons of two or more average velocities is 

 proposed in a companion paper by Pierce and Hebenstreit.^ This amplifier 

 contains input and output portions in which signals are impressed on and 

 extracted from the electron flow by electromagnetic circuits and a central 

 portion in which gain occurs purely by interaction between streams of elec- 

 trons without any circuits being involved. A small signal theory for coinci- 

 dent electron streams of two d-c. velocities is presented in Pierce and Heben- 

 streit's paper. 



In this paper a description of the construction and operation of an amplifier 

 of this kind will be presented. Departures of the actual conditions in the 

 amplifier from the assumptions of the theory limit the expectations of quanti- 

 tative agreement. It is believed, however, that the evidence for gain arising 

 from the interaction between two streams of electrons is clear, and that the 

 broad frequency response predicted by the theory has been confirmed. 



2. Description or Amplifier 



The frequency range near 200 Mc was chosen for the first experimental 

 test of the proposed method of amplification for reasons of convenience. 

 The theory indicates that current density requirements increase with fre- 

 quency, but that these requirements become severe only at the higher micro- 

 wave frequencies. Availability of circuit parts and test equipment, rather 

 than anticipated difficulties at higher frequencies, led to the choice that was 

 made. 



The essential features of one of the double-stream amplifier tubes which 

 has been constructed and operated are represented in Fig. 1. The out- 

 put helix was identical with the input helix in construction and connection 



1 A New Type of High Frequency Amplifier, J. R. Pierce and W. B. Hebenstreit, this 

 issue of the B. S. T. J. 



52 



