An extended-interaction klystron: Efficiency and bandwidth

A three-cavity extended-interaction klystron, with cavities consisting of resonated sections of ring-bar structure, was tested in pulsed operation near 25 kV at 1100 Mc/s. The active length of the output resonator was variable between one and five resonant half wavelengths. The input and the intermediate cavities were tuned continuously to simulate a wide-band stagger-tuned bunching section. The dependence was investigated of the efficiency and the saturated bandwidth on the length and the loading conditions of the output resonator, and on the beam velocity. Data are presented which lead to the following conclusions: As the cavity length is increased, the peak efficiency rises up to a point and then remains constant, while the bandwidth increases proportional to cavity length. As the loading is reduced, for a given cavity length, the efficiency generally rises monotonically until further reduction in loading results in the onset of regenerative cavity oscillations at the frequency of the design resonance. The necessary suppression of regenerative oscillation in adjacent resonances becomes more difficult as the cavity length is increased, and a basic limitation on cavity length is given by the quality of the coupler, which must be capable of providing uniform and heavy loading over a broad frequency range.