The multiplet cavity: A buncher for broad-bandwidth klystron amplifiers

The bandwidth of a klystron output cavity scales (approximately) as p^0.8P^0.2, where p is the beam perveance and P is the beam power. For high-perveance (p>10 μpervs) high-power (P>10 kW) electron beams, it is relatively straightforward to design a broad-band output cavity. However, the design of the input cavity of the broad-band klystron is in some ways more difficult. The purpose of the input cavity is to produce a velocity-modulated electron beam with a frequency-dependent modulation amplitude that will optimize the bandwidth of the entire klystron system, while providing a magnitude of velocity modulation large enough to minimize the length of the klystron. This paper shows how a multiplet (multiple cavity) buncher cavity can be designed to provide broad-band (>20%) operation while keeping short the drift section length of the klystron