Description:
<jats:p>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 Vs driven by the signal is the same as the signal frequency ωs. On the other hand, the frequency of the induced cavity voltage Vh driven by the beam head is the cavity resonance frequency ω0. An expression of the induced voltage Vh is obtained by making use of the Laplace transformation. The induced voltage Vh 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 τr satisfies ω0τr=2nπ where n is an integer. The amplitude of the whole cavity voltage oscillates with the beat wave frequency Δω=ω0−ωs. This amplitude oscillation may play an important role in pulsed high-power klystrons.</jats:p>