The biased gap klystron

A commercially available 4 cavity klystron was modified so that d.c. bias could be applied across the interaction gaps, and a considerable increase in efficiency resulted. Efficiencies greater than 65% were obtained (with gain greater than 40 db) without depressing the collector of the tube. By varying the beam power, efficiencies of greater than 60% were obtained over an 8:1 range of power output without sacrificing gain, thus the flexibility of the tube was also enhanced. Experimental evidence indicates that several different factors are responsible for the increase in efficiency, and the effect of bias on these factors is clearly illustrated. The application of bias across the interaction gap is shown to cause a remarkable reduction in beam loading impedance by eliminating slow secondary electrons and also results in the enhancement of density modulation as well as a signficant reduction in velocity spread. Preliminary results also indicate that the phase of a biased gap tube can be varied quite accurately over an extremely wide range by adjusting the bias; this is a characteristic which is clearly desirable for phased array radar application. Finally, the results of applying bias across the gaps of a tube fitted with a depressed collector are discussed.