Design and optimization of quasi-optical mode converter for 210-GHz <i>TE</i> 22,6 high-power gyrotrons

High-power pulsed gyrotron oscillators operating in the short millimeter-wave range typically utilize high-order cavity modes, requiring efficient and compact quasi-optical mode converters to maximize their performance and efficiency. This work details the design and optimization of a compact quasi-optical mode converter aimed at transforming TE22,6 at 210 GHz has been developed. The converter integrates a high-efficiency Denisov-type launcher, designed using geometric optics and coupled-mode theory, along with a mirror system comprising a quasi-elliptical, an elliptical, and a parabolic mirror that is optimized through vector diffraction theory. The design utilizes MATLAB for parametric analysis and Feldberechnung für Körper mit beliebiger Oberfläche simulations to evaluate the electromagnetic field distribution within the launcher and at the output window. Through precise optimization of the launcher radius, perturbation amplitude, and perturbation length, we achieved efficient mode conversion and beam shaping within a compact 127 mm design. Notably, the cut length is 20 mm, constituting 15.75% of the total launcher length, ensuring a well-defined Gaussian beam profile with minimal diffraction losses. Simulation results demonstrate that the scalar Gaussian mode content and vector Gaussian mode content at the output window are 99.2% and 98.6%, respectively, indicating high mode purity and efficient power transfer. The shortened launcher length and optimized design parameters provide a compact and efficient solution, outperforming earlier models while maintaining high performance. This highlights the effectiveness of the proposed design in achieving high-power, high-frequency millimeter-wave applications with minimal size and high efficiency.