Influence of beam head effects on high-power klystron amplifier

Transient behavior of the cavity excitation caused by beam head effects in high-power klystrons is investigated. Recognizing that the input cavity in a klystron can be excited by the input microwave signal and the head of the electron beam, it is shown that the frequency of the induced cavity voltage V-s driven by the signal is the same as the signal frequency omega (s). On the other hand, the frequency of the induced cavity voltage V-h driven by the beam head is the cavity resonance frequency omega (0). An expression of the induced voltage V-h is obtained by making use of the Laplace transformation. The induced voltage V-h caused by the beam head is expressed in terms of the current-change profile in time. The magnitude of the induced voltage caused by the beam head is inversely proportional to the beam rise time, thereby decreasing drastically for a large value of the beam rise time. It is also shown that the beam head effects are completely negligible whenever the beam rise time tau (r) satisfies omega (0)tau (r)=2n pi where n is an integer. The amplitude of the whole cavity voltage oscillates with the beat wave frequency Delta omega=omega (0)-omega (s). This amplitude oscillation may play an important role in pulsed high-power klystrons. (C) 2001 American Institute of Physics.