CHAPTER XVI 

 DOUBLE-STREAM AMPLIFIERS 



Synopsis of Chapter 



IN TRAVELING-WAVE TUBES, it is desirable to have the electrons 

 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 electrons, which entails both loss of 

 efficiency 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 the double-stream amplifier the gain is not obtained through the inter- 

 action of electrons with the field of electromagnetic resonators, helices or 

 other circuits. Instead, an electron flow consisting of two streams of elec- 

 trons 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.^'^'^'^ Electromagnetic 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. 

 The important factors in the interaction are the electric field, which stores 

 energy and acts on the electrons, and the electrons themselves. The charge of 

 the electrons produces the electric field; the mass of the electrons, and their 

 kinetic energy, serve much as do inductance and magnetic stored energy in 

 electromagnetic propagation. 



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

 B.S.TJ., Vol. 28, pp. 33-51, January 1949. 



' A. V. Hollenberg, "Experimental Observation of Amplification by Interaction be- 

 tween Two Electron Streams," B.S.TJ., Vol. 28, pp. 52-58, January 1949. 



* A. V. Haeff, "The Electron-Wave Tube — A Novel Method of Generation and Ampli- 

 fication of Microwave Energy," Proc. IRE, Vol. 37, pp. 4-10, January 1949. 



*L. S. Nergaard, "Analysis of a Simple Model of a Two-Beam Growing- Wave Tube," 

 R.C.A. Renew, Vol. 9, pp. 585-601, December 1948 



' Some similar electromechanical waves are described in papers by J. R. Pierce, "Pos- 

 sible Fluctuations in Electron Streams Due to Ions," Jour. App. Phys., Vol. 19, pp. 231- 

 236, March 1948, and "Increasing Space-Charge Waves," Jour. App. Phys., Vol. 20 

 pp. 1060-1066; Nov. 1949. 



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