Abstract
Emerging high-frequency accelerator technology in the terahertz regime is promising for the development of compact high-brightness accelerators and high resolution-power beam diagnostics. One resounding challenge when scaling to higher frequencies and to smaller structures is the proportional scaling of tolerances which can hinder the overall performance of the structure. Consequently, characterizing these structures is essential for nominal operation. Here, we present a novel and simple self-calibration technique to characterize the dispersion relation of integrated hollow THz-waveguides. The developed model is verified in simulation by extracting dispersion characteristics of a standard waveguide a priori known by theory. The extracted phase velocity does not deviate from the true value by more than $ 9 \times 10^{-5} ~\%$. In experiments the method demonstrates its ability to measure dispersion characteristics of non-standard waveguides embedded with their couplers with an accuracy below $ \approx 0.5~\% $ and precision of $ \approx 0.05~\% $. Equipped with dielectric lining the metallic waveguides act as slow wave structures, and the dispersion curves are compared without and with dielectric. A phase synchronous mode, suitable for transverse deflection, is found at $ 275~\text{GHz} $.
Highlights
Emerging high-frequency accelerator technology in the terahertz regime is promising for the development of compact high-brightness accelerators and high resolution–power beam diagnostics
The developed model is verified in simulation by extracting dispersion characteristics of a standard waveguide a priori known by theory
THz-driven accelerators have recently garnered interest for their promising acceleration gradients, compact footprints, and relatively small wavelengths which support the formation of short femtosecond electron bunches [1,2,3,4,5,6,7] and high resolution–power diagnostics [8,9]
Summary
THz-driven accelerators have recently garnered interest for their promising acceleration gradients, compact footprints, and relatively small wavelengths which support the formation of short femtosecond electron bunches [1,2,3,4,5,6,7] and high resolution–power diagnostics [8,9]. The central frequency of the produced waveforms depend on the crystal temperature [17], providing a way to control the phase velocity inside the structure. Optical methods have been used to measure the dispersion characteristics of a structure in the THz regime. The phase difference between these two structures instead of the absolute phase shift, the phase velocity is deduced. This approach requires a precise knowledge of the length difference, and high machining precision for identical cross sectional and horn geometry. We introduce an error network model to characterize the phase shift in integrated high frequency structures (220–330 GHz). The results and limits of the error network model are discussed
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