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Description
High-power radio-frequency (RF) cavities, such as RFQs, may require multiple input couplers to circumvent the breakdown limit. With advances in semiconductor amplifiers, each coupler is often connected to a single source. Although all amplifiers are synchronized in amplitude and phase by an LLRF system, calibration or control errors may persist. These errors, along with disparities in the external Q-factor, affect the amplitude and phase of the voltage seen by the beam and, consequently, the energy gain. An imbalance between the different RF sources can also lead to excessive reflected power at the couplers. This article presents a numerical simulation method based on the open-source Scilab/Xcos software, capable of predicting not only the steady-state behavior but also the transient behavior of such a system: it is applied to the ESS RFQ and to a new RFQ developed at CEA Saclay for industrial purposes. As an example of the results, the reflected power is distributed uniformly in steady-state and transient between the couplers when the external Q-factors differ, provided that all sources deliver signals of equal amplitude and phase. Countless failure scenarios can be investigated.
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