1350 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



As in the klystron, the mput resonator produces both the slow and the 

 fast waves with equal magnitudes. As each wave travels, it induces 

 currents in the resistive wall surrounding it and dissipates power in the 

 wall. Thus, the power in each wave must decrease as the wave travels. 



The fast wave has a positive power, and so for its power to decrease 

 the amplitude must decrease. Thus, in the resistive-wall region the 

 amplitude of the fast space-charge wave decreases exponentially ^^ith 

 distance. 



Because the slow space-charge wave has a negative power, its power 

 can decrease only if the amplitude of the wave increases, so that the 

 power flow becomes less (more negative). Thus, in the resistive-wall 

 region the amplitude of the slow space-charge wave increases exponen- 

 tially ^\ith distance; the wave has a negative attenuation; it is amplified 

 as it travels. 



If we put the output resonator far from the input resonator, the ampli- 

 tude of the fast space-charge wave will be very small there, but the 

 amplitude of the slow space-charge wave may be very large. Its current 

 will produce a large voltage across the output resonator. As in the case 

 of the klystron, this voltage ^nll increase the amplitude of the slow space- 

 charge wave, thus decreasing the power flow in the electron stream. 



The resistive wall amplifier has a feature which the klystron lacks ; the 

 process of amplification involves an actual growing wa^^e along the elec- 

 tron stream. 



THE EASITRON; increasing WAVE IN A LOSSLESS SYSTEM 



Consider a tube somewhat similar to the resistive wall amplifier, but 

 in which the beam is surrounded, not by a lossy tube, but by a series of 

 pill-box resonators, as shown in Fig. 4. Imagine that the resonators are 

 so tuned that at the operating frequency they present a lossless negative 

 susceptance to the electron beam. 



TUBE COATED WITH 

 RESISTIVE MATERIAL 



:^ 



Fig. 3 — In a resistive-wall amplifier the currents excited in the lossy wall bj- 

 the slow, negative-power wave decrease the power in the wave, so that the ampli- 

 tude of the wave must increase. 



