Design of the High-Q approach notch filter for 60 GHz collective Thomson scattering system

This manuscript presents the design and implementation of a high-performance waveguide-based notch filter centered at 60 GHz, tailored for use in collective Thomson scattering (CTS) diagnostics systems on next generation burning plasma device in China. The filter features an ultra-narrow notch bandwidth (< 0.4 GHz) and achieves over 90 dB rejection at the target frequency, significantly outperforming conventional designs with ~ 2 GHz bandwidth. By employing optimized cylindrical cavity resonators and precise waveguide aperture tuning, the filter maintains minimal insertion loss across the passbands (56–59.8 GHz and 60.2–64 GHz), ensuring full coverage of the ion temperature-dependent scattering spectrum. The design’s high-quality factor (Q) and robust performance, validated through electromagnetic simulations, make it ideal for protecting sensitive nanowatt-level receivers from multi-megawatt gyrotron interference. Practical implementation considerations, including compatibility with WR-15 waveguides and modular integration, highlight its suitability for next-generation fusion diagnostics. This work advances millimeter-wave filter technology, offering a reliable and scalable solution for high-precision plasma measurements in demanding fusion environments.