Frequency and Time Domain Modeling of Coupled Cavity Structures

Summary form only given. Accurate large-signal simulation of linear beam devices having coupled-cavity interaction or output structures will be essential to design wide bandwidth, high power amplifiers, including multiple-beam amplifiers. To achieve this capability, we will extend the slow-timescale, time-domain model used in the klystron code TESLA to treat the case when the external cavities are coupled. This new model will retain the existing detailed interaction physics model in the beam tunnel region necessary for accurate large-signal simulation, including DC and AC space charge effects. We present research results comparing alternative models for fast time-domain simulation of the external coupled-cavity circuit, and address the steps necessary to integrate with the TESLA interaction physics model. The existing klystron model treats individual cavities using a simple resonant equivalent circuit to represent the part of the cavity external to the beam tunnel. When coupled to the electromagnetic fields inside the beam tunnel, the resonance characteristics are modified, and must be matched to obtain the true resonant frequency, Q, and R/Q for each cavity. While this is straightforward for a single mode in an isolated cavity, the problem becomes more complex when cavities are coupled. Approaches to resolve this problem will be described.