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End date: 2024 × Start date: 2020 × Publisher: College Park, MD : American Physical Society × WGL Institute: FBH ×

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Now showing 1 - 2 of 2
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    Generalization of coupled S-parameter calculation to compute beam impedances in particle accelerators
    (College Park, MD : American Physical Society, 2020) Flisgen, Thomas; Gjonaj, Erion; Glock, Hans-Walter; Tsakanian, Andranik
    In this article, a decomposition approach for the computation of beam coupling impedances is proposed. This approach can account for the mutual electromagnetic coupling in long accelerator structures consisting of several consecutive segments. The method is based on the description of the individual segments using a multimodal network matrix formulation in which the charged particle beam is considered as an additional port. Then, the generalized multimodal network matrices of all segments are combined to a multimodal network matrix of the complete structure. The beam coupling impedance as well as the scattering parameters of the full structure are recovered as particular matrix elements in this multimodal network matrix. The new method generalizes Coupled S-Parameter Calculation (CSC) introduced in earlier work such that charged particle beams are considered. Consequently, the introduced scheme is referred to as CSC. Application examples for realistic accelerator components such as the simulation of a full TESLA 1.3 GHz-cavity of the European XFEL are provided. These simulations demonstrate the high accuracy and numerical performance of the proposed method.
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    Influence of vacuum chamber port terminations on beam coupling impedances
    (College Park, MD : American Physical Society, 2023) Flisgen, Thomas; Gorgi Zadeh, Shahnam; Gjonaj, Erion
    Vacuum chambers of particle accelerators are typically equipped with radio-frequency couplers. The couplers are employed to excite modes for particle acceleration, to extract the energy of higher-order modes, or for diagnostic purposes. From a network theory perspective, these couplers represent terminal ports by which means the structure can exchange energy with its exterior. Usually, these ports are terminated with fixed impedances corresponding to the characteristic impedances of the coaxial lines attached to them. In this paper, we investigate the influence of the termination conditions of vacuum chambers on beam coupling impedances. For this purpose, we introduce a novel approach that allows us to determine beam coupling impedances for arbitrary port terminations. A full-wave Maxwell solver is employed to determine a generalized scattering matrix of the vacuum chamber and its couplers terminated with prespecified reference impedances. Often, these impedances are chosen to be the characteristic line impedances of the waveguides so that coupler ports are free of reflection. Using the generalized scattering matrix, the beam coupling impedances can be readily determined by means of a computationally inexpensive postprocessing step that takes into account arbitrary impedance loads at the coupler ports. Thus, the influence of various port terminations on the beam coupling impedances can be conveniently examined. This is relevant to improve older structures that were designed when no sophisticated design tools were available or to improve the operation of existing structures for a purpose they were initially not designed for. Using the proposed approach, we investigate the 33-cell 200 MHz traveling-wave accelerating structures of the SPS at CERN. It is shown that port termination conditions do have an important influence on the beam coupling impedance and, therefore, must be taken into account in beam stability considerations.