研究目的
To demonstrate that the frequency bandwidth of circular corrugated waveguides can be compromised by diffraction losses to miter bends and gaps, and to show that theory underpredicts these losses when corrugation depth differs from λ/4.
研究成果
The simulations show that when corrugation depth differs from λ/4, miter bend and gap losses are higher than theoretically predicted, due to nonideal HE11 mode patterns. This explains experimental losses in systems like JET reflectometry and ITER LFSR. For broadband systems, reducing miter bends is recommended; for multiple-frequency systems, techniques like Bragg reflectors can mitigate losses, as demonstrated for ITER ECH dc breaks.
研究不足
The FFT model does not account for electromagnetic reflections and is limited to simpler geometries. FEM simulations are computationally intensive and only feasible for small gap components, not miter bends, with current resources. The study does not include space harmonics, water vapor absorption, curvature, or tilt losses, which may affect high-frequency results.
1：Experimental Design and Method Selection:
The study uses Fast Fourier Transform (FFT) and Finite-Element Method (FEM) simulations to model HE11 mode losses in corrugated waveguide miter bends and gaps at arbitrary corrugation depths. FFT is used for parametric scans due to lower computational intensity, while FEM handles complex geometries like dc break components.
2：Sample Selection and Data Sources:
Simulations are based on ITER-relevant parameters (e.g., waveguide radius, corrugation depth, period, width) and compared to experimental data from JET reflectometry, DIII-D ECE, and ITER LFSR test stands.
3：List of Experimental Equipment and Materials:
Computational tools include FFT and FEM models; specific equipment is not detailed beyond simulation setups.
4：Experimental Procedures and Operational Workflow:
For FFT, the miter bend is modeled as a waveguide cross with sequential steps for field propagation and truncation. For FEM, COMSOL Multiphysics is used with port boundary conditions, impedance boundary conditions, and perfectly matched layers (PMLs) to simulate gap losses.
5：Data Analysis Methods:
Data analysis involves comparing simulation results to theoretical predictions and experimental measurements, using statistical comparisons and mode decomposition.
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